I know this is quite an old post but I just thought I'd clarify a few things so as not to confuse anyone searching for information on fire extinguishers.
crazycanuck said:
If this is true, you need to go on a refresher course because some of what you write is nonsense.
crazycanuck said:
you have a class ABC type fire ext. A is for burning solids such as wood ,paper etc. B is for gas or grease fires etc and C is for any electrical fire such as electric panels,your iron stove etc.
Best way to remember is if it burns to an ash its an A, A is for ash.
B is for Barrel the container you store petrol and grease in .
C is for Current all electric items
no it's not
Briefly, your fire extinguisher have rating numbers i.e. 13A 233B
The letters refer to the class of fire risk and the number refers to the size of fire the extinguisher can put out UNDER TEST CONDITIONS.
Classes of risk:
Class A risks - Solids (Wood, paper, straw, etc)
Class B risks - Flammable liquids and liquifiable solids (butter, lard etc)
Class C risks - Gaseous fires
Class D risks - Metal fires
Class F risks - Cooking oils
The largest A rating you will get on an extinguisher is a 55A - which means that it'll put out a wooden "crib" of a certain design that is 5.5M long. (A 13A would be 1.3M long etc.) A 55A is an enormous fire to see. It's actually hard to believe that an extinguisher will put out a fire of such a size. I'll see if I can find a photo from a recent fire test we did.
The largest B rating for a portable extinguisher is a 233B - This is a heptane/water fuel fire of 233 litres total. That's 156 litres of fuel and 77 litres of water in a metal dish of 3 metre inside diameter.
You won't find a fire rating number for C or D risks and F class extinguishers generally have a 75 rating.
Just a note on Foam extinguishers..... there's a school of thought that because fat fryers are liquid that a B class extinguisher will be ok to use on a fat fire. Not so, you need to get cooking oil to about 350°C before it will auto ignite - this fact makes it different from the fuel type fires because the actual liquid is very hot. Because of the high temperatures involved, using a class B foam extinguisher is not recommended for use on fat fires. You need a class F extinguisher for fat fires - the foam in a F type extinguisher basically turns the oil into a soap.
crazycanuck said:
Now yor ext. being charged is not enough, over a long period of time the powder inside will seperate from the nitrogen gas (nonflamable) and become hard if this happens the nitrogen can't expell the power out of the nozzle (the powder is monomonium phosphate ,not harmful) so you MUST shake the ext. about every 6 months to keep it loose, if yours is packed turn ext. upside down and with a rubber mallet carefully rap the side and bottom you will hear a different sound if the bottom is hard keep tapping until the bottom souns hollow then shake to break up any lumps.
Extinguishers can be filled with dry air as well as nitrogen. The ABC dry powder is mono ammonium phosphate and ammonium sulphate. This business of shaking the extinguisher to free up the powder isn't really necessary although having said that they do still teach it in service engineers training course to BS5306-3:2003. I say it's not really necessary because before you fire test a dry powder extinguisher, it must be subjected to 500 drops onto a rigid steel plate from a height of 15mm at a frequency of 1 a second (as specified in EN 3 Annex K.2). Believe me, that compacts the powder properly. The dry powder in the extinguisher has tiny gaps between the particles that are filled with pressuised nitrogen or dry air - once there extinguisher is operated the gas amongst the powder will rush up through the siphon tube and out of the hose (if fitted) taking the powder with it.
crazycanuck said:
Note : depending on quality of ext. it should be good for 20 years, if it's a cheap one you probably have plastic valve system ,in this case discard and buy new one. A cheap one is anything with a plastic head and dial.
BS5306 recommends that powder extinguishers (stored pressure or cartridge) are subjected to a test discharge every 5 years (10 years for a factory sealed type). However, it's generally cheaper to buy a new one rather than pay for the extended 5 year service. Plastic parts are fine but are subject to UV degradation so you need to look for signs or crazing or white marks on plastic parts.
breezer said:
..so long as the guage is fine it shold be ok.
There's generally a small hole in the gauge glass that allows testing of the gauge. I won't say how to test it on here because you shouldn't really be messing with extinguishers if you don't know what you're doing.
crazycanuck said:
You worry me.
I hope this has been of some use. If anyone wants any more information, just ask.
Cheers,
gcol
