Q.7 Types of fire extinguishers and performance characteristics exactly
Many types of fire extinguishers are currently available, and each one has certain advantages and disadvantages. For that reason, it is important to understand the capabilities of each type of extinguisher when selecting one to provide protection for a specific hazard or area.
These are available in two types: the pump-type extinguisher discharges the water through a pump operated by the user, and the pressurized extinguisher uses air pressure to discharge the water.
Pump-type extinguishers are not commonly used. Although some operations
may still have and use them, pressurized water extinguisher will most often be employed in situations where water is the appropriate extinguishing agent.
Pressurized water extinguisher has a capacity of 2.5 gallons (9.5 liters) and are suitable for use on class A fires only. They have a range of approximately 30 feet (9.2 meters) when initially discharged and a discharge time of about one minute. They are pressurized with 100 psi (690 kilopascals) of compressed air.
Water extinguishers have several advantages. In many situations, water is easy to clean up and causes little or no additional damage. The extinguisher is inexpensive to recharge and can easily be returned to service by in-house personnel with limited training. In addition, the soaking ability of water is a major advantage in fighting class A fires. There are also a number of disadvantages to water extinguishers. For example, these units are only effective on class A fires and can be dangerous if used on any other class of fire. The extinguishers are also relatively heavy.
In any area that is not continuously heated, the unit is subject to freezing. Antifreeze can be added to prevent freezing, but that makes maintenance more difficult.
A specialized type of water-based extinguisher is the water mist variety. These extinguishers use distilled water and a nozzle that discharges a fine mist to achieve a Class A & C rating for the extinguisher. Water mist extinguishers are available in 1.75 and 2.5 gallon (6.6 and 9.5 liter) sizes. Their range is 10 to 12 feet (3 to 3.7 meters) and discharge time is between 72 and 80 seconds.
Portable foam extinguisher are modified pressurized water extinguisher and are also available in two types. The premix foam extinguisher contains a mixture of water and foam concentrate within the extinguisher. An aerating nozzle is typically used to make foam from the foam solution as it is discharged. The cartridge-type foam extinguisher contains water only in the body of the extinguisher. At the time of discharge, the water flows through a cartridge containing pellets that make foam when mixed with the water. The other construction features of the extinguisher are similar to a water extinguisher.
Foam extinguisher has a capacity of 2.5 gallons (9.5 liters) and are suitable for use on class A and B fires. They have a range of slightly less than the 30 feet (9.2 meters) typical of water extinguishers, and their discharge time is about one minute.
They are pressurized with 100 psi (689 kilopascals) of compressed air.
Both foam extinguisher types have several advantages. In many situations, foam is easy to clean up and causes little or no additional damage. The extinguisher is relatively inexpensive to recharge and can be returned to service by in-house personnel with proper training. Class B fires can be controlled with foam extinguishers. Unlike any other type of portable fire extinguisher, foam extinguishers can cover Class B spills with foam to help prevent ignition.
Foam extinguishers also have a number of disadvantages. For example, these units are only effective on class A and B fires and can be dangerous if used on class C or D fires. The extinguishers are relatively heavy. In any area that is not continuously heated, the unit is subject to freezing. Antifreeze can be added to prevent freezing, but that makes maintenance more difficult. Foam extinguishers are also available in wheeled units, and their most common size is 33 gallons (125 liters).
DRY CHEMICAL EXTINGUISHER
Portable dry chemical extinguishers are available in two types. The stored pressure extinguisher contains a dry chemical agent and pressurizing gas, usually nitrogen, within the extinguisher. The valve head and gauge are,
which shows the tamper seal and pin. This type of extinguisher is available in many sizes ranging from 2.5 to 30 pounds (1.1 to 13.6 kilos).
