Classes of fire. Methods of extinguishing fires (Demonstration). Fire extinguishers. Portable and stationery. Fire detectors and alarm.Automati
Classes of fire.
FIRE
Fire is the visible effect of the process of combustion – a special type of chemical reaction. It occurs between oxygen in the air and some sort of fuel. The products from the chemical reaction are completely different from the starting material. Combustion is when fuel reacts with oxygen to release heat energy.
Classes of fire
- Class A - fires involving solid materials such as wood, paper or textiles.
- Class B - fires involving flammable liquids such as petrol, diesel or oils.
- Class C - fires involving gases.
- Class D - fires involving metals.
- Class E - fires involving live electrical apparatus. (Technically ‘Class E’ doesn’t exists however this is used for convenience here)
- Class F - fires involving cooking oils such as in deep-fat fryers.
Methods of extinguishing fires (Demonstration).
All fires can be extinguished by cooling, smothering, starving or by interrupting the combustion process to extinguish the fire. One of the most common methods of extinguishing a fire is by cooling with water.
To understand how best to extinguish a fire, there must first be an appreciation of the three elements that make up the ‘fire triangle’: heat, fuel and oxygen. As fire is primarily a chemical reaction, removing one or more of these three factors will prevent the combustion from taking place.
Fire Triangle
Heat is required to ignite a fire, and will continue to be generated as the fire burns. For intentional fires, this could be as simple as the striking of a match. For accidental fires however, ignition can occur as a result of obstructing ventilation on machinery that heats up, or flammable materials being too close to heater.Fuel can be anything that is combustible, such as wood, petroleum and spirits, and a number of gases. Solid fuels must reach a critical temperature in order to ignite, while many liquids release flammable vapours even when cold. Gases are the most hazardous and temperamental state, and can combust instantaneously.The air feeding a fire only needs to be made up of 16% Oxygen in order to react with the heat and fuel. Generally, at low/normal altitude, the level is over 20%.
EFFECTIVE FIRE EXTINCTION
If the three parts of the ‘fire triangle’ are kept in mind, extinguishing a small blaze should be a matter of common sense. The principles of fire extinction state that a fire will be put out if one of the three elements are removed, and this can be done using three different approaches, as detailed below…
COOLING
Removing the heat is one of the most effective methods of fire extinction available, which is why water is a popular extinguishing material. The fire will go out so long as the heat generated by the fire is less than that which is absorbed by the water.
Remember: water is not an appropriate extinguishing material to use on electrical fires, as well as those caused by cooking oils/fats or other flammable liquids.
STARVING
While cooling removes the heat/ignition element of the ‘fire triangle’, starving the blaze of its fuel source approaches extinction from a different angle. A raging fire will burn itself out if it runs out of flammable materials, such as a bonfire out in the open that isn’t in contact with any other wood or dry grass. Similarly, a gas fire will immediately extinguish if the gas supply is cut off – you only have to look at a gas stove or Bunsen burner to see that.
SMOTHERING
As the other key component present in the chemical reaction that causes combustion, removing oxygen from the equation is the final way of extinguishing a fire. For example, smothering a frying pan blaze with a fire blanket reduces the oxygen to below the 16% required to react, while covering a candle with a glass will snuff it out in a vacuum.Smothering is a technique that is mostly applicable to solid fuel fires, although some materials may contain enough oxygen within their own chemical makeup to keep the blaze burning.
Fire extinguishers,Portable and stationery.
TYPES OF PORTABLE FIRE EXTINGUISHERS:
Spray Foam (Cream) type extinguishers: Here a chemical foam is made to form over the fire so that oxygen supply is cut off and fire dies down.
Dry Chemical Powder type extinguisher: Here the fire is controlled by the inhibiting action of the dry chemical powder which breaks the chain reaction.
Types of extinguishers
WATER EXTINGUISHERS
Water extinguishers are one of the most cost-effective ways to fight Class A fires, those fuelled by solid materials such as paper, wood and textiles.
