What is Fire?
Fire is a chemical reaction in which energy in the form of heat is produced and it releases light, heat, and flame. Heat is necessary to begin the combustion process. Oxygen in air acts as an oxidizer and fuel acts as a reducing agent and burning material. It is the oxidation of a substance (which burns i.e. fuel) accompanied by heat, light, and flame. Due to incomplete combustion, it evolves smoke and carbon monoxide which creates invisibility and a toxic atmosphere for firefighters.
What is a fire triangle?
According to the old concept, three elements are necessary to start a fire. Fire is not possible if any one of these elements is not available. They are:
- Fuel (Solid, liquid, and gas).
- Heat or source of ignition (spark, flame, etc).
The absence of any of the three will result in the extinguishing of the fire.
Factors contributing to fire:
- Easy availability of combustible material like rubbish, solvent, paper, wood, etc.
- Easy availability of air, oxygen, or oxidizing material.
- Sources of ignition like a spark, static discharge, contact of hot surfaces, friction, etc.
- Continuous running machinery without proper lubrication and maintenance.
- Non-flame-proof electrical fitting in flammable areas.
- The habit of smoking in flammable areas.
- No provision of fire detectors in fire-prone areas.
- No provision of fire extinguishers in fire-prone areas.
- Open handling of flammable substances.
- No compliance with fire safety rules.
Some hidden factors contributing to fires are:
- Chemical reaction going out of control.
- Sudden stoppage of cooling media protecting flammable reaction or distillation of solvent.
- Trapping of metal parts, nails, etc. in rollers or moving machinery giving sudden spark.
- Non-availability of inert material on the reaction of flammable substances.
- Sudden lightning from the sky.
Classification of fire
Class A- Fire involving ordinary compatible material like wood, textile, paper, fibers, etc, or vegetables where the cooling effect of water is essential for extinction.
Class B- Fire in inflammable liquids like oil, grease, solvents, petroleum products, varnishes, paints, etc where a blanketing effect is essential. ( foam, co2, DCP, sand bucket).
Class C- Fire involving gaseous substances under pressure where it is necessary to dilute the burning gas at a very fast rate with inert gas and powder. (co2, DCP).
Class D- Fire involving metals like magnesium, Aluminium, zinc, potassium, etc where the burning metal is reactive to water and which requires special extinguishing media or technique. ( DCp, special dry powder for metal fire sand bucket ).
Class E – Fire involving electrical equipment where the electrical non-conductivity of the extinguishing media is of first importance. (co2, DCP, sand bucket same as claimer A & b fire).
Stages of Fire :
Mostly fire develops in four stages as under
- Incipient stage – No visible smoke, flame, or more heat developed. Invisible combustion particles are generated over a period of minutes, hours or days. Ionisation detectors respond to these particles.
- Smoldering stage – Visible smoke generation. Photoelectric detectors can detect this smoke.
- Flame stage – Flame starts after pointing of ignition. Smoke decreases and heat increases. Infrared detectors can detect this stage.
- Heat stage – Heat, flame, smoke, and gases are produced in large amounts. Thermal detectors respond to this stage.
Fire prevention and protection system
Fire prevention :
This is an activity directed towards the elimination of possible and potential sources of fires. It mainly indicates measures to avoid the inception of fires. Where the source cannot be eliminated or avoided, exercise sufficient control to ensure its safe usage. The activity also involves control overhandling, storage, and the process of combustibles.
Fire Protection :
This is an activity directed towards limiting the spread of fire to its place of origin by resorting to design, compartmentation, utilization of fire-resistive materials, provisions of safe means of escape, control by portable and fixed automatic extinguishing systems.
Fire protection is a wider term that includes fire prevention stated above and fire fighting mentioned below. Fire detection, prevention, extinguishment or control, all aim to protect plants, people, and property.
Fire Fighting :
This is an activity directed towards provisions of proper fire fighting equipment, proper maintenance, personnel with proper organization, training program, and readiness to fight the fire.
This is an activity to minimize the damage due to fire, smoke, and water to the uninvolved property.
Return to normalcy :
This is a contingency plan where the various steps are laid down to bring back the industry, to the productive stage from the crippling damage due to the fire.
