Ventilation in Area with N2 bottle leak 1

[browserman]

Hi,

We are buliding a vessel, with approx 20 200 litres bottles, each containing Nitrogen at 180 barg.

The plan is to have a two speed fan system to purge the area in the event of N2 leakage and a low level O2 alarm, say 19% O2.

My question is; Can I simply calculate the N2 volume added to the air, and then calculate how much air I need to flow through the room to clear/dilute the N2 rich air, or do I need to add some fancy factors for the N2 that are not displaced straight away.

I was looking at the simple way, saying that x volume if Nitrogen added (at atm pressure) will result in:
Air needed = X N2 x 79/21.
Does this make any sense at all ?

cheers

Even

 

[MintJulep]

There is lots of information and some standards dealing with battery room ventilation.

I would suggest using the same methods.

 

[TonsRus]

This is a life safety issue, so you might look into NFPA.
It definately is a code issue, so at least provide the minimum cfm/sq.ft. required, and watch where your air flow paths are, via. high and or low inlets and outlets.

Steve

 

[quark]

Sometime back Lilliput and I exchanged some spreadsheets on the very issue, but that was for LN2 storage and it included some evaporation calculations also. He was referring to Industrial Ventilation book. At the end we both got about same result. There is a thread on this and search for it.

 

[browserman]

Thank you.

 

[quark]

Check it.

 

[browserman]

I found the information needed, thanks for all your help.

1. Room Size and Ventilation
The Procedure Assessment (COSHH-related) will take into account the location of work and room size. Staff should be made aware of the increased risk of oxygen depletion in a small room. The volume of the room, volume of cryogenic liquid, and room ventilation, should be considered collectively. If the room is mechanically ventilated, a contingency plan should be developed which identifies, in the event of a possible failure of the air handling system, how personnel would be notified.

Cold rooms are poorly ventilated small rooms and must not be used for the storage of liquid nitrogen vessels.
The risk assessment should calculate the oxygen concentration in the room which results from the loss of the entire contents of the liquid vessel in a short period of time (i.e. the worst case scenario). The resulting oxygen concentration is calculated using the following formula:


%O2 = 100 x Vo
Vr

Where for nitrogen,

Vo = 0.21 (Vr – Vg)
Vg = gas release, in litres spilled x 683, divided by 1000 to convert to m3
Vr = room volume in cubic metres.

If oxygen levels could fall below 18%, suitable control measures should be implemented. For example, where practicable, filling or storing vessels in a more suitable, better ventilated room, fitting a permanent oxygen monitor, or the use of smaller storage vessels should be considered.

Note: In all cases, only the minimum volume possible of cryogenic liquid should be handled.

Worked examples of calculations for liquid nitrogen can be found in the BCGA Code of Practice CP30 or obtained from the College Health and Safety Office.

 

[quark]

That is right. The spreadsheet I sent you can be useful as a counter check. I, once again, reiterate that you should consider 19.5% oxygen instead of 19 and 18%. Oxygen indicators should be placed at working height at strategic locations depending upon the room size and geometry.

Good luck,

 

[browserman]

Thanks Quark, I totally forgot to check the E-mail account, had a look at the spreadsheet and that is spot on. As this is a UK operated vessel, I will use DNV for 3rd party verification and standard compliance, so if I find out anything more, I will post this too.