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FAQ page title

1) What is the required upstream aerosol level for leakage testing? Upstream Aerosol Leakage Level for Leakage Testing

2) Will using aerosol to test filters cause excessive loading and shorten the filters usable life?

3) Where should upstream challenge aerosol be introduced into a filter system that is being tested?

4) What type of PAO (polyalphaolefin) does the FDA accept for filter leakage certification tests?

5) How much compressed air volume does a Type III-A Laskin nozzle aerosol generator need?

6) What is the particle size distribution of a Laskin nozzle generator using PAO (4 cSt polyalphaolefin)?

7) What is the particle size distribution of a Laskin nozzle generator using DOP (DEHP)?

8 ) What is the particle size distribution of a Thermal generator (TDA-5A/5B) using PAO (4 cSt polyalphaolefin)?

9 ) What is the particle size distribution of a Thermal generator (TDA-5A/5B) using DOP (DEHP)?

10) What is the PAO particle size distribution of a Thermal generator (ATI-5C)?

11) What is the recommended shelf life of 4cSt PAO (polyalphaolefin)?

12) Can a TDA-5B be used to test Biological Safety Cabinets (BSC's)?

13) What happens if the photometer sample flow drops below its normal operating range of 28.3 lpm +/- 2.8?

14) What is the effect of the "Straylight" value on photometer operation?

15) How does sample flow effect photometer response?

16) What is the response time of an ATI aerosol photometer? (See FAQ 29)

17) Can a mono dispersed "HOT" aerosol penetrometer use PAO-4 (Emery 3004) instead of DOP (DEHP)?

18) Is there a "Portable" compressor available, capable of supplying the air volume required for 3 or 6 Laskin nozzles?

19) What is the liquid capacity of ATI Laskin Nozzle Aerosol Generators?

20) Aerosol photometer "Internal Reference" usage?

21) What causes an unstable photometer display?

22) What are acceptable substitutes for DOP (DEHP)?

23) Return Material Authorization number use

24) Comparison of particle count (#/cm3 or #/ft3) to mass weight per volume (ug/l)

25) Without Data Acquisition Software (DAS 1 or 2) how can 2i Digital Photometer data be captured, stored and imported to a spreadsheet?

26) Aerosol Generator Recalibration

27) Aerosol Concentration

28) Aerosol Photometer Recalibration

29) Aerosol Photometer Response

30) Laskin Nozzle Aerosol Concentration

31) Laskin Nozzle Generator Conversion from DOP to PAO

32) Converting the TDA-5A/5B Generator from DOP to PAO Operation

33) Aerosol Photometer Calibration with DOP/PAO

34) TDA-4A/4Blite/4B Compressor Requirements

35) Mass Flow versus Volumetric Flow

36) ATI TDA-5A/5B Comparison Study of DOP Substitutes

37) Leak Testing with Particle Counter

38) PAO-4 (Emery 3004) Liquid

39) Concentration Measurement with Photometers

40) TDA-5B, 5A (5C) Pulsing/Wet Aerosol Output

41) Using the Digital TDA-2G Aerosol Photometer

42) More Emery vs. DOP (Follow-up to FAQ #22)

43) TDA-5A/5B Background Penetration Readings

44) Thermal Generator Inert Gas Propellant: Applicable to TDA-5A, TDA-5B & ATI 5C

45) Year 2000 Compliance (Y2K)

46) Aerosol Correction Factors

47) TDA-2G & TDA-2GN Quick Reference Guide

48) 2H & 2HN Quick Reference Guide

49) ASTM D2986-95A (1999) Standard

50) HEPA Vacuum Testing

51) ATI PAO-4 (4 cSt PAO) Food contact

52) How to capture data ouput on a 2i Aerosol Photometer

53) What does the Hazard symbol referenced on the GHS compliant SDS for PAO-4 mean in relation to filter testing?


1) What is the required upstream aerosol level for leakage testing?

Most current industry standards and recommended practices require a minimum of 10 micrograms per liter (ug/l) as an upstream aerosol challenge concentration. While higher concentrations can be used, 10-ug/l is the minimum that may be used while still remaining in compliance.  All of ATI's aerosol photometers are designed to operate and provide valid leakage results at the upstream challenge concentrations ranges currently in industry use.

2) Will using aerosol to test filters cause excessive loading and shorten the filters usable life?

Not really.

Polydisperse aerosol is used to challenge the "integrity" or leakage of filters, framework, connections, etc., as well as the filter media itself. Therefore people ask, "How much aerosol is needed?"  The answer is about 11 drops for a 24 x 24 x 12 filter operating at 1,000 cfm.

The example below uses 10-ug/l (micrograms per liter) of PAO-4 as an upstream challenge.
Example: Assuming a typical 24" x 24" x 12" HEPA filter has an average of 65 pleats. The pleat size is 22.5" x 10.5". If we take this information and multiply it, we come up with the average HEPA filter containing approximately 213 ft2 of media.

We will also calculate the amount of liquid we will aerosolize to challenge this 213 ft2 of media for a leakage test as well as capture & entrain. To figure out how much liquid we will introduce to these filters, we have to calculate how long it will take to scan the filter. If you use a photometer with a rectangular isokinetic probe, it will take 1.6 minutes. This is calculated by figuring the scanning rate of 2 inches per second. Since the filter is 24 inches wide, one scan per 12 seconds across the face of the filter would be allowed. Since the probe width is 3 inches and the filter is 24 inches high, 3” into 24” equals 8 passes. The test time will be 96 seconds (1.6 minutes) with each pass taking 12 seconds, and 8 passes to cover the entire area in overlapping strokes.

The next calculation is the amount of liquid that will be aerosolized and spread evenly over the 213 ft2 of media. Using the system operating flow of 1,000 cfm, we multiply 1,000 cfm x 28.3 to convert to 28,300 liters per minute.  Next the 28,300 liters per minute is multiplied by the 0.00001 grams per liter which means 0.283 grams of liquid must be aerosolized to obtain a challenge of 10 micrograms per liter.

Because this test will take 1.6 minutes, we will multiply 0.283 grams x 1.6 and arrive at a total of 0.4528 grams of PAO-4 needed for the testing time required.

Using the 0.819 g/ml specific gravity of PAO-4, the required 0.4528 grams is equal to 0.55 ml of PAO-4. 

For low viscosity liquids it is generally considered appropriate to allow 20 drops per 1 ml of liquid.  This would mean that 11 drops of PAO-4 (20 drops x 0.55 ml) would be ALL of the PAO-4 needed to challenge this filter at 10-ug/l for a 1.6 minute leakage test. 

Those eleven drops would be evenly spread over a space approximately equal to the area inside the paint (3 second area) of a basketball court.

10 ug/l =0.000010 g/l
22.5” x 10.5” x 130 (65 pleats) = 30712.5 in2 / 144 = 213.28 ft2
1 cfm = 28.3 lpm, 1000 cfm = (28.3 lpm x 1000) = 28,300 lpm
28,300 x 0.000010 g/m = 0.283 g/m
0.283 g x 1.6 minutes/test = 0.4528 g/test

3) Where should upstream challenge aerosol be introduced into a filter system that is being tested?

Adequate aerosol mixing upstream can usually be obtained by introduction at least ten duct diameters upstream of the filters, or by introducing it upstream of baffles or turning vanes in the duct. When neither of these methods is practical, a Stairmand disk located four to six duct diameters upstream will aid in achieving satisfactory mixing. A Stairmand disk is a plate with the same geometric shape as the duct section that blocks the central half of the duct area. Air flowing past the disk creates vortices on the leeward side that compel turbulent and thorough mixing of the introduced aerosol and the dilution air stream.  The required diameter of the Stairmand disk may be calculated using the following information.

Stairmand disk diameter equals the pipe (or duct) diameter divided by the square root of two (1.414213).
This means that a 12 inch duct would require a Stairmand disk 8.5 inches in diameter.

4) What PAO (polyalphaolefin) does the FDA accept for filter leakage certification tests?

The FDA, in their original 1996 CGMP (Current Good Manufacturing Processes) release was specific in the type that was approved as a replacement for DOP (DEHP).

ATI's position is that PAO (polyalphaolefin) with a CAS # 68649-12-7 is acceptable by FDA definition. The full text of the referenced CGMP document is available here.

Since the release of the CGMP note mentioned above ATI has performed testing of 4 cSt PAO with a CAS# of 68037-01-4, and found that there is no measurable difference in the particle size distribution, standard deviation or leakage measurements obtained.

5) How much compressed air volume does a Type III-A Laskin nozzle aerosol generator need?

Each Type III-A Laskin nozzle consumes approximately 2.64 cfm (75 Liters) of air at 20 psi (1.4 bars) and total air consumption is a factor of the number of nozzles in use. Therefore the maximum theoretical compressed air volume required at 20 psi is 7.92 cfm for a three nozzle generator and 15.84 for a six nozzle generator.

The applied pressure (20 psi for DOP & 23 psi for PAO-4) should be measured at the nozzle inlet and must remain constant to allow calculation of the aerosol generator output. Please note, ATI only recommends calculations when using fewer than 3 nozzles due to interaction of the nozzles in a confined space.

Air compressor performance specifications that will show output volume (cfm) versus pressure (psi) are available from most vendors and will make selection of an appropriate compressor less difficult.

6) What is the particle size distribution of a Laskin nozzle generator using PAO (4 cSt polyalphaoelfin)?

TDA-4Blite (operating a single Type III-A Laskin nozzle) @ 20 psi using PAO-4

Number Surface Mass Volume
Particle Size Particle Size Particle Size Particle Size
median (nm) 245 415 528 528
mean (nm) 281 454 549 549
geo. mean (nm) 248 407 503 503
mode (nm) 233 429 594 594
geo. st. dev. 1.65 1.62 1.55 1.55

7) What is the particle size distribution of a Laskin nozzle generator using DOP (DEHP)?

TDA-4Blite (operating a single Type III-A Laskin nozzle) @ 20 psi using DOP (DEHP)

Laskin nozzle using DOP @ 20 psi

Number Surface Mass Volume
Particle Size Particle Size Particle Size Particle Size
median (nm) 254 430 546 546
mean (nm) 291 468 563 563
geo. mean (nm) 256 420 517 517
mode (nm) 241 429 685 685
geo. st. dev. 1.66 1.61 1.54 1.54

8) What is the PAO-4 (4 cSt polyalphaolefin) particle size distribution of a Thermal generator (TDA-5A/5B)?

TDA-5B Thermal Condensation Type Aerosol Generator using PAO-4 (4 cSt polyalphaolefin) operating at standard set up parameters of 408° C (765° F) with a 50 psig inert gas supply pressure.

