Using an extinguisher safely and when not to

Knowing how to use a portable extinguisher is only half of the skill. The other half is knowing when not to use one. Every year, people are injured or killed trying to fight fires that were already too large, in rooms filling with smoke, with the wrong extinguisher or without an escape route. This lesson covers the decision to fight or leave, the steps of using an extinguisher (often remembered as PASS), technique for different classes of fire, what to do after the fire is out, and the training requirements that apply. Reading this lesson is not a substitute for hands-on training: you should discharge a real or training extinguisher on a controlled fire or simulator, under the supervision of a qualified instructor, before you are expected to use one at work.

Awareness only: this lesson does not qualify you to fight fires. OSHA 1910.157(g) requires hands-on or practical extinguisher training where employees are expected to use extinguishers, and you must follow your site's emergency action plan.

The decision: fight or leave

The first priority in any fire is people, not property. Before anyone picks up an extinguisher, three things must already be happening or done: the alarm has been raised so others can evacuate, the fire department is being called, and someone knows you are attempting to fight the fire. Then ask yourself a short series of questions. If the answer to any of them is no, leave immediately, closing doors behind you.

• Is the fire small and contained, for example no bigger than a wastebasket, and not spreading?
• Is the room free of heavy smoke, and is the air breathable at standing height?
• Do I have a clear exit behind me, so I can retreat without passing the fire?
• Do I know what is burning, and is the extinguisher the right type for it?
• Is the extinguisher large enough, and have I been trained to use it?
• Am I physically able to do this, and do I feel confident?

Many organizations simplify this to a rule: fight only fires that are no bigger than you, ideally smaller than a wastebasket, and only if you can keep the exit at your back. Many employers choose a total evacuation policy instead, in which no employee is expected to fight fires and everyone leaves when the alarm sounds. That is a legitimate choice, and it changes the training and equipment duties (Lesson 4).

Why fires outgrow extinguishers so quickly

Lesson 1 described how fires grow: a small fire can grow to fill a room within a few minutes, and flashover can occur in under five minutes in a modern furnished room. A typical 4.5 kg (10 lb) multipurpose extinguisher discharges for only 10 to 20 seconds, and a small 2.3 kg (5 lb) unit for 8 to 12 seconds. That is enough for a fire the size of a wastebasket or a small pan, but not for a burning sofa, a stack of pallets or a pool of fuel spreading across a floor. Smoke is also a fast-moving hazard: a few breaths of thick smoke can disorient you, and toxic gases such as carbon monoxide and hydrogen cyanide can cause collapse within minutes. The decision to fight must be made quickly, and abandoned quickly if things change.

PASS: using an extinguisher

Most extinguishers are operated the same way, summarized by the acronym PASS: Pull, Aim, Squeeze, Sweep.

• Pull the pin. Hold the extinguisher upright and pull the safety pin, breaking the tamper seal. Some models have a different release mechanism; read the label during training, not during a fire.
• Aim low, at the base of the fire. Point the nozzle or hose at the fuel that is burning, not at the flames above it. Hitting the flames does little; the agent must reach the fuel surface.
• Squeeze the handle (lever) slowly and evenly to release the agent. Releasing the handle stops the discharge on most models.
• Sweep from side to side across the base of the fire, covering the whole burning area, until the fire appears to be out.

Start from a safe distance, typically 2 to 3 m (6 to 10 ft) for most dry chemical units and closer for CO2, and move forward as the fire diminishes. Keep low to stay below heat and smoke. Watch the area after the fire appears out, because it may reignite, and be ready to repeat the process or to leave.

