Walk through any workplace and you will see extinguishers in different colors and sizes. Each type is made for certain fires. You should read the label before an emergency, not during one.
Common types
- Water (pressurized water): for Class A only. It cools the fuel. Never use it on electrical, flammable liquid or cooking oil fires.
- Dry chemical, multipurpose (ABC): the most common in workplaces. It fights Class A, B and C fires. It leaves a powder residue that can be hard to clean and irritating to breathe.
- Dry chemical, BC: for Class B and C, not for ordinary combustibles.
- Carbon dioxide (CO2): for Class B and C. It leaves no residue, so it suits electronic equipment. It has a hard horn and no pressure gauge. The horn gets extremely cold and can cause frostbite. In small, closed rooms the gas can reduce the oxygen you breathe.
- Wet chemical (Class K): for cooking oils and fats in commercial kitchens. It cools and forms a soapy layer on the oil.
- Dry powder (Class D): for combustible metals. A given powder is made for specific metals, so it is not interchangeable.
- Water mist and clean agent: used in places such as hospitals, server rooms and clean rooms. Read the label for the classes.
The label and the symbols
Every extinguisher carries a label that shows:
- the classes it can fight, in letters or pictures (a trash can and wood for A, a flame and can for B, a plug for C);
- crossed-out pictures that show where not to use it;
- the operating instructions, usually the four steps of PASS;
- the testing laboratory mark;
- how often it must be maintained.
Under 29 CFR 1910.157 only approved extinguishers may be used, meaning they are listed or labeled by a nationally recognized testing laboratory such as UL or FM.
Ratings
Numbers before the letters show how much fire the extinguisher can handle:
- Class A rating such as 2-A: the number compares the extinguisher's power on ordinary combustibles with an amount of water. A higher number means more.
- Class B rating such as 40-B: the number relates to the size of flammable liquid fire the extinguisher put out in standard tests. Higher means more.
- Class C, D and K carry no number.
A bigger rating means a bigger extinguisher, which is often heavier and harder to handle.
The pressure gauge
Most stored-pressure extinguishers have a gauge. If the needle is in the green zone, the pressure is correct. If it is in the red or the extinguisher is not charged, it will not work and you should report it.
Where extinguishers should be
- Visible and accessible, not hidden behind boxes or doors.
- On a hook, bracket or wall mount so that they cannot fall.
- Placed by travel distance. For Class A fires, an extinguisher must be 75 feet or less from any employee. For Class B hazards it must be 50 feet or less from the hazard area.
- NFPA 10 gives mounting heights. For extinguishers up to 40 pounds, the top should be no higher than 5 feet above the floor. Heavier ones are mounted lower.
- Near exits and near the specific hazards, such as a kitchen or paint store.
Choose the right one
Look before you leave the exit. If the label does not show the class you need, do not use that extinguisher.
Key points
- Water for A only. ABC for A, B and C. CO2 for B and C. Wet chemical for K. Dry powder for D.
- The label shows the classes and the instructions.
- Higher numbers mean more fire-fighting capacity.
- Green zone on the gauge means charged.
- Extinguishers must be visible and reachable.