Portable fire extinguishers are mandatory in every building. ABC dry chemical (monoammonium phosphate, NH4H2PO4) is the multipurpose choice in the great majority of facilities. NFPA 10 (Standard for Portable Fire Extinguishers) defines travel distance, rating, hydrostatic testing and monthly inspection.
Fire Classes
- A: ordinary solid combustibles (wood, paper, textiles)
- B: flammable liquids (gasoline, thinner)
- C: energized electrical equipment (panels, switchgear)
- D: combustible metals (magnesium, sodium) - special dry powder agents
- K: cooking oils and fats (vegetable and animal) - wet chemical
ABC covers three classes universally.
ABC Mechanism
Monoammonium phosphate (MAP):
- Class A: heat decomposes it into metaphosphoric acid, which coats paper and wood surfaces
- Class B: chain reaction interruption (radical scavenging)
- Class C: non-conductive (dielectric)
- Corrosion risk: combined with moisture it can damage electronics - clean up promptly after discharge
NFPA 10 Rating and Distribution
NFPA 10 Tables 6.2.1 and 6.3.1:
- Class A, light hazard: 2A - 23 m max travel
- Class A, ordinary hazard: 3A - 23 m
- Class B, light hazard (small quantities of flammable liquid): 5B - 9 m
- Class B, ordinary hazard: 10B - 15 m
- Typical 6 kg ABC: 4A:55B:C rating - office-appropriate
Inspection and Testing
- Monthly visual: pressure gauge, tag, unobstructed
- Annual: certified technician, full service
- Every 6 years: internal inspection, powder-clumping check
- Every 12 years: hydrostatic test (visual + pressure)
- Records: maintain tag and logbook
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