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Contents
  1. 1How an extinguisher works
  2. 2Agents and what they do
  3. 3Classes and ratings
  4. 4Role in fire protection
  5. 5People and training
  6. 6Requirements and maintenance
  7. 7Limits, side effects and incident experience
  8. 8See also
  9. 9Notes
  10. 10References

A fire extinguisher is a portable device, carried by hand or on wheels, that holds a limited supply of extinguishing agent for attacking a fire while it is still small.[1][2] Extinguishers contain water, foam, dry chemical powder, carbon dioxide, wet chemical solutions or halon. Each Extinguishing agent works in its own way and suits some fires better than others.[3][4] In the United States, the rating on an extinguisher combines a number for its relative effectiveness with letters for the Fire classes on which it was found to be effective.[5]

Extinguishers belong to manual fire suppression, which people carry out with portable extinguishers, hoses or manually operated fixed systems.[6] A report of the US Nuclear Regulatory Commission describes a fire in its earliest stage as one that portable extinguishers or small hoses can still control without protective clothing or breathing apparatus.[7] Incident reviews describe fires that defeated several extinguishers but were then put out quickly with water.[8][9] Fire engineering analyses customarily assume that occupants will not fight a fire effectively unless they are specially trained.[10]

How an extinguisher works

An extinguisher stores its agent under pressure, or together with a gas that drives it out. Dry chemical powder consists of fine particles coated to prevent caking, and an inert gas projects the powder onto the fire.[11] Carbon dioxide is stored as a gas liquefied under pressure and provides its own pressure for release.[12] A portable extinguisher with aqueous film-forming foam closely resembles a stored-pressure water extinguisher, except for its special nozzle.[1]

Sizes vary widely. Aqueous film-forming foam extinguishers are usually available as hand-portable models of 9 litres and as wheeled models holding 125 litres.[1] The supply of agent is limited. At one US nuclear power plant, three portable extinguishers together discharged about 32 kg (70 pounds) of dry chemical on a small fire of rags and debris.[9]

The technology has changed over time. Carbon tetrachloride became available as early as 1907 and was used mostly in hand-pump portable extinguishers, because it conducted little electricity and left no residue. It caused a number of accidental deaths and serious injuries through its toxicity, and its use was halted during the 1950s.[13] Methyl bromide, which was found in the late 1920s to be more effective than carbon tetrachloride, was never used in portable extinguishers because of its high toxicity.[13]

Chemical foam extinguishers, in which a reaction between sodium bicarbonate and aluminium sulphate produced the foam and pushed it out, are now generally regarded as obsolete. Their manufacture in the United States stopped in 1969, and the National Fire Protection Association (NFPA) recommends replacing them.[14][1] The US Army also introduced portable extinguishers with halon 1301. Under the Montreal Protocol, however, the production of halons in the developed countries ended on 31 December 1993.[15][16]

Agents and what they do

NUREG-1805, a report of the US Nuclear Regulatory Commission, names four ways to put out a fire. They are separating the fuel from the flame, removing or diluting the oxygen, cooling the fuel or flame, and adding chemicals that change the combustion chemistry. More often several of these act at once.[3] Water cools a burning solid, so that it gives off less flammable gas, and cools the flame.[3] It is the most commonly used extinguishing agent, mainly because it is widely available and inexpensive and absorbs a great deal of heat as it turns into steam.[17]

Portable agents cool, blanket, coat, inhibit chemistry or reduce oxygen.
Portable extinguishers use several different extinguishing mechanisms. Based on Iqbal and Salley (2004), pp. B-15–B-16.

Water also has clear limits. It is unsuitable for certain water-reactive materials, with which it can produce heat, flammable or toxic gases, or explosions.[17] Burning hydrocarbon fuels float on water and keep burning, and water under very hot oil turns to steam and throws out burning oil.[17][18] Firefighting foam overcomes the floating problem by forming a layer on the liquid that keeps out air and stops the fuel from evaporating.[19] Foam is water-based, however, so it shares the risk of electric shock from live equipment.[20]

