Firefighting, Part 2

The Fire Extinguishment Theory

As has already been mentioned since the fire triangle was discussed, a fire cannot happen if even just one element is absent. This is core of the Fire Extinguishment Theory which states: "to extinguish a fire, interrupt or eliminate the supply of any or all the elements of fire." Essentially, fire can be eliminated by decreasing the temperature, eradicating the fuel supply, suffocating the fire, or by stopping the chemical reaction.

4 General Methods of Fire Extinguishment

1. Extinguishment by Temperature Reduction

   • Cooling the environment, usually done by adding water into the system

   • Decreasing the temperature of the fuel itself to the point where it can no longer produce vapors that burn

2. Extinguishment by Fuel Removal

   • Stopping the flow of liquid fuel

   • Inhibiting the production of flammable gases

   • Removing the solid fuels at the fire path

   • Letting the fire burn until all fuel is consumed

3. Extinguishment by Oxygen Dilution

   • By introducing inert gases

   • By separating oxygen from the fuel

4. Extinguishment by Chemical Inhibition This is usually done on gas or liquid fires using specialized dry chemicals or halons that interrupt the production of flames.

Methods of Extinguishing the Different Classes of Fires

Class A Fires: by quenching and cooling

Class B Fires: by smothering or blanketing

Class C Fires: by non-conducting extinguishing agent; the safest procedure is always to de-energize the circuit

Class D Fires: by using specialized agents marked specifically for metals

Class E Fires: by a combination of the aforementioned

Types of Fire Extinguishers

1. Water Fire Extinguishers filled with water, used to fight Class A fires

2. Liquified Fire Extinguishers contains CO, used to fight Class A, Class B, and Class C fires

3. Dry Chemical Extinguisher contains chemical powders

4. Foam Extinguisher contains sodium bicarbonate (NaHCO3), a foam stabilizing agent in a larger compartment, and a solution of aluminum sulfate in an inner cylinder; the reaction between the two solutions creates a stabilized form of CO2 bubbles

5. Soda-acid Fire Extinguisher filled with NaHCO3 mixed with water

6. Vaporizing Liquid Fire Extinguisher contains non-conducting liquid, generally carbon tetrachloride or chlorobromethane

7. Carbon Dioxide Fire Extinguisher effective against burning liquids and electrical fires

Extinguishing Agents

These are specialized chemicals used in putting out fires. Examples include:

1. multi-purpose dry chemicals

2. Halon 1211 or bromochlorodifluoromethane

3. aqueous film forming foam (AFFF)

4. CO2

Markings Required on Fire Extinguishers

All fire extinguishers manufactured or sold in the Philippines must bear the following:

1. date of original filling

2. chemical contents

3. type

4. operating instructions and safe procedure in usage

5. name and address of the manufacturer

6. name and address of the dealer

General Operating Procedures for Fire Extinguishers

The general operating procedures for the usage of fire extinguishers may be remembered using the acronym PASS.

P PULL Pull the pin at the top of the extinguisher.

A AIM Aim the nozzle or outlet at the base of the fire.

S SQUEEZE Squeeze the handle to discharge the extinguishing agent.

S SWEEP Sweep the nozzle sideways all across the fire to disperse the extinguishing agent.

After the fire is put out, check the material and ensure that there are no smoldering embers that could trigger a re-flash. Before leaving the area, make sure that the fire is properly and completely put out.

Firefighting Equipment

When a fire that has broken out grows beyond the capacity of a fire extinguisher or similar basic first response, firefighters come in with their specialized equipment.

There are three groups of basic firefighting equipment:

Fire Vehicles

Note that there are also generalized firefighting vehicles that are equipped with portable ladders of various types and sizes. Additionally, these carry forcible entry tools like axes, power saws, and sledge hammers.

There are also special fire vehicles designed for specific purposes such as airport crash tenders and hazardous materials units. These vehicles can spray foam or dry chemicals that are appropriate for responding to aircraft fires.

Fire Prevention and Public Safety

As already mentioned, the job of the fire department does not begin and end with putting out fires. It is also imperative that they educate the community on preventing fires to help promote safety.

Different Methods of Fire Prevention

1. Laws and regulations

2. Fire safety inspections

3. Public education