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# Negative pressure

## Negative pressure

(OP)
Does anyone know of an equation that relates room volume, extract rate and the pressurisation of the room?

For instance if i was to extract 0.6m3/s out of a room 150m3, what would be the subsequent negative pressure. Now i guess around -25Pa, but is there an equation to tell me differently before the commissioning stage of the project commences?

### RE: Negative pressure

Use the keyword Room Pressure(s) and do the search. There are many threads that deal with this subject. The main criterion to establish room pressures is the leakage rate across the room.

### RE: Negative pressure

I recommend looking at ANSI Z9.5. It's intended for laboratory design, but includes an equation. I think you might be looking for a "leakiness" factor, which is very much empirical. I've worked on BSL-3, ABSL-3, and DA standard ABSL-3+ rooms, isolation rooms and toxic compounding. So far nothing has been as good, in my experience, as differential volume control. That's worked better than commissioning with up to 4 IWG on positive pressure for determining leakiness, then trying to correlate to negative pressure on a leakiness factor. Lot easier to do, setting a photohelic and varying a variable volume pressure independent air valve until you get the corresponding differential volume. "Leakiness" doesn't stay constant over time, using a photohelic, or any type of sensitive dP, preferably with milliamp output, to a pressure independent control valve has always worked for me before.

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