Dry chemical powders are very common in manual extinguishers, and their most common use is on relatively small flammable liquid fires.[21] Common types include sodium bicarbonate, potassium bicarbonate and monoammonium phosphate, which is known as "ABC" or multipurpose powder.[11] The powders probably act mainly by removing reactive chemical species from the flame, and they also absorb heat and block radiation.[21] Monoammonium phosphate also forms a glassy coating over the burning surface, which makes it the only common powder considered effective against deep-seated fires.[21]

Carbon dioxide is an electrically non-conductive inert gas that is suitable for Class B and Class C fires. It puts out a fire by lowering the concentration of oxygen, of fuel vapour or of both until combustion stops.[22] It has a long history as an extinguishing agent, mainly for flammable liquid fires and fires in electrical equipment.[12] Wet chemical agents, solutions of water with potassium carbonate, potassium acetate or potassium citrate, are listed in NUREG-1805 for cooking oil and fat fires.[23][4]

Classes and ratings

The fire classes used in the United States come from NFPA 10, Standard for Portable Fire Extinguishers. Its 2002 edition, as summarised in NUREG-1805, has five classes. Class A covers ordinary combustibles such as wood, paper and many plastics, Class B flammable liquids and gases, and Class C energised electrical equipment. Class D covers combustible metals, and Class K cooking appliances with vegetable or animal oils and fats.[24] The halon chapter of the SFPE Handbook of Fire Protection Engineering (third edition, 2002) shows only four classes, A to D, so the letters depend on the document and its edition.[25]

The rating number shows relative effectiveness, and the letters show the classes of fire on which the extinguisher has been found to be effective.[5] Ratings are based on standardised tests developed by Underwriters Laboratories.[26] A hand-portable foam extinguisher of 9 litres, for example, is rated 3A:20B, and a wheeled unit of 125 litres is rated 20A:160B.[1] For Class C the rating reflects the non-conductive properties of the agent. Once electrical equipment has been de-energised, extinguishers designed for Class A or Class B fires can be used safely.[4][24]

The class table in NUREG-1805 shows why the letters matter. It states that water and water-based extinguishers should never be used on Class D metal fires, and that a Class D extinguisher must suppress the fire without reacting physically or chemically with the metal.[4] Among the powders, monoammonium phosphate is not recommended for kitchen fires involving hot fat because it is acidic; an alkaline powder such as potassium bicarbonate is preferred.[21]

Role in fire protection

Portable extinguishers are one layer among several. The US Nuclear Regulatory Commission's defence-in-depth approach aims to prevent fires, to detect, control and extinguish quickly those that do occur, and to protect safety functions if a fire is not put out promptly.[27] Portable extinguishers form part of the second layer, together with detectors, fixed suppression systems, hose stations, hydrants and fire brigades. The approach recognises that the first two layers are not always entirely successful.[27]

In the same handbook, Grant gives an example for a computer room in which each stage of a fire has its own control measure. Portable extinguishers, together with an automatic halon system, serve the incipient stage, while automatic sprinklers serve the stage before flashover.[2] A US fire risk method for nuclear power plants similarly notes that small fires are likely to be put out immediately with portable extinguishers.[28] A fire has moved beyond this early stage when firefighters need thermal protective clothing or breathing apparatus, or have to crawl to stay below the smoke and heat.[7]

Extinguishers and an automatic Sprinkler system complement each other. NUREG-1805 notes that human response, such as discovering the fire and the travel of a fire brigade, usually takes much longer than the time sprinklers need to control a fire in its early stages.[29] In its study of the World Trade Center, the US National Institute of Standards and Technology (NIST) noted that the sprinklers there were designed to control fires. Manual intervention with hand-held extinguishers or hose lines was generally needed to put out all of the burning, especially in areas shielded from the sprinkler spray.[30]

In fire engineering design, the International Fire Engineering Guidelines (2005 edition) count manual suppression equipment among the measures for detection, warning and suppression.[31] Suppression by building occupants, using extinguishers and hose reels, may be taken into account if appropriate criteria are used.[32] The guidelines add that it is customary to assume that occupants will not engage in effective firefighting unless they belong to a specially trained site emergency response crew.[10] Professional Firefighting by the fire service is treated separately.[10]