Number Surface Mass Volume
Particle Size Particle Size Particle Size Particle Size
median (nm) 257 321 356 356
mean (nm) 273 334 365 365
geo. mean (nm) 259 318 350 350
mode (nm) 241 334 372 372
geo. st. dev. 1.41 1.37 1.35 1.35

*The TDA-5B aerosol distribution listed above is characteristic of the operating conditions and settings present at the time of testing. Particle size distributions generated during field usage will change depending upon the ambient temperature, humidity and equipment settings in use.

9) What is the DOP/DEHP particle size distribution of a Thermal generator (TDA-5A/5B)?

TDA-5B Thermal Condensation Type Aerosol Generator using DOP (DEHP or Dioctyl Phythalate) operating at standard set up parameters of 408° C (765° F) with a 50 psig inert gas supply pressure.

Number Surface Mass Volume
Particle Size Particle Size Particle Size Particle Size
median (nm)





mean (nm)





geo. mean (nm)





mode (nm)





geo. st. dev.





*The TDA-5B aerosol distribution listed above is characteristic of the operating conditions and settings present at the time of testing. Particle size distributions generated during field usage will change depending upon the ambient temperature, humidity and equipment settings in use.

10) What is the PAO-4 (4 cSt polyalphaolefin) particle size distribution of a Thermal generator (ATI-5C)?

ATI-5C Thermal Condensation Type Aerosol Generator using PAO (Poly-alpha Olefin) operating at standard set up parameters of 408° C (765° F) with a 50 psig inert gas supply pressure.

Number Surface Mass Volume
Particle Size Particle Size Particle Size Particle Size
median (nm)





mean (nm)





geo. mean (nm)





mode (nm)





geo. st. dev.





*The ATI-5C aerosol distribution listed above is characteristic of the operating conditions and settings present at the time of testing. Particle size distributions generated during field usage will change depending upon the ambient temperature, humidity and equipment settings in use.

11) What is the recommended shelf life of 4 cSt PAO (polyalphaolefin)?

The shelf life for 4 cSt PAO (ATI PAO-4) is ten (10) years from date of shipment when kept in the original, sealed and unopened container.  The usage life of an open container, tightly sealed between uses, is one (1) year. The product shall be stored in a temperature controlled, dry, environment between 15 and 30 °C while avoiding exposure to UV or direct sunlight.

12) Can a TDA-5A, TDA-5B or ATI 5C be used to test Biological Safety Cabinets (BSC's)?

ATI does not recommend the use of the TDA-5A, TDA-5B or ATI 5C or any other thermal condensation based aerosol generator for use in the certification of Biological Safety Cabinets.  IEST RP034 specifically cautions against this practice and NSF/ANSI 49-2008, Annex F specifically calls out for the use of a Laskin nozzle style generator or equivalent during certification.  Thermal condensation generators such as ATI's 5-series produce a smaller mass particle size, as well as a larger volume. These types of generators are designed primarily to allow testing of high air flow systems that cannot be adequately challenged by Laskin nozzle.

13) What happens if the photometer sample flow drops below its normal operating range of 28.3 lpm +/- 2.8?

Reduction of the photometer sample flow to a level below the lower tolerance limit, while using the internal reference settings for the 100% level, results in a slight increase in displayed leakage value. This higher value is the result of velocity changes of the aerosol passing through the light scattering chamber's area of observation. The reduced velocity results in a more conservative evaluation of the filter under test. If an actual upstream aerosol sample was being used to establish a 100% point (ratiometric mode), the unit’s aerosol response is self correcting for the decreased flow rate and standard accuracy conditions would be maintained.

14) What is the effect of the "Straylight" value on photometer operation?

The straylight value is an indication of the optical conditions of the Light Scattering Chamber (LSC) at a given moment in time and as such, does not have a tolerance range established. Increases in the straylight occur through ordinary usage over the standard annual calibration cycle. Sudden and/or catastrophic increases in the straylight value, typically the result of component failure or operator error may render the unit inoperable. Some examples of catastrophic failure are introduction of liquid to the scattering chamber, formation of condensation on the optics, large accumulations of solid particulate and failure of discrete components within the LSC. Photometers which remain operable, even with elevated straylight values, are still capable of accurately measuring filter leakage values.

15) How does sample flow effect photometer response?

A reduction of the sample flow to a rate below the lower tolerance limit, while using the internal reference settings for 100% levels, results in an increase in the displayed leakage value.  This higher value is the result of a decrease in the aerosol velocity as it is passing through the light scattering chamber's (LSC) area of observation.    The decreased velocity of the aerosol results in a more conservative evaluation of the filter under test.  

An increase in sample flow, however uncommon, results in the opposite effect. Increased velocity decreases the displayed leakage value and results in a liberal assessment of the filter performance and the potential for passing a "bad" filter.

These effects are one of the reasons for the ±10% limits paced upon the sample flow requirements in aerosol photometer testing protocols.

If an actual upstream aerosol sample was being used to establish a 100% point, the units aerosol response is self correcting for the change in velocity and standard unit leakage accuracy conditions would be maintained.

16) What is the response time of an ATI aerosol photometer?

Please see FAQ #29

17) Can a mono-dispersed "Hot" aerosol penetrometer use PAO-4 (4 cSt polyalphaolefin) in place of DOP/DEHP?

Testing was performed in 1992 by the U.S. Army to determine a DOP replacement candidate material for use in "Hot" mono-dispersed aerosol filter penetrometers. The results of that study concluded that PAO-4 (then known as Emery 3004) was an acceptable replacement for DOP in not only mono-dispersed "Hot" testing, but in poly-dispersed "Cold" testing applications as well. The full text of that report is available at CRDEC-TR-333.

18) Is there a "Portable" compressor available, capable of supplying the air volume required for 3 or 6 Laskin nozzles?

Unfortunately we have been unable to identify a specific portable compressor having the capacity to source 18 CFM at 20 psi. In all known instances a compressor of that capacity is wheeled, and incorporates a reservoir tank, and therefore is not readily portable.

Most common applications where the TDA-4B is used require only a portion of the full output capacity, typically 1 to 2 nozzles. For these applications one possible solution is the Rolair model FC1500HBP2. The manufacturer's rated output is 3.6 cfm @ 100 psi.

In those applications that require full-output an in-house compressed air source is typically utilized.
Please contact ATI Customer Service if you need any further assistance.

19) What is the liquid capacity of ATI Laskin Nozzle Aerosol Generators?

The liquid volume capacity of ATI's Laskin Nozzle Aerosol Generators is provided in the table below.

Model Laskin nozzles Liquid capacity @ mid-point Liquid capacity @ maximum
TDA-4B 1, 2, 3, 4, 5 or 6 3.38 liters 4.5 liters
TDA-4Blite 1, 2 or 3 2.3 liters 3.05 liters
ATI 6D 0.5 (2 jets) or 1.5 (6 jets) 0.68 liters 0.95 liters

Liquid consumption rates for Laskin nozzles:
(Multiply consumption rate, listed below, by the number of nozzles in use)

28 ml/hour of PAO-4 oil consumption per nozzle when operating @ 23 psi
23.4 ml/hour of DOP/DEHP oil consumption per nozzle when operating @ 20 psi

20) Aerosol photometer "Internal Reference" usage?

  1. Internal reference function:
    1. Using the internal reference factor (on a digital photometer) causes the operating program to display 100% when exposed to the light level equivalent to the chosen reference concentration. 
    2. Choosing a reference of 100 results in a displayed reading of 100 % when 100-ug/l is sampled.  In this manner the %Leakage display of a digital photometer can be used to interpret the measure concentration directly as mass concentration per volume (ug/l or mg/m3).
  2. Example of usage:
    1. Using varying reference factors will result in the photometer displaying 100% when sampling aerosol concentration corresponding to the selected value.  Choosing a reference of 65 as an example will cause the unit to display 100% when the photometer samples 65-ug/l of aerosol concentration.  The lower observed scattered light intensity is scaled upwards by a factor of 1.53 to display 100%.
  3. “Out of Tolerance” condition on detector response:  Examples
    1. A low reference response condition is where the photometer reports a concentration value less than physically present.  This has the effect of under-reporting leakage levels and potentially passing filters that having failing characteristics. Worst case scenario.

Conditions of example:    

  • Photometer has a reference value set to 100.
  • Reference response is low.  The photometer reads 75-ug/l when 100-ug/l is sampled.
  • The 100% set point for photometer response is not obtained by sampling a real-time aerosol upstream of the filter under test.

A leakage rate of 0.010% would be reported as 0.0075% due to the 25% reduction in response.

A high reference response condition is where the photometer reports a concentration value greater than physically present.  This has the effect of over-reporting leakage levels and potentially failing filters that having passing characteristics.  Better than “Worst case scenario.

Conditions of example:   

  • Photometer has a reference value set to 100.
  • Reference response is high.  The photometer reads 125-ug/l when 100-ug/l is sampled.
  • The 100% set point for photometer response is not obtained by sampling a real-time aerosol upstream of the filter under test.
  • A leakage rate of 0.010% would be reported as 0.0125% due to the 25% increase in response.

Relavent Notes: 
The reference tolerance on all ATI photometers to date is ± 10%.

When utilized for filter leakage certification, every effort should be taken to use an actual sample of the “Upstream” aerosol concentration.  The Reference feature should be used for obtaining a working 100% set point only as a last resort.

Displayed % Leakage values are limited to 135% of the chosen 100% set point regardless of whether an aerosol sample or Internal Reference was used.  A photometer having a value of 65 chosen as the reference factor has a reading ceiling of up to 135% of the 65 chosen as the reference factor, or 87.8-ug/l.  The 135% display limit is caused by range limitations of the amplifier. 

21) What causes an unstable photometer display?

Occasionally the % Leakage display on a photometer may become erratic for no apparent reason when not sampling and the photometer in the clear position.

Please be aware that some movement in the right most decimal place is a normal occurrence. A typical unit will display an occasional 0.0001% or 0.0002% while the Internal Reference setting or 100% level chosen is 100-ug/l. As the Internal Reference setting or 100% concentration level is decreased there is a proportional increase in the movement observed. A 0.0001% movement at 100ug/l will become 0.0010% when the 10ug/l is selected. For this reason ATI recommends displaying only three (3) decimals when using an upstream Internal Reference setting or aerosol challenge of less than 50-ug/l.

In the absence of particulate contamination within the sampling chamber, there could also be an anomaly caused by electro-magnetic interference (EMI), radio frequency interference (RFI), or a combination of both.

