Classification of Fire

 Chemistry of Fire:

• A fire can occur with the presence of oxygen, a source of ignition and suitable material that acts as a fuel.

• These three components are represented by the three sides of a triangle known as the Fire Triangle.

• Further research on the concept of fire led to the fourth element called the Chemical Chain Reaction leading to the formation of Fire Tetrahedron.

• Fire does not develop on its own, it is developed under certain favourable conditions. So, the most basic fire safety measure is to keep the fuel source and sources of ignition separately at a safer distance.

Fire Triangle:

        Fuel, Heat and Oxygen are the three components of the fire triangle.

• Fuel refers to any combustible solids, liquids or gases.

• Heat refers to energy capable of starting combustion. The source of heat energy can be a lighted fire, static electrical discharge, short circuit, heat arising from metal to metal contact without lubrication and so on.

• Oxygen is present in the atmosphere and its 21%

• Fire does not spread, when any one of these three components is absent. 

Fire Tetrahedron:

• The base of a fire tetrahedron represents the fourth component in a fire triangle. 

                                  

• It is the 'chain reaction' due to the molecular combination of fuel, oxygen and heat energy. 

• When you break the chain reaction, fire does not spread.

Classification of Fire:

• There are currently two standards, defining classes of fires according to the nature of the material undergoing combustion.
• International Organisation for Standardization (ISO standard 3941)
• National Fire Protection Association (NFPA 10)

• Fire classifications are generally indicated as A, B, C, D and F (or K).

International Organisation for Standardization (ISO standard 3941)*		National Fire Protection Association  (NFPA 10)
Class A	Fires involving solid materials, usually of organic in nature, in which combustion normally takes place with the formation of glowing embers	Class A	Fires in ordinary combustible materials such as wood, cloth, paper, rubber and many plastics
Class B	Fires involving liquids or liquefiable solids	Class B	Fires in flammable liquids, oils, grease, tars, oil-based paints, lacquers and flammable gases
Class C	Fires involving gases	Class C	Fires, which involve energized electrical equipment where the electrical non-conductivity of the extinguishing medium is of importance. (When electrical equipment is de-energized, extinguishers for Class A or B fires may be used safely.)
Class D	Fires involving metals	Class D	Fires in combustible metals such as magnesium, titanium, zirconium, sodium, lithium and potassium.
Class F	Fires involving Cooking oils	Class K	Fires involving cooking grease, fats and oils
*Comite Europeen de Normalisation (CEN standard EN2) closely follows ISO standard 3941

[The above-mentioned table is as per IMO Resolution A.951(23) - Improved Guidelines for Marine Portable Fire Extinguishers (Adopted on 5 December 2003)]

Basic Principles of Fire Fighting:

• As we know that oxygen, heat source and fuel form the main elements which can start the fire.

• If we manage to remove any one of these we can prevent the spread of the fire.
• Removing the Oxygen is by Smothering.
• Removing the Heat by Cooling.
• Removing the Fuel by Starving.  
• Removing the above-mentioned elements will interrupt the Chain reaction.

Classification of Fire Extinguishing Mediums:

        At Present the type of extinguishing medium recommended for the use on the various categories of fires are listed below

Extinguishing Medium	Recommended for use on Fires Involving
Water Water with additives	Wood, Paper, Textiles and Similar materials
Foam	Wood, Paper Textiles and Flammable Liquids
Dry Powder / Dry Chemical (Standard/ Class B,C)	Flammable liquids, Electrical equipment and Flammable Gases
Dry Powder / Dry Chemical (Multiple or General Purpose/ Class A,B,C)	Wood, Paper, Textiles, Flammable liquids, Electrical Equipment and Flammable gases
Dry Powder / Dry Chemical (metal)	Combustible Metals
Carbon dioxide	Flammable Liquids and Electrical Equipment
Wet Chemical for Class F or K	Cooking Grease, fats or oil fires

[The above-mentioned table is as per IMO Resolution A.951(23) - Improved Guidelines for Marine Portable Fire Extinguishers (Adopted on 5 December 2003)]

Reference: IMO Publications & Documents - Resolutions - Assembly, IMO Resolution A.951(23)