People and training

Whether an extinguisher is used depends on the people present. In the SFPE Handbook, Bryan describes how a person who has recognised a fire evaluates the threat. The person then either evacuates the building or fights the fire, for example by fetching an extinguisher or operating a manual fire alarm.[33] People with firefighting training or experience, in surroundings they know, are likely to choose more adaptive actions. In one office building fire, regular occupants fought the fire and alerted others, while visitors attending training sessions mostly evacuated.[33]

Studies of residential and other fires give an idea of how often people fight fires. In a British study of 2,193 people in 952 fires, 14.7 percent showed firefighting behaviour, against 22.9 percent of 584 people in 335 mainly residential fires in a US study.[34] In the US study, fetching an extinguisher was the first action of 4.6 percent of the participants.[34]

In US nuclear power plants, a fire watch is a person who provides extra cover, for example during hot work, or makes up for an impaired fire protection system. Fire watches should be trained to recognise fire hazards, to use fire extinguishers and to follow notification procedures.[6] A US method for counting fire events treats a fire as potentially challenging when a hose stream, several portable extinguishers or a fixed suppression system were needed.[35] A hot-work fire also counts if active intervention was needed, even when the fire watch put it out quickly, although the use of a single extinguisher should not be the only indicator.[35]

Requirements and maintenance

Requirements for extinguishers depend on the code or standard that applies and on its edition. In the United States, NUREG-1805 lists NFPA 10, Standard for Portable Fire Extinguishers (2002 edition), among the current NFPA standards. It notes that NFPA codes are revised on cycles of 3 to 5 years, so the edition in force at the time of design is the code of record.[36] The SFPE Handbook refers to NFPA 10 for the selection and placement of portable extinguishers.[1] Citing NFPA 10 and a handbook chapter on extinguisher use and maintenance, NUREG-1805 describes three hazard levels by the amount of Class A and B materials present. Light hazard can include offices and classrooms, ordinary hazard shops and parking garages, and extra hazard woodworking, vehicle repair and cooking areas.[37]

New York City shows how requirements can sit in different documents. NIST found that the 1968 New York City Building Code had no requirements for fire extinguishers, because it required occupant hose reels instead.[38] For the World Trade Center, the Port Authority nevertheless required portable extinguishers in all spaces. It followed a Fire Department of New York directive of 17 September 1980 and section 27-4009 of the New York City Fire Prevention Code of 1 July 1988.[39]

Maintenance is part of Fire safety management. The International Fire Engineering Guidelines state that active fire protection equipment, including suppression equipment, needs particular attention to ensure proper installation, commissioning, management and use. Its maintenance should follow the relevant codes, standards and manufacturer's literature.[40] The New Zealand part of the guidelines adds that the fire safety of a building depends on the ongoing functioning of its fire safety system. Inspection, testing and maintenance programmes should therefore have due regard to New Zealand standards and legislation.[41] Among the information notices of the Nuclear Regulatory Commission listed in NUREG-1805 is one of 11 April 2001 titled "Neglected Fire Extinguisher Maintenance Causes Fatality".[42]

Limits, side effects and incident experience

Dry chemical powder has side effects. Its sudden release and unexpected re-ignition of the fire are hazards, and although the powders are non-toxic, they can cause temporary breathing difficulty and reduce visibility.[43] All powders need significant cleaning after use, and some corrosion or damage is possible.[21] Powders become sticky when heated, and applying water to the residue speeds up the corrosion of equipment.[9]

At the Point Beach 1 nuclear power plant in 2001, three portable dry chemical extinguishers failed to put out a small fire, which re-ignited twice. The fire brigade then put it out easily with about 57 to 76 litres (15 to 20 gallons) of water from a hose line.[9] White powder covered about half of the containment basement floor, and NUREG-1805 concludes that the cleanup effort called for a more careful choice of extinguishing agent.[9]

Powder clouds reduce visibility, coat equipment and require cleanup while hot fuel can reflash.
Extinguishing also creates post-discharge hazards and restoration needs. Based on Iqbal and Salley (2004), pp. H-29–H-30.