EMI is caused by electrical and electronic devices that are operated by line voltage or batteries. RFI is caused by turning electrical and electronic appliances on and off. It can also be caused by particular circuits in certain appliances or electrical devices. For example, EMI is commonly experienced in an office when a printer is positioned too close to the computer monitor. The EMI radiating from the printer affects the video scanning electron beam that is viewed on the monitor. This causes the images on the monitor to behave erratically, appearing to be gyrating and wriggling. The problem can be solved by increasing the distance between the printer and monitor.

Likewise, EMI and RFI can cause the % Leakage display of a photometer to behave erratically. Most photometers contain a photomultiplier tube that is very sensitive to EMI and RFI. One method of reducing EMI and RFI interference in a photomultiplier tube is to shield it by covering it with a metal tube containing a small hole. This technique is employed in ATI photometers.

Sometimes an anomaly caused by EMI or RFI will resolve itself. If it does not, one of the easiest solutions to reduce EMI or RFI in a photometer is to move the photometer a few feet in one direction or another. Often, this will reduce the interference to a point where it is insignificant. Another possible solution is to plug the unit into a different electrical outlet. This may decrease or eliminate any interference entering through the AC power connection.

22) What are acceptable substitutes for DOP (DEHP)?

Customers concerned with potential health problems to people working with Di [2-ethyhexyl] phthalate (DOP or DEHP) have inquired about acceptable substitute liquids for DOP. As a manufacturer of test equipment, ATI does not control which substitutes can be used. However, ATI recommends, in order of preference, the following substitute liquids:

  1. PAO (ATI-PAO 4)
  2. Ondina EL
  3. White Mineral Oil
  4. DOS / DEHS (Dioctyl-sebacate)
  5. PEG400/Polyethylene Glycol
  6. Peanut Oil
  7. Sunflower Oil
  8. Cottonseed Oil
In January 1992 the Army Surgeon General's office gave its approval for the use of 4 cSt PAO in lieu of DOP for U.S. Army filter test equipment, followed by the Food and Drug Administration in December 1996 for FDA regulated facilities. Because of these approvals, ATI has placed 4cSt PAO at the top of its recommended list of substitutes.

ATI has performed several studies on the various substitute liquids and found no significant difference in aerosol distribution. However, tests revealed that for the same generator pressures, different concentration values where achieved depending on the substance used. This should be taken into account if a photometer's reference feature is calibrated for a liquid other than the one in being used.

Many ATI customers who selected corn oil as an alternate liquid consequently encountered maintenance difficulties. Many of these customers are now switching to PAO which, in ATI's estimation, is the best substitute from a maintenance and operational point of view. The second most popular choice has been mineral oil and customer feedback indicates few maintenance problems.

23) Return Material Authorization number use

ATI uses a Return Material Authorization (RMA) procedure to provide better service and support to customers returning equipment for service.

ATI issues RMA numbers for all recalibrations. When a customer calls to receive an RMA Number, ATI will request Purchase Order information and other appropriate details required to enter a Sales Order. When the equipment arrives, the Sales Order is already in place to improve turn-around time.

Please contact ATI for the most current prices for repair and service of ATI equipment. If a written estimate is required prior to servicing the instrument, it should be requested along with the RA number and noted on the Purchase Order. There is an additional one-hour labor charge for this service. ATI's standard operating procedure is to advise customers of any major repair charges incurred prior to recalibration.

When returning an analog photometer (Models TDA-2C, TDA-2D or TDA-2E) for service and recalibration, the aerosol challenge liquid for the Internal Reference must be specified. The ATI Service Department can calibrate a photometer to either DOP or PAO. All of ATI's more recent photometers (Analog models TDA-2GA & ATI 2HA & Digital models TDA-2G, ATI 2H & ATI 2i) are calibrated using both DOP and PAO as standard practice.

24) Comparison of particle count (#/cm3 or #/ft3) to mass weight per volume (ug/l)

Frequently, particle counter response levels are compared to light scattering photometer response. Because of the differences in the technologies used this sometimes causes confusion. Particle counters are designed to operate at particulate levels that are significantly lower than those used by photometers. The table below contains data taken from a Condensation Nucleus Counter. This shows the total number of particles (cumulative for ALL particles between approximately 0.1 and 1.0 um) and the corresponding particulate mass weight per unit volume. Please keep in mind that the relationship between particle size and mass is a cube function of the particle diameter. Increasing or decreasing the diameters or the standard deviation of the particle distribution used for analysis greatly effects the relative mass.

ug/l Total particles per cm3 Total particles per ft3
0.0001 5.56E+00 157,442
0.001 5.56E+01 1,574,417
0.01 5.56E+02 15,744,169
0.1 5.56E+03 157,441,686
1 5.56E+04 1,574,416,860
25 1.39E+06 39,360,421,500
100 5.56E+06 1.57442E+11

The table example data was obtained using an aerosol reagent with a density of 0.819 g/ml, count median diameter of 0.229 um, mass median diameter of 0.528 um and a count geometric standard deviation of 1.7. The 25 ug/l data point (in BOLD) was used to extrapolate all other data points referenced within the table.

25) Without Data Acquisition Software (DAS 1 or 2) how can the 2i Digital Photometer data be captured, stored and imported to a spreadsheet?

Even though DAS1 and DAS2 software are not compatible with the ATI 2i data output format, information can still be captured, stored to a file and imported into spreadsheet programs for statistical analysis or report generation. An example using RealTerm and Microsoft Excel is located at the following page (Click Here).

26) Aerosol Generator Recalibration

The aerosol generators ATI manufactures employ Laskin nozzles to produce aerosol. The Laskin nozzles are fabricated in strict accordance with Figure 4 of Naval Research Laboratory (NRL) Report #5929. These nozzles are then fitted into a Model III-A configuration generator. As indicated by the NRL Report, the aerosol produced in this configuration is sub-micron in size and highly reproducible.

The NRL Report also shows that if the nozzle is configured with half of the normal four jets, the airflow through it and the amount of aerosol produced is also reduced by half.

Experience has shown that these nozzles will not change significantly over their life time; however, they are subject to clogging if the compressed air supply is not filtered. If the jets of the nozzles become clogged the amount of aerosol output will be reduced. If this issue if left unaddressed, the nozzles will clog, ultimately causing the nozzle to produce little or no aerosol.

Because of the mechanical nature of the nozzle aerosol production, ATI does not recommend returning them for service on a regular basis. If the nozzles become clogged however, the unit should be returned for service. This same philosophy is also applicable to thermal aerosol generators, models TDA-5A, TDA-5B & ATI 5C, which use vapor condensation instead of Laskin Nozzles to generate aerosol.

With ISO 9000 quality programs gaining widespread use and acceptance, customers may requset a National Institute of Science & Technology (NIST) traceable certification on a generator pressure gauge. In addition, some certifiers have been asked for NIST traceable certification of the aerosol size distribution produced. ATI can provide gauge calibration, as well as aerosol size distribution for additional fees. Please contact one of ATI's customer service representatives for current pricing.

27) Aerosol Concentration

Over the past three decades, many ATI customers have asked questions regarding the amount of concentration required to accurately evaluate and test the integrity of a high efficiency particulate air filtration system.

To answer these questions, David W. Crosby of ATI wrote an article regarding concentration for Performance Review, the technical journal of the Controlled Environment Testing Association (CETA). This article appears in Volume 1, #5, Spring of 1994. A copy of this publication can be obtained from CETA, phone #202-737-0204.

In summary, the article critiques the subject of concentration and today's trend to use less concentration to challenge filtration systems. As indicated in the article, ATI concurs with the National Environmental Balancing Bureau (NEBB) guidelines for cleanroom certification which dictate the use of a challenge concentration between 20 and 60 micrograms per liter. While ATI photometer QA test procedures require that they be capable of obtaining a 100% setting from 10 micrograms per liter while maintaining a stable 0.000% reading, ATI does not advocate using such a low challenge unless necessary. Challenge concentrations of less than 10 micrograms per liter, though possible, are not recommended because of the resulting increases in instrument display instability.

June 2005 Update-
Since the above article was written, customers have questioned whether ATI photometers are accurate using concentrations below 20 micrograms per liter of upstream concentration.  The answer to this question has always been YES!  The reference to 20 micrograms per liter was intended to maximize stability in the photometer response while operating at a level considered "low" at that time. 

The solid-state amplifier circuit in ATI photometers, since the 1970's, was designed to accurately operate using a minimum of 10 micrograms per liter.  That basic design criteria remains true to this day.  ATI's newer "digital" photometer designs carry over the same operational amplifier used in the older analog instruments.  These newer digital units incorporate design improvements to the scattering chamber and operational controls to further enhance photometer stability at 100% using 10 micrograms per liter as a base setting.

28) Aerosol Photometer Recalibration

Frequently, customers inquire about recalibrating ATI Aerosol Photometers at various intervals. As a manufacturer of aerosol photometers, ATI can only make recommendations about recalibration cycles. The actual recalibration interval is controlled by each individual's corporate or company quality assurance program. For example, the Charleston Naval Shipyard has a Quality Assurance Program which dictates that any instrument using an analog meter indicator shall be recalibrated on a semi-annual basis. Therefore, they return the instrument every six months for recalibration to comply with their internal Quality Assurance Program.

ATI has numerous validated calibration records which demonstrate that the current TDA-2D, 2E, 2G, ATI 2H & 2i Series Photometers maintain their accuracy for a minimum of one year under normal usage. Therefore, ATI's maximum photometer recalibration interval is one year. While ATI can issue calibration certification for less than 12 months at customer request, we cannot issue calibration certification stating an interval greater than 12 months.

This one year interval may be extended at the discretion of the customer, however, that extension should be documented and controlled by their internal QA department.

29) Aerosol Photometer Response

The Photometer RTC (Response Time Constant) is the time necessary to achieve a reading 63% of the final reading.
The values provided below are intended to help the photometer user calculate the response time constant applicable to their usage.

These calculations assume a 28.3 lpm (1 cfm) sample flow rate.

Sample train is assumed to be a cylinder 13 feet (long) by 1/4 inch (ID) and is based on the characteristics of current industry photometer using a sample probe or 12 foot length of sample tubing.

Cylinder volume = πr2h     

r=0.125 in
r2=0.015625 in2
h=156 in (13 feet total sample tube length)
            7.659 in3 = 0.126 liters (total sample tube volume)

28.3 lpm sample rate
            0.266 seconds per sample transit time to area of observation

Leakage display refresh rates:

ATI Photometer models

  • 2E=0.266 seconds + 3 seconds (assumed jeweled meter full-scale response time)
  • 2G=1.0 second @ maximum display refresh rate
  • 2H=1.0 seconds @ maximum display refresh rate
  • 2i=0.4 seconds @ maximum display refresh rate


30) Laskin Nozzle Aerosol Concentration

The purpose of this bulletin is to summarize the basics of concentration expected from a Laskin Nozzle aerosol generator, which includes the ATI Models TDA-4B, 4Blite, 6C & ATI 6D.