Ten-pound (4.5 kilo) units are the most commonly used in building fire protection. Small units of 2.5 pounds (1.1 kilos) are commonly placed on forklifts and in vehicles. Discharge times vary from 8 to 20 seconds, and the discharge range is from 5 to 30 feet (1.5 to 9.2 meters). The cartridge operated dry chemical extinguisher contains dry chemical agent in the body of the extinguisher and a separate cartridge of pressurizing gas.
When the extinguisher is needed, its main body is pressurized from this cartridge. The top of the extinguisher including the charging handle is the extinguisher with the cartridge guard removed so the charging cylinder is visible. The discharge nozzle for a cartridge operated extinguisher. The sizes and discharge times and ranges are similar to stored pressure extinguishers.
Both types are available with either major class of dry chemical agent: regular dry chemical or multipurpose dry chemical. Regular dry chemical may be used on class B and C fires. Multipurpose dry chemical is effective on class A, B, and C fires.
Dry chemical extinguishers are also available in wheeled units whose sizes range from 50 to 350 pounds (22.6 to 159 kilos). Their discharge range varies from 15 to 45 feet (4.6 to 13.7 meters), and their discharge time is from 30 to 150 seconds.
Both types of dry chemical extinguishers have several advantages. They offer rapid fire control, particularly for class B fires. The units are not subject to freezing, so they can be placed outside or in unheated areas. The cartridge operated extinguisher is relatively inexpensive to recharge and can be returned to service by inhouse personnel with proper training.
Stored pressure extinguishers, however, can not be recharged in-house without costly, specialized equipment and more extensive personnel training. There are also a number of disadvantages to dry chemical extinguishers. For ex-ample, regular dry chemical is not effective on class A fires.
Multipurpose dry chemical, although effective and approved for use on class A fires, is not as effective as water. Also, both types can make a mess that is difficult and costly to clean up. In situations involving delicate electronic equipment, the cleanup costs can be higher than the initial fire damage.
CARBON DIOXIDE EXTINGUISHER
Carbon dioxide (CO2) extinguishers contain carbon dioxide forced into its liquid state by pressure. This type of extinguisher is available in several sizes from 2.5 to 20 pounds (1.1 to 9 kilos). Discharge times range from 8 to 30 seconds, and the discharge range is from 5 to 8 feet (1.5 to 2.4 meters).
Small carbon dioxide units have a discharge horn attached by tubing, whereas larger units have a discharge horn at the end of a flexible hose. Carbon dioxide extinguishers are also available in wheeled units. Their sizes range from 50 to 100 pounds (22.6 to 45.4 kilos). Their discharge range varies from 3 to 10 feet (0.9 to 3 meters), and their discharge time is from 10 to 30 seconds.
Carbon dioxide extinguishers have several advantages. They can be used on
class B or C fires, and since carbon dioxide does not leave a residue, cleanup is not a problem. The units are not subject to freezing, thus they can be placed outside or in unheated areas.
There are also a number of disadvantages to carbon dioxide extinguishers. The units are not suitable for class A fires. Static electricity can build up during discharge of the extinguisher and could feasibly ignite an explosive atmosphere or damage sensitive electronic circuits. These extinguishers cannot be recharged in-house without the purchase of specialized equipment and personnel training.
DRY POWDER EXTINGUISHERS
Dry powder extinguishers are available in stored pressure and cartridge operated units ( containing one of several available dry powder agents. This type of extinguisher is available in 30-pound (13.6 kilo) cartridge operated units. The agent is also obtainable for manual application with a scoop. Discharge times range from 30 to 60 seconds, and the discharge range is from 6 to 8 feet (1.8 to 2.4 meters).
Dry powder extinguishers are also available in 150 and 350 pound (68 and 159 kilo) wheeled units. Dry powder extinguishers are suitable only for class D fires and are the only effective fire control agents for this type of fire. Dry powder agents must be evaluated in relation to the specific combustible metal that is being protected. These extinguishers can be recharged in-house.
WET CHEMICAL EXTINGUISHERS
Wet chemical extinguishers are designed for use on class K cooking oil fires. This is a relatively minor exposure in most industrial settings. Food preparation areas for industrial cafeterias would require this type of coverage if frying and other oil-based cooking is done.
