1. #1
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    Default CO2 extinguishers

    What is the normal filling pressure for carbon di oxide extinguishers.

    we have SCBA's in our facility. THe filled air pressure is 300 bar. This is reduced by the demand valve. What will be the air pressure in the face mask?

    Vinay

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    Maybe I mis-understood your question, but CO2 extinguishers are filled to their stamped full weight.

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    I am sorry but I have posted two questions and thank you for the response.

    1) we have CO2 extinguishers ;they do not have a pressure gage. I asked the safety technician and he told me the extinguisher is having CO2 at 150 bar. Is this true if not what is the pressure in a CO2 extinguisher when filled to their stamped weight?

    2) we have MSA SCBA's the cylinders are filled with air at 300 bar. When fitted on an users face what will be the approx pressure in the face piece after pressure reduction by the demand valve?

    vinay

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    1) Most importantly, you need to verify with the manufacture of the extinguisher what the pressure capacity are. US has very specific requirements and are stamped on the bottle such as max pressure and hydrotest dates.

    With disclaimer out of the way...
    1 psi = 0.06894757 bar (rounded)

    Based on your safety guys 150 bar, it converts to 2176 psi (rounded)

    That said...

    A 10# has a max working pressure of about 850 psi if aluminum and 195 psi if steel. These do vary and it's important you know what material is the bottle made of and when it was made to make sure you don't over pressure it.

    You most likely have a 20 or 25 pound extinguisher. Again, this is a guess based on the information you have. You need to really look it over and get the supplier involved if you need more specific numbers. When these things are repainted, they tend to spray heavy and it can fill stamping.

    2) Again, it's a manufacturer's question and the make/model of the SCBA is needed but we can get you in the general ballpark...

    300 bar = 4351 psi.

    First stage regulator drops bottle pressure to 80 psi (5.5158 bar rounded).

    Second stage drops it to 1 to 1.5 inches of water (pressure output at the face which converts to 0.002490889 (+/-) of bar at the face) and 500+ litres per mimute (500 x 2.119 = 1059.5 cubic feet per hour) of flow.

    In other words, pressure at tghe face mask is slightly over atmospheric and will flow enough air if your under moderate stress (for most people anyway).

    All conversions are assuming sea level.

    Be safe and hope this helps, R2
    Last edited by robertr2m; 05-17-2009 at 03:29 PM.

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    Thanks,
    Your replies are indeed more than helpful.As I begin my career as a trainer I want to dessimate the right information to my colleagues.

    The SCBA information was helpful. You mean to say that there are two regulators on the outlet of the SCBA cylinder. One regulator which has the alarm at 60 bar fixed and one at the face piece?
    If normal human air consumption is 40L/min why is there a flow of 500+ litres per min. Can we assume that a person can consume 10 times the normal air when he hyper ventilates?

    CO2 extinguisher you say Aluminium is 895psi(58bar) and why steel is only 195psi(13.4bar)? is there a typo


    Vinay

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    Hey Vinay,

    CO2 - It's a typo... should be 950 psi... sorry

    SCBA - A two stage regulator has one at the tank (somewhere between the tank valve and the mask regulator, usually mounted on the pack frame) that drops it from bottle pressure (2400 psi low pressure and 4500 psi high pressure) to 80(ish) psi and then a second regulator at the face mask that drops it to 1.5 wc.

    The 40 lpm rate is based on a respiration rate of 24 breaths per minute with a volume of 40 liters per minute (lpm) (1.41 cu. ft.). This number is not derived from firefighting activities. NIOSH arrives at this number by placing the SCBA on a machine that simulates an average adult male’s breathing rate at a normal workload. It's then used as the constant when determining the ACR which is way off since very few of us are average adult male's w/ varies in lung capacity and O2 absorption and conversion proficiency. Also, the level of work is harder thus the increase in over all air consumption.

    The flow rate is higher so you don't over-breathe your mask and cause a negative pressure in an IDLH atmosphere. Basically, it keeps a positive pressure mask, positive pressure. Even though it feels like your sucking a vacuum, your not.

    I'm trying to do 2 things at once and didn't have my handy-dandy conversion chart so apologies for psi and no bar .

    And your welcome, glad to help.

    Be safe, R2

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    Any good SCBA systems (eg. MSA and Dräger ) will at the first stage take pressure down to 8 bar. Other systems will be in the 10-5 bar range as well.

    CO2 extinguishers have the gas compressed to around 58 bar, so that it can be kept in a liquid state. This may vary between manufacturers and models, but this is what we have. Stationary central systems might have more, the larger 50 litre gas tubes are 200 bar.

    There is sort of isn't any good point to have CO2 unless it can be kept in a liquid state (higher pressure than 50 bar or kept cool) while it could be possible with a stationary system might, it's probably not worth it.

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    Vinaydeep I realise it is a year since you posted this, but I though I would toss in my ten cents worth. Your question suggests you don't quite understand the difference between a compressed gas in a cylinder (like Air, Nitrogen or Oxygen) and a vaporising liquid (like Propane or CO2).
    With a compressed gas, you just squeeze gas into the cylinder and as you charge it, the pressure goes up and as you empty it the pressure comes back down. You can check the contents with a pressure gauge.
    With a vaporising liquid, like CO2, the pressure in the cylinder will be the same whether it is full or empty. As long as there is some liquid in the cylinder, the rest of the cylinder will be full of vapour, at the vapor pressure of the particular product. If this is CO2, at a tempreture of 20 degrees celcius the pressure will be 58 bar or 830 psi. The only thing which will change this pressure is if the tempreture goes up or down, regardless of how much or how little liquid there is in the cylinder.
    For that reason, the cylinders are filled and checked by measuring the weight of liquid they are being charged with. A common size for CO2 extinguishers was 7lbs (3kg approximately) of liquid CO2.
    The extinguisher works by allowing liquid CO2 to come up to the nozzle where it expands into vapor again, thus the extinguishers either have a long nozzle if they have a single hole at the discharge point, or two opposite holes pointing into the sides of a short discharge nozzle to allow the expanding liquid/vapor mix to spiral around the inside of the nozzle several times as it expands. The extinguisher is considered "empty" when there is only vapor, not liquid comming out.
    Jim Maclean. IACOJ NZ branch

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