Makeup air requirements for chemistry lab?

[asarkisov]

I'm needing to get a selection for a new makeup air unit for an existing chemistry lab which has fume hoods. I was told by a coworker that chemistry rooms need to be negatively pressurized which would mean the makeup air supply cfm would need to be less than the exhaust cfm, however I don't know where in ASHRAE the exact ratio is located. Someone I work with said the supply cfm was about 10% less than the exhaust cfm, but I was hoping to find the exact section where the figure is written out.

 

[Gregg Harris]

I'm needing to get a selection for a new makeup air unit for an existing chemistry lab which has fume hoods. I was told by a coworker that chemistry rooms need to be negatively pressurized which would mean the makeup air supply cfm would need to be less than the exhaust cfm, however I don't know where in ASHRAE the exact ratio is located. Someone I work with said the supply cfm was about 10% less than the exhaust cfm, but I was hoping to find the exact section where the figure is written out.

Try ASHRE 62.1 you need a balanced air exchange from 4 to 12 air changes per hour depending what part of the building is being served, such as chemical mixing ,storage, etc. and could require under emergency situation up to 20 air changes per hour.