Passive Air Sampling

• Passive air means inactive air.(inactive air sampling).
• Air flow is not disturbed.
• Is also called Settle plate method or sedimentation technique.
• During this time particles are settle down on the media plate by gravitation force.
• This method is still widely used as a simple and inexpensive way.
• Each operational shift expose plates 4-5 hours period. (As per USP General chapter 797).
• At least 1 cubic meter (m3) air should be tested.
• Incase of critical manufacturing operation extended for more than 8 hours expose one more set of plates.
• Collect all the plates after completion of 4 hrs exposure time.
• For Exmple less than 4 hours exposures, to be establish the In-house limits, because all guidelines limits given CFU/ 4hours only.
• After exposure close the lid and incubate the plates inversely.
• Incubation temperature at 20-25° C have been used for 72 hours, next 30-35° C for 48 hours.
• Lower incubation temperature encouraging for Fungal, mesophilic organisms  and slow growing organisms.
• Higher incubation temperature encouraging for Bacteria.
•  In this method Pre incubated 90 mm SCDA (Soybean Casein Digest Agar or Tryptic Soya Agar) with glycerol plates  is better for Passive air sampling.
•        SCDA used for cultivation of wide variety of micro organisms in pharmaceutical procedure.
• Glycerol prevent the media evaporation or dehydration.(Quantity of the glycerol depending upon the validation study).
• The positive point of this method is that viable contamination could be checked for long hours.
• But drawback is also there with this method as it could only check viable contamination which collect or deposit over the media plate during exposure hours.
• So, location for plate exposure should be properly selected and justified based on the risk assessment studies.
• Passive air sampling is 4/1/1 scheme. It means for 4 hour exposure, 1m above the floor, about 1 m away from walls.
• After completion of incubation observe the count under colony counter.