Material Safety Magnesium and Fire Hazard - Fact or Exaggeration?
When it comes to the use of magnesium in production, sceptical voices are repeatedly raised with regard to the risk of fire and explosion. However, the accident-free use of magnesium is purely a question of safety precautions. So what do you have to consider when handling magnesium?
Magnesium is well known for its safety concerns in the industry due to its combustive, reactive nature when produced or stored in certain forms. The metal is often associated with a high risk of fire and explosion. Nevertheless, foundries process thousands of tons of molten magnesium every day. When working with molten magnesium, special care must be taken because the metal reacts with a wide variety of materials like air and water. Despite these potentially hazardous properties, handling magnesium in production is perfectly safe if the following aspects are considered and appropriate safety precautions are taken.
1. Magnesium Reacts with Various Materials
Most magnesium melting pots are made of steel, but molten magnesium can react exothermically with iron oxide. Therefore it is especially important to keep the inside area of the pot clean and free of scale (oxides of iron). Likewise, scale should be removed regularly from the furnace to prevent a reaction with molten magnesium in the event of a pot failure. As strong reactions can also occur in contact with small amounts of silica, the refractory materials used for the furnace must have a high alumina or magnesia content. To avoid accidents, the equipment should be checked regularly for defects. Furthermore, the gas feeding system should be designed to evenly distribute cover gases over the melt because high concentrations of cover gases can severely corrode the steel cover and melting pot.
2. Protective Gases Prevent Oxidation
Since magnesium reacts with oxygen, it must be ensured that the molten metal is not exposed to it under any circumstances. Otherwise, the molten magnesium could ignite and burn. Protective gases, such as sulphur dioxide - mixed with nitrogen, argon or air and carbon dioxide or other cover gases can successfully prevent oxidation. Another already proven method is to cover the magnesium melt with molten chloride salts so that air contact with the surface is prevented.
3. Water and Magnesium - An Explosive Mixture
If a fire breaks out, it must be extinguished as quickly as possible. But what intuitively sounds like the right solution in conventional fires must be avoided in foundries at all costs: Water. If molten magnesium comes into contact with moisture, this can lead to dangerous explosions. It is therefore essential to ensure that tools are preheated to 100 °C before being introduced into the molten material so that they are free of condensed liquids. Sand or a dry fire extinguishing material of class D, such as G-1 powder and foundry flux, is suitable for extinguishing magnesium fires.
4. A Proper Building Structure Minimizes Risks
It is clear from the above-mentioned points that safety when handling magnesium begins with the requirements for the building. When it comes to safety equipment, it should therefore be noted that automatic sprinklers should not be installed over melting operations, heat treating furnaces, or in storage/production areas containing magnesium in finely divided forms. Furthermore, magnesium foundry structures should be built with non-combustible materials and the floors around melting operations should be hard burned or vitreous paving block. The heat from molten magnesium can release the water of hydration in concrete which will cause it to spall, sometimes explosively. And last but not least, buildings should be grounded to protect against lightning strikes.
5. Protective Equipment Avoids Burns
In a foundry, employees work with molten magnesium with a melting point of about 650° C. Since the safety of the employees is the first priority, every company should invest in protective equipment that meets applicable statutory codes. For example, fire-resistant clothing and safety boots with spats protect against skin contact with the hot metal.
No Danger from Magnesium Components
The high safety precautions in foundries with trained personnel are one thing, but what about the use of magnesium components in practice? The all-clear can also be given here, as the high hazard potential relates mainly to magnesium alloy products with pure magnesium in the form of powder or ribbons used for photographic and pyrotechnic purposes as well as high school chemistry experiments. It is therefore true that finely divided magnesium is highly combustive, but solid magnesium parts will not burn until heated above the melting point. Therefore magnesium alloys are widely used in jet engines, in the structures of military and civilian helicopters, and hundreds of auto components. Examples for magnesium components that are built into cars can be explored with the help of a 3D demonstrator.