Metal Fires: Why Water and CO₂ Can Make the Fire Worse
At first glance, metals do not appear to be typical fuels. Many metals are difficult to ignite in solid form. The situation changes with swarf, dust or fine powders. Their large surface area allows metals such as magnesium, aluminium, titanium, sodium and lithium to burn violently.
These fires belong to fire class D. They reach extremely high temperatures and may react with extinguishing agents that are routinely used on other types of fire.
What happens when water is used?
In a metal fire, the intense heat can cause water to vaporise suddenly. Some metals also react chemically with water, potentially releasing flammable hydrogen.
Using magnesium as an example, the reaction can be represented in simplified form as follows:
Magnesium + water → magnesium oxide + hydrogen
The released hydrogen can ignite. If it mixes with oxygen in the air, an explosive oxyhydrogen reaction may also occur. Water therefore does not reliably extinguish the fire. It can make the situation considerably worse and spread burning material.
Why does a CO₂ extinguisher not work?
Carbon dioxide extinguishes many liquid fires by displacing oxygen at the seat of the fire. This is not sufficient for highly reactive metals.
Burning magnesium can extract the oxygen contained in carbon dioxide, allowing the metal to continue burning. In simplified form, the reaction is: Magnesium + carbon dioxide → magnesium oxide + carbon
In this case, a CO₂ extinguisher has no extinguishing effect. It is therefore just as unsuitable for metal fires as water, foam or conventional ABC dry powder.
In the video: extinguishing tests with CO₂ and water
The video first shows an attempt to extinguish the metal fire with carbon dioxide (CO₂). Water is then applied. Both tests demonstrate why these extinguishing agents are unsuitable for burning magnesium. The test was carried out under controlled conditions and must not be reproduced independently.
How are metal fires extinguished?
Metal fires require special Class D metal-fire extinguishers. The powder is applied carefully and at the lowest practicable pressure. It covers the burning metal, separates it from atmospheric oxygen and limits radiant heat. Depending on the metal, the work process and the hazards present in the workplace, other suitable specialist extinguishing agents may be required. Their type, quantity and provision must therefore be determined through the risk assessment and the fire safety plan.
In the event of a fire: warn people, leave the danger area, call the emergency services and explicitly tell the fire brigade that a metal fire is involved. Only trained persons should attempt to extinguish the fire, using the correct extinguishing agent and without putting themselves at risk.
Specialist fire training on request
Practical training in fighting metal fires is not part of our standard fire safety assistant course. Businesses that process or store combustible metals, or that generate metal swarf and dust, require separate instruction.
We offer specialist fire training on request. The content is tailored to the metals, work processes and operational hazards present at the site.
Would you like to arrange specialist fire training for your business? Contact us.
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