James R. Stringer
(Reference: Power Engineering Third Class Edition 2.5; Part A2; Chapter 15: Fire Protection Systems)
Class A fires involve ordinary combustibles like wood, cloth, paper products. The symbol is an A within a green triangle (tip: think of the green triangle as a tree for wood. The A even resembles a tree!).
Class B fires involve vapour-air mixtures on top of surfaces of flammable liquids like gas, grease, oils. The symbol is a B within a red square (tip: think of the B in the square as in a Barrel of oil).
Class C fires involve energized electrical equipment. The symbol is a C within a blue circle. (tip: think of a circle as the tip of a wire of conduit).
Class D fires involve combustible metals like magnesium, sodium, and even titanium. The symbol is a D within a yellow star. (tip: think of the star as a pentagram and then think heavy metal!)
Class K fires involve cooking fats and greases. The symbol is a K within a black hexagon (tip: think of K as in kitchen and the hexagon as a frying pan).
Dry chemical fire extinguishers are one of the most common types that stop the chemical chain reaction associated with a fire to fight class A, B, and C fires when they are multi-purpose. The multi-purpose extinguishers of today use ammonium phosphates (some may have sulphates as well). They are mostly used in portable extinguishers and used when a significant fire must be fought with a small quantity of material.
Gaseous extinguishers change the concentration of fuel oxidizing agent so it is either below or above the flammability limit. These types are commonly used with class C fires to prevent electric shock using inert agents (nitrogen, carbon dioxide) or halons and halogenated hydrocarbon agents.
Dry powder extinguishers are designed to fight against class D fires like those associated with sodium, potassium, magnesium. The powder smothers the fire and stops it from spreading.
Water of course is used to fight Class A fires by cooling the fuel/oxidizing agent below the ignition temperature.
Foams are materials added to water to improve the ability of wetting fuel surfaces. They are either chemical or mechanical foams.
Chemical Foams are produced through a chemical reaction between different substances where carbon dioxide is released and creates a foam of bubbles. Chemical foams are close to obsolete in North America.
Mechanical Foams are formed by mechanically mixing the air and a foam solution with water. These foams are usually used to fight Class B fires where the foams are able to separate the fuel and oxidizing agent (air) using a barrier. They however can also be used to fight Class A fires as well.
| Name | Notes |
| Protein | Natural occurring chemicals (hoofs), chemicals added to protect against freezing/corrosion, picks up fuel it is being applied to |
| Fluoroprotein | Spreads across fuel better, reduction in fuel picked (vs Protein) |
| Aqueous Film Forming Foam (AFFF) | Very rapid extinguishment (knockdown), fluoro and hydro-carbons |
| Synthetic | Expansion ratios (low=20:1) (medium=up to 200:1) (high: >200:1) |
| Alcohol Resistant Concentrates (ARC) | Fights fires involving water soluble fuels (above fights non-soluble), based off of AFFF with added chemical, widely used |
Most importantly, it is how we react when we notice there is a fire. There are 3 steps we should prioritize when faced with a fire condition:
- Set off an alarm. This can be using a pull station, calling for help, or sounding an alarm but it is imperative we let everyone know there is a fire condition and to let the proper authorities know. Studies show that people assume others have already set an alarm off and that they don’t want to be redundant or cause a problem; never assume this! Always do your part to make all occupants of a property safe. No fire is too small!
- Complete a risk assessment. What hazards are there? Can you control the fire? Do you have help? Can you escape? Being able to combat a fire when it is controllable can save lives and reduce damage to property, plant, and equipment. Above all, we want to be safe – if a fire seems out of control or one is not confident on how to use extinguishing equipment, safely evacuate the building.
- Safely evacuate. When evacuating a fire condition, never turn your back on the fire when you are leaving. Always back away while facing the fire. Personal safety is paramount, so if a fire seems to be escalating or you do not know the extent of a fire – always safely evacuate and offer support to others evacuating.
