SW09 – Fire Prevention and Fire Fighting in a Shed

So what is the best way to fight a fire?  No to start one of course.  Bloody obvious huh, but when was the last time you really looked at your shed, and the degree of fire risk out there?

Fire requires 3 things to exist: heat, fuel, oxygen. Remove one of these three factors, and fire cannot exist.  Decrease any of the three, and the fire is diminished.  This is not only true for fighting the fire, but also preventing it.  We can’t reduce the amount of available oxygen (nor do we want to), so that limits us to fuel and heat.

Heat – a source of ignition – it could be a spark from a welder, or a grinder, match or cigarette (for those that smoke), friction, electrical fault, a flame (yeah, there are times when a naked flame is useful, such as braising up a bandsaw blade, or selectively burning a finish on a project) and so on.  If your activity is planned, then ensuring that the sparks etc are not going to end up somewhere undesirable is a very smart move.  When grinding a piece of metal for example, the individual sparks would struggle to start anything, but as you grind, the slag you produce can build up, and so can the heat.  Any pieces that fall off the item being ground will also have a significant amount of heat in them as well.

But even heat, and oxygen is not a problem, until you add fuel.  A well planned workshop (especially one that includes welding) sets aside an area for this sort of hot work, and the main part of that is removing fuel from that section, and shielding the rest of the workshop from the random sparks.

Controlling the fuel in a workshop is your single-best method of preventing a fire.

A large collection of timber is a fuel load. A huge pile of wood shavings is a risk.  Sawdust is a real risk (ever thrown a handful of sawdust on a fire – it burns very fiercely because of the amount of surface area of the fuel).  And of course, fuel (as in petrol, gas, paint thinners and other hydrocarbons etc).  These are particular volatile, so where possible, I’d simply store them in a separate location (such as a secondary shed).  Managing the overall fuel load of your shed is a very sensible step.  If you are going to store volatile materials, consider where they are stored.  Are they near your escape route?  Are they near any potential sources of ignition?  Can you store them in a cabinet specifically for that purpose?  That has a couple of benefits – not only does it mean all volatiles are together, and not scattered randomly around the shop, but it gives you a specific location that you can isolate from risky activities, and where it comes to fire fighting, the cabinet itself helps restrict air to the fire.  Even better would be one with specific entry points for firefighting equipment, so where you realise a fire is inside, an extinguisher can be used to fill the cabinet with extinguishing agent without having to open the cabinet at all (allowing free oxygen to increase the fire).  Of course, if there is a fire in there and you are storing volatiles, explosion is also a real risk so running away might just be the better option.

Know what you have in the shed, and even consider having an inventory of the various fuel locations.  Imagine it as if there is a fire brigade attending – what would you tell them what was in there, and where it was?  Given the sorts of chemicals we do store, is it so silly to have created a risk plan?  If nothing else, it means you have had to analyse everything you do have stored, and where it is, and have actively chosen their quantities and locations.  It also raises one other point – just because something isn’t a fuel, doesn’t mean you shouldn’t be aware of its existence.  Some things that burn (actually, many things that burn) can produce some incredibly toxic chemicals in the presence of heat / fire.  I’ll come back to this point, but the very simple rule is “treat smoke as toxic gas – breathe it and die”.  Sound a bit melodramatic?  It isn’t.  I can’t be any more blunt than that.  When I was fire fighting in the Navy, our trainers used to let off smokies to simulate the fire.  You had about 30 – 60 seconds for the initial attack (with fire extinguishers) before you had to evacuate, shut down the compartment and have the full-blown fire team (with breathing apparatus) make a full re-entry.  To accentuate the point, the trainers liked putting CS gas into the smoke so you weren’t tempted to stick around.  (CS gas- a while crystalline solid in powder form which is a respiratory and skin irritant – not dissimilar to tear gas).

Now you can start seeing why prevention is so much better than cure – fighting an uncontrolled fire is no where near as much fun as using the tools that are starting to burn.