Technique by class of fire

• Class A: sweep the base of the burning material and soak or break apart smoldering material if it is safe; dry chemical leaves a coating that resists reignition, but deep-seated fires may need water from the fire department.
• Class B, spills: start at the near edge and sweep across the surface, pushing the fire away from you. Do not aim directly into a pool of liquid from close range, because the force of the discharge can splash burning liquid. Never use water.
• Class B, pressurized gas: a burning gas leak should usually not be extinguished unless the gas supply can be shut off; extinguishing the flame while the gas continues to flow can create an explosive vapor cloud. Shut off the gas if it is safe to do so and leave.
• Class C: shut off the power at the source if you can do so safely, then treat the fire as class A or B. Use only non-conductive agents while equipment may be energized.
• Class D: apply the class D agent gently to bury the burning metal, using the low-velocity applicator, without scattering it. Never use water or ordinary extinguishers.
• Class K: turn off the heat source if safe, activate the hood system if it has not operated, then use the class K extinguisher with a gentle, sweeping application to avoid splashing the oil. Never use water or carry a burning pan.

Hazards of extinguishers themselves

Extinguishers are pressure vessels and their agents have hazards. Dry chemical discharges create a dense cloud that reduces visibility and irritates the eyes and lungs; in a small room, it can make escape harder. CO2 displaces oxygen and is dangerous in confined spaces, and the discharge horn becomes extremely cold, causing frostbite if held. Clean agents can decompose in fires to produce irritating gases. Damaged or corroded cylinders can rupture. Never use an extinguisher that looks damaged or has a gauge out of range, and report it.

After the fire

Even when a fire appears to be out, the fire department should be called to check for hidden fire in walls, ceilings and equipment. Leave the area, close doors and report to the warden or person in charge. The extinguisher must be removed from service and recharged or replaced, and a replacement installed. The incident should be reported and investigated, like any near miss or incident, to understand why the fire started and how to prevent a repeat (HSE-103). Clean-up of dry chemical residue should be done promptly, because monoammonium phosphate is corrosive to electronics and metals.

Training requirements

Under OSHA 1910.157(g), where an employer provides portable extinguishers for employee use, it must provide an educational program on the general principles of extinguisher use and the hazards of incipient-stage firefighting, upon initial employment and at least annually. Employees designated to use firefighting equipment as part of an EAP must receive hands-on training upon initial assignment and at least annually. An employer with a total evacuation policy, a written EAP and an FPP, and which does not expect employees to use extinguishers, may be exempt from parts of 1910.157.

Live-fire training is increasingly delivered with propane-fired simulators or laser-based trainers, which allow workers to practice PASS safely without the environmental impact of discharging dry chemical. Training should be documented, including the date, content, trainer and names of participants.

Fire blankets and other first-response tools

Fire blankets are sheets of fire-resistant material used to smother small fires, such as a burning pan on a domestic-style stove, a small wastebasket fire or burning clothing. To use one, pull the tabs to release it from its container, hold it in front of you with your hands protected by the folded edges, place it gently over the fire, turn off the heat source if possible, and leave it in place until the material has cooled completely. A fire blanket is not a substitute for a class K extinguisher in a commercial kitchen, but it is useful in staff kitchens, laboratories and workshops. Other tools sometimes found at work include sand buckets for small metal fires and spill containment, and emergency shut-off switches for fuel, gas and electrical supplies, which are often the most effective way to stop a fire from growing.

Human factors in firefighting decisions

People make poor decisions under stress. They underestimate how quickly a fire is growing, overestimate their ability to control it, focus narrowly on the flames and lose track of smoke and escape routes, and feel a strong sense of responsibility for equipment or property. Some keep trying after the extinguisher is empty. Training that includes realistic scenarios, clear decision rules and the explicit message that leaving is always an acceptable choice helps counter these tendencies. Supervisors must never pressure workers to fight fires, and workers who choose to leave rather than fight should be supported. The goal is not to save the building; it is to make sure everyone goes home.

Working in pairs

Where possible, two people should respond to a fire together: one fights the fire and the other watches the fire, the smoke and the exit, carries a second extinguisher and calls the attempt off if conditions worsen. If the first extinguisher fails to control the fire, the second person can make one more attempt, but if two extinguishers have not controlled a fire, it is beyond the incipient stage and both should leave, closing doors behind them. Responders should report what they did to the coordinator and firefighters, including what was burning, what agents were used and whether anyone may still be inside.