Fighting Magnesium Fires

Magnesium and its alloys present special problems in fire protection. Magnesium combines so readily with oxygen that under some conditions water applied to extinguish magnesium fires may be decomposed into its constituent elements, oxygen and hydrogen. The oxygen combines with the magnesium, and the released hydrogen adds to the intensity of the fire. None of the commonly available inert gases are suitable for extinguishing magnesium fires. Magnesium will burn in the atmosphere of carbon dioxide. It may also burn in an atmosphere of nitrogen to form magnesium nitride. For these reasons, any of the common extinguishing methods that depend on water, water solutions, or inert gases are not effective on magnesium chip fires. Halogen-containing extinguishing agents (the halons) react violently with burning magnesium. However, inerting with noble gases, e. g. helium or argon, will extinguish burning metal.

The method of extinguishing magnesium fires depends largely upon the form of the material. Burning chips and small parts must be smothered and cooled with a suitable dry extinguishing agent, e. g., graphite and dry sodium chloride. Where magnesium dust is present, care must be taken to prevent a dust cloud from forming in the air during application of the agent because this may result in a dust explosion.

Fires in solid magnesium can be fought without difficulty if attacked in their early stages. Often, it may be possible to remove surrounding material, leaving the small quantity of magnesium to burn itself out harmlessly.