When we think of fire hazards, our minds often go to common sources—wood, paper, gasoline, or even electrical equipment. However, one of the most dangerous types of fires is a metal fire (Class D fire), which involves combustible metals such as magnesium, zirconium, and titanium. These fires are uniquely hazardous due to their extreme temperatures, violent chemical reactions, and self-sustaining nature. Understanding the science behind these fires is crucial for both industrial safety and fire prevention efforts. Here are 5 reasons why Class D fires are so dangerous.
1. Extreme Heat and High Burn Temperatures
2. Difficult to Extinguish
Putting out a Class D fire is not just challenging—it’s dangerous if done incorrectly. Unlike traditional fires that need external oxygen, Class D fires can sustain themselves by splitting molecules apart. This means that molecules such as water can be split, freeing oxygen to continue to fuel these fires. This makes simply cutting off air access ineffective—specialized extinguishing agents are required.
3. Hydrogen Gas
In addition to a Class D fire’s self-fueling capability, traditional fire extinguishing methods like water or foam are not only ineffective against Class D fires, but can actually make the situation worse. When water is introduced to burning metal, it can lead to a catastrophic increase in fire intensity.
As mentioned in the previous section, the extreme heat of a Class D fire can split water molecules (H₂O) into hydrogen and oxygen. The liberated oxygen will feed the fire, and the liberated hydrogen will effectively become hydrogen gas – known for being highly flammable. This unique chemical property makes water one of the worst choices for extinguishing a Class D fire.
4. Class D Fires Occur in At-risk Environments
Class D fires are primarily a concern in industrial settings where combustible metals are processed, stored, or used in manufacturing. Some of the most at-risk environments include:
- Aerospace and automotive manufacturing, where metals like magnesium and titanium are commonly used
- CNC machining and metal fabrication shops, where small metallic chips can accumulate and ignite
- Laboratories and chemical plants, which may store reactive metals like lithium and sodium.
These environments require strict safety protocols, as even a small spark or improper disposal of metal shavings can trigger a fire.
5. Traditional Fire Extinguishers Won't Work
Standard fire suppression methods, such as water, foam, or carbon dioxide, are ineffective against Class D fires. Water can make the situation worse while carbon dioxide extinguishers are ineffective due to the unique chemical properties of burning metals.
Plus, fire extinguishers require personnel to manually discharge the system in close proximity to the fire, putting themselves at risk and leaving room for human error during the discharge process.
“Fire blankets,” a solution marketed to combat small-scale Class D fires, require even more direct, close-range human intervention.
Class D fires require specialized extinguishing agents, such as:
- Dry Powder Agents – These agents, typically composed of powdered graphite, sodium chloride (NaCl), or copper, work by absorbing heat and forming a crust over the burning metal, cutting off its oxygen supply.
- Automatic Fire Suppression Systems – These systems use heat sensors to detect and suppress fires before they grow out of control, offering a proactive approach to fire safety, without the need of immediate human intervention.
Mitigating Class D Fire Risks
Given their destructive potential, mitigating is a necessary step to effectively manage Class D fire risks. Some key strategies include:
- Proper storage of combustible metals in well-ventilated areas away from ignition sources.
- Regular maintenance and cleaning to prevent the buildup of small metal chips, which are highly flammable.
- Employee education and training to ensure workers understand the dangers of metal fires and the correct response protocols.
Suppressing Class D Fires
Even with responsible mitigation, cutting Class D metals carries an inherent risk of fire.
Dedicated Class D fire suppression systems, like the new solution from Firetrace, automatically detect and contain fires before they spread.
The Firetrace Class D Fire Suppression System is a pre-engineered local application system designed for automatic, targeted protection of CNC machines, collection bins and drums where combustible metals are present..png?width=450&height=236&name=Class%20D%20Kit%20-%20LinkedIn(warehouse%20BG).png)
When a fire ignites, the system’s heat-sensitive detection tubing bursts upon exposure to extreme temperatures, triggering the release of Amerex Super D Dry Powder directly onto the fire —without the need for human intervention.
Once deployed, the agent forms a heat-absorbing crust, smothering the fire, cutting off oxygen, and preventing reignition—buying time for response without exposing workers.
Conclusion
Class D fires represent a unique and often underestimated hazard in industrial and manufacturing environments. Their extreme temperatures, violent reactions with water, and ability to sustain themselves make them one of the most dangerous types of fire. Understanding the science behind these fires and implementing specialized suppression methods is critical to protecting people, equipment, and facilities from catastrophic damage. By taking the necessary precautions, industries can reduce the risk of these fires and ensure a safer working environment for everyone involved.
Talk To an Expert
At Firetrace, we provide fire suppression options suitable for a wide range of applications, including environments where Class D fires may occur. Not sure what you need for your shop? Talk to one of our fire suppression specialists to discuss your needs and concerns. Contact us today to schedule your free consultation.