THEORY OF FIRE-II

Fuel, Heat, and Oxygen

The three ingredients that cause fires are heat, oxygen, and combustible material. When all three components are present, combustion takes place.
• Combustible material (Fuel).
• Ignition Source (Heat).
• Oxygen.

Fuel
Fuel or combustible material, which acts as a fuel source for fire, i.e., paper, wood, clothes, any solid combustible material, fiber, textile fiber, gasoline, kerosene, grease, tar, fingernail polish, magnesium, sodium, potassium, titanium or aluminum, cooking oil, vegetable oil, etc.

Heat
Ignition source or heat source means flame, spark which ignites sufficient heat, or flame for combustion or fire.

Oxygen
Oxygen which is the most common factor and is available everywhere in the form of air.

An explosion is defined as the process in which combustion occurs and spreads rapidly so as to create a high pressure. In this case, the fire expands from a source of ignition and develops high pressure when restricted in an area.

Explosions have lower and upper limits (of dust concentration). A lower limit of explosion indicates that the concentration of dust particles is below the lower limit of explosion. Below this level, the dust concentration will not explode even on ignition. This happens because the heat produced under such circumstances is not sufficient to affect other dust particles. Alternatively, there could be a dust concentration of explosive levels but there may not be enough oxygen to start the fire. To counter the hazards of fire and explosions, it is necessary to know the characteristics of the dust. For example, fine aluminum dust explodes at very low limits of explosion whereas coarse aluminum dust does not catch fire even under the influence of another source of heat.

Fire Hazards

Fire hazard is a situation in which there is a risk of harm to people or property due to fire. Fire hazards can take the form of various ways that fires can easily start, such as a blocked cooling vent or overloaded electrical system, ways fires can spread rapidly, such as an insufficiently protected fuel store or areas with high oxygen concentrations, or things which, in a fire, pose a hazard to people, such as materials that produce toxic fumes when heated or blocked fire exits.

The Indian Fire Protection Association reports 85% of fire deaths occur in the home, making fire prevention a top priority in every home.


Electrical hazards
• Damaged wiring.
• Damaged plugs.
• Damp or wet wires.
• Overloaded motors.
• Broken switches, outlets, or sockets.
• Problems with lighting fixtures.
• Faulty heating elements.
• Overloaded circuits.
• Liquids near computers.
• Computers without surge protectors.


Housekeeping hazards
• Piles of scrap, waste materials, and trash.
• Sawdust, metal or plastic powder that can form an explosive mixture with air.
• Obstructed aisles.
• Blocked emergency exits.
• Material covering up fire extinguishers, exit signs, and alarms.
• Blocked sprinkler heads.


Friction hazards
• Hot bearings.
• Misaligned or broken machine parts.
• Choking or jamming materials.
• Poor adjustment of moving parts.
• Inadequate lubrication.


Process or operation-related hazards
• Cutting and welding operations, which use open flames and produce sparks.
• Molten metal, which can ignite combustibles or fall into cracks and start a fire that might not erupt until after the work is done.
• Processes that heat materials to high temperatures.
• Drying operations where materials in dryers can overheat.
• Grinding operations that produce sparks and dust.
• Processes in which flammable vapors are released.


Storage hazards
• Material stacked too high blocking sprinkler heads (need 18-inches clearance from head).
• Flammable or combustible material stored too close to heat sources.
• Flammable materials not stored in special containers and cabinets. Inadequate ventilation in storage areas.
• Material that might react with one another stored together.
• Material stored in damaged containers
• Material stored in unlabeled containers
• Containers not tightly sealed


Smoking hazards
• Ignoring "No Smoking" signs.
• Smoking around flammable or combustible materials.
• Throwing matches and cigarettes or cigars on tables or workbenches.
• Tossing butts on the floor or grass without properly extinguishing them in an ashtray or ash can.
• Tossing lighted butts or matches out windows or doors.
• Smoking in bed.
• Leaving a cigarette/cigar unattended.
• Smoking in areas where there is an accumulation of sawdust, plastic or metal powders that may become explosive.