There are four different types of water extinguishers: water jet, water spray, water with additives and water mist or fog.
- Water jet extinguishers work by spraying a jet of water at the burning materials, cooling them and preventing re-ignition. They should not be used on live electrical equipment.
- Water spray extinguishers use a very fine spray of water droplets, each droplet is surrounded by air which is non-conductive. Most water spray fire extinguishers carry a 35 kV dielectric test approval which means they have been tested on a 35,000 Volt electrical source at one meter.
- Water extinguishers with additives are water extinguishers with foaming chemicals added. The water loses its natural surface tension meaning that it can soak into the burning materials more effectively. Adding the chemicals to the water means that a smaller extinguisher can produce the same fire rating as a larger, water only, extinguisher.
- Water mist, or fog, extinguishers apply water in the form of mist, or fog, the droplets are much smaller than those from the water spray extinguisher. The smaller the droplet, the larger its surface area in relation to its size, the quicker the droplet evaporates which absorbs the heat energy faster. The downside is the smaller the droplet the less it weighs and therefore the less powerful the cloud of water.
All water extinguishers have a red label.
FOAM EXTINGUISHERS
Foam fire extinguishers can be used on Class A and B fires. They are most suited to extinguishing liquid fires such as petrol or diesel and are more versatile than water jet extinguishers because they can also be used on solids such as wood and paper. The foam extinguishes liquid fires by sealing the surface of the liquid, preventing flammable vapour reaching the air and starving the fire of fuel. They are not suitable for use on free flowing liquid fires.
Foam extinguishers have a cream label.
POWDER EXTINGUISHERS
Powder extinguishers are a good multi-purpose fire extinguisher because they can be used on Class A, B and C fires. They can also be used on fires involving electrical equipment however, they do not cool the fire so it can re-ignite. Powder extinguishers can also create a loss of visibility and may create breathing problems. They are not generally recommended for use inside buildings unless there is absolutely no alternative.
Powder extinguishers have a blue label.
CARBON DIOXIDE EXTINGUISHERS (CO2)
CO2 extinguishers are ideal for places with a lot of electrical equipment such as offices or server rooms because they are safe to use on fires involving electrical apparatus. Carbon dioxide extinguishers do not leave any residue, unlike a foam extinguisher. They can also be used on Class B fires, those involving flammable liquids such paraffin or petrol. CO2 extinguishers work by smothering the fire and cutting off the supply of air.
Carbon Dioxide Extinguishers (CO2) have a black label.
WET CHEMICAL EXTINGUISHERS
Wet chemical extinguishers are suitable for use on Class F fires involving cooking oils and fats, such as lard, olive oil, sunflower oil, maize oil and butter. They are extremely effective, when used correctly. The wet chemical rapidly knocks the flames out, cools the burning oil and chemically reacts to form a soap-like solution, sealing the surface and preventing re-ignition. Although they are primarily designed for use on Class F fires, cooking oils and deep fat fryers. They can also be used on Class A fires (wood, paper and fabrics) and Class B fires (flammable liquids).
Wet chemical extinguishers have a yellow label.
FIRE BLANKETS
Fire blankets are primarily for use on hot oil fires such as frying pans or small deep fat fryers. They can also be used on someone whose clothing has caught fire. They work by smothering the fire, stopping access to the oxygen fuelling it and extinguishing it.
Fire detectors and alarm.
- Detection systems are based on smoke, heat, flame, gas leakage, combustion, water flow.
- Conduction/Convection Heat detection: Housing of detector has a fusible element that melts at a specified temperature causing electrical contact to activate a fire alarm.
- Smoke detector: These are used to detect fires in the incipient stages.
- Heat detectors: They respond to high temperatures caused by fire.
- Flame detector: Detects light from flames where rapid development of flame occurs.
- Electromagnetic detectors: They employ photocells sensitive to infrared and ultraviolet light emitted by the fire.
- Water flow detector: It indicates because the other detector types (smoke, flame or heat) is activated and starts the water sprinkler system.
