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

2) Will using aerosol to test filters cause excessive loading (clogging) 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 does the FDA require for filter leakage certification tests?

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

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

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

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

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

10) What is the recommended shelf life of PAO (CAS # 68649-12-7)?

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

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

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

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

Most current standards and recommended practices require a minimum of 10 micrograms per liter (ug/l) as an upstream aerosol challenge. While higher concentrations can be used, 10-ug/l is the minimum that may be used and still have a valid leakage certification test.  All of ATI's aerosol photometers were designed to operate at upstream challenge concentrations between 10 and 100 ug/l.

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

Poly-dispersed aerosol is used to challenge the "integrity" or leakage of the plenums, framework, connections, etc., and the filter media itself. Therefore people ask, "How much aerosol is needed?"

The example below uses 50 micrograms per liter as an upstream challenge.
Example: Let's use a filter bank that is 10 feet x 10 feet and utilizes (25) 24" x 24" x 12" HEPA filters. The normal 24" x 24" x 12" HEPA has an average of 65 pleats. The pleat size is 22 1/2" x 10 1/2". If we take this information and multiply it, we come up with the average HEPA filter containing approximately 213 square feet of media. If you multiply this by 25 (for the 25 HEPA filters in the bank) we come up with a total of 5,325 square feet of media absorb. We will also calculate the amount of liquid we will aerosolize and let this 5,325 square feet of media absorb. 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 bank. If you use a photometer with a rectangular isokinetic probe, it will take 40 minutes. This is calculated by figuring the scanning rate of 10 feet per minute. Since the filter bank is 10 feet wide, one scan per minute across the face of the filters would be allowed. Since the probe dimension is 3 inches and the bank is 120 inches high, 3 into 120 equals 40 strokes. The test time will be 40 minutes (each stroke taking 1 minute, it requires 40 strokes to cover the entire area).

The next calculation is the amount of liquid that will be converted into an aerosol and spread over the 5,325 square feet of media. This equals 0.00283 grams per cfm (calculate 100 micrograms per liter x 28.3 for one cubic foot per minute). Since the system is a 25,000 cfm system, we multiply 25,000 x .00283 grams per cfm which totals 70.75 grams of liquid we will aerosolize to obtain a challenge of 100 micrograms per liter in this 25,000 cfm filtration system. Because we will run this test for 40 minutes, we will multiply 70.75 x 40 minutes and come up with a total of 2,830 grams of liquid that we will aerosolize to challenge the in-tegrity of the 25,000 cfm filtration system with 100 micrograms per liter. The 2,830 grams is equal to 99.8 ounces of oil spread over 5,325 square feet of media (equivalent to a 12 inch wide roll of filter media just under a mile long). How can we clog this filter system? If we decide to only use 36 ounces to test the filter system, we could then challenge it with 36.1 micrograms per liter (equal to three-12 ounce containers).

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 provide 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.

The Stairmand disk diameter equals the pipe (or duct) diameter divided by the square root of two (1.414213).

4) What type of PAO does the FDA require for filter leakage certification tests?

Several differing opinions on the correct PAO to use have arisen recently. The FDA, in their original CGMP (Current Good Manufacturing Processes) release was specific in the type that was approved as a replacement for DOP (DEHP).

"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."

CGMP Notes (Vol. 4, Number 4), December 1996.

ATI's position is that PAO with a CAS # 68649-12-7 is acceptable by FDA definition. The full text of the referenced CGMP document is available at: http://www.fda.gov/cder/hdn/cnotesd6.htm.

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

Each Laskin nozzle being used in a generator consumes approximately 2.64 cfm (75 Liters) of air at 20 psi (1.4 bars) and total air consumption is proportional to the number of nozzles in use. Therefore the maximum compressed air requirement for a three nozzle generator is 7.92 cfm at 20 psi and a six nozzle generator would need 15.84 cfm at 20 psi. The applied pressure of 20 psi needs to remain constant to allow calculation of the aerosol generator output. Air compressor performance specifications that will show output volume (cfm) versus pressure (psi) are readily 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?

TDA-4Blite (Type III-A Laskin nozzle) @ 20 psi using PAO (Emery 3004)

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

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

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

TDA-5B Thermal Condensation Type Aerosol Generator using PAO (Poly-alpha Olefin)

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

TDA-5B Thermal Condensation Type Aerosol Generator using DOP (Dioctyl Phythalate)

The manufacturer's stated shelf life for PAO (CAS# 68649-12-7) is three (3) years in the original, sealed and unopened container.  The shelf life of an open container, that is tightly sealed between uses, is one (1) year.

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

ATI does not recommend the use of the TDA-5B 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 49-2002, Annex F specifcally calls out for the use of a Laskin nozzle style generator or equivalent during certification.  A TDA-5B generator is not considered a Laskin nozzle equivalent aerosol generator.

12) 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 an increased displayed leakage value. This higher value is the result of an increase in residence time of the aerosol passing through the light scattering chamber's area of observation. The longer residence time of the aerosol 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, the unit’s aerosol response is self correcting for the decreased flow rate and standard accuracy conditions would be maintained.

13) 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 point in time and as such, do not have a tolerance range established. Increases in the straylight usually occur through ordinary usage over the annual calibration cycle. Sudden and/or catastrophic increases in the straylight value typically are the result of operator error or component failure and 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 breakage of discrete components within the LSC. Photometers which remain operable, even with elevated straylight values, are still capable of accurately measuring filter leakage values.

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