Description of Each Class of Fire and Applicable Extinguishers

Class A Fire
Class A fire contains carbonaceous material (carbon contaminated material), like wood, fibrous materials, paper, furnishing materials etc.
So the suitable extinguishing agent for Class A fire is water and only water, so the person on the spot has to follow the following procedure: -

First:
If a person encounters Class A fire the first thing he is should do is anyhow inform his office mates, friends or any person who is available in that location by any medium.

Second:
Inform the nearest fire brigade or fire fighting team, meanwhile the person in charge can make a team and try to cut off the fuel supply (burning material) or provide a sufficient amount of water against the fire as soon as, and in sufficient amount.


Class B Fire
Class B fire has different categories: -

For volatile petroleum fire:
Volatile petroleum means whose flash point (flash point is the lowest temperature at which the vapors of a substance are available in sufficient quantity to produce a momentary flash when a flame is applied.) is below 60? C, like petrol, oil, solvents, paint and waxes. So suitable extinguishing agent for such kind of fire is foam extinguisher, CO2 or dry powder extinguishers and hence the person on the spot has to follow the following procedure: -

First:
If a person encounters class B fire the first thing he should do is anyhow inform his mates, friends or the any person who is available in that location by any medium.

Second:
Inform the nearest fire brigade or fire fighting team, meanwhile the person in charge can make a team and try to make a boundary for burning liquid and if there is CO2 or Dry Powder or foam extinguishers then he can utilize extinguishers in a proper manner against the fire.


For Nonvolatile petroleum Fires:
Nonvolatile petroleum means whose flash point is below 60? C and above, like alcohol.

Suitable extinguishing agents for such kind of fire are Foam extinguisher, CO2 or dry powder extinguishers and the person on the spot has to follow the procedure similar to the case of volatile fire.


For Chemicals or Paint Fires:
This kind of fires contains very light flash point.
Suitable extinguishing agents for such kind of fire are foam extinguisher, CO2 or dry powder extinguishers and the person on the spot has to follow the above described procedure.


Class C Fires:
A class C fire is one of the most common fires in industries, offices, and households, etc, .i.e., electrical fires. This kind of fire occurs due to short circuit, circuits switch board, radio or electrical equipment or due to overloading, spark etc. It involves energized electrical equipment, where a nonconducting gaseous (clean agent or smothering) agent is needed. Once the electrical power is taken away, the fire goes back to class A or B fire. Electrical fires are not considered to constitute a fire class on their own, as electricity is a source of ignition that will feed the fire until removed, when the electrical supply has been isolated the fire can be treated generally. However, we should always isolate the electrical supply before fighting the fire. If this is not possible then a nonelectrical conducting extinguishing agent is to be used regardless of the power status on all occasions.

Some electrical equipment can store, in capacitors, lethal voltage, even if their power supply has been isolated, we have to always use extinguishers containing nonelectrical equipment such as CO2, dry powder firefighting extinguishers.


Class D Fire:
Class D fire involves combustible metals such as magnesium, sodium, potassium, titanium, and aluminum. In such cases water is generally ineffective or even dangerous.

This type of fire occurs in chemical industries, laboratory etc. Special dry powder is produced for class D fire, particularly those involving alkali metal such as sodium and potassium. These dry powders extinguish metal fires by flushing the powder to form a crust, which excludes oxygen from surface of the molten. A specific agent is added to prevent from sinking into the surface of the molten material.


Class E Fire:
Class E fire involves in commercial cooking appliances with vegetable oils, animal oils, or fats at high temperatures. This kind of fire occurs in large catering kitchens, restaurants and takeaway establishments, etc. This fire is difficult to extinguish because of high auto ignition temperature.
Conventional extinguishers are not effective for cooking oil fires, as they do not cool sufficiently or may even cause flash back, thereby putting the operator at risk. This fire needs extinguishers containing a specially formulated wet chemical, which when applied to the burning liquid cools and emulsifies the oil, extinguishing the flame, sealing the surface and preventing re-ignition.