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Role and Calculation of Air Changes per Hour in Clean Room Area


Determination of the air velocity in CFM and air changes per hour ACPH in pharmaceutical clean rooms and also know its requirements in different cleanroom classes like 100, 1000, 10000, 100000.
Air changes in pharmaceutical clean room play an important role in maintenance of HVAC clean room quality. Air changes per hour are the number of total replacements of any room’s air in one hour.

Clean RoomIf the supply of the air by HVAC system in one hour is equal to the volume of the room then it will be one air change per hour. Rooms having 60 air changes per hour will have 60 times air supply then the volume of the room. FDA recommends maintaining the minimum 20 air changes per hour in clean rooms.

How to Calculate the Air Changes Per Hour (ACPH Formula):

First of all determine the velocity of the air below the HEPA filter in feet per minute. It is determined at the four corners and the center of the filter and the mean of the five readings are determined.
V = (V1+V2+V3+V4+V5)
                     5
V = Velocity observed at each point

Now calculate the area of the filter by multiplying the length and width of filter in feet.
A = l x w
l = length of HEPA filter
w = width of HEPA filter

Calculate the total air volume per minute supplied in the clean room by the following formula:
T = A x V
A = Area of HEPA filter in square feet
V = Average air velocity in feet per minute

Calculate the total air in the room multiplying the length, width and height of the room in feet.
Volume = L x W x H

Now we can calculate the Air Changes per hour using the following formula:
Air Changes per Hour =    T X 60 
                                         Volume

Requirement of number of air changes per hour for any room depends on the class of the room, number of personnel working in the area and frequency of access the room. Cleanliness of any clean room is maintained by the air changes per hour. More air changes per hour are required for the better clean room class then the lower one.

Related: Prevention of Cross- contamination by HVAC System

More air changes per hour are required to maintain the area where dust is generated as in granulation and tablet compression areas. In these areas dust is to be removed in a short period, hence more air changes per hour are required. Following is the list of the air changes per hour in different classes of classified area.

Cleanroom Class
ISO Class
Required Air Change per Hour
100
ISO 5
240-480
1,000
ISO 6
150-240
10,000
ISO 7
60-90
100,000
ISO 8
5-48

Therefore the air changes per hour shows the quality of the air in the cleanroom that helps the maintenance of the clean area quality.

Also see: Pharmaceutical Contamination and its Control
Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
Email: .moc.enilediugamrahp@ofni Need Help: Ask Question


4 Comments so far : Add yours...

Harald Flechl said...

Air changes are not a requirement, they are a recommendation and are based on a rule of thumb. Air change rate alone is no guarantee for an effective air-flow in a clean room - depends on situation of supply and extract grids, number and activity of personnel,....

Harald Flechl said...

Air changes are not a requirement, they are a recommendation and are based on a rule of thumb. Air change rate alone is no guarantee for an effective air-flow in a clean room - depends on situation of supply and extract grids, number and activity of personnel,....

Prashant Reddy said...

CAN U PLEASE TELL ME HOW TO CALCULATE THE CFM REQUIRED FOR A ROOM

Muhammad Bilal said...

CFM= Volume of room x ACH / 60
Note: ACH means air changes in one hour

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