Hello all
First post, and it’s a lengthy one. I joined this forum especially to ask this, so please bear with me.
It concerns a fire risk assessment, specifically on the type of fire extinguishers required. I'd like people to poke as many holes in this as possible, so do your worst. I’d like to thank in advance any and all who reply.
Names of organisations omitted deliberately.
I am a chemist, and work in a chemical analysis laboratory, related to law enforcement ? We have approximately 50 litres of solvents in the lab, mostly in 2.5 litre glass Winchester bottles, and appropriately stored in fire-resistant cabinets. (HSE guidance suggests 50 litres maximum, before anyone picks up on that)
Most of the solvents are flammable/highly flammable, and most are polar solvents, i.e. water-miscible. Methanol accounts for about 50% of our stock in the lab but we also stock ethanol, IPA, acetone and acetonitrile, all of which are polar and water-miscible. We also have some non-polar solvents, which are immiscible with water.
So that’s the background.
A fire risk assessment was done for the building but no consideration appears to have been given to types of flammable liquids in use. It seems that there’s been decision made that flammable liquids = Class B = AFFF extinguishers.
When I joined our health and safety team, I carried out my own informal fire risk assessment. Rather than the whole lot going up in flames, the scenario I considered most likely would be if someone dropped a 2.5L bottle of solvent. In the unlikely event that this ignited, we should probably have a way of extinguishing it.
From previous experience, I knew that AR-AFFF extinguishers exist, but to strengthen my argument I discussed it with a local Fire Service Fire Safety Enforcement Officer and asked whether it was actually necessary. His advice was that AR-AFFF should be used for any fires where hydrocarbons or solvent fuels were involved.
So, I asked the higher-ups about getting at least one for our lab, but also raised the question about the need for them in other labs within our organisation. Bureaucracy ensued.
Health and safety advisors and competent fire risk assessors from a sister organisation gave their advice. Long story short, the decision has been made that we don’t need them and that our existing fire extinguishers are sufficient. We currently only have AFFF and CO2 extinguishers in, and near, our lab.
The advice they provided states that:
Either [AFFF or AR-AFFF] will be suitable, which is why our fire risk assessors have never highlighted this as an issue. AR-AFFF is only necessary for medium-to-large fires in high risk facilities such as refineries, pharmaceutical plants etc. As we’re only using “relatively small quantities” AR-AFFF is unnecessary.
I have questioned this advice, arguing that AFFF is totally unsuitable for a methanol (MeOH) fire (or many of the flammable liquids we stock), as the foam will be rapidly broken down and the liquid will continue to burn. If anyone has evidence that AFFF is suitable for a solvent fire, I would genuinely love to read it.
Points I made, referencing Fire Service Manual, Vol 1 – Physics and Chemistry for Firefighters:
There are three types of flammable liquids, and AFFF is only suitable for some of them. It is not suitable for polar, water-miscible solvents. Quantity is, largely, irrelevant.
MeOH will extract the water from AFFF and mix with it, so using this type of extinguisher can potentially make the situation worse. Essentially, all you’d be doing is adding water to it, resulting in a much larger pool of burning liquid.
[I’m told there’s “no evidence” that using AFFF on a methanol fire can make it worse, despite, well, all the evidence.]
MeOH fires, once ignited, can continue to burn even at a 4:1 ratio of water:MeOH, and can require almost 90% dilution with water to extinguish. As an example, a 2.5L methanol fire could require 22L of water to extinguish it. (We have 9L AFFF extinguishers.)
CO2 can extinguish a MeOH fire, but given that MeOH burns with a near-invisible flame it can be difficult to tell whether it has actually been extinguished. So, to rely on that alone is not wise.
Water mist has been suggested as safe, but there is evidence that it doesn’t extinguish a MeOH fire (see link to RISE document below).
Powder can’t be used indoors, as per the current British Standard advice.
So AR-AFFF is the best, most appropriate extinguisher to have in our lab, along with a CO2 extinguisher.
I plan on pushing for AR-AFFF but before I start questioning the competence of these advisors, I would like to know if I’m being unreasonable, or if you dispute any of the above points. Info on your background would help my peace of mind too, if you don’t mind providing that.
Sincerely, many thanks.
