# What is the minimum pressure differential required for ISO Class 8 Clean Room?

#### SGquality

##### Quite Involved in Discussions
I would like to know what is the minimum pressure differential required for ISO Class 8 clean room ?

I am asking this question because one of our clean room has a pressure differential of 0.02 inches water (clean room to gowning) and 0.01 inches water (gowning to outside). I feel this is too low to show positive pressure.

#### Ronen E

##### Problem Solver
Moderator
I would like to know what is the minimum pressure differential required for ISO Class 8 clean room ?

I am asking this question because one of our clean room has a pressure differential of 0.02 inches water (clean room to gowning) and 0.01 inches water (gowning to outside). I feel this is too low to show positive pressure.

Hi,

ISO 14644-4:2001 - Cleanrooms and associated controlled environments — Part 4: Design, construction and start-up - Annex A (informative) - Control and segregation concepts - says (s. A.5.3):

The pressure differential between adjacent cleanrooms or clean zones of different cleanliness level should lie typically in the range of 5 Pa to 20 Pa, to allow doors to be opened and to avoid unintended cross-flows due to turbulence.
(...)
In situations when pressure differentials at the lower end of this range are accepted, special precautions should be taken to ensure accurate measurement of separating flow or pressure and to prove the stability of the installation.

5 to 20 Pa is approximately 0.02 to 0.08 inch water.

Excessive pressure differentials are not recommended due to the risk of creating turbulent flows.

#### Ninja

##### Looking for Reality
Trusted Information Resource
Perfect link from Ronen,

note, however, that it is worded as guidance not requirement. As you go to address/improve it, you are guiding toward industry norms...not correcting an NC. That approach may help you get folks on board instead of arguing with you.

good luck!

#### Ronen E

##### Problem Solver
Moderator
Perfect link from Ronen,

note, however, that it is worded as guidance not requirement. As you go to address/improve it, you are guiding toward industry norms...not correcting an NC. That approach may help you get folks on board instead of arguing with you.

good luck!

True, the annex is an INFORMATIVE part of the standard, not a NORMATIVE part.