Fire Protection Blog | Firetrace Fire Suppression System

What Is A Class D Fire?

Written by Firetrace International | Feb 20, 2025 6:03:58 PM

Within industries such as CNC machining and manufacturing, it’s difficult to overstate the importance of understanding—and mitigating—the risk of a Class D fire. Because these fires, which involve combustible metals, burn at extremely high temperatures, they can effectively fuel themselves as molecules are split apart.

Keep reading for a brief overview of Class D fires, including their primary causes and some best practices for their prevention and suppression. Let’s start, though, by defining Class D fires and providing a straightforward Class D fire example.

What Is A Class D Fire?

Different industries face different types of fire risk, largely depending on the industry-specific processes, equipment, and materials they use. Among these are Class A, B, C, D, and K fires, with their primary difference being the materials involved. 

So, what materials are Class D fires? Consider the following:

  • Class A fires involve combustible materials like paper, cardboard, cloth, wood, and some plastics.
  • Class B fires involve flammable liquids, like fuels, oils, and paints.
  • Class C fires involve charged electrical equipment, including appliances, circuit breakers, and outlets.
  • Class D fires involve combustible metals like titanium, magnesium, zirconium, aluminum, and sodium.
  • Class K fires involve various types of flammable oils and greases.

What Is a Class D Fire Example?

Because Class D fires involve certain combustible metals, they pose a threat within the types of industrial environments that process, store, or use them. While class D fires may not be incredibly common, they still pose a very real danger in environments like manufacturing and machining facilities, as well as some chemical plants. 

There are three primary ways a Class D fire can ignite, including through…

  • Accidental ignition of material during welding or machining processes,
  • Improper handling or storage of combustible materials, and
  • Sparks or heat generated by machining equipment reacting with combustible materials.

While basic fire prevention measures can be effective and easy to implement, completely eliminating all risk of fire isn’t a realistic goal. That’s why understanding the risk is important, and implementing a comprehensive approach to Class D fire suppression that minimizes the risk of damage to people or equipment should be a priority.

How Do You Extinguish a Class D Fire?

Depending on the size and location of the fire, a Class D fire can be actively suppressed with a handheld Class D fire extinguisher, automatic fire suppression system, or a combination of these methods.  For smaller Class D fires, a common approach is to use sand or sand like material as well.

While handheld extinguishers are effective and easy to work, an automatic fire suppression system offers several unique benefits, including the ability to detect Class D fires more quickly—and suppress them fully, before they can spread.

Modern fire suppression systems also incorporate heat sensors or detection tubing, enabling them to automatically activate when needed. This represents an undoubtedly safer and more effective approach than using a Class D fire extinguisher, which requires a human operator to confront the fire at its source (subjecting the user to not only the danger of the fire itself, but the toxic fumes these fires can produce as well).

What Is a Class D Fire Extinguisher For?

A Class D fire extinguisher is used for smothering a Class D fire with an extinguishing agent before it can become more widespread. It works by applying a specific type of powder, which effectively blankets the burning material and prevents it from receiving the oxygen it needs to grow and spread. Uniquely formulated for Class D fires, Class D fire extinguisher powder typically contains materials like powdered graphite, granular sodium chloride (NaCl), and fragments of copper (Cu). 

Again, while Class D fire extinguishers are useful, they do have drawbacks, making them an imperfect solution in environments with a Class D fire risk. The biggest of these relates to how they are used—specifically, that they require active application, meaning a human operator has to confront the fire directly. A much safer, proactive solution is the installation of a modern fire suppression system, which we’ll take a closer look at next. 

What Is a Class D Fire Suppression System?

Another (better) approach to fighting Class D fires involves the implementation of a Class D fire suppression system, tailored to the specific environment. For example, Firetrace provides is a pre-engineered local application system designed for automatic, targeted protection that can be installed within machinery, equipped with detection tubing that can trigger the system before a fire can spread and, in some cases, before it can even be perceived, posing less risk to people and equipment.

Can Class D Fires Be Prevented?

No, Class D fires cannot be 100% prevented. However, there are ways to mitigate the risk. It’s always best to have effective measures in place for preventing its spread and limiting how much damage it can do. Returning to the CNC machining example, a well-rounded approach to Class D fire protection includes best practices like…

  • Performing regular, routine maintenance on all machinery,
  • Confirming that all equipment and parts are in good working order and undamaged,
  • Replacing equipment and parts when needed,
  • Keeping work areas clean and clear of debris, especially combustible materials, and
  • Educating employees on Class D fire causes, prevention, and suppression.

Unfortunately, there is no way to prevent Class D fires entirely—even when proper precautions are taken. That’s why it is so important to understand the dangers of Class D fires and how to effectively suppress them.

Consult Our Team to Learn More

At Firetrace, we offer a range of versatile fire suppression solutions, ready to be tailored to your unique environment. Our experienced team of experts is ready to help you better understand the risk Class D fires pose and explore your options for fire suppression. To learn more, get in touch with us today.