The standard Laskin III-A Nozzle has four jets located beneath four entraining holes. The volume of compressed air required to produce a given amount of aerosol depends on the pressure of compressed air applied to the nozzle.

The original design research was conducted by Echols and Young of the Naval Research Laboratory. This information is covered in Naval Research Laboratory Report #5929, dated 26 July 1963. Using this report and it's Appendix, the DOP concentration versus pressure of the Laskin Nozzle can be extrapolated. Using the report information, it can be shown that when 20 psig is applied to the nozzle and diluted with 135 cfm of air, the DOP output of one Laskin Nozzle provides a concentration of 100 micrograms per liter. The data also indicates that each nozzle requires 2.67 cfm of compressed air to maintain the 20 psig pressure drop.

Over the years, the impression has been that the only way the Laskin Nozzle Generator can be used is by applying 20 psig to the nozzle. According to the Echols & Young Report, as you increase the pressure, the concentration increases and as you decrease the pressure, the concentration decreases. Further studies by Dr. Melvin First at the Harvard School of Public Health and Wendell Anderson at the Naval Research Laboratory have shown that by varying the pressure up and down on the Laskin Nozzle, the aerosol size distribution is not significantly affected (*). Wendell Anderson has also concluded that two of the jet holes may be plugged to obtain half of the standard concentration. Also, if three jets are plugged the concentration drops to one-fourth of the standard output concentration. This information is useful for customers who want to test air filtration systems that operate at lower than 135 cfm and other special low flow applications.

Detailed information on the Laskin Nozzle and its use is available in Section 8 of the U.S. Department of Energy, Nuclear Air Cleaning Handbook. Dr. First's reference is available in the American Industrial Hygiene Association's 1983 Journal, Pages 495 - 500.

ATI presented a paper to the Institute of Environmental Sciences (IEST) in 1993 which confirmed that the liquid level did not have significant effect on aerosol concentration. This data begins on Page 559 of the 1993 IEST Proceedings, Volume I.

* Recent testing by ATI has shown that there is a noticeable increase in both the CMD (count median diameter) and MMD (mass median diameter) of the Laskin nozzle aerosol when the applied pressures are at or below 10 psig. While this will not alter the results of most leakage testing, the increase in diameter will cause any concentration measurement relative to a photometer's internal reference to shift significantly due to changes in scattering intensity.

31) Laskin Nozzle Generator Conversion from DOP to PAO

What is necessary to convert my TDA-4 series or TDA-6 series Laskin Nozzle Aerosol Generator to Poly-Alpha Olefin (PAO)? Most Government agencies and departments are changing from DOP to PAO because DOP has listed on the suspected carcinogen list.

Since Dr. Hugh Carlon of the Army Chemical Center has completed research on Emery 3004, the Surgeon General has accepted PAO as an acceptable substitute for DOP in the U.S. Army. The Department of Energy and their various test sites, along with the Food and Drug Administration, are also accepting PAO as a replacement for DOP. Research conducted by the Army Chemical Center and Dr. Hugh Carlon has also shown that PAO is safe.

To convert TDA-4 series or TDA-6 series Generators from DOP to PAO:

  1. Drain the existing DOP liquid from the unit.
  2. Fill the reservoir to approximately half way on the sight gauge with PAO liquid.
  3. Drain the reservoir to eliminate any residue DOP remaining in the reservoir.
  4. Refill the reservoir to approximately half way on the sight gauge with PAO.
  5. Operate the unit as normal.
Correction Factors (Analog units)

As long as systems are tested in the normal manner, no adjustments are required. However, adjustment will be required if a situation should arise where the photometer used for detection is calibrated to DOP, the generator contains PAO, and the use of the Internal Reference is necessary.
The reason for this is that PAO has a different refractive index and gives a more intense photometric response than DOP. Therefore, a factor (of DOP) must be incorporated to insure accuracy if an upstream sample cannot be obtained to establish a 100% baseline and an Internal Reference for DOP must be used with some other liquid in the generator.

The CETA Performance Review, the technical journal of the Controlled Environment Testing Association, contains an article detailing the particulars on factors and adjustments required. This article was published in the Winter of 1993, Volume 1, No. 2. A copy can be obtained by calling CETA at (202) 737-0204.

32) Converting the TDA-5A/5B Generator from DOP to PAO Operation

DOP was put on the suspected carcinogen list years ago and an extensive amount of research work has been done by Dr. Hugh Carlon at the Army Chemical Center in Edgewood, MD to find a safe replacement liquid.

Because of Dr. Carlon's published findings at the International Society of Nuclear Air Treatment Technologies and the Institute of Environmental Sciences Annual Technical Committee Meeting, the majority of the filter testing industry has moved away from DOP to PAO-4 (4cSt polyalphaoelfin).

ATI has conducted a formal study on substitute liquids for the TDA-5A/5B and found that the best replacements for DOP are PAO-4 & Ondina EL Oil. ATI also determined that corn oil and mineral oil cannot be used.

Procedures required to convert the TDA-5A/5B from DOP to a substitute liquid are outlined in ATI Procedure PCL-051-WI. A flow meter capable of accurately measuring 10 lpm as well as a digital thermometer with a type 'J' thermocouple input capable of reading temperatures up to 800 º F are required to perform this procedure.

The ATI Service Department can convert your TDA-5A/5B and provide a complete service checkup at the same time.

33) Aerosol Photometer Calibration with DOP/PAO

A photometer can be used regardless of aerosol liquid substitution because by setting 100% by sampling actual upstream aerosol, the photometer is "calibrated" to the system under test. In normal situations, a sample of the aerosol-air mixture upstream of the filter under test is sampled and the gain level is adjusted to obtain a 100% baseline. The photometer is then set to the CLEAR mode and an air sample is drawn through a reference filter with all particulate removed from the air stream.

At this point on analog photometers, the unit can be switched to normal operating range, usually 0.1% or 0.01%, and the straylight control used to adjust the 0.000% baseline. Digital units require pressing the Zero key to set the 0.000% baseline. Establishing the 100% and 0.000% baselines constitutes calibrating the photometer to the filtration system under test (ratiometric mode).

There are some instances (i.e., biological safety cabinet certification) where an upstream sample of the aerosol air mixture cannot be obtained. In this situation, the concentration is calculated and the sensitivity of the photometer adjusted to the correct level using the Internal Reference feature of the photometer. When the Internal Reference feature is used, the photometer must be calibrated to the specific aerosol reagent in use or the result will not be accurate. This is because DOP and various substitutes used in the field have different refractive indexes and they give different concentrations and photometric responses for the same weight per volume.

For additional technical information regarding photometric responses and particle size distribution, please refer to "Concentrations Produced By A Laskin Nozzle Generator" written by David W. Crosby of ATI and "Characteristics Of Laskin Nozzle Generated Aerosols" written by Dr. Mel First at the Harvard Air Cleaning Laboratory, Page 109 through Page 125 in the 1990 21st DOE/NRC Nuclear Air Cleaning Conference Proceedings.

David W. Crosby has also written an article which was published in Performance Review, the technical journal of the Controlled Environment Testing Association, which details various factors and correct adjustments to compensate for substitute liquids. A copy of this article can be obtained by calling CETA, telephone (202) 737-0204.

The ATI Service Department will calibrate an older photometer to either DOP or PAO-4. TDA-2GA and later analog photometers, as well as all digital models, have PAO-4 and DOP Internal Reference values stored from the Factory. A customer returning a pre TDA-2GA analog photometer for recalibration should specify the desired liquid.

34) TDA-4A/4Blite/4B Compressor Requirements

The TDA-4A, 4Blite & 4B Aerosol Generators use Laskin Nozzles to generate aerosol. These require large amounts of compressed air. Each nozzle, when operating at 20 psig pressure, requires 2.65 actual cubic feet a minute (acfm) of compressed air. If the number of the nozzles is increased, the quantity of compressed air will also increase. Therefore, when using three nozzles at 20 psig instead of one nozzle, the amount of compressed air required will triple to 7.95 acfm.

The maximum air pressure required is approximately 22 acfm at 30 psig. This air compressor capacity requires a relatively large, non-portable compressor.  Operation of these generators using less than 3 nozzles is possible with a portable compressor of approximately 1-1/2 HP.

Please see ATI FAQ # 18 for more information.

35) Mass Flow versus Volumetric Flow

Mass flow measures just what it says, the mass or weight of the gas flowing through the instrument. Mass flow (or weight per unit time) units are given in pounds per hour (lb/hour), kilograms per sec (kg/sec) etc. When your specifications state units of flow to be in mass units, there is no reason to reference a temperature or pressure. Mass does not change based on temperature or pressure.

However, if you need to see your results of gas flow in volumetric units, like liters per minute, cubic feet per hour, etc. you must consider the fact that volume DOES change with temperature and pressure. To do this, the density (grams/liter) of the gas must be known and density changes with temperature and pressure.

When you heat a gas, the molecules have more energy and they move around faster, so when they bounce off each other, they become more spread out, therefore the volume is different for the same number of molecules.

Think about this: The density of Air at 0°C is 1.29 g/liter. The density of Air at 25°C is 1.19 g/liter

The difference is 0.1 g/liter. If you are measuring flows of 100 liters per minute, and you don’t use the correct density factor then you will have an error of 10 g/minute!

Volume also changes with pressure. Think about a helium balloon with a volume of 1 liter. If you could scuba dive with this balloon and the pressure on it increases. What do you think happens to the weight of the helium? It stays the same. What would happen to the volume (1 liter)? It would shrink.

Why is the word “standard” included with the volume terms liters and cubic feet in mass flow applications?

A mass flow meter measures mass …and we know we can convert to volume. To use density we must pick one (or standard) temperature and pressure to use in our calculation. When this calculation is done, the units are called standard liters per minute (SLM) or standard cubic feet per minute (SCFM), for instance, because they are referenced to a standard temperature and pressure when the volume is calculated.

Using the example at the bottom of this page, we can see a standard liter can be defined differently. The first balloon contains 0.179 grams of Helium at 0°C and 760 Torr (density of 0.179 grams/liter). Heat up that balloon to room temperature and the volume increases, but the mass has not changed. The volume is not 1 liter anymore, it is 1.08 liters.

So to define a standard liter of Helium at 25°C we must extract only one liter from the second balloon and that liter weighs only 0.164 grams.

If a mass flow meter is set up for STP at 0° C and 760 Torr, when it measures 0.179 grams of He, it will give you results of 1 SLM. If a second meter is set up for STP at 25° C and 760 Torr, when it measures 0.164 grams, it will give results of 1 SLM.