Fires in energised electrical equipment have repeatedly defeated portable extinguishers in US nuclear power plants. At Waterford 3 in 1995, attacks with carbon dioxide, halon and dry chemical extinguishers failed. Water was permitted only about 90 minutes after the fire started, and the fire was then under control within 4 minutes.[8] At Prairie Island 1 in 2001, more than 20 portable carbon dioxide extinguishers were used over about 1.5 hours on a breaker fire, and two fire brigade members were treated for heat exhaustion.[44] A review of high-energy arcing faults in electrical switchgear notes that in severe events the first extinguishers may be ineffective whatever the agent, and that such fires were finally put out with water.[45]

Delivery is a further limit. In a deep-seated fire, Smouldering continues below the surface, where an agent cannot easily reach the seat of the fire.[46] A gaseous agent can put out the visible flames at once while glowing combustion continues inside, and the fire can then re-ignite when air returns.[47] Low-expansion foam works well on a flat pool fire but is not particularly effective on running fuel or a pressurised spray.[19]

Extinguisher discharge reaches a pool but leaves shielded and deep fuel hot.
Manual extinguishing depends on delivery, coverage and remaining fuel condition. Based on Scheffey (2002), p. 4-88 and Iqbal and Salley (2004), pp. B-43–B-44.

Gaseous agents also have hazards of their own. Carbon dioxide replaces the oxygen in the air, and people become unconscious at a concentration of 10 percent by volume.[12] Grant notes that the high concentrations needed to extinguish a fire with carbon dioxide make the protected space lethal to people.[2] In battery rooms with lead-acid batteries, NUREG-1805 advises against discharging an extinguisher directly onto a battery, because the thermal shock may crack its case or cover.[48]

See also

Notes

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 Scheffey and Hickey (2002), p. 4-126.
  2. ↑ 2.0 2.1 2.2 Grant (2002), p. 4-155.
  3. ↑ 3.0 3.1 3.2 Iqbal and Salley (2004), p. B-15.
  4. ↑ 4.0 4.1 4.2 4.3 Iqbal and Salley (2004), p. B-16.
  5. ↑ 5.0 5.1 Iqbal and Salley (2004), p. F-25.
  6. ↑ 6.0 6.1 Iqbal and Salley (2004), p. F-29.
  7. ↑ 7.0 7.1 Iqbal and Salley (2004), p. F-38.
  8. ↑ 8.0 8.1 Iqbal and Salley (2004), p. H-21.
  9. ↑ 9.0 9.1 9.2 9.3 9.4 Iqbal and Salley (2004), pp. H-29–H-30.
  10. ↑ 10.0 10.1 10.2 National Research Council of Canada et al. (2005), p. 1.7-7.
  11. ↑ 11.0 11.1 Iqbal and Salley (2004), p. B-55.
  12. ↑ 12.0 12.1 12.2 Iqbal and Salley (2004), p. B-41.
  13. ↑ 13.0 13.1 Grant (2002), p. 4-150.
  14. ↑ Iqbal and Salley (2004), p. B-63.
  15. ↑ Grant (2002), p. 4-151.
  16. ↑ DiNenno (2002), p. 4-173.
  17. ↑ 17.0 17.1 17.2 Fleming (2002), p. 4-72.
  18. ↑ Iqbal and Salley (2004), p. B-58.
  19. ↑ 19.0 19.1 Scheffey (2002), p. 4-88.
  20. ↑ Iqbal and Salley (2004), p. B-60.
  21. ↑ 21.0 21.1 21.2 21.3 21.4 Iqbal and Salley (2004), p. B-56.
  22. ↑ Iqbal and Salley (2004), p. F-12.
  23. ↑ Iqbal and Salley (2004), p. F-70.
  24. ↑ 24.0 24.1 National Fire Protection Association (2002), as cited in Iqbal and Salley (2004), p. B-13.
  25. ↑ Grant (2002), p. 4-153.
  26. ↑ Iqbal and Salley (2004), p. F-23.
  27. ↑ 27.0 27.1 Iqbal and Salley (2004), p. 1-2.
  28. ↑ Nowlen et al. (2005b), p. 11-17.
  29. ↑ Iqbal and Salley (2004), p. 10-1.
  30. ↑ Evans et al. (2005), p. 9.
  31. ↑ National Research Council of Canada et al. (2005), p. 1.2-10.
  32. ↑ National Research Council of Canada et al. (2005), p. 1.7-1.
  33. ↑ 33.0 33.1 Bryan (2002), pp. 3-318–3-319.
  34. ↑ 34.0 34.1 Bryan (2002), pp. 3-322–3-323.
  35. ↑ 35.0 35.1 Nowlen et al. (2005b), pp. C-8–C-9.
  36. ↑ Iqbal and Salley (2004), p. E-1.
  37. ↑ Conroy (1997) and National Fire Protection Association (2002), as cited in Iqbal and Salley (2004), p. B-14.
  38. ↑ Lew et al. (2005), p. 151.
  39. ↑ Grill and Johnson (2005c), p. 17.
  40. ↑ National Research Council of Canada et al. (2005), p. 1.7-8.
  41. ↑ National Research Council of Canada et al. (2005), p. 0.3-8 (Part 0, New Zealand).
  42. ↑ Iqbal and Salley (2004), p. D-14.
  43. ↑ Iqbal and Salley (2004), p. B-57.
  44. ↑ Iqbal and Salley (2004), pp. H-30–H-31.
  45. ↑ Nowlen et al. (2005b), p. M-3.
  46. ↑ Iqbal and Salley (2004), pp. B-39–B-40.
  47. ↑ Iqbal and Salley (2004), p. B-43.
  48. ↑ Iqbal and Salley (2004), p. 16-11.

