Magnesium wheels

[TFEM]

Just done a staff training session and the question was asked about the flammability of magnesium wheels and whether specialist (Class D) extinguishers should be used.
I understand the way flammable metals should be treated in their "raw" form but what about the manufactured end product? I've done a little poking about and it would seem that they are flammable....but at what level? When they get ultra hot or when they've been driven tyreless thereby releasing "finings" which then ignite?
Any help appreciated.
John

[lancsfirepro]

When you say "wheel" I'm assuming you mean a car sized wheel.  In their finished form I wouldn't be concerned.  Magnesium swarf and filings will quite readily burn but the heat required to burn a solid lump like a wheel would be pretty substantial and therefore unlikely unless you have a fire surrounding it.  But okay, lets say you did have a fire surrounding a magnesium wheel so that it would burn - the wheel rolls away from the fire and stops, giving you a pure metal fire.  Will a class D extinguisher suffice?  Very unlikely in my opinion.  A magnesium wheel would more than likely be a larger sized wheel off a sports car so probably around 18" in diameter.  That's a big amount of magnesium to attack with a class D extinguisher.  Class D extinguishers don't carry a fire rating to tell you what size of fire can be extinguished but any videos I've seen of class D extinguishers in action need to use a lot of extinguishing media to put out a fairly small amount of burning metal.  Think of a cereal bowl size.
If the fire cannot be left to burn out, then I would more likely consider sand (and lots of it) as a more cost effective and readily available solution.

[Golden]

I really wouldn't get anything specialised as Lancs says above the heat required to ignite a wheel would probably mean fire service involvement anyway. Any sand would have to be bagged and dry (properly dried) sand that is quite expensive, also all of the class D powders used to be ridiculously expensive so you would have to ask is it cost efficient unless its a process risk when you would have to make provisions. Magnesium is not easy to ignite unless its very thinly cut into magnesium ribbons/swarf and any normal industrial processes should recognise the risk and take measures to control it before any significant amounts caught fire.

As trainers we used to have great fun in RTA scenarios (yes they were still RTAs back in those days!) by loading up a car with magnesium swarf before setting it alight; it used to cheer us up to see the look of surprise on those fire-fighters faces when they put a jet through the window!

[nearlythere]

As trainers we used to have great fun in RTA scenarios (yes they were still RTAs back in those days!) by loading up a car with magnesium swarf before setting it alight; it used to cheer us up to see the look of surprise on those fire-fighters faces when they put a jet through the window!

Bummer. Now you tell me.
Subject to a suitable and sufficient fire risk assessment I'm sure.

[lancsfirepro]

Any sand would have to be bagged and dry (properly dried) sand that is quite expensive...

For the record, kiln dried sand is readily available (used for sanding block paving) and whilst more expensive than building sand, is still only about £3 a bag.

[SamFIRT]

Where would be the need for a first aid extinguisher? As has already been discussed a fire that involves metal wheels ( or bodywork) will require a fire appliance to deal with it.

[lancsfirepro]

Like this one? Wait while about 1min 10secs.
http://www.youtube.com/watch?gl=GB&hl=en-GB&client=mv-google&v=KY9ri-UOoLo&nomobile=1

[Golden]

Yes that's the one .... how we laughed

We did do a full safety briefing and told them to expect some fireworks. There was a serious side in the techniques of approaching of a vehicle on fire and it used to take a few minutes to extinguish meaning the other crew members had to work hard on the second car to protect the casualty .. it wasn't all fun. As Sam has commented below - if there's enough fire to get a reasonable amount of magnesium alight then fully trained and equipped personnel (including PPE) should be used to deal with it; that of course could be trained workers.

[AnthonyB]

If the wheels are well alight you need more than an extinguisher!

Class D extinguishers are becoming more common on US fire engines to deal with the increasing use of flammable metals under the bonnet.

Incidentally Cetrimax ABC powder, once the most commonly used powder in the UK (except for Pyrene & Chubb) is Class D rated for magnesium and was tested to DIN standards achieving an extinguishing ratio of 12kg ABC powder for 1kg of magnesium shavings using a normal extinguisher with a low velocity lance fitted