Most people are familiar with fires involving wood, liquids or electricity. But in certain industries, there’s another much more dangerous type of fire risk.
Class D fires, as defined under BS EN 2:1992, involve combustible metals such as magnesium, aluminium, titanium, potassium and lithium (note: not Lithium-ion batteries – more on that below).
They burn incredibly hot, can be difficult to extinguish, and need very specific equipment and response procedures. In this blog, we’ll explain what Class D fires are and where they’re likely to occur. We'll also cover how to prevent them, how to extinguish them safely and what equipment is required.
What is a Class D fire?
A Class D fire involves flammable metals. These fires are rare, but when they do happen, they can spread quickly and cause significant damage.
You’ll typically find Class D fire risks in environments such as the metalworking and machining industries. However, they are also a common fire risk for laboratories and test facilities, aerospace and defence manufacturing facilities, military operations and automotive and electronics production
It’s important to note that Lithium-ion battery fires are not Class D fires and cannot be treated with Class D extinguishing agents.
Common causes of Class D fires
According to the UK Health and Safety Executive (HSE), the leading causes of metal fires are linked to poor storage and handling practices.
Some of the most common triggers include:
- Sparks from grinding or machining
- Buildup of fine metal dust or shavings
- Flammable metals exposed to open flames or hot surfaces
- Chemical reactions from improperly stored metal powders
- Static discharge near reactive metals
Like many fire risks, these hazards are preventable with the right awareness, housekeeping and control measures.
Preventing Class D fires: Best practice
Class D fires are notoriously hard to fight, so prevention is the best protection. Here are some practical steps you can take:
- Carry out regular risk assessments to identify reactive metals and dust
- Install ventilation and dust extraction systems
- Use explosion-proof equipment in high-risk areas
- Store metal powders in sealed, approved containers
- Deliver fire safety training that includes specialist response procedures
For high-risk environments, a comprehensive prevention plan is just as important as the equipment on the wall.
Suppressing a Class D fire
If a Class D fire does break out:
- Switch off nearby machinery, if it’s safe to do so
- Isolate and evacuate the area, and avoid exposing others to fumes or flying debris
- Use a dedicated suppression agent, such as PyroFlow Active granules, to smother the flames
- Contact the Fire Brigade with clear details on the materials involved
Do not use water or standard extinguishers, as they can make the fire worse.
What extinguisher should you use on Class D fires?
Standard extinguishers, such as foam, water or CO2, are not suitable for Class D fires.
These fires require a specialist powder extinguisher specifically designed for metal fires. They work by dispersing fine dry powder directly onto the fire, creating a heat-resistant crust that cuts off oxygen and prevents burning fragments from spreading.
Importantly, they come with a long hose and low-velocity applicator, not a typical nozzle, to avoid disturbing burning metal particles.
Class D Fire FAQs
Are Class D fires common?
Not in most workplaces, but in industries that work with flammable metals, they are a serious concern.
Can water be used on a Class D fire?
No. Water can cause a violent reaction with metals like magnesium or sodium. It’s extremely dangerous and must be avoided.
What’s the difference between Class D and Lithium-ion battery fires?
It’s easy to confuse the two. Lithium-ion batteries contain lithium compounds, not pure metal, and burn in a different way. They are not Class D fires and require different extinguishing agents such as Lith-Ex or specialist fire blankets.
In addition to our Lith-Ex fire extinguishers, the Firechief® range of fire safety products also includes fire blankets, suppression systems, signage and products for all types of fires. For information, call us on +44 (0)330 999 0019 or email sales@firechiefglobal.com.
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Disclaimer
The information contained within this blog is provided solely for general informational and educational purposes and is not intended as a substitute for professional advice. Before taking any actions based upon this information, we advise the reader to consult all relevant statutory or regulatory guidance and, where necessary, to consult a qualified fire or industry regulation professional. The use or reliance on any information contained herein is solely at the reader's risk.