ABC / BC Powder ?

[Goodsparks]

Ok, Read a few extinguisher threads on here, and looked a little further but i`m a still confused.
Monnex and purple K powders are both specified for high class B fire risks, I understand the chemical breakdown of monnex and how it extinguishes the fire.

Most extinguisher manufacturers i`ve come across sell ABC DP extinguishers which have a 43 or 55A rating and 233B rating.
All of the 9KG monnex extinguishers I have come across still only have a 233B rating.
If its so good, why does it have the same fire rating as a more versatile, cheaper agent ?
Do the BS tests stop at 233B or somthing?

Cheers
Paul

[AnthonyB]

Answer in one word - EUROPE

The highest fire rating for portable extinguishers under EN3 (& thus BESEN3 in the UK) is 233B as it was deemed that any larger fire could not be safely approached by persons in normal workwear (the people in the test fires have fire retardent clothing, helmets, face shields & respirators)

A catalogue from the good old multicoloured days of BS5423 will show you that the typical 8/9 kilo Monnex extinguisher achieved a 296B:C and a 12 kilo could reach the dixxy heights of 377B:C

Monnex can tackle bigger fires, but another factor is speed - theres a faster knockdown too.

You don't see BC powder much these days as theres no point - the cost difference is negligible nowadays and you might as well get the Class A cover for a minimal extra cost - this also gives more applications to sell your powder extinguishers to!

Most BC powder is only used in the domestic/automotive market where it is used in the cheap aerosol extinguishers sold in halfords etc for cars & the US import domestic "Kitchen" extinguishers by Kidde etc

BC powder used to be popular because its all there was originally - simple sodium bicarbonate powders predate MAP powders by just over a decade and were common even until the ends of the 80's as they were cheaper. Pyrene/Chubb and Nu-swift were leaders in advocating ABC Powder as standard in extinguishers with examples dating back to the 60's

Being alkaline BC powders did actually have a limited effect against what are now Class F fires (in those days cooking oils were still lumped in with Class B) hence why lots of kitchens, particularly in local authority premises, had them as wel as being used in early cooker hood systems. ABC, being acidic has no saponification properties and is no good on Class F unless you have an endless supply to keep applying until the fat temp drops.

Take care with ABC Powder ratings - they can vary wildly depending on the %age of MAP in them - some cheap imports had ratings as low as 21A:144B:C for 9 kilo, whilst high % MAP models like the MoD contract Powder Elite by Chubb has a 55A:233B:C rating (that would probably have been 296B if not for EN3). If you are doing class A or more importantly Class B risk calculations to determine extinguisher coverage you need to be careful when replacing extinguishers

[Goodsparks]

Cheers Anthony, All is now clear. Out of interest, are mobile units given a fire rating in the same way? Guessing even the cheapest 50kg powder unit is gonna have a rating exceding 233B?

Oh, and one other quickie - Can you use standard AFFF in a foam extinguisher with a branchpipe? if you can - will the fire rating differ from FFFP ?

Paul

[AnthonyB]

Mobile units are subject to a different EN - BS EN 1866:1999. A complicated rating system exists dependant upon the media (water, foam, powder etc) and whether its Class A or B. CO2 is not covered.

Most specifications for mobile units work on the old fashioned premises of mass - just like with portables in pre-fire rating days x area requires a water extinguisher of at least y litres, x risk requires either a y kg be powder or z kilo monnex or a kio CO2.

With regard to foam branchpipe extinguishers - for decades all non chemical foam extinguishers were branchpipe and over the years went through P, FP & AFFF as the foam compound. Until the last few years all foam branchpipe extinguishers were AFFF unless you bought Angus Alcoseal models with AR-FFFP.

Now the few manufacturers of foam branch extinguishers seem to use FFFP - certainly Thomas Glover, Chubb & Amerex do. UK Fire britannia are the only AFFF branchpipe still made routinely.

Any case where you fill an extinguisher with the wrong agent voids the fire rating, voids any warranty and is in breach of the BS. With pwders this can also be dangerous. Failure to perform adequately would result in liability falling on the person who filled it wrongly.

Most AFFF branch extinguishers got a 13A:183B rating for 9 litres. FFFP models are similar, but can have higher ratings (21A &/or 233B). the property of the foams are different, the FP element of FFFP giving better stability and burnback resistance, plus most of these extinguishers are AR-FFFP so you'd loose your polar solvent/alcohol capability.

Considering that the cost difference between a bottle of AFFF refill for a 9 litre ext is only minutely less than that of a AR-FFP refill there is no real cost advantage - better to stick with the designed foam compound and avoid problems later on.

Don't forget most AR-FFFP branchpipe extinguishers now use 90g cartridges instead of the 71 or 75g used in the old AFFF models - use the wrong cart & you'll get poor performance.

SUMMARY - AFFF will work (not as well) in a AR-FFFP branchpipe - but you shouldn't do it!

[Goodsparks]

cheers again Anthony,
I don`t service extinguishers commercially  and would not entertain the idea of engineers using the incorrect materials at any of our sites.
I have a couple of S/S stored pressure foam extinguishers that need recharging and i`ve aquired a couple of gallons of AFFF, thats all.

Paul

[AnthonyB]

If they are Chubb Stainless Steel, such as ex-MoD ones you can use AFFF - if you let me know make model & age I will find out what you can put in

[Goodsparks]

They are ex-mod - Amerex model 250 (9.4 l (183B)) 1985

Any info would be great.

Paul

[AnthonyB]

Ah yes, for a while the MoD dabbled in Amerex alongside Chubb for stainless waters & foams & in the mid-90s 2kg powders.

My historical database of extinguishers reveals that the model 250 of that era was, as was usual for the time, charged with 6% AFFF. I don't have the exact charge but normally it was 0.57L of concentrate.

The MoD stuff wasn't a special (other than the NATO & crowsfoot labelling)as other than with Angus FFFP was not considered for portable use. The MoD wanted to stick with one concentrate and there would have been hundreds of strike knob Rampart/TG AFFF branch extinguishers still in use at the time (& the odd chemical foam)

[Goodsparks]

thanks again, AFFF it is then.

Paul