36) ATI TDA-5A/5B Comparison Study of DOP Substitutes


Block Temperature

Internal Pressure


Photometric Concentration


DOP/DEHP 750-760F 5 psig 10-11 lpm 60% with metering valve
fully open
Aerosol stream is very stable, uniform and dry
After varying the concentration from one end of the
range to the other, aerosol is still very stable and
DOS/DEHS 780-790F 4.75 psig 6 lpm 75% Aerosol stream is dry and uniform. However, occasional
clogging of the block occurs from higher block
(Emery 3004)
760-775F 5 psig 7 lpm 75% Aerosol stream is dry and uniform. Very stable through
an entire run cycle. An increase in flow resulted in
aerosol wetting out.
Approved by FDA, DOE, US Army, Surgeon General
as DOP replacement
Ondina Oil 760-780F 5 psig 7 lpm 75% Aerosol stream is dry and stable. Wetting out did not
occur until temperature was reduced to 670 F.
Pulsation did not occur until temperature reached
Corn Oil 750-760F 5 psig 10 lpm N/A Aerosol stream extremely wet. Increasing temperature and  reducing flow resulted in no aerosol output at all. 


Mineral Oil 750-760F 5 psig 10 lpm N/A Aerosol stream semi-wet. Increasing the temperature and
reducing flow resulted in drier stream of aerosol but
clogged the block very quickly.

37) Leak Testing with Particle Counter

Possible isues Testing Filter Systems with a Particle Counter

  1. Particle counters used in filter testing report the number of particles in a specific sample volume. To do so accurately, a sample must be taken at a specific location for fixed period of time. If a sample is time only allows a fractional portion of the reportable volume, the count value must be extrapolated to a uniform constant volume adding error to the measurement.
  2. Particle counters will only give accurate counts up to approximately 300,000 particles per cubic foot per minute (or 30,000 particles per cubic foot in 6 seconds). Concentrations higher than this introduce large COINCIDENCE LOSS which leads to errors of 5-20%, depending on the aerosol concentration and the particle counter. It is industry acknowledged that two identical particle counters manufactured and calibrated by the same company will not produce identical results when exposed to the same aerosol sample under field conditions.
  3. A good example of the accumulation of errors is one manufacturer's filtration system, which purports to use 10E6 to 10E7 particles per cubic centimeter which requires diluters to sample the upstream challenge concentration. This equates to 2.83 x 10E10 to 2.83 x 10E11 particles per cubic foot. The diluters are 10:1 units which have a 5-10% error margin. By placing 2 diluters in series, the error margin increases to 10-20%, and gives a dilution of 100:1. The lower concentration is 2.83 x 10E10 particles/cu. ft. = 2.83 x 10E10/100 = 2.83 x 108 particles/cu. ft. or 283 million particles per cubic foot. Particle Counters CANNOT count that many particles accurately. Therefore, any downstream sample reading, even for less than 1 minute, would not be reliable.
  4. From a practical standpoint (forgetting diluter error, count error, etc.) and just calculating scanning time, the filtration test system becomes unwieldy. Using an Isokinetic Probe, per IEST Recommended Practice, sampling at 1 cfm and with an opening of 3" x 0.5", it would take 384 readings (counts) at 6 seconds each, or 38.4 hours to scan a 24" x 24" HEPA filter. Remember, in addition, a 10 - 20% error rate due to extrapolating what the particle count would be for a full minute by adjusting the count obtained in just 6 seconds by a factor of 10.

A particle counter counts the number of particles passing through its viewing area. Most particle counters don't pass the entire 1 cfm sample through the viewing area but only a portion which introduces more counting error.

Knowing the sample flow rate (1 cfm) and the duration of sample time (1 minute), it can be determined how many particles were in that one cubic foot sampled for one minute. This is what they were designed to do, and as such, make an excellent monitor for clean or sterile areas.

An aerosol photometer is a true ratio detector since it measures particles "en masse" and all of the particles travel through its viewing or detection area. ATI photometers are capable of measuring mass concentrations as high as 600 micrograms per liter and are sensitive enough to measure accurately and instantaneously concentrations down to 0.00001 micrograms per liter. Using an ATI photometer, the same 24" x 24" HEPA filter can be scanned in accordance with IEST and other Standards in 1.6 minutes. If there is any area that has leakage > 0.01%, it can be pinpointed in seconds.

An excellent article on this subject was printed in Performance Review, a peer reviewed technical journal published quarterly by the Controlled Environment Testing Association (CETA). The article titled HEPA & ULPA Filter Installation Leak Tests by Ulrich Dietrich appeared in the summer of 1995 edition. For a copy, contact CETA at (202) 737-0204.

38) PAO-4 Liquid (aka Emery 3004)

ATI frequently receives many different questions from customers regarding the use of Emery 3004. This Technical Bulletin addresses the most frequently asked questions.

EMERY 3004 was a trade name for 4 cSt polyalphaolefin (PAO-4), CAS #68649-12-7. The Henkel Company originally manufactured Emery 3004 PAO which was used in the initial research performed by Dr. Hugh Carlon et al. ATI carries 4 cSt polyalphaolefin, sold under the name PAO-4, in stock for the convenience of its customers. It is sold in 1 or 5-gallon containers and can be shipped via UPS or Federal Express. The 5-gallon container has a built in pour spout to aid customers in filling the aerosol generators.

The US Army Surgeon General has approved 4cSt PAO as the official replacement liquid for Di (2-ethylhexyl) phthalate (DOP, DEHP), CAS #117-81-7. Please note that it is not up to the liquid manufacturer to approve it for a specific use. Most government agencies or departments do not approve anything. For example, 4 cSt PAO is not approved by the Department of Energy. However the Department of Energy accepts the use of PAO as a replacement for DOP. In a letter from Robert L. Sorensen of the Food and Drug Administration to the Director of Quality Assurance of Eli Lilly and Company he states that based on submitted documentation, research work, and papers, the FDA concurs with the military that 4cSt PAO is an acceptable replacement for DOP.

There have recently been rumors that PAO manufactured at different sites are not suitable replacements for DOP/DEHP.

The following is an excerpt from the Food & Drug Administrations Human Drug CGMP Notes (Vol. 4, Number 4), December 1996.

"The original manufacturing site which produced the Emery 3004 (PAO) for the data submitted has changed since the study and Emery 3004 (PAO) is now manufactured at a different site. Discussions with the Army and the companies involved in the original studies indicate the product remains the same from the new site of manufacturing. CDER has also compared the original specifications and the new site specifications along with data from the Material Safety Data Sheets and agrees that there is no significant difference in the product from either site."

"The Chemical Abstracts Service (CAS) number which identifies this product also remained as 68649-12-7."

"Other reported alternatives used in the industry include DOS (Di (2-ethylhexyl) sebacate) and Ondina Oil. However, no manufacturer has yet submitted all the necessary data to evaluate these alternatives."

"As such, Emery 3004 PAO with the CAS number 68649-12-7 still remains an acceptable replacement for DOP."

Contact for further information:
Michael J. Verdi, HFD-322
Phone: 301-594-0095

The full text of the referenced document is available HERE.

Other relevant developments that ATI feels its customers should be aware follow:

  1. Beginning in the mid-2000's some manufacturer's of 4 cSt polyalphaolefin began using dual CAS#'s to define the product they were producing. 4 cSt polyalphaolefin previously identified as CAS# 68649-12-7, began including CAS# 68037-01-4, even when supplied by the same manufacturer under the same product number. The explanation was that the "New" CAS#, 68037-01-4, more accurately defined the product than the older number.
    ATI has performed comparison testing on aerosol characteristics relevant to both filter leakage and efficiency testing and found no reportable difference between the two CAS identified products. The aerosol particle size distribution produced, aerosol properties and photometric response were the same.

  2. The U.S. Army, in conjunction with some Government attorneys, has acquired patents on the use of this liquid to generate aerosols. The first patent number 5,059,349 was issued on 22 October 1991. This patent is very specific in nature and covers the use of PAO and its use as a liquid to generate a monodispersed aerosol in the ATI TDA-100 Aerosol Penetrometer that is used for measuring the efficiency of respirator filters. The second patent 5,059,352 was issued on the same date. This particular patent covers the liquid PAO and its use in a prototype aerosol penetrometer that is no longer used for performing aerosol filter testing. The third patent 5,076,965 was issued on 31 December 1991 and covers the use of PAO liquid as the substance in a TSI model 8110-filter tester. These three patents really have no application in the normal in-place filter certification work that is carried out world wide in the pharmaceutical, electronic, and aerospace industries, although it is believed that one pharmaceutical company did pay the Army for a license agreement.

39) Concentration Measurement with Photometers

A question that has arisen many times over the past thirty some years is whether or not the ATI Photometer can be used to measure concentration levels.

The answer to the question is an emphatic yes, but it's given with a very big caveat.

An aerosol photometer reacts to particulate that is drawn through the viewing area, (optical convergence point) and scatters light forward. The greater the amount of particulate, the greater the light scattered forward. This light is optically focused on a photomultiplier tube which converts the light to an electrical current. This current is sent to the amplifier for amplification, signal processing, and display. Therefore an aerosol photometer is an excellent, instantaneous concentration indicator.

The mathematical formula for the light scattered forward by the particle is not a very difficult, complex formula. Basically, it says that the larger the particle, the more light scattered forward and it is exponential. For example, an aerosol photometer will give you the same signal for ten one-micron particles as it would for one ten-micron particle. Since the aerosol photometer looks at particulate matter en masse, it would be a good instrument for indicating concentration. To obtain accurate results, the photometer must be calibrated to the aerosol whose concentration is to be measured.

A good example of this is, in the early 60's the Naval Research Laboratory (NRL) started calibrating ATI photometers against the aerosol generated in a Q-127 Aerosol Penetrometer which generates a monodispersed aerosol. David W. Crosby, of ATI, designed and patented an adjustable Light Leak that could be set at any point and used to adjust the photometer sensitivity to any particulate concentration level for a specific aerosol. In modern ATI photometers this is currently called the Internal Reference.

