CO2 extinguishers- - Volume of gas discharged at NTP

[kurnal]

Quick query- someone has put a 2kg CO2 extinguisher in a very small under floor electrical switchroom - its  a confined space of about 15 cubic meters
My recommendation was to remove it as I would not want someone in such a confined space trying to do the heroic bit. But  in trying to do the maths on asphyxiation risk I know there is 2kg CO2 as a supercritical liquid, the vessel is 3 litres water capacity and the pressure is 45 Bar. If it were a pressurised gas it would be simple- but what volume of gas at NTP will be evolved on fully discharging the extinguisher?

Probably one fr Anthony?

[John Dragon]

1Kg of CO2 will fill a space of 0.56 cubic metres. (I will try to find where this is writ, should have it somewhere)

[AnthonyB]

In general 1kg of CO2 will produce about 0.5 cubic metres of free gas at atmospheric pressure.

The liquid CO2 expands 450 times in the horn.

Source - Manuals of Firemanship.

If it's small then BS5306-8 states it should be located outside the special risk room. Problem is Powder will have it's own major issues in this area - Bring back BCF!

You could always go for a 1kg CO2 or if you want to be really cautious (& money no object) install either an FE-36 extinguisher or a Distilled Water Mist extinguisher (i.e. Amerex).

If the risk of asphyxia from Co2 is very real then so is the risk from combustion products of the fire and no extinguisher use inside the area advised - CO2 on the outside, attack from the hatchway only?

[kurnal]

Thanks everybody, knew I could rely on you

[BLEVE]

Hi all
Just by way of clarification, there is no risk of asphyxiation in the event of discharging 2 Kg Co₂ extinguisher within a space of 15 m³ volume, even assuming zero ventilation/no air change.

Volume of space = 15 m³
Density of CO₂ gas NTP = 1.87 kg/m³

Volume of O₂ in confined space :  0.21(15m³(2kg/1.87kgm³)

= 0.21(15-1.0690
=0.21((13.93)
= 2.92 m³ O₂

Concentration of O₂ in room: (100*2.92m³)/15m³ = 19.5%

No risk of asphyxiation

However:

Concentration of CO₂ in confined space: 100*1.069m³/15m³= 7.12%

CO₂ is toxic ans STEL 15 minute is 1.5% 15 minutes

Hence no asphyxiation risk but definately risk of exposure to toxic agent but less likely if evacuating following discharge

[BLEVE]

1Kg of CO2 will fill a space of 0.56 cubic metres. (I will try to find where this is writ, should have it somewhere)

John D

Gas expansion of CO₂ from liquid to gas is 0.54m³ from saturated liquid at -20C and 0.44 m³from saturated liquid in a cylinder at 288K

[CivvyFSO]

1Kg of CO2 will fill a space of 0.56 cubic metres. (I will try to find where this is writ, should have it somewhere)

John D

Gas expansion of CO₂ from liquid to gas is 0.54m³ from saturated liquid at -20C and 0.44 m³from saturated liquid in a cylinder at 288K

This might be a stupid question, but how does this work when you have stated in your other calcs that the density of CO₂ at normal temp and pressure is 1.87kg/m³?

That to me would indicate that the volume of 1kg of CO₂ NTP would be: 1/1.87=0.53m³/kg

[BLEVE]

Dunno,
Took it at face value from British Compressed Gas Association.

but from my own calculation

Density CO2 at -20 degrees (253K) is 2.12 kg/m³ giving 0.47 m³

would have to drop temp to -40 (233K) to result in 2.3 Kg/m³  0.44m³

similarly 15 degrees (288K) gives 1.89kg/m³   0.52 m³


44.01/0.0821*⁰K = g/l

[BLEVE]

Thats okay Civvy,

My pleasure, don't mention it 

[CivvyFSO]

Thats okay Civvy,

My pleasure, don't mention it  

I didn't mention it. The reason being; I thought that now you have proved yourself wrong your main priority would be wanting to say sorry to John Dragon for correcting his 'approximation from memory' that seemed to be way closer to the actual truth than your poorly construed, mathematically explained, version.  

But if you require gratitude to stoke up your apology-boiler prior to operating it, then: "Ta!!!!!!!!!!!!!!!!!  "

44.01/0.0821*⁰K = g/l

'Degrees' Kelvin? Shurely shome mishtake? If you are going to impress anyone with science you really need to put some more effort into it.   

[Davo]

Gents

Density is 1.842 at NTP
see below


http://www.engineeringtoolbox.com/gas-density-d_158.html

Therefore the correcct answer is 0.54

NTP is 1 atmospehere and 20 centigrade


What we now need is the calculated effect of a fully discharged extinguished in a confined space as described ..........................zzzzzzzzzzzzzzzz


davo

[BLEVE]

In actual fact civvy I was not correcting John D, I was pasting information directly from BCGA

You want to watch that chip on your shoulder though

[BLEVE]

Davo

1.828 kg/m3 @ 293.15 K

Giving 0.54 m3/kg

Same result for 02 conc

But CO2 7.29% instead of 7.12

[CivvyFSO]

You want to watch that chip on your shoulder though

My sincere apologies for not bowing down and doffing my cap the moment I see some maths m'lud.   

[BLEVE]

Can't see you problem, the post asked a question re asphyxiation hazard associated with CO2 in a specific space. The question was not answered and cannot be answered without a calculation. If you have a difficulty or insecurity with that then that's your problem mate