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Marine Fire Prevention and Control

Classifications of Fire Fire Extinguishing Agents Firefighting Procedures

Classifications of Fire

In order to successfully put out a fire, you need to use the most suitable type of extinguishing agent—one that will do the job in the least amount of time, cause the least amount of damage and result in the least danger to crew members. The job of picking the proper agent has been made easier by the classification of fire types, or classes, lettered A through D. Within each class are all fires involving materials with similar burning properties and requiring similar extinguishing agents. However, most fuels are found in combinations, and electrical fires always involve some solid fuel. Thus, for firefighting purposes, there are actually seven possible fire classes. Knowledge of these classes is essential to firefighting, as well as knowing the burning characteristics of materials found aboard vessels.

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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.

Fire Extinguishing Agents
Agent Advantages Disadvantages
Water
  • Always Available
  • Excellent cooling properties
  • Provides protection for fire party
  • Best choice for Class A
  • Not to be used on Electrical Fires
  • Can reduce stability
  • Can spread Class B fires
  • Damages/destroys equipment
Foam
  • Forms air-tight blanket over burning liquids
  • Minimal chance of re-flash
  • Can be used from distance-around corners, from upper decks
  • Not to be used on Electrical Fires
  • Damages/destroys equipment

Dry-Chemical
  • Knocks down flames
  • Fast and effective
  • 15' range
  • Rated for Class B and C fires
  • Minimal Protection against re-flash
  • Highly corrosive to electronic equip.
  • Agent can cake and solidify in container
Carbon Dioxide
  • Safe for Class C
  • Non-corrosive, non damaging to equip.
  • Minimal chance of re-flash in sealed space
  • Effective on small Class A & B fires in open spaces
  • Displaces oxygen - can kill firefighters
  • No re-flash protection in open spaces
Halon
  • Safe for Class C
  • Non-corrosive, non damaging to equip.
  • Minimal chance of re-flash in sealed space
  • Effective on small Class A & B fires in open spaces

  • No re-flash protection in open spaces
  • In very hot fires, can generate deadly phosgene gas
  • No longer available after 2000 AD

 

Procedures for Fighting a Fire Onboard

Signal: Continuous sounding of ship's whistle & General Alarm
for at least 10 seconds


FIND the fire, the location, and its size
INFORM the Captain immediately to:
  • Sound the general alarm to muster the crew and notify all hands
  • Make a distress call to Coast Guard and nearby vessels
  • Activate emergency firefighting equipment
RESTRICT the fire
  • Shut off air supply to the fire - close hatches, ports, etc.
  • De-energize electrical systems in affected space
  • Set fire boundaries to confine the fire
  • Shut off fuel supply and ventilation
  • Maneuver vessel to minimize the effect of wind on the fire
  • Prior to activating fixed extinguishing system, ensure that all personnel have been evacuated from the space
EXTINGUISH the fire
  • Determine class of fire, appropriate equipment, extinguishing agent and method of attack
  • Overhaul and set re-flash watch
  • Muster crew to account for all personnel
  • If unable to control fire, prepare to abandon the vessel

Warning:

As soon as water is used for extinguishing, dewatering procedures should commence to avoid impairment of stability!


Related Articles:
PWC Tips - Fire OnBoard - by Scott Collier and the PWC Zone.
Also see the Boating Basics Online Safety Course 

 

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