A fire alarm in your shed is a very good idea, but you can’t just get any old one.  Most commercially available ones (the cheap ones) work on smoke.  Fine for inside the house (unless you are a bad cook!), no good in a dusty shed environment.  Out there, you need one that works on heat, or fire detection (visual), or combustion product detection.

So onto fire fighting.  There is one fundamental rule before we go any further.  NEVER put yourself at risk – if you think there is any danger or threat to yourself, evacuate, and close the door behind you.  (Once a fire is burning, minimising available oxygen will help slow the speed).  And don’t even think of doing a re-entry by yourself – the speed that the situation can change in the room while you are not in there is incredible.  Leave that to the professionals (and I guarantee you that they will use a team, not an individual when they choose to enter).

There are 6 classes of fire (these are Australian, it might be different where you are)

Class A – Ordinary Combustible Solids
Wood, paper, cloth, plastics, rubber, coal, carbon based compounds etc.

Class B – Flammable & Combustible Liquids
Petrol, oil, paint, thinners, kerosene, alcohol, etc.

Class C – Flammable Gases
L.P.G., Butane, Acetylene, Hydrogen, natural gas and Methane etc.

Class D – Combustible Metals
Magnesium, aluminium, sodium or potassium etc.

Class E – Electrical Fires
Computers, switchboards, power-boards, etc.

Class F – Cooking Oils and Fats
Cooking oils and fats usually found in industrial kitchens etc.

Each has a specific approach for fighting, and a range of equipment that is used.  In a typical shed, you could have pretty much any of the above (although I’d be asking some interesting questions if you managed to get a Class D fire!)

An electrical fire is an interesting one – because of the electricity involved, a fire is classified as E, even when there are also other classes involved.  It is a shame that there is now a Class F – it used to be that E was the top level, and only when power was isolated that the other class of fire (B or A typically) then took over, allowing a different fire fighting approach.

So lets look at each class, and why they are in our sheds (and some examples that are specific to us (and by no means comprehensive)

Class A – wood and sawdust obviously

Class B – paint, thinners, kero, petrol, (and I hope no home distilleries!)

Class C – butane torch, acetylene welder, LPG bottle (BBQ or heating)

Class D – well let’s hope not.  If you have a class D fire, they are a bastard to extinguish.

Class E – any fire that includes live electrical equipment is automatically Class E until the power is isolated.

Class F – polishes, waxes etc will come under this class.

So what fire fighting equipment do you have in your workshop?  Any?  A fire extinguisher?  Fire blanket? Hose?

I’m not going to pretend that this article will be able to train you in actually attacking a fire – so the following is only some points to include, rather than being “the authority”.  Getting some real training from your local fire brigade on initial response fire fighting is invaluable (and very informative) (and is definitely fun!)

If you can’t attack a fire within 60 seconds, it is probably too late – fires grow FAST.  I can’t reinforce how fast they grow in words, so just believe me when I say it.

Hit the fire hard with your first aid appliance – don’t be squeamish about using up the extinguisher.  Many can’t be stopped once they are released anyway.  And many will only provide a few seconds at best of fire fighting capability.   Having a Fire Blanket in the shed is not a bad move either.

They work in different ways, depending on the extinguisher and the type of fire.  In my workshop, I have dry powder.  Not my favourite agent, but it can be effective.  It works to break the chemical reactions in the fire, while smothering the fire itself (eliminating the oxygen), so it has a 2 pronged approach.  It can also be used on electrical fires, and that is important.

CO2 is less popular these days, certainly in the public arena.  It is used to deplete the oxygen, and remove heat.  Care in confined spaces is obviously important (you need oxygen too!) Too often they find themselves being used to quickly cool a beverage anyway – not much use when a fire occurs.

Water and AFFF extinguishers are not a great idea in this case – it is too likely that the fire start as Class E (given how much electrical equipment is in our workshops).  AFFF is particularly suited for liquid fires, such as a petrol spill, but again unless you are trained, you can easily not use the equipment correctly  and therefore find it too ineffective.

Get low, avoid smoke, hit hard, and be ready to retreat.  If at any stage you are not certain of your own safety, evacuate.