References

  • Bryan, J. L. (2002). Behavioral response to fire and smoke. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 3-315–3-341). National Fire Protection Association; Society of Fire Protection Engineers.
  • DiNenno, P. J. (2002). Halon replacement clean agent total flooding systems. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-173–4-200). National Fire Protection Association; Society of Fire Protection Engineers.
  • Evans, D. D., Peacock, R. D., Kuligowski, E. D., Dols, W. S., & Grosshandler, W. L. (2005). Active fire protection systems (NIST NCSTAR 1-4). National Institute of Standards and Technology.
  • Fleming, R. P. (2002). Automatic sprinkler system calculations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-72–4-87). National Fire Protection Association; Society of Fire Protection Engineers.
  • Grant, C. C. (2002). Halon design calculations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-149–4-172). National Fire Protection Association; Society of Fire Protection Engineers.
  • Grill, R. A., & Johnson, D. A. (2005c). Post-construction modifications to fire protection and life safety systems of the World Trade Center towers (NIST NCSTAR 1-1H). National Institute of Standards and Technology.
  • Iqbal, N., & Salley, M. H. (2004). Fire Dynamics Tools (FDTs): Quantitative fire hazard analysis methods for the U.S. Nuclear Regulatory Commission Fire Protection Inspection Program (NUREG-1805). U.S. Nuclear Regulatory Commission, Office of Nuclear Reactor Regulation.
  • Lew, H. S., Bukowski, R. W., & Carino, N. J. (2005). Design, construction, and maintenance of structural and life safety systems (NIST NCSTAR 1-1). National Institute of Standards and Technology.
  • National Research Council of Canada, International Code Council, Department of Building and Housing, & Australian Building Codes Board. (2005). International fire engineering guidelines (2005 ed.). Australian Building Codes Board.
  • Nowlen, S. P., Najafi, B., Wyant, F. J., Forester, J., Kazarians, M., Kolaczkowski, A., Joglar, F., Funk, D., Hannaman, G., & Anoba, R. (2005b). EPRI/NRC-RES fire PRA methodology for nuclear power facilities: Vol. 2. Detailed methodology (NUREG/CR-6850; EPRI 1011989). Electric Power Research Institute; U.S. Nuclear Regulatory Commission, Office of Nuclear Regulatory Research.
  • Scheffey, J. L. (2002). Foam agents and AFFF system design considerations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-88–4-122). National Fire Protection Association; Society of Fire Protection Engineers.
  • Scheffey, J. L., & Hickey, H. E. (2002). Foam system calculations. In P. J. DiNenno, D. Drysdale, C. L. Beyler, W. D. Walton, R. L. P. Custer, J. R. Hall Jr., & J. M. Watts Jr. (Eds.), SFPE handbook of fire protection engineering (3rd ed., pp. 4-123–4-148). National Fire Protection Association; Society of Fire Protection Engineers.
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