This will also be an issue on a larger scale if the processes
of the manufacturing facility involve cooking.
Extinguisher ratings are used to determine which classes of fire can be controlled effectively and safely with the extinguisher being tested. Ratings also provide a guide to the size of fire an extinguisher will control. All extinguishers receive a class rating. Extinguishers for class A fires are given a numerical rating from 1A to 40A which is based on a relative scale.
A 4A extinguisher, for example, will control a fire approximately twice as large as a 2A extinguisher. Class B extinguishers are rated numerically from 1B to 640B based on the approximate square footage of a spill fire they can control. A 10B extinguisher will extinguish a spill fire of approximately 10 square feet (0.9 square meters).
Fire tests are conducted using wood and excelsior for class A extinguishers.
Class B extinguishers are tested on n-heptane fires in square pans using a liquid depth of two inches. Extinguishers for class C fires do not undergo fire tests but are tested for nonconductivity of electricity. Special tests using the specific combustible metals are employed for class D extinguishers.
The two largest testing laboratories for portable fire extinguishers are
Underwriters’ Laboratories and Factory Mutual. Extinguishers for use in industrial environments should have been approved by at least one and preferably both of these organizations.
SELECTION OF EXTINGUISHERS
The selection of an appropriate extinguisher for a particular area depends upon several factors. Illustrates general considerations that must be evaluated. The extinguisher must be rated for the class or classes of fire that could be expected in the area being protected. This is the first consideration when selecting an extinguisher. The process of identifying the general type of extinguisher suitable for the various fire classification combinations is illustrated in Figure 7.28. This chart helps to narrow the selection options based on the class of fire.
The materials that are being protected influence the choice of extinguisher. In a warehouse storing paper goods, for example, a water-type extinguisher would be more suitable than a multipurpose dry chemical. Although the dry chemical extinguisher is rated for class A fires, it does not offer the penetration ability that water does for deepseated fires in class A materials.
The type of equipment and property being protected is another important consideration. Some extinguishing agents offer more rapid fire control than others but may have corresponding disadvantages like the potential to cause additional damage to the equipment.
For example, dry chemical agents generally offer the most rapid control of flammable liquid fires, however, if electronic equipment is present in the same area, the residue left by dry chemical agents may cause more damage than the fire. In this example, carbon dioxide, halon, or any of the halon substitutes would be more effective agents. The opposite situation can also occur. If an area outside the structure, a loading dock, for example, is being protected, consider that the dry chemical agent is much less affected by wind than carbon dioxide.
Every extinguishing agent used for portable fire extinguishers has advantages and disadvantages that must be considered when selecting the appropriate one for protecting a specific hazard. Agent compatibility is another consideration that will affect the choice of extinguisher. If the area being protected contains methyl ethyl ketone, a polar solvent, a regular foam agent will not be effective.
The potential severity of the fire must also be evaluated in order to determine the size of the extinguisher that will be required. If, for example, an extinguisher must be chosen to protect a quality control lab area that uses flammable liquids in quantities up to a pint, the extinguisher selected will need only limited fire control capability. If the area to be protected is a 4 by 8 foot (1.2 by 2.4 meter) dip tank, a much greater fire control capability will be necessary.
NFPA #10 divides fire severity potential into three classifications: light (low),
ordinary (moderate), and extra (high). These classifications, within the context of the standard, are used to determine specific requirements for items like the distribution of extinguishers. Used in general terms during the evaluation of extinguisher protection, the hazard classifications help assess the severity of the potential fire in a specific area. Low hazard includes areas such as offices, classrooms, and other general use areas.
The quantity of class A materials in these areas is relatively insignificant. Small amounts of class B materials may be present as well. Moderate hazard includes light manufacturing, stores, workshops, and some warehouses. The quantity of class A and B materials is greater than in low hazard areas. High hazard includes manufacturing, vehicle repair, and warehouses, where the quantity of class A and B materials is greater than in moderate hazard areas.
