Step 1: Measure the length, width and height of the room using a good old fashioned tape measure 🙂 This will determine the size of the room or in other words its volume.
Length x Width x Height =
Step 2: Using a device called a ‘balometer’ measure the air supply coming out of the HEPA terminal. You do this by holding the balometer up to the HEPA terminal. The balometer will catch the downstream of air flowing into the cleanrooms and measures the cascade speed.
 Step 3: Once you have your cascade speed your next step is to multiply this figure by 3,600 and divide by the room volume.
 3,600 = Number of seconds per hour
Remember to round up to 1 decimal point on your final answer!
Example formula:
Cleanrooms measurements:
Length 9m x Height 7.2m x 2.8 = 181.44 cm3
Cascade speed is: 0.44
(0.44 x 3,600 ÷ 181.44 = 9 air changes/hr)
You can see from the above formula this cleanrooms has 9 air changes per hour. Would this be acceptable for preventing particle contamination?
Answer: No! EU GMP Annex 1 states the minimum requirement for cleanrooms air change rates is 20 air changes per hour.