Here's how the Internal Reference works. When an aerosol photometer is returned to ATI for recalibration it is thoroughly cleaned, optically realigned, electronically calibrated, performance checked, and then it is calibrated to a specific aerosol. The current default aerosol ATI uses is DOP. ATI generates a polydisperse aerosol of a known NIST traceable concentration. After the photometer has been thoroughly warmed up, a sample of this known concentration aerosol is drawn into it and the photometer sensitivity is adjusted for a reading of 100%. If a DOP polydisperse aerosol sample is then drawn in and a reading of 50% is obtained it indicates that there is a concentration of 50 micrograms per liter. It is easy to assume that the same response would be obtained if another aerosol were measured that was generated by the same nozzle and a similar liquid. Unfortunately this is not true. Some information on this subject is available in a paper David W Crosby presented at the 21st International Department of Energy/Nuclear Air Cleaning Conference in 1990. (This paper is also is available in the 1993 Proceedings of the Institute of Environmental Sciences on page 559.) Basically, even if the aerosol size is similar, the refractive index is different for different liquids and therefore photometric responses will differ from the gravimetric real time concentration measurement.

This explains the "large caveat" mentioned earlier. To have an accurate indication of the concentration, a photometer must be calibrated to the specific aerosol that will be sampled.

To calibrate a photometer to a specific aerosol:

  1. Warm up the photometer for a minimum of 30 minutes so that it is thermally stable. This will minimize any temperature or electronic drift.
  2. Adjust the photometer with the Internal Reference to a 100 microgram per liter concentration of DOP aerosol.
  3. Using the record out jack of the photometer, feed the signal to a recorder for hard copy results.
  4. Sample the aerosol and, while sampling the aerosol with the photometer, also draw a sample through a personal sampler cassette, or similar device. If there are large concentrations of particulate you may only need to run this test 10 to 15 minutes. If the concentrations of particulate are very low you may want to run this over an 8-hour period to get quantifiable results.
  5. Look at the data to calculate a factor that you must use with your photometer for future measurements of this type.
A good example of this application occurred in a Washington, DC, suburb where an ATI customer had to guarantee that during construction no dirt would get into the computer system and cause a head crash. ATI decided to continuously monitor the area in the vicinity of the computer main frame heads of their class 10,000 clean room. Since the area was a clean area, very low readings were obtained on the photometer after it was set up and calibrated for a 100 microgram per liter concentration level. ATI sampled the air in the same area through a 47- millimeter gravimetric sample pick up, as outlined in the above referenced paper. At the same time ATI started sampling with the photometer and feeding the signal to a strip chart recorder for hard copy data. ATI ran this test for 8 hours and weighed the gravimetric pickup sample. The results obtained measured 0.0094 micrograms per liter, rounded off to .01 micrograms per liter while the photometer reading averaged 20 on the 0.1% range or a reading of 0.02%. This 0.02% is equivalent to a 0.02 microgram per liter concentration indication. This worked out quite well since there was a factor of 50 percent.. In other words, the photometer would read twice the actual concentration in the area. In this case the factor was quite high since the monitored area was environmentally controlled. In the general work place and with other aerosols the factor usually is not as large since more particulate and larger size particulates are found in these areas.

Even if the photometer can't be calibrated to the actual aerosol being monitored, the concentration, in most cases, can be instantly read within approximately 20%. A gravimetric test can be performed to establish a correlation factor to make the result of the photometer more accurate.

40) TDA-5B, 5A (5C) Pulsing/Wet Aerosol Output

Problems with the aerosol output of the thermal generators seem to occur frequently. Since DOP and PAO are hydro-carbon products, carbon builds up in the heater block.

To correct this problem, it is assumed that the heater block and heaters are working properly.
That is, the unit is maintaining a 765 ± 15 º F or 405 ± 10 º C operating temperature, and there is no carbon build up restricting the heater block nozzle. To check for nozzle restriction, insert a piece of wire (such as a paper clip) into the nozzle tip while it is operating to remove any residue which may have accumulated.  Caution: The nozzle tip is very hot.  Use a pair of long nose pliers to hold the wire.

If the heater block and heaters are working properly and the heater block nozzle is not restricted, the problem should be with the setting of the internal regulator.   Either it is adjusted for too much flow or it has failed.   The problem may be solved by not having the metering valve fully open (try 3/4). This will reduce the flow of liquid to the block and minimize droplet formation at the nozzle tip. These droplets are normally the cause of aerosol pulsation.

5 series Generator Output Adjustment procedure

41) Using the Digital TDA-2G Aerosol Photometer

This bulletin is intended to familiarize users of "old fashioned" analog photometers with knobs and switches with the digital design by comparing the TDA-2D or TDA-2E photometers with the digital TDA-2G model.

To Perform 100%

Analog Unit - To set the 100% baseline in the analog unit, the range switch would first be set to the 100% range, the selector valve would be turned to upstream and a sample of the aerosol air mixture challenge upstream of the filtration system under test would be drawn into the photometer. Then the gain control would be adjusted for a 100% reading.

TDA-2G - To accomplish the same thing on the digital TDA-2G unit, the <ENTER> key is pressed, then 100 and <ENTER> again. The selector valve is turned to the upstream position to input the aerosol sample. Since the unit is auto ranging there is no range switch to place in the 100% position; it is done automatically. The red LED over the 100 key is illuminated while the unit is setting the 100%, and extinguishes when the process is completed. The red LED over the 0 key illuminates and flashes prompting the user to straylight or 0% the unit by pressing the <ENTER> key.

Establishing 0.000% (Straylight)

Analog Unit - On the analog unit , after 100% was set, the selector valve was switched back to the clear position to allow particle free air to be drawn through the detector from the internal HEPA filter. The range switch was then placed in the 0.1% or 0.01% range and the straylight control adjusted for a 0 indication on the analog meter.

TDA-2G - In the digital 2G unit, after the 100% has been established the red LED on the 0 key flashes to prompt the user to 0 or straylight the unit. This is accomplished by placing the selector valve in the clear position and then pressing the <ENTER> key. The digital unit will automatically zero (straylight) itself, beep, and extinguish the red LED on the 0 key to indicate straylight is completed. The display reads either 0.000 or 0.0000, depending on whether three or four decimal places were selected. Now the 100% and 0.000% baselines have been established which means the photometer is ready to test the system to which it was just calibrated.


Analog Unit - For testing on the analog unit, the selector valve was placed in the downstream position which then drew a sample, usually through the scanning probe, and the user began to scan the filter system. If the reading went up, the range switch would need to be switched to a higher range so that the needle on the analog indicator wouldn't be off-scale. The user would again scan and move the probe about trying to pinpoint the maximum reading indicating where the leak was emanating from the filter.

TDA-2G - To do this with a digital unit is essentially the same; that is, the selector valve is turned to the downstream position and the filter system scanned. The main advantage with the new digital unit is that it is not necessary to switch sensitivity ranges because of the auto ranging feature. The display is digital and there is a bar-graph below the numeric display for an analog indication. The user can either observe the bar-graph and concentrate on looking for a peak reading or can observe the digital display.

Concentration Measurement

Analog Unit - To measure concentration with the analog unit, the manufacturer instructions were followed to activate the Internal Reference signal with the push button switch and set the gain control for a reading of (typically in the ATI units) 10%. This established a gain level or sensitivity level such that if 100 micrograms per liter of DOP (or PAO, if the unit was calibrated for PAO) was drawn into the unit, the gain control would read 100%. This was a nice feature since, if the user wanted to know what the challenge concentration was, the INT REF could be used to establish the 100 microgram per liter sensitivity, the selector valve could be switched to upstream and, if the reading obtained on the system under test was 65%, it followed that the system had a concentration of approximately 65 micrograms per liter.

TDA-2G - This is an occasion where the new digital unit is a much better performer than the analog unit. First of all, there are three Internal Reference settings: P1 for DOP, P2 for PAO, and P3 for any other alternative liquid, and all that is necessary for P3 is entering a factor. For instance, if mineral oil is to be used and the systems under test are normally tested with DOP, the factor for mineral oil (which is 0.90) would be used. To set the sensitivity to 100 micrograms per liter on the digital TDA-2G, the <ENTER> key is pressed, followed by Ref then <ENTER>. P1 flashes on the display if the unit was programmed for DOP, P2 if programmed for PAO, and P3 if programmed for an alternate liquid. A number will be displayed, normally 100 (this number may be reduced if desired) and the unit automatically sets the sensitivity level to 100 micrograms per liter of either PAO or DOP, whichever has been selected. Once this has been completed, a red LED flashes on the 0 key prompting the user to 0 or straylight the unit.

This is accomplished by placing the selector valve in the clear position and then pressing the <ENTER> key. The digital unit will automatically zero (straylight) itself, and when it is complete beep and extinguish the red LED on the 0 key to indicate straylight is completed. The display reads either 0.000 or 0.0000, depending on whether three or four place display was selected. Now the valve selector is switched to upstream just like the analog unit and the display reads concentration in micrograms per liter. If an upstream reading was taken on the system described for the analog unit, the TDA-2G display would read 65.0 representing a concentration of 65 ug/l.

100% Adjustment Without Upstream Sample

All certifiers must occasionally adjust the sensitivity of the photometer to a calculated concentration level because it is impossible to get an upstream sample to do this. An excellent example of this is a contaminated biological safety cabinet.

Analog Unit - With the TDA-2D or TDA-2E, concentration had to be calculated and then the concentration calculation had to be used to determine the Internal Reference setting for a correct sensitivity level. This was one of the most complicated operations using the photometer and it was difficult to learn. Essentially the total flow of the cabinet would be measured; for example, assume a total flow of 540 CFM. Since it is known that one Laskin nozzle at 20 psig provides 100 micrograms per liter into 135 CFM, that 135 can be divided by the new CFM (540), assuming one nozzle, resulting in a calculation of 25 micrograms per liter. Since the concentration is now 1/4 of 100 micrograms per liter the Internal Reference setting would be increased from the normal 10% to 40% (4 times the gain) to have the correct sensitivity for 25 micrograms per liter.

TDA-2G - All that is necessary to do this on the TDA-2G is to press the <ENTER> key, followed by the REF key, then scroll up or scroll down until the calculated concentration is displayed (which in this case is 25 micrograms per liter) and press <ENTER> again. The unit automatically adjusts the sensitivity level of the photometer to display 100% when exposed to 25 micrograms per liter of concentration, and then prompts the user to 0 (stray light) again.


Analog Unit - The TDA-2D unit didn't have an alarm unless it was ordered as a special option. Generally a contact meter was used and the red pointer was set to the point of ALARM. In the later versions of the TDA-2E photometer an electronic ALARM was developed that could be set at any point on the unit or disabled. An audible ALARM sounded when that set point. was exceeded.

TDA-2G - The digital TDA-2G has two types of alarms. The first alarm is a visual alarm; when the alarm set-point has been exceeded the display will flash on and off visually indicating that the alarm set point has been exceeded. The second alarm is an audible alarm. The visual and audible alarms can be enabled or disabled.

