Definition
A fire involving combustible metals such as magnesium, titanium, sodium, or potassium. Class D fires require specialized dry powder extinguishing agents, because water, foam, and standard chemical extinguishers can intensify the burning or cause violent reactions.
Plain English
A fire where the thing burning is a metal. These fires need a special powder to put them out — water makes them worse.
Context Anchor
Seen in aircraft maintenance fire-safety procedures, especially around magnesium or titanium parts, metal dust, and shop areas where metal is cut, ground, or machined.
Derivation
The U.S. National Fire Protection Association (NFPA) classifies fires by letter (A, B, C, D, K) based on the type of fuel burning. 'D' was assigned to combustible metals. Knowing the letter tells you which extinguisher works — and which ones will make things worse.
Why Pilots Care
Aircraft engines and components often contain metals that create Class D fires, which need special dry-powder extinguishers.
Grounding Statement
A Class D fire is dangerous because the metal itself is burning, not just something on or around the metal.
Intuition Check
Class D does not mean Class D airspace, and it does not mean the fourth level of seriousness. Here it means the fire category for burning metals.
Example Sentence 1
After a hard landing, the technician noticed the magnesium wheel was glowing — a Class D fire risk that required a dry powder extinguisher, not water.
Example Sentence 2
A Class D fire in the workshop required the correct dry powder extinguisher.