Potable Fire extinguishers include both self-contained fire extinguishing equipment that can be carried by one person and wheeled units that can be handled by one or two people. Due to their limited capacity, fire extinguishers are designed to control fires that are just starting or that are of limited size.
Fire Extinguishers Location?
Fire extinguishers need to be located near the equipment to be protected, but not so close that they can become involved in the fire or that a person cannot reach them. The suggested distance from their point of use is between fire extinguishers is 5 and 15 m. From any grade level point in a process plant, the maximum horizontal distance to a dry chemical extinguisher should not exceed 15 m. Fire Extinguishers locations should be conspicuous, clearly marked, and visible from several directions. The locations should not be blocked with materials or equipment that might conceal or impede access to them.
Table below provides guidance regarding the selection of portable extinguishers.
Fire Extinguishers Selection
|Class A – ordinary combustible hazards
|Water can be used. Multipurpose dry chemical may be considered for some warehouse facilities and offices where lightweight fire extinguishers are desirable for easier handling.
|Class B – flammable liquids and gases
|The following fire extinguishing materials can be used:
▪Multipurpose dry chemical
|Class C – electrical hazards and delicate electronic equipment
▪Dry chemical (an effective agent but difficult to cleanup and may damage the equipment)
Major Types of Fire Extinguishers
Water Fire Extinguishers
The superior cooling capacity of water over other extinguishing agents makes it particularly effective on fires involving ordinary combustibles such as wood, paper, fabrics, or rubber. Water extinguishers do not require extensive cleanup after use and they are non-corrosive to electronic circuitry, unlike dry chemical extinguishers. When water extinguishers are subject to freezing weather antifreeze is added.
Carbon dioxide (CO2) is stored in fire extinguishers in the liquid phase. It vaporizes when released thereby smothering a fire by excluding the air (oxygen) needed for combustion. As already noted, Carbon dioxide extinguishers are preferable to water or dry chemical extinguishers where water damage and fouling of delicate electrical, electronic, or laboratory equipment cannot be tolerated or where cleanup is a consideration.
If a CO2 fire extinguishers are discharged in a confined space then that space must be ventilated once the fire is extinguished.
Many types of dry chemical extinguishing agents are available. Those shown below are used in the process industries.
▪Potassium bicarbonate base (Purple K); and
Sodium bicarbonate was the original dry chemical extinguishing agent. The chemical currently available is a mixture consisting primarily of sodium bicarbonate with various additives to improve flow and storage characteristics. Chief among the additives is a silicone polymer. It is used to prevent moisture absorption and consequent caking of chemical. It works by interrupting the propagation of the flame. Its electrical resistivity is high, and it is nontoxic. This agent may be used for extinguishing fires involving flammable liquids, gases and electrical equipment. It is not effective in extinguishing deep-seated fires in ordinary combustibles.
Potassium bicarbonate chemical, whose physical properties are similar to sodium bicarbonate, is effective at extinguishing fires involving flammable liquids and gases. It is also suitable for use on fires involving electrical equipment. It is not effective in extinguishing deep-seated fires in ordinary combustibles.
Monoammonium phosphate based chemical is effective in controlling and extinguishing fires involving flammable liquids and gases, ordinary combustible materials, and electrical equipment. It is recommended where piped water is not available, where freezing conditions are expected, or where a combination of different classes of hazards exists. It has physical properties similar to the sodium bicarbonate chemical but is more effective on flammable liquid fires. It is corrosive to electronic circuitry. It should not be mixed bicarbonate dry chemicals. A chemical reaction can occur in the extinguisher that generates CO2 and other gases; the pressure buildup could rupture the extinguisher.
A portable fire extinguisher is a device used to put out fires of limited size. Portable extinguishers are classified by expected application on a specific type of fire (i.e., A, B, C, or D) and the expected area of suppression. The four types of fires are grouped according to the type of material that is burning. Class A fires are those in which ordinary combustibles such as wood, cloth, and paper are burning. Class B fires are those in which flammable liquids, oils, and grease are burning. Class C fires are those involving live electrical equipment. Class D fires involve combustible metals such as magnesium, potassium, and sodium.
The numerical rating on the fire extinguisher is a relative rating number. It is assigned by recognized testing laboratories for the amount of average fire area that can be extinguished according to methods established by the National Fire Protection Association (NFPA). The rating does not equate to the amount of square feet that can be expected to be extinguished by an individual using the extinguisher.
Classes of Fire & Appropriate Extinguishers
The classes of portable fire extinguishers manufactured and used in industry are defined below. Other countries have similar classifications (although these may not be exactly the same).
Extinguishers for Class A fires
Class A fire extinguishers are usually water-based. Water provides a heat-absorbing (cooling) effect on the burning material to extinguish the fire. Pressurized water extinguishers use air under pressure to expel the water which is directed with a short hose.
Extinguishers for Class B fires
Class B fires are put out by excluding air, by slowing down the release of flammable vapors or by interrupting the chain reaction of the combustion. Three types of extinguishing agents are typically used—carbon dioxide, dry chemical, and foam water for fires involving flammable liquids, greases, and oils. Carbon dioxide is a compressed gas agent that prevents combustion by displacing the oxygen in the air surrounding the fire. The two types of dry chemical extinguishers include one that contains ordinary sodium potassium bicarbonate, urea potassium bicarbonate, and potassium chloride base agents.
The second, multipurpose type contains an ammonium phosphate base. The multipurpose extinguisher can be used on Class A, B, and C fires. Most dry chemical extinguishers use stored pressure to discharge the agent, and the fire is extinguished mainly by the interruption of the combustion chain reaction. Foam extinguishers use an aqueous film-forming foam (AFFF) agent that expels a layer of foam when it is discharged through a nozzle. It acts as a barrier to exclude oxygen from a fire.
Extinguishers for Class C fires
The extinguishing agent in a Class C fire extinguisher must be electrically nonconductive. Both carbon dioxide and dry chemicals can be used for electrical fires. An advantage of carbon dioxide is that it leaves no residue after the fire is extinguished. When electrical equipment is not energized, extinguishers for Class A or B fires may be used. Note that since an extinguisher rated solely for a Class C fire is not manufactured, and an ABC- or BC-rated fire extinguisher will have to be specified for this hazard application.
Extinguishers for Class D fires
A heat-absorbing extinguishing medium is needed for fires in combustible metals. Also, the extinguishing medium must not react with the burning metal. The extinguishing agents, known as dry powders, cover the burning metal and provide a smothering blanket.
The extinguisher label provides operating instructions and identifies the class or classes of the fire on which the extinguisher may be used safely. Approved extinguishers also carry the labels of the laboratories at which they were tested.
Portable fire extinguishers should be positioned in all process facility areas so that the travel distance to any extinguisher is 15 m (50 ft) or less. They are generally sited on the main walkways or exits from an area, near the high hazard itself and near other emergency devices. They are mounted so individuals can easily retrieve them, typically approximately 1 m (2.5 ft) from the walking surface with red highlighting at the mounting location.
NAFFCO Fire Extinguishers
Wheeled Fire Extinguishers
Chinese Fire Extinguishers
Portable Fire Extinguishers
Wheeled Fire Extinguishers
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