Fire Alarm Inspections
Those of you who have taken the Nautical Know How Boating Basics Online Course may remember discussion of the fire triangle which is composed of heat, fuel and air. These three things are needed to make a fire, remove any one of them and the fire is extinguished.
To move into a slightly more advanced theory of fires, there is a fourth ingredient necessary for fire, and the "fire tetrahedron" more accurately demonstrates the combustion process. A tetrahedron is a solid figure with four triangular faces. It contains the four things required for combustion; fuel (to vaporize and burn), oxygen (to combine with the fuel vapor), heat (to raise the vapor to its ignition point) and the chain reaction (the chemical reaction among the fuel, oxygen and heat). Remove any of these four and you have no fire.
Class A Fires—Fires of common combustible solids such as wood, paper and plastic are best put out by water, a cooling agent. Foam and certain dry chemicals, which act mainly as smothering or chain-breaking agents, may also be used.
Class B Fires—Fires caused by flammable liquids such as oil, grease, gas and other substances give off large amounts of flammable vapors and require smothering agents to do the job. Dry chemical, foam and carbon dioxide (CO2) may be used. However, if the fire is being supplied with fuel by an open valve or broken fuel line, you must first shut down the source of the fuel. This action alone may stop the fire or at least make it easier to put out.
In a gas fire, it is important to shut down the source of the fuel. Attempting to put out the fire without shutting down the sources, creates an explosive hazard that is more dangerous than the fire itself.
If may be necessary to put out a gas fire before shutting down the fuel supply in order to save a life or reach the supply valve, but these should be the only exceptions.
Combination Class A and B Fires—Water fog and foam may be used to smother fires involving both solid fuels and flammable liquids or gases. These agents also have some cooling effect on the fire. In enclosed spaces, CO2 may also be used. Caution: CO2 robs the air of oxygen and can suffocate a person using CO2 to put out the fire in enclosed spaces.
Class C Fires—For fires involving energized electrical equipment, conductors or appliances, non-conducting extinguishing agents must be used such as CO2, Halon and dry chemical. Note that dry chemical may ruin electronic equipment. Always attempt to remove the source of electricity to remove the chance of shock and the source of the ignition.
Combination Class A and C Fires—Since energized electrical equipment is involved in these fires, non-conducting agents must be used. CO2, Halon, and dry chemicals are best. CO2 reduces the oxygen supply, while the others break the chain reaction. REMEMBER: Always try to de-energize the circuit.
Combination Class B and C Fires—Again, a non-conducting agent is required. Fires involving flammable liquids or gases and electrical equipment may be extinguished with Halon or dry chemical acting as a chain reaction breaker. In enclosed spaces, they may be extinguished with CO2.
Combination Class D Fires—These fires may involve combustible metals such as potassium, sodium, and their alloys, and magnesium, zinc, zirconium, titanium and aluminum. They burn on the metal surface at very high temperature, often with a brilliant flame.
Water should not be used on Class D fires. It may add to the intensity and cause the molten metal to splatter. This, in turn, can extend the fire and inflict serious burns on those near by.
Combustible metal fires can be smothered and controlled with special agents known as dry powders. Although many people use the term interchangeably with dry chemicals, the agents are used on entirely different types of fires: dry powders are used only to put out combustible metal fires; dry chemicals may be used on other fires, but not on Class D fires.