Common causes of industrial fire
|1||Electricity||Standard and safe wiring, overload protection, double insulation and earthing on portable equipment, ELCB and waterproof cord in a wet environment, use of proper flameproof equipment in a hazardous area, and periodical inspection.|
|2||Bad housekeeping||Storing rubbish, waste, oil, grease, etc. in a waste bin with closed cover, regular cleaning, and inspection, storage tank of flammable liquids, dust collectors, safe disposal, inspection.|
|3||Smoking and matches||No smoking notices, separate smoking booths, checking of a matchbox, lighter, etc. at security gates.|
|4||Hot surfaces||Good insulation, fencing, ducting for smokes and flue.|
|5||Friction||Good lubrication, proper belt tension, alignment, dust removal, inspection, and maintenance.|
|6||Excessive heat||Cooling, temperature controls, trained operators, and supervisors.|
|7||Welding cutting||Special place or a portion, heat resistant floor, spark control, keeping flammable substances away, hot work permit, flammability test in thank before hot work.|
|8||Flame and Combustion||Proper design, operation, and maintenance, sufficient ventilation and ignition safety, heat insulation, hood, chimney, keeping flame away, trips and interlocks.|
|9||Self-ignition||Keeping environment cool and dry, necessary ventilation and protection, keeping ducts and passages of waste and smoke clean, separate store of highly flammable materials, not to put oil-soaked rags on hot surfaces, lagging cladding.|
|10||Exposure||Barrier wall, sprinklers on fire path, wire glass in windows.|
|11||Ignition sparks||Proper equipment, closed combustion chamber, spark arrester on flammable vent and vehicle exhaust, flare, trip.|
|12||Mechanical sparks||Machine guarding to avoid entry of foreign particles, fencing, magnetic separator, non-sparking tools.|
|13||Moulten hot substance||Proper equipment with handles, better operation, and maintenance, non-mixing of water.|
|14||Static electricity||Grounding, bonding, ionization and humidification, vehicle earthing while transfer through the pipeline, earthing of the vessel, equipment and piping, flow rate reduction, avoiding flammable atmosphere, splashing and settling, conductive shoes and flooring, additive to change liquid resistance, keeping filters away from storage tanks, avoiding oil drops in water, etc.|
Fire load determination
Fire load is the concentration or commit of combustible material in a building per sq mt of floor area. It is defined ad the amount of heat released in kilocalories by the fuel per sq meter of the area of premises. Fire loads are useful to calculate the water requirement to quench the fire. As when water comes in contact with the burning surface, it absorbs heat. 1 cc of water absorbs 1 cal of heat when the temperature is raised by 1 degree Celcius. Then it should be considered that all fuel does not burn at a time and all water does not absorb heat as it flows away.
- Low fire load < 1 lakh B Th u
- Moderate fire load Between 1 to 2 lakh B th u
- Higher fire load more than 2 laKh B th u
Fire-resistant building material
Inflammable areas when building materials and paints are used should have good fire resistance. Steel and masonry are fire-resistant materials. Fire resistive structural material should be selected depending upon the type of fire possible. There are three types of material:
- Non flammable viz metal,brick, clay, asbestos, concrete, gravels, ceramics, etc.
- Hardly flammable like staw brick, dry gypsum plaster, fire board, linoleum, etc.
- Flammable as organic origin like wood, cardboard, felt, paper, etc.
Fire safety of building plant, exit, equipment
A fire stop is a fire cheek well or non-flammable material with a fire-resistance limit of at least 2.5 h. it may be a blend or with fire-resisting doors or gates. Stopping can be the internal-external, roof, or separate fireproof walls. They are constructed to intersect the floor, ceilings, and roofs with a fireboard of 30 cm over the roof from nonflammable materials. The fire-resistant limit of doors and gates in stopping should be more than 1.5 h. The total area of such an opening should not be more than 25% of the total surface area of the stopping.
Six principles of fire prevention
- Fire prevention engineering.
- Regular periodic inspection.
- Prevent the start of the fire.
- Early detection and extinguishment.
- Limiting the spread and damage due to fire and fire control.
- Prevention of personal injuries from fire or panic, including prompt and orderly evacuation of personnel.
- and orderly evacuation of personnel.
Fundamental methods of fire control are –
- Eliminate the oxygen of the air.
- Remove or shut off the fuel supply.
- Reduce the temperature below the kindling point and
- Break the chain reaction continuing the fire.
To stop the fire occurrence, the following prevention activities are desired –
- Fire Inspection.
- Hot-Work Permit.
- Fire Brigade and Drills.
- Fire-retardant treatments.
- Communication facility.
- Protecting nearby buildings.
- Assessment of fire risks.
Portable fire extinguishers
These are always desirable for quick manual use on small fires and for the period till automatic equipment or outside firefighters work. All such extinguishers are a Water system, carbon dioxide, foam extinguisher, Dcp,
Soda acid (water type extinguisher):
The extinguisher is useful for class A fires. It should not be used on fire of electricity, oil, chemical or metal. Its normal capacity is 9 lits (14 kg) and is to be used in the range of 6 to 8 meters. It consumes within 1 to 1.5 mins. It should be checked every three months. It is held vertically up by standing up to 4 to 5 mt away from the fire after opening the plunger.
It is struck on the hard surface. A small (H2so4) bottle breaks and due to its mixture with soda bicarbonate solution, co2 is generated. The presence of co2 throws water at a distance. Its bottom & handle are held by two hands and water is prayed on fire to extinguish it.
Carbon dioxide extinguisher
- It is useful on class E i.e. electrical fire because CO2 is non conductive gas. It can be used on class B and C fire also, as it diminishes oxygen to control fire.