To do this, the <ENTER> key is pressed, followed by the ALARM key. Either three or four dashes will be displayed to indicate that both the audible and visual alarms have been disabled and the alarm light will flash red. If the alarm light was already on, indicating that the alarm had been previously set, a reading will be displayed which will be the actual alarm set point. If the dashes are displayed indicating that the alarm features were disabled, the alarm key must be pressed once more before the set point can be adjusted.

To increase or decrease the set point, the up scroll or down scroll  keys are pressed to change it to the desired set point , then <ENTER> is pressed again. Both the visual and audible alarms are now going to activate when the set point just entered is exceeded. When programming parameters, there is an option (L1) to turn the audible ALARM on or off.


Programming the TDA-2G consists of selecting the photometer's operating parameters. The unit is turned on and when self-diagnostics are completed the display contains a series of 8's and the bar-graph is illuminated. At this point, if the <ENTER> key is pressed followed by the scroll up key, the L0 parameter is displayed. If the unit is up and running and the <ENTER> key is pressed followed by the scroll up key, the L0 parameter is also displayed. L0 sets the parameters selected using the L1 through L10 parameters.

Pressing the scroll up and scroll down keys scrolls through the parameter list. When L1, the parameter for the audible ALARM is displayed, the <ENTER> key is pressed and scroll up and scroll down keys are used to turn the audible ALARM on or off; when the ALARM is enabled a 1 is displayed and when it is disabled a minus sign is displayed. When the ALARM is set to the desired operating mode, <ENTER> is pressed and the display returns to the parameter list.

To change, another parameter use the scroll up and scroll down keys to display the desired parameter, scroll through the options for the displayed parameter, and press the <ENTER> key when the desired option is displayed. L2 allows the display rate to be changed and L3 allows the 100% sample time to be adjusted. L4 selects the number of decimal places displayed and L5 selects the Internal Reference. The Internal Reference choices are P1 for DOP, P2 for PAO, and P3 which is a DOP based correction factor for the desired substitute liquid. The L6 setting displays the number of operating hours on the unit and L7 allows the unit to be reset to the factory defaults which are listed in the operating manual. L8 indicates the software revision that currently is installed on the unit and L9 allows the bar-graph to be enabled or disabled. Finally, L10 allows the intensity or brightness of the display to be increased or decreased. Consult the operating manual for more details on these programmable features.

42) More Emery vs. DOP (Follow-up to FAQ #22)

It is ATI's understanding that the US Army has sent letters to certifiers demanding a $20,000 license fee to use this liquid. Steve Halsey, a member of the International Air Filter Certifiers Association (IAFCA), has begun a dialogue with the US Army patent attorney in regards to this fee.

If you encounter problems with the US Army or want additional information on this controversial subject, please call Steve Halsey at (703) 351-5077 or fax at (703) 435-1744. You may write to Steve Halsey at Halsey Rains & Fox, 2111 Wilson Boulevard, Suite 800, Arlington, VA 22201.

43) TDA-5A/5B Background Penetration Readings

It has been brought to the attention of ATI by some very knowledgeable and highly experienced certifiers that high penetration readings can be obtained while scanning HEPA filter systems with thermally generated polydisperse aerosol. If the same systems were tested with cold generated (Laskin Nozzle) aerosol, the penetration results would be 0.000% penetration. The penetration readings obtained with the thermally generated aerosol will vary from .002% to >.01% depending on the size, media, and manufacturer. This reading is obtained anywhere on the downstream side of the filter. This phenomenon is typically called a background reading or "bleed-through".

To resolve this anomaly, ATI advises certifiers to use the straylight control to eliminate the background reading and scan as usual on the analog photometers, and to reset the 0% while scanning on TDA-2G or 2H digital photometers. Leakage values exceeding the failure threshold of the filter are produced by a different phenomena and will generate readings distinguishable from the background penetration.

The aerosol particle size produced by thermal generators is significantly lower than the cold aerosol, approaches the Most Penetrating Particle Size (MPPS) and therefore passes through the filter media more readily. Sample data, obtained from ATI thermal generators, is available beginning at FAQ #8 showing this smaller particle size.

44) Thermal Generator Inert Gas Propellant: Applicable to TDA-5A, TDA-5B & ATI 5C

Many customers inquire about the gas requirements of the poly-dispersed aerosol generator manufactured by ATI. The older version is the model TDA-5A and the current model is the TDA-5B. The major difference between the two models is not the capacity or capabilities of the generator, but improvements requested by customers over the years. The heater block assembly and heaters are the same in both units. The major improvements are a larger reservoir which allows testing up to four hours at full capacity whereas the old TDA-5A would run out of liquid in twenty to thirty minutes and would have to be refilled with whichever liquid was in use (DOP or PAO). The other improvements include: a digital temperature indicator of heater block temperature, controls mounted on the front panel with the discharge on the rear panel, ergonomic handle, and a larger cabinet.

Both units use approximately 20 standard cubic feet per hour of compressed gas. An inert gas is used since the heater block temperature is above the flashpoint of either DOP or PAO. ATI recommends the use of nitrogen; it makes no difference whether Oil Pumped (OP) or Water Pumped (WP) nitrogen is used. The reason for this recommendation is the availability of nitrogen at any gas supply house. Also, there are B tanks or 60 cubic foot cylinders of this gas available. The B tank will allow about 3 hours operation of the TDA-5A or TDA-5B unit and the 60 cubic foot cylinder will allow about 4 hours of operation. Another advantage of the B tank or the 60 cubic foot cylinder is that they weigh only about 30 pounds, are small, and are portable.

Other gases that are readily available are CO2, argon, neon, and helium. CO2 is available in smaller cylinders which lend themselves to portability. Over the years, ATI customers have reported successful use of argon and neon. At a demonstration of the TDA-5A unit to engineers at Dahlgren Naval Surface Weapons Laboratory in VA, the only gas available was helium, which worked fine.

The important factors about the gas are:
1) It will not support combustion &
2) A two-stage regulator is used to supply the pressure to the TDA-5A or TDA-5B generator.

A two-stage regulator maintains a relatively constant output pressure, where a single stage regulator's output varies extensively since the pressure of the bottle starts at 2200 lbs. per square inch gauge and then continually drops in pressure as it is used. It is imperative that the pressure to the TDA-5B aerosol generator be adjusted to 50 lbs. per square inch gauge. The reason for this is that there is an internal pressure regulator which is factory adjusted individually on each unit for optimum performance. If the supplied generator inlet pressure to a pre-adjusted regulator is changed, its output will also change, and this will affect operation of the unit. On units that are experiencing a marginal reduction in operational efficiency, a decrease in the supplied pressure from the 50 psi level will result in an increase in inert gas flow through the block. Under some circumstances this will provide a sufficient change in the operating characteristics to allow continued use without altering the aerosol size characteristics. If the aerosol output should become "wet", use of the generator must be discontinued immediately until the unit is serviced.

Nitrogen used by ATI for in-house testing purposes has the following properties:

Molecular Weight: 28.01
Specific Volume: 13.8 CF/lb
Flammable Limits: Nonflammable
CGA Valve: 580
DOT Name: Nitrogen, Compressed
UN No.: UN1066
DOT Class: 2.2
DOT Label: Nonflammable Gas
CAS Registry: 7727-37-9

Inert Gas Consumption rate: ~20 CFH @ 50 PSIG generator inlet pressure.

45) Year 2000 Compliance (Y2K)

Many of our customers have asked if the year 2000 will affect the operation of our portable aerosol photometers and aerosol generators.

The answer to this question is no. The majority of ATI's portable equipment does not contain microprocessors and the associated clock circuitry. This includes not only all of our portable photometers, but also our non-electronic units, such as aerosol generators.

The equipment that does include clock circuitry was designed to be Y2K compliant.

46) Aerosol Correction Factors

Aerosol Generators
The nozzle pressure values discussed below are for use when substitute liquids are chosen for producing aerosol rather than DOP and the aerosol output of a Type III-A Laskin nozzle generator must be calculated.


  • DOP-20 psi applied with dilution airflow of 135 cfm yields 100 mg/m3
  • PAO-23 psi applied with dilution airflow of 135 cfm yields 100 mg/m3

    13,500 X (# of nozzles in use) ÷ total filter airflow (CFM)= Aerosol concentration (mg/m3)

Adjustment of the nozzle pressure to accommodate the reagent in use is independent of the
photometer internal reference reagent setting discussed below. 

Aerosol Reagent

Nozzle Pressure (PSI)

PAO-4 (CAS 68649-12-7 or 68037-01-4)

DOS/DEHS (CAS 122-62-3)


white mineral oil (CAS 8042-47-5)


polyethylene glycol (CAS 24322-68-3)


paraffin oil (CAS 8012-95-1)


corn oil (CAS 8001-30-7)


Aerosol Photometers

Photometer internal reference factors are multipliers used to adjust the reference setting required for a 100% reading.
They are only necessary when using an aerosol reagent that the photometer has not set up to use during factory calibration.
There are two examples that follow, one for analog and one for digital photometers.

Note: Both Analog and Digital photometers apply the internal reference factor to the 100% reference value used for DOP.

Aerosol Reagent Internal Reference factor
DOP/DEHP (CAS 117-81-7) 1.00
PAO-4 (CAS 68649-12-7 or 68037-01-4) 0.73
DOS/DEHS (CAS 122-62-3) 0.96
white mineral oil (CAS 8042-47-5) 0.90

polyethylene glycol (CAS 24322-68-3)


paraffin oil (CAS 8012-95-1)


corn oil (CAS 8001-30-7)



Example 1: Analog series - TDA-2D, TDA-2E

  • DOP-10.0% setting required for 100% response to 100 mg/m3
  • PAO-7.3% setting (10.0% x 0.73 correction factor) required for 100% response to 100 mg/m3
  • DOS-9.6% setting (10.0% x 0.96 correction factor) required for 100% response to 100 mg/m3
Example 2: Digital series - TDA-2G & 2H
  • DOP with P1 selected - 100 required for 100% response to 100 mg/m3
  • PAO with P2 selected - 100 required for 100% response to 100 mg/m3
  • DOS with P3 selected - 0.96 (0.96 X 100 DOP value) required for a 100% response to 100 mg/m3

Note: The above correction factors apply only to air operated generators. If a thermal type generator, TDA-5A, TDA-5B or 5C is being used the upstream concentration must be sampled to obtain a 100% setting.