Finally, once you are out of the building (and the fire brigade has been contacted), establish boundary cooling.  This is taking your hose, and putting as much water onto the outside of the building (and surroundings) as you can.  If you can maintain a film of water on the building, the fire will be contained.  If you can’t, then try to maintain a film of water on the surrounding buildings and combustibles.  If your shed is going up, you don’t want the house going as well.

Now let’s hope that reading (and writing) this has been academic only, and you never have to experience the real deal.  I’ve been in countless training exercises (and have conducted countless ones as well) in all positions of a fire fighting team, from initial attack, through the full BA wearing hose teams, and damage control coordinator. (I used to be the aft damage control officer on a warship, and we had to train to deal with fire, flood, toxic gas, radiation, casualty, etc etc, and combinations of those too.)  I’ve also had to coordinate the attack on a number of real ship-based fires, and in every case they had the same source.  Linseed oil.  Take a rag and rub linseed oil on some timber, then take the rag, screw it up and throw it in a bin.  And a few hours later, you have a fire.  It is definitely another take-home point.  Be careful not to leave yourself any booby traps.  If I have had something occur (such as a smoldering fire like I had last year), I don’t put it out then bugger off for a beer.  Hang around for a while, do some other tasks, and reassess the incident.  Make sure it is really out, and not just gently smoldering away.  A fire in the middle of the night is a lot less fun than you’d imagine.

Just to pick up on that point further.  Spontaneous ignition is a REAL danger.  A rag or similar (and especially steel wool) that has been used to apply a finish (and particularly an oil finish) can easily spontaneously combust hours later.  Steel wool when it burns is going to produce a very hot fire fwiw – you might get a Class D fire in your workshop after all.  If you compact the rag into a tight(ish) ball, heat has an opportunity to build, and build, to the point where it begins to smolder.  Then burn.

Disposal of these can be done one of two ways.  Either lay them out to dry (not scrunched up), or store them in a bucket of water for later disposal.

As to the ‘dangers’ of sparks in the dust system, especially static electricity, let’s just say that I have my opinions on that topic, and it isn’t something I take any particular precautions against.  I’ve no doubt that you do get a good static buildup with PVC piping and dust flow – I’ve been walloped plenty of times on that score, particularly from a cyclone unit, but in a small shop situation I tend to consider the concept as an urban legend.  One of these days, I am going to set up an actual experimental rig to prove, or disprove it as far as I can.  In one report I read, it suggested that the occurrence in the UK was 1 dust collection related explosion every 2 years.  Given how many woodworkers (and pro shops) are over there, I would be wondering then if for those individual bi-annual cases whether there wasn’t some other factors involved.  If you are really concerned, grounding the PVC piping to your shed (if the shed is metal) should be more than sufficient to deal with any possible risk.

Finally, two things to take away (if nothing else).  DO NOT put yourself at risk.  It is only a shed.  DO NOT breathe the combustion products (smoke). It is toxic, and it will kill.

This is NOT a comprehensive document on fire prevention and fire fighting.  If you didn’t know some of the above-points, then I strongly recommend attending a training course.  They are fun, and you learn a lot!

9 Responses

  1. Stu,
    An excellent article.
    Could we have a little more on spontaneous combustion from fluids like linseed oil and other products.
    I also worry about using 4″ hoses connected to dust extractors to clean workshop floors where wood shavings and dust, screws and nails can be sucked up, hit the metal fan blade and cause a spark.
    Frank

  2. Good contribution to SW09, Stu.

    To pick up Frank’s point, this is another reason to use a pre-separator in your DC system. It means that metal objects will drop into the pre-sep bin before they get to the impeller blades. I put mine in for another reason – because curlies from my handplanes kept clogging the impeller input because of the mesh over it – but I have noticed that there have been significantly fewer sickening metal on metal crunches in the impeller since it was installed!

    BTW it seems that Mark Spagnuolo is trying to replicate the auto-combustion of finish impregnated rags experiment. If he gets it on film, this would be very interesting to see.

    Jeremy

  3. […] Fire Prevention and Fire Fighting in a Shed […]

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