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# PRESSURE RELIEF VENTING IN CO2 SYSTEM

## PRESSURE RELIEF VENTING IN CO2 SYSTEM

(OP)
Hi all,
I have designed a CO2 protection for a little electrical room (4m x 4 m x 4m). Now I would like to size the free venting area of the pressure relief venting. In order to do that I have followed the NFPA 12 requirements, using the formula:
Where Q= is the flow rate, in this case 22 kg/min
p = the allowable strenght of enclosure, i.e. 1,2 KPa
X =free venting area (mm^2)
Since the result is almost 0,005 m^2 I would like to ask if in this case the pressure relief venting could be avoided.

### RE: PRESSURE RELIEF VENTING IN CO2 SYSTEM

Well you math demonstrates that it is needed [0.005m2 (7.75 in2)]. In order to say it isn't needed, you'd have to increase your "allowable wall strength", however 1.2 kPa (25 lbs/ft2) is rather high for commercial wall construction. I'd be more interested to know how you came up with 1.2 kPa and what the walls are constructed of. Brick walls can't handle a great deal of lateral loads. Steel on the other hand can. You need to take into consideration the "weakest link", which are doors frames, ducts and dampers.

Regards,
DM

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

### RE: PRESSURE RELIEF VENTING IN CO2 SYSTEM

(OP)
Hi DM2,
thank you very much for the answer. It is a concrete structure with masonry brick. I found this value of allowable strength in the NFPA 12 Table A.5.6.2.
Which is the limit value of m2 that can tell me if I need a pressure relief venting or not? Because obviously if you use this formula (X= 239*Q/radq(P)), you always obtain a number.
thanks

### RE: PRESSURE RELIEF VENTING IN CO2 SYSTEM

Explain the function radq(P) as I am not familiar with it.

### RE: PRESSURE RELIEF VENTING IN CO2 SYSTEM

Chicopee,
Good question. It should be the square root of P (wall strength in kPa). The equation can be found in NFPA 12, 2015 edition, section 5.6.2.2
The math does works however.

Regards,
DM

"Real world Knowledge isn't dropped from a parachute in the sky but rather acquired in tiny increments from a variety of sources including panic and curiosity."

### RE: PRESSURE RELIEF VENTING IN CO2 SYSTEM

(OP)

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