47) TDA-2G & TDA-2GN Quick Reference Guide


To enter setup mode press <ENTER> then the UP arrow
L0- Run L1- Audible Alarm
L2- Display Rate
L3- 100% Sample Time
L4- Decimal Places
L5- Internal Reference
L6- Hour Meter
L7- Factory Defaults
L8- Software Revision
L9- Bar graph
L10- Display Intensity
Use the UP or DOWN arrow to select and <ENTER> to view setting


<ALARM> Led Flashes - (displayed indicating alarm is disabled)
<ALARM> Last alarm set point displayed, use the UP or DOWN arrows to change
<ENTER> Alarm set point entered and LED will stay lit


<ALARM> Set point displayed
<ALARM> displayed indicating alarm will be disabled
<ENTER> Alarm disabled


3-Way Valve to Clear
<REF> P1 100.0 or last reference setting displayed, use the UP or DOWN arrows to change
<ENTER> Scans 15 seconds, then 0 LED flashes
<ENTER> Sets 0% - approx. 5 seconds Ready for Testing


Sample Line Connected & 3-Way Valve to Upstream
<100> Led Flashes
<ENTER> Bar graph Scans, then 100 flashes and averages 100% for duration of L3 Setting, Zero LED flashes, Turn 3 - Way Valve to Clear
<ENTER> Sets 0% - 5 seconds
Ready for Testing

UPSTREAM CHALLENGE QUICK CHECK FEATURE- (Will function only if INT REF was established previously)

3-Way Valve to Upstream with Sample Line Connected (Now displays 100%)
<REF> Bar graph scans 15 sec.
Displays actual Upstream concentration for 5 seconds
Bar graph scans and unit returns to 100% baseline

48) 2H & 2HN Quick Reference Guide


To enter setup, press < D> then < ENTER >
Press < D > or < Ñ> then < ENTER > to select function, then < D > or < Ñ> to change

L0        Run
L1        Audible Alarm (On/Off)
L2        0 Sample Time (5 to 120 seconds)
L3        100% Sample Time (5 to 120 seconds)
L4        Decimal Places (3 or 4)
L5        Internal Reference (Current Selection Displayed)
L6        Hour Meter
L7        Factory Defaults
L8        Software Revision
L9        Bar graph (On/Off)
L10      Display Intensity
L11      Optic Option (Check at Start=0, or every Zero=1)
L12      Zero Purge Time (0 to 120 seconds)
L13      100% Purge Time (0 to 120 seconds)


< ALARM >   Displays Status (On or Off ), < D> or < Ñ> to change, < ENTER > to exit
< ALARM >   Pressed a second time before < ENTER >, displays Set Point, (0.010 by default) < D> or < Ñ > to change
< ENTER >   Accept Alarm Set Point. Displays On/Off status again, < D> or < Ñ> to change.
< ENTER >   Accept status and return to RUN mode. Alarm LED will remain lit.

*Note: Use L1 to turn the audible portion of the alarm On or Off.


Set Selector Valve to CLEAR
< REF >       (Blinks)

< ENTER >   Calibration reagent ( PAO or DOP ), also * USER or * HIGH
Use < D> or < Ñ> to change

< ENTER >   Displays ug/l of concentration to be displayed as 100 when sampled
Use < D> or < Ñ> to change       

< ENTER >   (O Blinks)
< ENTER >   Checks Optics (Settings L11=1) and Sets 0% 

Ready for Testing

* USER is a stored sampled concentration saved by the user, to be displayed as 100%.

*Note:  This value is stored in memory until a new value is sampled and saved by the user.

To set: After completing the setting 100% procedure below, Press the REF button and “USER ” will be displayed. Press <ENTER>, 0 will blink; turn the Selector Valve to CLEAR , and press <ENTER>

*HIGH allows sampling of concentrations above 130ug/l, exceeding 200ug/l. This setting should only be used for sampling quickly and sparingly, as such concentrations will adversely affect the cleanliness of the optics


Connect Upstream Sample Line & set Selector Valve set to UPSTREAM
    <100> key LED flashes
<ENTER>   Bar graph scans .The unit averages 100% for a time defined by the L13 setting. When the <0> LED                    flashes, turn the Selector Valve to Clear
  Checks optics (if L11=1) and sets 0%. 

*Note: This setting can be saved by pressing REF , <ENTER> , and resetting 0 ).

(See *USER above) 

Ready for Testing



GREEN- Optics clean, Internal Reference within 5% of original value
ORANGE- Optics affected, Internal Reference shifted to 5% to 10% of original value
RED- Optics compromised, Internal Reference shifted by more than 10%.  Do NOT rely on Internal Reference.

*Note: The unit can continue to be operated by using the SETTING 100% procedure above.


GREEN- Flow within 5% of 1 CFM
ORANGE- Flow within 5% to 10% of 1 CFM
RED- Flow is more than 10% above or below 1 CFM

*Note: The flow is factory established through 12' of sampling tubing.

49) ASTM D2986-95A (1999) Standard

Standard Practice for Evaluation of Air Assay Media by the Monodisperse DOP (Dioctyl Phthalate) Smoke Test (Withdrawn 2004)


Developed by Subcommittee: D22.01

Withdrawal Rationale:
The dioctyl phthalate (DOP) smoke test is a highly sensitive and reliable technique for measuring the fine particle arresting efficiency of an air or gas cleaning system or device. It is especially useful for evaluating the efficiency of depth filters, membrane filters, and other particle-collecting devices used in air assay work.

Formerly under the jurisdiction of Committee D22 on Sampling and Analysis of Atmospheres, this practice was withdrawn in December 2004. This practice is being withdrawn because the procedure is 34 years-old and the apparatus identified (the Optical Owl) is no longer available.

ATI Editorial Note: This standard, while withdrawn, was the commercial equivalent of Mil-Std 282 (1956) and is sometimes referenced in relation to HEPA efficiency testing. Still available as a reference document, it provides an easy to understand explaination of the methodogy and equipment used for challenging and photometrically qualifying HEPA media efficiency.

50) HEPA Vacuum Testing

Many of ATI's customers have asked what standards or procedures are available for in-place leakage testing of HEPA vacuums, also known as Negative Pressure Filtration Units (NPFU) or Portable High Efficiency Air Filtration equipment (PHEAF).

While several standards organizations are in the process of developing industry-wide test standards, there are currently none available for release. There are a few procedures available that can be readily adapted to vacuum cleaner testing in similar industries or applications. Links for these are posted below:

Brookhaven National Laboratory - BNL IH62350
The Environmental Abatement Council of Ontario - EACO guidelines on testing HEPA vacuums.
Air Techniques International - NPFU Article "On-Site Leak Testing of Negative-Pressure Filtration Units"

51) ATI PAO-4 (4 cSt PAO) Food contact

There have been inquiries regarding the use of PAO-4 in applications where there may be "food" contact.
ALL PAO-4 sold by ATI has been registered by the manufacturer and accepted by the
NSF Nonfood Compounds Registration Program (White Book) for category code H1.
NSF registration numbers 049545 & 131844

"H1 - Lubricants with incidental food contact

Preparations permitted for use as lubricants and anti-rust agents, or as release agents on gaskets or seals of tank closures, where there is possibility of incidental food contact must be formulated in compliance with CFR, Title 21, Section 178.3570 and other sections referenced therein. The amount used should be the minimum required to accomplish the required technical effect on the equipment so treated. When a product is used as an anti-rust film, it should be removed by washing or wiping before putting the equipment back into service."

52) How to capture data ouput on a 2i Aerosol Photometer

Connect the unit to your PC USB port using a standard USB cable.

One of the easiest programs for capturing data is probably Windows® terminal available in the Windows OS inclusive through version XP. See your Windows® documentation for version specific setup procedures.

There are also many freeware and purchase options to choose from if desired.

1. PuTTY (

2. RealTerm (

3. TeraTerm (

From the terminal program the data may be imported into a commercially available spreadsheet program and formatted.

Configure the USB port in use by the photometer to the following settings:
Baud Rate – 9600, Data Bits – 8, Parity – none, Stop Bit – 1

Data is output at the end of each screen update during the testing cycle in the following format.

Monitoring Mode:
To start the reporting, the operator should press the play/pause function key.
When the operator has concluded the testing, they must press the stop function key to end the reporting. Pause is not available while operating in monitoring mode.

Continuous Mode:
The continuous reporting mode will output one % leakage reading approximately every second to the USB port of the instrument. The data consists of the penetration value in a comma delimited format. The Continuous reporting mode provides a data output identical to the legacy equipment TDA-2G and TDA-2H.

53) What does the Hazard symbol referenced on the GHS compliant SDS for PAO-4 mean in relation to filter testing?

When the ATI PAO-4 Safety Data Sheet, PN 1800101, was updated to align with the Globally Harmonized System of Classification and Labeling of Chemicals (GHS), it became classified as an Aspiration Hazard under A.10 Aspiration Hazard in OSHA’s Hazard Communication Standard updated March, 2012.

Per the GHS classification requirements, ATI PAO-4 is an Aspiration Category 1 Hazard for the following reasons:
  1. ATI PAO-4 is present at a concentration greater than or equal to 10% in liquid form.
  2. ATI PAO-4 is a hydrocarbon that exhibits a kinematic viscosity less than 20.5 cSt (centistokes) at 40 C.

For these reasons, the following health hazard pictogram must be shown:


The above regulation applies when a worker is handling ATI PAO-4 directly in liquid form which includes adding it to an aerosol generator for filtration testing. Proper precautions must be taken to minimize worker exposure.

During filtration testing, ATI PAO-4 is diluted with air to produce a poly dispersed sub-micron oil mist. This step dramatically reduces the concentration of ATI PAO-4 that workers are exposed to during filtration testing.

The two most common aerosol generators manufactured by Air Techniques are the Model TDA-4B Laskin nozzle generator and the Model TDA-5B/ATI 5C thermal condensation generator.

For both generators, the maximum ATI PAO-4 concentration is found at the aerosol introduction point of the filter system. In the case of the Model TDA-4B, the maximum concentration is 30.6 milligrams of ATI PAO-4 per liter of air. For the Model TDA-5B/ATI 5C thermal generator(s), the maximum concentration is 2.3 grams of ATI PAO-4 per liter of air.

The typical exposure for an end-user, upstream of the filter under test, should not exceed 100 micrograms of ATI PAO-4 per liter of air and is typically between 10 and 20 micrograms per liter of air. An end-user downstream of the filter under test will be exposed to a level of ATI PAO-4 that is typically less than 0.1% of the upstream concentration. This means that the maximum exposure downstream is 0.1 micrograms per liter of air.

The ATI PAO-4 aerosol used in filtration testing is actually a mixture of ATI PAO-4 droplets suspended in air. End-user exposure to ATI PAO-4 both upstream and downstream of the filter is significantly reduced to the point where the ATI PAO-4 concentration is far below 10% of the liquid/air mixture.

Therefore, ATI PAO-4 is not an Aspiration Hazard for end-users in filtration testing applications and the pictogram showing a health hazard need not apply.

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