- It is not advisable to use it in a closed room as more CO2 may be inhaled.
- Open doors and windows before using it in a room.
- It should not be used on fires of metal, sodium, potassium and metal hydrides.
- It is available in 2 kg, 4 kg, 6.8 kg, and 22.5 kg capacities. Small cylinders have handles and big cylinders have wheels. Its range is 1 to 1.5 M. CO2 pressure is at 64 to 70 bars. It should be checked every three months.
Foam extinguisher –
It is used on grade B small fires. It should not be used on metal or electrical fire. It is available in a 9-liter cylinder and is used in a 4 to 6-meter range. It consumes within 1.5 mins. It is available in wheel mounted trolley of 18 lits and 150 ltr capacity for longer use. It should be checked every three months.
By standing 3 to 4 meters away from the fire, the plunger is pulled up and turned right up to a slot. It is shaken by turning 180 degrees twice. Then it is held inverted. By chemical reaction, co2 is generated which throws foam outside. The foam is not thrown directly in the fire but it is thrown on a nearer hard surface so that because of striking further foam is generated and spread on the burning surface. It stops oxygen availability for burning and controls the fire. Foam is effective up to 120 degrees Celcius only.
They make us alert for fire fighting. The main function of any fire detection system are:
- To give alarm to start up extinguishing procedure.
- To give early warning to area occupants to escape.
Dry chemical powder (dcp) extinguisher –
This can be used on any class of fire. Therefore it is known as ‘universal type extinguisher’. It is generally used on fire of flammable liquid. It is not effective on fire of benzene, ether, etc. For metal fire, special powder extinguishers are available. 1, 2, 5, and 10 kg. extinguishers in cylinders and 68 kg. in wheel models are available.
- A 10 kg. cylinder is consumed within 12 to 15 seconds and its range is 3 to 6 M. A 68 kg. cylinder is consumed within 1 to 1.5 minute and its range is 6 to 8 M. Both should be checked at 3 months interval.
- By standing 3 to 8 M near fire, the cylinder is shaked twice by turning 180 degrees, a safety clip is removed and plunger is pressed or struck so that CO2 bottle breaks and it throws dry chemicals out. The dry powder blankets the burning surface, stops O2 contact and CO2 coming out also diminishes O2 proportion. Therefore fire is controlled by double action. Its long nozzle should be turned in wind direction like a broom.
Industrial fire detectors and alarms:
Two main functions of any fire detection system are:
- To give alarm to start-up extinguishing procedure, and
- To give early warning to area occupants to escape.
- Though fire detectors and alarm systems are separate systems but the latter has to operate just after the former operates.
They are of six types: Wet pipe, Dry pipe, Pre-action deluge, Combined dry pipe & Pre-action & Sprinkler for limited water supply system. Automatic alarms separated by the flow of water should be a part of sprinkler installation. Such an alarm may be connected to a central fire system. the sprinkler should be regularly checked to avoid their failure to work.
- Sprinkler should be selected on the basis of temperature rating and occupancy. Normal detector setting is 68 degrees C. sprinkler heads normally cover 12 m3 per head.
- Automatic sprinklers are most efficient and widely used. It reduces insurance premium considerably.
Fire Emergency Action Plan
It is similar to an on-site emergency plan the key elements are as given below
- Assess all possible fire emergencies or the maximum forceable loss(MFL factor). Mark fire /explosion prone areas on the factory plan.
- Assess resources(man, material, equipment) available in the plant and make a list of them, with their location contact phones and incharge person.
- Assess resources needed from outside and make a list of them with a place of availability, contact person and phone number.
- Prepare a central control room for coordination of emergency time and activities.
- Prepare an organized group of key persons who will act to control the emergencies. SMC, IC and other responsibilities should be decided. Rehearsal may be carried out to shape their action.
- All communications system shall be maintained in workable order, new system should be prepared if necessary.
- Double gates (one for enter,one for exit) unobstructed inner raods and proper sign board shall be displayed.
- House keeping shall be regularly checked & materials removed.
- Fire water, working order of fixed fire installation and placement of charged portable exinguishers should be regularly checked.
- Alternate power souce shall be kept ready.
- Runners shall be arranged to act in the event of communication failure.
- Distinctive garment or cap, band, etc shall be given to the emergency controller.
- Decide assembly prints for safe gathering by other people.
- keep arrangement for medical, security, and transport in readiness to handle the emergency.
- Train fire fighting crew, medical staff and other workers for their emergency time and proper emergency time activities.
- It should be assured before restarting the normal work that fire is fully extinguished, environment is cooled, debris removed, etc.
Duties of the fire watch
- The primary duty of the fire watch is the prevention of fire. He should constantly on the watch for changing conditions, flammable and combustibles, spark containment, and for any abnormal event.
- The fire watch must have firefighting equipment appropriate to the potential hazard.
- The fire watch shall observe for at least 30 minutes after completion of the hot work operation.