Active Air Sampling

• Is also called Volumetric air sampling because in this monitoring method an instrument (air sampler) is used to sample the air.
• As per guidelines 1m3 or 1000 liters air should be sampled per location for volumetric air sampling.
•           In this method Pre incubated 90 mm SCDA (Soybean Casein Digest Agar or Tryptic Soya Agar) plates  is better for Active air sampling
•        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.
•       After completion of incubation observe the count under colony counter.
• The positive point of this method it can give more accurate data of viable count as  compare settle plate exposure because air is forcefully  sucked by the air sampler during sampling.
• But sample duration time of this method is very less and can not be used for continuous hours like settle plate method. 
• one location at least 400-1000 liters air should be tested.

Types of methods:

1. Sieve impaction method
2. Slit to Agar air sampler
3. Centrifugal sampler

Different type of samplers:

1. Millipore - M air and T air
2. Sartorius - Model MD 8
3. Merk -        MAS 100
4. Hi media -  LA637
5. PBI -           SAS Super ISO 100

• Air samplers was placed in the center of each room at a  height of approximately 1 meter above the floor
• The sampler was disinfected with 70 % ethanol.

Advantages:

• Most official guidelines refer to cfu/m3.
• Sample collection is rapid.

Disadvantages:

• Device difficult to sterilize.
• Expensive method
• Noisy
• Different samplers given different results.
• The same sampler same place and same time given different result.
• The sampler must be frequently calibrated
• The air flow is Disturbed

Efficiency of the sampler (%) 
= Test sampler count / Total count (from membrane sampler) X 100

Air sampling:

X = Pr X 1000/V

X = Cfu/m3

r = colony forming units counted on 90 mm plates.

Pr = probable count obtained by positive hole correction from table against r value.

V= volume of air sample.

Ex: 1

r = 20

Pr = 25

X = 25 X 1000 / 500

X = 50

Volume = Flow Rate

M3  ( 1000 L) = 100 L /1 minute = 10 minutes.

Ex : 2

• If sample volume is 500 liters (0.5m³) and the no of colonies is formed are 100, then the converted no of colonies (using feller-table) will be 119.
• Than the CFU/M³  will be 119/0.5 = 238 CFU/M³  

Sampler and lid cleaning:

1. under laf bench kept

2. Spray the some alcohol on the perforated lid top

3. Leave the instrument continuously running for about 5 minutes (500 liters) 

MERK:

• 300 holes sieve : with blue line silver colour
• 400 holes sieve: only silver colour