Young adult male wearing a relaxed fit blue Hawaiian shirt with white and yellow patterns, dark sunglasses in an outdoor backyard setting with greenery, wooden fence, and smoke from a fire pit. 4:51
TheBackyardScientist channel icon TheBackyardScientistOriginal creator 3M views Save

Why you never spray water on a magnesium fire

A magnesium fire starter is meant to start a fire a few shavings at a time. The Backyard Scientist would like to know what happens if you light the whole block. more

The block comes with a flint on top. The usual plan is to shave a little magnesium into a pile and strike sparks onto it, which gives you a bright fire even on a wet, rainy day. He skips the shaving and puts a blow torch to the whole thing.

Hands strike flint against steel, sending sparks onto dirt ground. A headline runs in white letters across the lower third.Save
Done the normal way, sparks from the flint land on a small pile of magnesium shavings.

Once it catches, it burns so hot and so bright that it hurts his eyes to look at it, even with sunglasses on. This is the same metal that lit the flash bulbs of old cameras and still goes into fireworks.

Magnesium is also famous for being hard to put out, so he tries dry ice first. Dry ice is frozen carbon dioxide, and it stops most fires by pushing the oxygen away. Magnesium plays by other rules. It pulls the oxygen it needs right out of the carbon dioxide and keeps burning until the bar is gone, leaving only a bit of black carbon behind.

Next he wants to try water, since he has heard it makes a big blast. He's out of fire starters, but he knows some cars use magnesium parts. The radiator support from one year of the Ford F-150 holds about 15 pounds of it. He pulls one at a junkyard for 50 dollars, when the same amount in fire starters would have cost 480 dollars.

He sets the new batch burning and sprays it, and the water only makes it worse. It bursts into a cloud of sparks and smoke that he says looks like a nebula. Bad for putting out a fire, he admits, but great if you want a cool slow-motion video. "I guess they weren't kidding," he says, "when they said don't put water on a magnesium fire."

Young adult male wearing a relaxed fit blue Hawaiian shirt with white and yellow patterns, dark sunglasses in an outdoor backyard setting with greenery, wooden fence, and smoke from a fire pit. The headline runs in white letters across the lower third.Save
A magnesium fire starter is meant to start a fire a few shavings at a time.

Sand is the better bet, since it smothers the metal. The best plan of all is not to light one in the first place. He has one more thing to show, though, so he waits for dark.

This time it is about how bright the stuff really is. Burning in the dark, the magnesium lights up his entire backyard. Then a moth flies straight into the glow, and he can only report that it flew in there.

A man in a patterned shirt stands outdoors at night with his mouth open. A headline runs in white letters across the lower third.Save
Out in the dark yard, he reacts as a moth flies into the burning metal.

That feels like a good place to stop. He says he has inhaled enough of this for one day, which may be the most sensible line of the night.