Validation of Compressed Air : Pharmaguideline

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Validation of Compressed Air

Compressed air validation including tests like determination of moisture content, presence of oil content and microbial evaluation.
Compressed air is used in the different areas of the pharmaceutical manufacturing facility. Compressed air may contain contaminants those may cause contamination in the pharmaceutical products. Therefore validation of compressed air is necessary to produce quality products.

Requirements for Validation Process

1. Dry Methanol
2. Oil mist detector tube
3. Sterile 0.45m membrane (47mm diameter)
4. Sterile Petri dishes
5. Sterile Soybean casein digest agar
6. Sterile MacConkey's agar
7. Sterile Brilliant green agar
8. Sterile Mannitol salt agar
9. Sterile Cetrimide agar
10. Sterile Soybean casein digest medium

compressed air validationValidation Method

The compressed air testing for the presence of moisture, the presence of oil and total viable aerobic count and pathogens that is directly coming in contact with the product or primary packaging materials.

1 Determination of Moisture Content

1.1 Bubble the sample air through about 150 ml. of dry methanol for 4 minutes 30 seconds at the rate of 5 L/min. (This gives 22.5 liters of air which is equivalent to 28.6 g. of air).
1.2 Dilute the methanol to 200 ml. in a volumetric flask. Record the ml. of KF required for 20 ml. of methanol removed from the 200 ml. flask. Let this reading be (X) ml.
1.3 Record the ml. of KF required for 20 ml. of Methanol from the same stock used for bubbling the air. Let this reading be (Y) ml.
1.4 Determine the sample reading in duplicate and calculate the two results separately by correcting blank reading. Calculate the % Moisture by using the following formula
                                                                    (X-Y) x KF Factor x 200 x 100
% Moisture in compressed air sample = ------------------------------------------------
                                                                             28.6 x 20 x 1000

2 Presence of oil (By using Oil mist detector tube):

2.1 Connect the flow meter through tubing’s to the point after 1 m filter of the compressed air line. Adjust the flow rate of 1 liter per minute with the help of adjusting knob.
2.2 Break tips off a fresh Oil mist detector tube carefully and inserts a tube into tube holder.
2.3 Attach the rubber tube holder to the flow meter outlet. Make the connection of the Oil mist detector tube so that sample inlet from arrow G ► on the Oil mist detector tube pointing and outlet from another end as shown in the figure.
2.4 Turn on the flow of compressed air and confirm the flow meter according to specification i.e. sampling flow rate of 1 liter per minute. Allow the compressed air to pass through the Oil mist detector tube for 7 hours (420 minutes).
2.5 (Flow meter set to 1 Liter / minute, \ for 420 minutes = 420000 ml of air is sampled).
2.6 As soon as sampling time is elapsed turn off the flow and remove the tube from the tube holder. Observe the color change layer reading marked on tube immediately. Observe the color change.
e.g. For Gastec oil mist Airtec tube color changes from Salmon Pink to Pale Blue.
2.7 Calculate the true concentration by the formula:
True concentration (mg/m3) = Tube reading x ------------------------
Note: If the tube reading is less than 0.2 mg/m3 report the results as less than 0.01 mg/m3

3 Microbial Evaluation

3.1 Sterilise the air sampling flask together with 100 ml SCDM, silicone tube for inlet & outlet.
3.2 Take the assembly to the sampling area and sanitize the sampling site with 70% IPA.
3.3 Open valve of the compressed air system for five minutes and allow air to pass out.
3.4 Insert the end of the inlet silicone tube over the sampling site and connect to flow meter and place the outlet of silicone tube connected to flow meter in sampling flask.
3.5 Impinge air in 100 ml of sterile Soybean casein digest medium for 20 minutes [Flow meter set to 50 Liter/minute, \ for 20 minutes = 1000 liters of air is sampled). In the laboratory, filter the whole content (i.e. 100 ml. SCDM in which 1000 liters of air has been sampled) through 0.45 m membrane filter. After filtration place the paper on Soybean Casein Digest Agar plate and incubate at 30-35°C for the total viable aerobic count for 5 days. After incubation count the number of colonies & record the results as CFU/m3.
3.6 Allow 1000 liter of air to be sampled in SCDM as per the above step. Incubate the medium flask at 36-38°C for 48 hours.
3.7 After incubation streak a loopful on the following selective media (Table 1). Invert and incubate the plates at 36-38°C for 48 hrs. After incubation observe the plates for colony characteristics (if developed) & compare with the standard table 2 given below. For further confirmation carry out Gram staining & conformity test.
Table 1: Name of organisms with their selective Media.
Sr. No.
Name of the Organism
Selective Medium / Media
Escherichia coli
MacConkey's agar.
Salmonella sp.
Brilliant green agar.
Pseudomonas aeruginosa
Cetrimide agar.
Staphylococcus aureus
Mannitol salt agar.
Table 2: Colony characteristics of different organisms.

Sr. No.
Selective Medium
Description of Colony
Cetrimide agar
Generally colorless to greenish.
Mannitol salt agar
Golden yellow
MacConkey's agar
Brick red colored colonies with precipitation of bile.
Brilliant Green Agar
Small, transparent and colorless or opaque, pinkish or white (frequently surrounded by pink or red zone.


1. Moisture Content: Not more than 0.25 %
2. Presence of oil: Not more than 0.01 mg/m3
3. Total Viable Aerobic Count: Alert: NMT 25 CFU/m3 Action: NMT 50 CFU/m3
4. Pathogens: E.coli, Salmonella Sp., Pseudomonas aeruginosa, Staphylococcus aureus should be absent.
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