Fire Extinguishers
A portable fire extinguisher is an active fire protection device used to extinguish or control small fires, typically in emergency situations. It is not designed for use on an out-of-control fire. For laboratory personnel, the effective use of an extinguisher relies on two factors: mastery of the P.A.S.S. technique (operation) and the strict recognition of Contraindications (when not to use a specific agent). Using the wrong extinguisher can result in electrocution, explosion, or chemical reaction
Operation: The P.A.S.S. Technique
The universal standard for operating a portable fire extinguisher is the acronym P.A.S.S. This sequence is designed to be recalled easily under extreme stress. Before initiating P.A.S.S., the user must ensure they have a clear exit path behind them and that the fire alarm has been activated (R.A.C.E.)
P - Pull
- Action: Pull the pin located at the top of the extinguisher handle
- Mechanism: The pin is a safety device that locks the handle to prevent accidental discharge. It is held in place by a plastic “tamper seal.” Pulling the pin breaks this seal
- Common Error: Squeezing the handle while trying to pull the pin. This puts pressure on the locking mechanism, making it impossible to remove the pin. The handle must be relaxed
A - Aim
- Action: Aim the nozzle (or hose) at the base of the fire
- Physics: The fuel source is at the bottom; the flames are just the visible gas burning above it. Spraying the top of the flames wastes the chemical agent and allows the fire to continue growing
- Distance: Start from a safe distance (usually 6-8 feet). If you are too close, the pressure of the discharge can splash burning liquid onto you. If you are too far, the stream won’t reach
Extinguisher Types & Contraindications
Selecting the wrong extinguisher in a laboratory is a critical safety failure
Pressurized Water (Class A)
- Description: Silver canister, water only
-
Contraindications
- Electrical Fires (Class C): FATAL RISK. Water conducts electricity. Spraying a live centrifuge or computer can send high-voltage current up the stream to the user, causing electrocution
- Liquid Fires (Class B): Burning oil/solvents float on water. The pressure of the spray can splash burning liquid, spreading the fire rapidly
Carbon Dioxide - CO2 (Class B, C)
- Description: Red canister with a large, black, hard-plastic discharge horn
- Operation Note: The gas is extremely cold (-110°F). Hold the horn only by the handle; holding the plastic cone can cause severe frostbite
-
Contraindications
- Class A Fires: CO2 does not cool the fuel effectively. It may blow the flames out momentarily, but deep-seated fires (trash cans, wood) often re-ignite once the gas dissipates
- Confined Spaces: CO2 displaces oxygen. Using it in a small, unventilated closet can asphyxiate the user
Dry Chemical - ABC (Class A, B, C)
- Description: Red canister with a hose and pressure gauge. Contains yellow monoammonium phosphate powder
-
Contraindications
- Combustible Metals (Class D): Standard ABC powder can react violently with metals like Sodium or Magnesium
- Sensitive Electronics (Operational Contraindication): While safe for electrical fires (non-conductive), the corrosive powder will destroy circuit boards. Using it on a $100,000 analyzer to put out a small fire will likely total the machine. (CO2 is preferred if safety permits)
- Visibility: The powder creates a dense cloud that can obscure vision and irritate the throat, complicating evacuation
Dry Powder (Class D)
- Description: Often Yellow canister. Specific for metals
- Operation Note: Requires a “soft flow” application. High pressure can blow burning metal fragments onto the user or around the room
-
Contraindication
- Standard Fires: These are specialized agents (like copper powder) intended to cake over metal. They are not effective for rapid knockdown of paper or liquid fires