AR-AFFF required? Laboratory solvents

[firefly]

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.

 

 

 

 

 

[AnthonyB]

Powder can be used indoors, it's a fallacy that the British Standard bans it, just that a consideration of the effects on discharge should be made in a H&S risk assessment.

The medium to large fires thing is a fallacy as portable extinguishers are made (& have been for over 50 years) specifically for smaller fires.

Some of the substances you mention fall into the Moderate category for foam destroying action but none are severe. They will destroy a foam blanket, particularly the thin film formed by the non aspirated spray of current extinguishers.

Even AR foams have a vastly reduced performance - a 9 litre low expansion branch-pipe AR-FFFP extinguisher would usually achieve a Class B rating of 183B-233B (the size of a test fire of aviation fuel/water mix in litres in a circular tray) but on Polar Solvents only gets a 34B rating.

You generally need to apply foam faster and in great quantities with Polar Solvents to compensate for the increased rate of breakdown of the foam blanket.

Fire fighting provision should be based on the advice in the MSDS which will usually say AR Foam - if you go against what it says you transfer all liability onto yourselves

Having said that, I've used standard AFFF on fire trays of iso-propanol  in the past (when we still did 'proper' live fire training) as at the time I had a good cheap supply and I found it burned cleanly (no smoke) but still had a clear yellow flame. Generally it took a little longer and a little more foam to extinguish, but a 6 litre extinguisher would cope with 2 or 3 litres. However the foam blanket quickly degraded so there would be a re-ignition risk and you wouldn't get the protection you normally would from using foam and it would be akin to having used CO2 or Powder.

If the expected fire size is only going to be a couple of litres at a time then you may get away with standard AFFF, but for any fire in depth or using greater quantities then AR compounds would be preferred. Bear in mind foam is best on contained fires and struggles with spills, primarily where the fire is running.

I've supplied them a couple of times over the years, many fire protection companies struggle to obtain them, but there are still 3 manufacturers offering them ex-stock so I can easily obtain them.

The main reason you are getting kickback will be simple - AR-AFFF & AR-FFFP extinguishers cost several times the price of standard foam extinguishers!

[firefly]

16 hours ago, AnthonyB said:

Powder can be used indoors...

Thanks very much, Anthony. That's very helpful. I appreciate you taking the time to post a comprehensive response.

 

 

[firefly]

So, for those interested. I finally got to the bottom of this. The reason why the fire risk assessors have stated that our current fire extinguishers are suitable, is that they will subdue a solvent fire long enough to allow an escape, with the caveat that the fire might well re-ignite once the solvent has completely destroyed the foam blanket.

Quite why they think it's sensible to recommend fire extinguishers which may not actually extinguish a fire, is beyond me, but at least I can understand their rationale. 

[AnthonyB]

Hardly mitigating the effects of fire as required by the legislation although it could secure escape. If you are unfortunate to have a fire that isn't controlled, the damage and disruption bill and investigation by the loss adjuster as to why it wasn't put out will no doubt see you do have them next time!