Requirements
Fire extinguisher types and classes, with maintenance and test intervals
The five fire classes
| Class | Fuel | Typical agent | Where you find them |
|---|---|---|---|
| A | Wood, paper, cloth, trash, plastics | Water, foam, multipurpose dry chemical | Offices, warehouses, corridors |
| B | Gasoline, oil, grease, solvents, propane | Dry chemical, CO2, clean agent, foam | Shops, fuel storage, loading docks |
| C | Energized electrical equipment | Dry chemical, CO2, clean agent | Server rooms, electrical rooms, labs |
| D | Magnesium, titanium, sodium, lithium | Dry powder (sodium chloride, copper) | Machine shops, metal fabrication, labs |
| K | Cooking oils and animal fats | Wet chemical (potassium acetate) | Commercial kitchens |
A single unit can carry several ratings; the red ABC dry chemical extinguisher covers the three most common classes and is the default in most commercial buildings.
Common extinguisher types and their intervals
| Type | Agent | Six-year internal exam | Hydrostatic test |
|---|---|---|---|
| Multipurpose dry chemical (ABC), stored pressure | Monoammonium phosphate | Yes, every 6 years | 12 years |
| Regular dry chemical (BC), stored pressure | Sodium bicarbonate | Yes, every 6 years | 12 years |
| Dry chemical, cartridge-operated | Various | Annual (opened each year) | 12 years |
| Carbon dioxide (BC) | CO2 | Not applicable | 5 years |
| Water, stored pressure (A) | Water or antifreeze | Not applicable | 5 years |
| Foam (AFFF, FFFP) | Foam solution | Not applicable | 5 years |
| Wet chemical (K) | Potassium acetate | Not applicable | 5 years |
| Clean agent (Halotron, FE-36) | Halocarbon | Yes, every 6 years | 12 years |
| Dry powder (D) | Sodium chloride, copper | Yes, every 6 years | 12 years |
| Water mist | De-ionized water | Not applicable | 5 years |
All types require the same monthly visual inspection (by trained staff) and annual maintenance (by a person certified under NFPA 10 §7.3). The six-year and hydrostatic intervals above apply to common types; confirm against the manufacturer's manual and the NFPA 10 edition your jurisdiction adopted.
Numerical ratings
Class A and B extinguishers carry numbers before the letter, for example 4A:80B:C. The Class A number is roughly equivalent to that many 1.25-gallon buckets of water; the Class B number is the square footage of flammable liquid fire a trained operator can extinguish. NFPA 10 sets minimum ratings by hazard level: for ordinary (light) hazard, a minimum 2-A rating with 75 ft travel distance; for extra (high) hazard, 4-A and 80-B with reduced travel distances.
Placement rules by class
- Class A: within 75 ft of travel from any point; minimum 2-A for light hazard, 2-A for ordinary hazard (with 3,000 sq ft per unit of A), 4-A for extra hazard.
- Class B: within 30 ft (5-B light, 10-B ordinary, 40-B extra) or 50 ft (10-B light, 20-B ordinary, 80-B extra).
- Class C: placed according to the A or B hazard in the same area.
- Class D: within 75 ft of the metal hazard.
- Class K: within 30 ft of the cooking appliance; a placard must instruct users to activate the hood suppression system first.
Choosing and recording type in your inventory
Record the type and size for each unit in your inspection system, because the six-year and hydrostatic intervals depend on it. A common audit finding is a facility that tracks monthly inspections perfectly but has CO2 units eight years past hydrotest because every unit was assumed to be on the 12-year cycle.
Frequently asked questions
Can I use an ABC extinguisher on a kitchen grease fire?
Not as the primary protection. Commercial cooking with vegetable or animal oils requires a Class K wet chemical extinguisher within 30 feet of the appliance. ABC dry chemical can splatter burning oil and does not saponify it.
What extinguisher is required for a lithium battery fire?
Lithium-ion battery fires are not Class D (that is for lithium metal). Current guidance is large volumes of water or specialized lithium-ion agents; consult your fire protection company and the battery manufacturer. NFPA is developing further guidance.
How do I tell the hydrostatic test date?
It is stamped on the cylinder collar or shown on a label near the base as month and year, sometimes with the tester's mark. If the date plus the interval for that type is in the past, remove the unit from service.
Track this automatically
FireGuard schedules the monthly interval for every extinguisher, walks your team through the checklist on a phone, shows which units were missed, and produces the records an inspector asks for. 45-day free trial, no card.
This guide is general information about NFPA 10 and OSHA 1910.157 and is not legal advice. Requirements vary by jurisdiction and edition adopted; your Authority Having Jurisdiction has final say.