Types of Portable Extinguishers and What They Put Out

These are the types you're most likely to meet and the classes they cover:

• Water (APW) — Class A only. Cools ordinary combustibles. Never on B, C, or D.
• Foam (AFFF) — Class A and B. Blankets a liquid surface to smother it. Conductive, so not for energized equipment.
• Carbon dioxide (CO₂) — Class B and C. Smothers and leaves no residue, so it's good for electronics and electrical — but short range and easily blown away outdoors.
• Dry chemical, multipurpose (ABC) — Class A, B, and C. The site workhorse. Leaves a corrosive powder residue.
• Ordinary dry chemical (BC) — Class B and C only, no A rating.
• Wet chemical — Class K (and light A). Cools and saponifies cooking grease so it won't re-flash.
• Dry powder — Class D only. A special metal-fire agent — not the same thing as dry chemical.

A few practical points that catch people out:

• CO₂ has a short reach (a few feet) and displaces oxygen — dangerous in a small enclosed space, and it can frostbite bare skin at the horn.
• Dry chemical residue is corrosive and makes a mess of electronics and machined surfaces — CO₂ or a clean agent is better around sensitive equipment.
• Foam and water conduct electricity — keep them off anything energized.
• "Dry chemical" and "dry powder" sound alike but are not interchangeable: only dry powder is made for combustible-metal (Class D) fires.

Before you rely on an extinguisher, read its faceplate and confirm it covers the fire classes you could actually face at that spot. A welding bay with fuel and energized gear wants ABC coverage; a metal-grinding station wants a Class D unit staged nearby; a kitchen wants Class K.

If the only extinguisher in reach is wrong for the hazard, that's a gap to flag before there's a fire — not something to discover with flames in front of you.