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| Fire detectors and alarm |
Automatic fire detectors cum extinguishing devices.
FIRE WARNING SYSTEM
These may be electrically powered manually operated systems, automatic fire detection system, or a combination of both. The usual components of these systems are discussed here:
Fire alarms: These can be set off by smoke detectors, heat detectors, sprinkler systems, or pull stations. The most common types of fire alarms are the ones operated by pull stations located in corridors, lobbies, & near elevators.
Sprinklers: These are found in most hotel establishments, especially in corridors & rooms. They are situated on the ceiling & automatically spray water when the temperature rises above a certain level.
Smoke detectors: These are set off by smoke. The two types of smoke detectors available are photoelectric detectors & ionization detectors. Photoelectric detectors are alarms triggered off when smoke blocks a beam of light emanating from the detector. In the ionization type of detector, the alarm sounds when the detector senses a shift in electrical conductivity between two plates.
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| Automatic fire detectors cum extinguishing devices |
Structural protection. Legal requirements.
FIRE LICENSE
Fire accidents are quite common in a country which boasts of amazing skyscrapers and luxurious occupational spaces. Though majestic and delicate in outlook, buildings of such kind are prone to unanticipated fire incidents, more so in a city like Delhi given the population surge and unplanned growth witnessed in the capital. Paying heed to the safety of such buildings and its occupants, the Building Bye-laws were adopted in a notification of the Delhi administration dated 23rd June 1983, which was updated time and again at later stages. In this article, we look at the procedure for obtaining fire license in Delhi.
REGULATORY LAW
Fire services in the country are covered under the ambit of the Twelfth Schedule of the Constitution of India, under the provisions of Article 243W of the constitution. The tasks mentioned in the Twelfth Schedule come under the purview of the various municipalities.
Fire prevention and protection responsibilities are primarily vested with the state governments, and the rules concerning the same are established in the form of State Regulations or Municipal By-Laws.
The regulations pertaining to India’s capital were regulated by the Delhi Fire Prevention and Fire Safety Act, 1986, until the introduction of a new Act. The current provisions concerning fire safety in Delhi are governed by the Delhi Fire Services Act, 2007 and Delhi Fire Service Rules, 2010.
NATIONAL BUILDING CODE
The National Building Code is drafted to dictate measures that will ensure fire safety, at least to a certain extent. The code mandates compliance with the requisite standards of fire safety essential for building occupants and users.
NBC code provisions have been incorporated by the various State Governments and Local Bodies in their respective regulations related to buildings.
Other regulations governing the provision include Section 38 of the Factories Act, 1948 and Section 37 of the same Act.
DOCUMENTARY REQUIREMENTS
The following documents are required to obtain a fire license or a No Objection Certificate (NOC) (the latter term is used in the jurisdiction of Delhi):
- Two sets of the proposed layout of the building.
- Questionnaire (duly filled in).
- Checklist certified by the Architect.
- Copy of the site plan.
- Copy of the service plan.
- Copy of any existent agreement.
- Copy of the bank guarantee.
- Copy of the undertaking.
- Copy of challan of the amount remitted.
NEED FOR QUESTIONNAIRE
The provisions concerning buildings covered under the Delhi Fire Services Act mandates its architect to submit a duly filled-in questionnaire, which must be supported with the plans. The answers should be properly indicated, so as to avoid inconvenience.
The guidelines for fire safety are generally issued within three weeks from the date of the date of receipt of the request.
ISSUE OF NO OBJECTION CERTIFICATE
The application for a No Objection Certificate (NOC) must be made to the Director of the builder/owner of the premises, upon the issuance of guidelines by the fire department. It is highly suggested that the owners or constructers abide by the rules specified by the department at the time of construction while approaching the director for obtaining the document. Any discrepancies must be reported to the Chief Fire Officer or the Director. The Director or Chief Fire Officer may also be approached in the event of a delay in carrying out the inspection or other relevant issues.
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| Structural protection and Legal requirements |
