Fire Extinguisher Types & PASS Method

Matching Extinguishers to Fire Classes

A fire extinguisher is not a universal tool. Each type is engineered for specific fire classes. Using the wrong one can be worse than using none at all.

The most common extinguisher on a typical commercial site is the ABC dry chemical — a multipurpose unit that handles ordinary combustibles, flammable liquids, and energized electrical fires. You should still verify the label on the unit before using it, because some sites stock Class K units in kitchens and Class D units in labs or workshops where they would not otherwise be expected.

The Danger of the Wrong Type

The single most important rule of extinguisher use: read the label and match the class before you act.

• Water on a Class C (electrical) fire — the water conducts electricity. You can be electrocuted, and the current can travel through the stream back to you.
• Water on a Class B (flammable liquid) fire — water is heavier than most flammable liquids. It sinks, the liquid floats up and spreads, and the fire expands across the floor.
• CO2 on a Class D (combustible metal) fire — some metals react violently with CO2, decomposing it and releasing oxygen that feeds the fire.
• ABC dry chemical on a Class D fire — standard dry chemical is not rated for metal fires and can cause a violent reaction.

When in doubt, do not fight the fire. Evacuate and let the fire department handle it.

The PASS Method

The PASS method is the universally taught technique for operating a portable fire extinguisher. The acronym stands for Pull, Aim, Squeeze, Sweep.

flowchart LR
    A["1. PULL the pin<br/>Break the tamper seal"] --> B["2. AIM at the base<br/>Not the flames"]
    B --> C["3. SQUEEZE the handle<br/>Discharge the agent"]
    C --> D["4. SWEEP side to side<br/>Cover the fuel surface"]
    D --> E["Fire out?<br/>Watch for re-ignition"]
    E -- Yes --> F["Back away facing the fire<br/>Do not turn your back"]
    E -- No --> G["Evacuate immediately<br/>Close door behind you"]

The Four Steps in Detail

1. Pull the pin — this breaks the tamper seal and unlocks the operating handle. Some units have a small zip-tie-style seal instead of a pin; pull firmly.
2. Aim at the base of the fire — the flames are the symptom; the burning fuel is the source. Aiming at the flames wastes agent and does nothing.
3. Squeeze the handle — this releases the extinguishing agent. Release the handle to stop the flow.
4. Sweep from side to side — cover the entire fuel surface until the fire is out, then watch the area for re-ignition. Back away while facing the fire; never turn your back on a fire you just put out.

A typical portable extinguisher discharges in 8 to 15 seconds. That is the entire window you have. If the fire is not out when the extinguisher empties, evacuate.

When to Fight and When to Evacuate

Before you even pull the pin, run this checklist:

• Is the fire small and contained to its origin (a wastebasket, a single appliance)?
• Is the fire in its early stage (just started, not spreading rapidly)?
• Do I have the correct extinguisher class for this fuel?
• Do I have a clear, unobstructed escape route behind me?
• Is the air safe to breathe — no heavy smoke, no toxic fumes between me and the fire?
• Has the alarm already been raised and the fire department called?

If you cannot answer yes to all of these, do not fight the fire. Evacuate, close doors behind you to limit oxygen, and let the professionals handle suppression. Property can be replaced; your life cannot.

Inspecting Extinguishers on Patrol

Extinguishers are part of your patrol inspection. On each round, confirm:

• The pressure gauge needle sits in the green zone (charged). A needle in the red means the unit is under- or over-pressured and must be serviced.
• The tamper seal is intact. A broken seal may mean the unit was used and not refilled.
• The label is legible — class rating and operating instructions are readable.
• The unit is in its marked location, visible and accessible (not blocked by boxes or equipment).
• The nozzle and hose are undamaged and unobstructed.

Log any deficiency and report it to your supervisor immediately. A missing or discharged extinguisher is a life-safety issue, not a paperwork problem.

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