Class B fires outside the scope of BS5306

[kurnal]

Been looking at a specialist foundry with oil quenching baths. They have a number of 45 Litre wheeled foam extinguishers in case of a fire in the baths. I wanted to confirm that these have been specced adequately.

Mindful that BS5306 part 8 does not cover a tank size exceeding 4.66 sq m I was considering calculating the requirement by  using minimum application rates (fireground formula) but then could not find any expansion ratio info for the small aspirating branchpipes on the extinguishers. Have visited a number of manufacturers and suppliers websites without success.
Any advice please?

[John Webb]

My experience with these machines is that the expansion is usually around 8-15 - depends on the foam compound used, the working pressure and the actual nozzle. I add the caveat that this is from work done 1984-88 using equipment of that time.

[kurnal]

Thanks John. Clearly the limits in BS5306 are related to the rate at which the media can be applied.

[AnthonyB]

In lieu of testing to find out the smaller low expansion branches actual rates the industry standard is 8:1 based on digging through the archive back to the days when hand and wheeled extinguishers were proper engineered devices and had suitably detailed technical literature.

A 9 litre low ex foam produces around 72 litres of finished foam, a 45 litre unit around 360 litres.

Typical output rates are up to 360l/min but you will get slightly less than that on some self contained trolleys - the current Norfolk Range 45 litre unit has a discharge time of 95 seconds, the 50 litre ABS model (Italian make popular with many independents) blasts it's content out in a straight 60 seconds.

All the different models have slightly different branch pipes and can be used with different media and different proportions, it's not an exact science, unless they are old Chubb/Pyrene units with FBX5 or mini FB branches.

If they have water hose reels the Chubb Hosemaster (if a variant still exists, a 'copy' used to be in the TG catalogue) is a handy way to get a large foam output and I have the exact data for these!

[Psuedonym]

If they have water hose reels the Chubb Hosemaster (if a variant still exists, a 'copy' used to be in the TG catalogue) is a handy way to get a large foam output and I have the exact data for these!

Hmm...wonder why that could be AB?? 

On another note, are there any training courses for wheeled units i.e. for the punter, that you know of other than a supplying company's ad hoc training?

[AnthonyB]

If you really want I'll post the Stats of a 20's Pyrene wheeled chemical foam engine....

Never seen any courses 'off the peg', you'd need to design a course and material and rent the Norwich or M-i-t-M fireground and fill some trays up and have a go!

I've some usage footage on my '71 Chubb film and there's plenty of powder trolleys being used in the US on Youtube (often wrongly!)

In essence it would need to be based around fire fighter foam training, with the proviso that you only have a short duration.

[kurnal]

From all of this I would summarise as follows:

If the size of the potential class B fire falls outside the test parameters described in BS5306-8  then it should have an automatic fixed installation.

Now is it right that an accredited firm should sell 100 litre foam extinguishers?
What is the market for these things?

[John Webb]

I would imagine that in the works you mention in your first posting, there would be too much risk of damage to a fixed system as the items are being moved into and out of the quenching bath? Would the roof height discount sprinklers being mounted on that? I have seen a 4m by 4m diesel fuel fire successfully tackled by AFFF or FFFP foam applied through standard sprinklers mounted 4.5m above the fire although the roof height in this case was some 50+m (Cardington Airship hanger!)

[JC100]

Why is there a market for these things?

HM Forces use 90 ltr foam trolleys in aircraft hangers, aircraft dispersal pans and in bulk fuel installation areas to quickly deal with any fires before the arrival of fire crews.

[AnthonyB]

They are also IIRC required to meet the requirements of the CAA at the really small airfields & helipads.

You would see a CO2 trolley and lance at the helipad and a AFFF unit on the back of a Land Rover.

Motorsport use trolley extinguishers as a cheap way of buliding a fast response firefighting vehicle - Donnington had a home made car with a Chubb 90 litre wheeled unit in the back of a fastish hatchback with all the rear seats etc ripped out in addition to their purpose built Chubb Jaguar car with the Perren unit in.

They are a hangover from the era of works fire brigades - cheaper and less training than an actual fire engine and more manoeuvrable inside a building.

Steel works used to have loads of the CO2 trolleys, the big chemical plant in Huddersfield had several 150kg Powder trolleys (and used Monnex).

They are still of value for specialist industries where a rapid on site fire fighting capacity beyond the small first aid attack is required - fixed systems are not always practicable.