Required Inert Gas design quantity (NFPA 2001)

[DieterVk]

I've done a fan test for a automatic fire extinguishing system with IG55 following the NFPA 2001, appendix C, enclosure integrity procedure.

Known data
CO2 quantity: 22,8 kg
Real concentration: 43%
Volume room: 29 m³
Max height room: 3,25 m
Minimal concentration: 38%
Temperature in the room: 21°C
Temp outside: 21°C​

The results aren't good:
Surface area leaks: 0,0592 m²
Max accepted surface area leaks: 0,0128 m²
Hold time: 2 min 10 sec
Concentration after 10 min: 22,2%​

Given that it is not possible to lower the amount of leak areas, how can I adjust the design to have a functional extinguishing system?
A secondary flooding is the only possibility I think. But how can I calculate the hold time and concentration after 10 min with a secondary flooding. I cannot find anything in NFPA 2001 nor CEO 4007.

Any help?

*edit

 

[stookeyfpe]

I have no understanding of IG55 but I am very familiar with NFPA 2001. I'm assuming you are aware that carbon dioxide is outside the scope of NFPA 2001 but something in IG55 is dictating an enclosure integrity test. I'm assuming this is the reason for the question.

CO2 system design requirements are in NFPA 12 and the standard doesn't require an enclosure integrity test. The standard does require a Full Discharge test.

 

[DieterVk]

Does nobody has any suggestions on secondary flooding?

 

[stookeyfpe]

Dieter:

You have two options:

A) Resolve whatever issues that are creating the relief paths for the CO2.
B) Increase the volume of CO2 to allow for a given mass loss of the fire extinguishing agent while maintaining the required design concentration for design duration

 

[DieterVk]

Stookeyfpe,

It's not CO2, it's inert gas.

A) The relief paths/leaks cannot be resolved as mentioned in my initial post.
B) This exactly is my question. How do I do this?

 

[IFRs]

Can you quantify the leaks?

 

[DieterVk]

Yes,

see my initial post:

The results aren't good:
Surface area leaks: 0,0592 m²
Max accepted surface area leaks: 0,0128 m²

 

[IFRs]

Can you estimate the leak rate?

 

[DieterVk]

My initial post holds all data available. From this I can derive three points:
1) t=0s ---> c=43%
2) t=130s ---> c=38%
3) t=600s ---> c=22,2%

So yes I can calculate the leak rate for this case. But as partial pressure and total pressure of the inert gas will be augmented, the leak rate also changes...

 

[IFRs]

I was expecting the leak rates in a units of flow. cubic meters per hour, etc. If you know the open area, and you know the pressure differential across the opening you can make some assumptions and calculate a leak rate. Then you can estimate or calculate a concentration and get the make-up flow needed. I may not be any real help here, just throwing darts...

 

[stookeyfpe]

DieterVk (Bioengineer)(OP)21 Mar 17 12:33
I've done a fan test for a automatic fire extinguishing system with IG55 following the NFPA 2001, appendix C, enclosure integrity procedure.

Known data
CO2 quantity: 22,8 kg

I can only respond to a question based on the information you presented. And CO2 is not a clean agent based on NFPA 2001.

 

[DieterVk]

Stookeyfpe,

My apologies, it's not CO2, it's IG55, a clean agent.

 

[cdafd]

Some reason the envlosure cannot be sealed better

 

[DM2]

IG55 is Argon.
The leak rate is affected by the discharge time (injection rate), which you have not specified. Slower (2 minutes vs 1 minute) flow rates lead to lower room pressures and therefore large leak area allowance.

I'm not sure what you mean by "Surface area leaks: 0,0592 m²". Is this the total leakage area? If so, than 1/2 the area would be used in the calculations for "Unclosable" openings to determine the "extended discharge rate" and therefore the additional Argon needed to compensate for the short hold time.

I'm also not sure what you mean by "Max accepted surface area leaks: 0,0128 m²". Is this the calculated maximum allowable leakage area in order to maintain the concentration for 10 minutes?

Have a look at NFPA 12 for guidance on "Unclosable Openings" The calculation methods would be similar with the exception of the vapor density, where you'd substitute Argon for CO2.

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."