User capabilities also affect the choice of extinguisher. The training the individual has in using extinguishers is the primary consideration. If training will be limited or nonexistent, the extinguishers should be simple and small. Larger extinguishers can be used on larger fires. The size and capability of the extinguisher can provide a false sense of security to an untrained operator. Fighting larger fires requires more training. Occupants without sufficient training should not be engaged in fighting large fires.
The untrained individual will be forced to exit the building when the agent is exhausted, and this will occur more rapidly with a small extinguisher. The
user’s physical ability to operate the extinguisher may be affected by physical or mental limitations. Strength limitations may also affect the size of the extinguisher that can be handled effectively by the individual.
The location where the extinguisher will be placed must be considered because the environment can have a major impact on which extinguisher will be most appropriate.
Temperature will affect water and foam extinguishers. They are subject to freezing and must either not be used in unheated areas or be modified with antifreeze solutions. Wind and draft will have an impact on the effectiveness of any gaseous agent. Carbon dioxide, in particular, is difficult to use effectively in windy conditions. Corrosive vapors in the area may deteriorate the extinguisher and the materials used in its construction and may determine how easily the unit is affected by these corrosive vapors. Extinguisher valve heads are typically available in both aluminum and brass, brass being the superior choice for a corrosive environment.
Agent reactivity and contamination must also be considered because some extinguishing agents may react with certain materials and chemicals. Contamination can also occur. For example, the use of a dry chemical extinguishing agent in a food processing area would require the disposal of all exposed food items. On the other hand, a carbon dioxide extinguisher used in this same area would not contaminate the food. The use of certain extinguishing agents in a confined area may present hazards to the individual using the extinguisher.
Carbon dioxide, for example, will exclude the oxygen in an area if a sufficient concentration is allowed to accumulate. The decomposition products of halon, when heated, can also be hazardous. The initial cost of fire extinguisher protection can vary significantly depending on what kind of extinguishers are used to achieve adequate protection. One way to improve the selection of extinguishers in terms of cost is to evaluate the facility as a whole rather than as individual areas.
A decision must be made as to whether getting the most effective protection or meeting minimum requirements is the goal. Of course, the quality of the extinguishers used will have a significant impact on the cost, but this difference is often well worth the initial investment. The cost of the extinguisher should be evaluated over the life of the unit, not just based on initial pur-chase price. Agent prices also vary, and the agent type selected will affect the initial cost. Purple K is more expensive than regular dry chemical, but if protection is required for significant flammable liquid issues, the extra cost is justifiable.
The size selected will affect initial costs. Many small units will cost more than fewer large units of the same type of extinguisher. Placement considerations may make additional smaller units the better choice. This must be evaluated in terms of the overall protection of the facility. When making the initial purchase of extinguishers, quotes should be obtained from several sources.
Final purchase prices can vary considerably from dealer to dealer. Always buy from a reputable source, preferably one that will also provide long-term maintenance and recharging services. Ongoing extinguisher costs should also be evaluated. For example, regular inspections will have to be performed. The time it takes to perform these routine inspections will, of course, depend on the number of extinguishers and the complexity
of the inspection.
The maintenance cost of extinguishers is influenced by the same factors as inspection costs. Hydrostatic testing must be performed periodically, and the costs of this maintenance and testing depend on the type and quantity of extinguishers that were selected. Some varieties of extinguishers are easier to maintain on an in-house basis. If inhouse maintenance is to be used, the selection of extinguishers can determine the cost involved and the difficulty of ongoing maintenance.
The cost of recharging extinguishers depends on the type of agent and on
whether it is done in-house or by an outside contractor. How recharging of the extinguishers will be handled should be part of the initial selection criteria. Standardization of extinguishers throughout the facility offers some advantages with respect to inspection, maintenance, and training. If extinguishers are already in place, continuing to use the same type may be the most effective selection.