Author Topic: Fire Ratings of Trolley Mounted AFF Extinguishers  (Read 83 times)

Offline Messy

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Fire Ratings of Trolley Mounted AFF Extinguishers
« on: March 13, 2019, 07:15:37 PM »
I am required to purchase a number of 45l trolley mounted AFFF extinguishers for a job where a particular risk involves flammable liquid use in an industrial setting and some storage - both in a remote rural part of the UK. (nowhere near London Colin)

https://www.safelincs.co.uk/britannia-norfolk-45ltr-wheeled-afff-foam-extinguisher/

Unfortunately, I am struggling to obtain a rating for this bulk type of fire extinguisher. I need to work this out to ensure I supply sufficient extinguishers for the risk, bearing in mind fire cover may be a long time coming. There is no life safety requirement, just business continuity concerns.

So can I use simple maths to multiply the 144B rating of a 6l AFFF to take into account the 45l capacity, or is it not as simple as that?  (It works out using that system that a 45l foam extinguisher will have a rating of 1080B)


It does not have to be a precise calculation, but merely an estimate

Offline AnthonyB

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Re: Fire Ratings of Trolley Mounted AFF Extinguishers
« Reply #1 on: March 13, 2019, 08:44:41 PM »
Some factors affecting the difference between the two:
- What foam is used: There are variants of AFFF giving different ratings
- Application rate and type: Foam portables are now usually a non aspirated spray discharge, most trolleys are still low expansion aspirated branchpipe type, the finished foam & performance will differ

If made to BS EN 1866, the standard for Mobile fire extinguishers, you can be sure that:
- The foam used would achieve at least 13A in a 9 litre portable extinguisher
- It would also achieve at least 183B in a 9 litre portable extinguisher

For reference's sake If it was powder it would have to be able to achieve at least 34A in a 9 kilo portable and would be fire rated IB, IIB, IIIB, or IVB for class B fires based on the following tests:
- All should be able to extinguish a fire test with 1 x 233B tray and 1 x 21B tray
- Each higher rating requires an additional 21B tray to be extinguished as well up to a total of 1 x 233B & 4 x 21B trays at IVB rating
- for each rating the proximity of the various trays alters

A lot of mobile extinguisher mandatory provision (e.g. small airfields) is based on media quantities rather than ratings so it never really took off as a requirement.

Perhaps looking at foam application rates for the fuels involved as if you were using hose & branchpipe from an appliance or hydrant network might give some input?
Anthony Buck
Fire Safety Technical Lead at a BAFE SP205 accredited consultancy

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Offline John Webb

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Re: Fire Ratings of Trolley Mounted AFF Extinguishers
« Reply #2 on: March 13, 2019, 09:24:44 PM »
I've used both 6l and larger foam extinguishers, including similar trolley extinguishers, and would urge caution on a direct multiplication. The main difference is that with a 144B tray you are covering an area of 4.5sq m (tray 2.4m diameter) which is easy to move round to quickly control the flames. A 1080B rating implies an area of 36sq m or a diameter of 6.8m - rather less easy to move round and a greater intensity of radiation as well. On the other hand the application rate and throw from the trolley extinguisher is greater than from a hand-held extinguisher. My gut reaction is to go for around half the direct multiplying factor, say 500B? But that suggestion is very much with little evidence to back it!

AnthonyB's comments re DP are interesting, but I assume it is far more likely that your liquid fuel fire will be a single large 'puddle' than a number of smaller ones!

Interestingly the biggest fire I ever tackled was a 40sq m fire of aviation gasoline (AVGAS) using a standard fire service hosereel spray nozzle (ie non-aspirating) using premixed AFFF solution through 19mm hosereel tubing - took about 2m 45s to put out. The fire service crew backing me up then tried a FB5X branch - its much higher application rate knocked down the fire in about 45s.
John Webb
Consultant on Fire Safety, Diocese of St Albans
(Views expressed are my own)