I'm not an expert on inflammable metals, but let me relate this story. My old ladder company is a quint, and one day they were dispatched alone to a car fire. When they got there they had a fire in the engine compartment of a Volkswagon. They stretched and 1 1/2" "Trash line". It was a while before they were heard from on the radio, but the next thing that was heard was "Charge the 1 3/4" ".
The next transmission was requesting an engine into the still alarm for water supply! Needless to say,
this caught peoples attention. They eventually figured out what was happening; they had a magnesium block on fire! Well, the fire did go out and noone got hurt, but they definitely took the long way around. After that, we started sending an engine and a ladder on all car fires and 2 weeks after that fire a Metal-X extinguisher showed up on Ladder 3. The unfortunate part of vehicle construction today is that the magnesium is not limited to the block of the engine. My only suggestion is that if the flame is bright white and the smoke is really white, you probably have a fire involving magnesium. There is a good video of a fire in a Jeep where the firefighter is right up on the vehicle and gets water on some magnesium. Cool light show, but kinda scary too. Use the reach of your stream before advancing to see how the fire reacts. If it reacts violently, try a Metal-X extinguisher and see if that knocks it down. Stay safe!
I went to a fullyy involved Mercury Moutaineer that was a torch job. There was no magnesium in the engine compartment area, but we did find some fire involving the components under that steering wheel in the fire wall area. It was in the fuse box area it was lighting up pretty good with water so we hit it with our METAL X that seemed to do the trick
Ultimately you should use a class D extinguisher but only for very small incidents.
I worked in a magnesium auto parts factory. We made all kinds of car parts like steering column mounts, tranny covers, engine mounts, exterior cowl(Mustangs), dash frames, seat frames, etc. So cars have more and more magnesium components now days. Keep in mind it takes a very hot fire to light it. The nature of magnesium is that it dissipates heat very well and not able to ignite until molten at about 650F.
As far as water goes when applied to a mag fire it will cause a (large) hydrogen explosion. Water can be used only to cool the magnesium containment but you need lots and lots(lots) not directly on the fire. And lots of time to wait for it to burn.
Keep in mind if you have a large magnesium car fire with the big white fire ball the FD PPE that you have doesn't do it. Temps can get up to 5000F. So stay way back and let it burn.
Long and short is if you have a very small (bright white) fire you want to use a dry means of smothering it. Providing you don't have anything like a class D extinguisher, you can use kitty litter or sand to smother it. But not the best since it will likely have some amount of moisture in it potentially causing an explosion. There is a product we used to use when I worked at the magnesium factory called Magsorb. It's expensive but worth it if you have a large molten fire.
We use Fire Blockade on all fires. It works like a foam but is a natural cooling agent made from a soy based product. Unlike foam it poses no hazard to the environment. It works just fine on mag. fires as well as structure fires. You might check it out. I have been in the service 22 years, I'm kinda hard to impress, but this stuff I find good.
Luis I am not sure what your experience is but you cannot use anything with water or moisture as I said you will create a hydrogen explosion. This is a huge safety risk for firefighters as water expands 1000 times and throws molten magnesium everywhere. This is just grade 11 science.
Refer to the fire tetrahedron. With magnesium you need to take away one of two things either heat or oxygen. You can't take away heat with water without causing an initial and sporadic mini explosions. Then as Todd mentioned you need an unlimited amount of water depending on the fire size. Mag in large quantity can be a very stubborn fire.
It's much easier if practical, to take away the oxygen by smothering it out with a number of products designed for liquid metal fires. eg.Class D extinguisher, Magnesium Foundry Flux, Dry G-1 Powder, Met-L-X Powder.
I worked in a magnesium foundry on emergency response so I know what I am talking about.
In our district we have a Honda plant that manufactures magnesium parts. We get shavings from the plant and have tried all kinds of extinguishing agents. Of course Class D extinguishers and MagSorb work best, but they are not feasable for large fires. In this case copius amounts of water and distance from the material are the best policy we have found.
Please remember I am not talking abut alot of Mag on fire. A lot of water and little product were ok, alot of product and little water it is not a good day. In cars we are looking at having Mag in the steering area, rims, and engine compartment. Most Engines can have enough water with minimum amount of product, now something with a bit more product try something else.
I work with titanium, which reacts to water similarly to magnesium. Water is really a last resort as has already been stated, you'll get quite a fireworks show. Class D (Metl-X) works on the small stuff but, it's usually easier to just let it burn itself out.
My take on this is that using a class D agent on a vehicle fire where magnesium has already been identified as part of the combustion is a waste. By this time, the vehicle is practically always beyond salvage, thus operations should concentrate on protecting exposures and crew safety. PPE and distance, plus copious water as Todd has mentioned. I just saw the price of a 30lb. class D extinguisher at $688! Personally, I would save it for fires where you must put out the metal. The YouTube video that shows the results of applying water to such fire is quite illustrative for those who haven't seen it: http://www.youtube.com/watch?v=iUmqhIVW3cM
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