Fire extinguisher

A fire extinguisher

A fire extinguisher is an active fire protection device used to extinguish or control a fire, often in emergency situations. Typically, a fire extinguisher consists of a hand-held cylindrical pressure vessel, containing a chemical agent which can be discharged to extinguish a fire.

Contents

Fire extinguishers have been a major part of fire prevention. The first, primitive fire extinguishers were most likely created shortly after fire was discovered. They come in a wide variety of sizes and shapes. Their greatest benefit is the convenience and the safety that they provide.

Use

The typical steps for operating a fire extinguisher (described by the acronym "PASS") are the following:

P—Pull the safety pin
A—Aim the nozzle at the base of the fire, from a safe distance (about six feet away)
S—Squeeze the handle
S—Sweep the extinguisher from side to side while aiming at the base of the fire

There are various types of extinguishers, which are used for different types of fires; using the wrong type can worsen the fire hazard, but using the right one can create a better situation. However, fire extinguishers are not a substitute for trained fire-fighting professionals with state-of-the-art equipment. They are, rather, a supplement to be used as a prevention measure—but once the fire is out of control, the safest recourse is to quickly leave the hazard area and call the fire department.

History

The modern fire extinguisher was invented by British Captain George William Manby in 1818; it consisted of a copper vessel with 3 gallons (13.6 liters) of pearl ash (potassium carbonate) solution contained within compressed air.

The soda-acid extinguisher was invented in the nineteenth century, which was comprised of a cylinder with 1 or 2 gal of water with sodium bicarbonate mixed into it. A vial was suspended in the cylinder containing concentrated sulphuric acid. Depending on the type of extinguisher, the vial of acid could be broken in one of two ways. One way used a plunger to break the acid vial, while the second released a lead bung that held the vial closed. Once the acid was mixed with the bicarbonate solution, carbon dioxide gas was expelled and thereby pressurized the water. The pressurized water was forced from the canister through a nozzle or short length of hose.

Around 1912, Pyrene invented the carbon tetrachloride, or CTC, extinguisher, which expelled the liquid from a brass or chrome container by a handpump; it was usually of 1 imperial quart (1.1 L) or 1 imperial pint (0.6 L) capacity, but was also available in up to 2 imperial gallon (9 L) sizes. The CTC vaporized and extinguished the flames by chemical reaction. The extinguisher was suitable for liquid and electrical fires, and was popular in motor vehicles for the next 60 years. However, the vapor and combustion by-products were highly toxic, and could cause death in confined spaces.

Classification

Internationally there are several accepted classification methods for hand-held fire extinguishers. Each classification is useful in fighting fires with a particular group of fuel.

Australia

Type Pre-1997 Current Class
Water Solid red A        
Foam Solid blue Red with a blue band A B      
Powder Red with a white band A B C E  
Carbon dioxide Red with a black band A (limited) B C E F
Vapourising liquid (not halon) Red with a yellow band A B C E  
Halon Solid yellow A B E  
Wet chemical Solid oatmeal Red with an oatmeal band A F

In Australia, yellow (Halon) fire extinguishers are illegal to own or use on a fire, unless an essential use exemption has been granted.[1]

United Kingdom

According to the standard BS EN 3, fire extinguishers in the United Kingdom, as all throughout Europe, are red RAL 3000, and a band or circle of a second color covering at least 5 percent of the surface area of the extinguisher indicates the contents. Before 1997, the entire body of the fire extinguisher was color coded according to the type of extinguishing agent.

Type Old Code BS EN 3 Color Code Fire Class
Water Signal Red Signal Red A          
Foam Cream Red with a Cream panel above the operating instructions A B     sometimes E  
Dry Powder French Blue Red with a Blue panel above the operating instructions A (Limited) B C   E  
Carbon Dioxide CO2 Black Red with a Black panel above the operating instructions A (Limited) B     E  
Halon Emerald Green Pre-03- Signal red with a green panel A B     E  
Wet Chemical No F Class Red with a Canary Yellow panel above the operating instructions A         F
Class D Powder French Blue Red with a Blue panel above the operating instructions       D    

The UK recognizes six fire classes. Class A fires involve organic solids, such as paper and wood. Class B fires involve flammable liquids. Class C fires involve flammable gases. Class D fires involve metals, Class E fires involve live electrical items, and Class F fires involve cooking fat and oil. Fire extinguishing capacity is rated by fire class using numbers and letters such as 13A, 55B. EN 3 does not recognize a separate E class—this is an additional feature requiring special testing (dielectric test per EN3-4) and inability to pass this test makes it compulsory to add a special label (pictogram) indicating the inability to isolate the user from a live electric source.

United States

There is no official standard in the United States for the color of fire extinguishers, though they are typically red, except for Class D extinguishers, which are usually yellow. Extinguishers are marked with pictograms depicting the types of fires that the extinguisher is approved to fight. In the past, extinguishers were marked with colored geometric symbols, and some extinguishers still use both symbols. No official pictogram exists for Class D extinguishers, though training manuals sometimes show a drill press with shavings burning underneath. The types of fires and additional standards are described in NFPA 10: Standard for Portable Fire Extinguishers.

Fire Class Geometric Symbol Pictogram Intended Use
A Green Triangle Garbage can and wood pile burning Ordinary combustibles
B Red Square Gasoline can with a burning puddle Flammable liquids
C Blue Circle Electric plug with a burning outlet Energized electrical equipment
D Yellow Star N/A Combustible metals
K Black Hexagon Pan burning Cooking oils

The Underwriters Laboratories rate fire extinguishing capacity in accordance with UL/ANSI 711: Rating and Fire Testing of Fire Extinguishers. The ratings are described using numbers preceding the class letter, such as 1-A:10-B:C. The number preceding the A multiplied by 1.25 gives the equivalent extinguishing capability in gallons of water. The number preceding the B indicates the size of fire in square feet that an ordinary user should be able to extinguish. There is no additional rating for class C, as it only indicates that the extinguishing agent will not conduct electricity, and an extinguisher will never have a rating of just C.

Installation

Fire extinguishers are typically fitted in buildings at an easily accessible location, such as against a wall in a high-traffic area. They are also often fitted to motor vehicles, watercraft, and aircraft—this is required by law in many jurisdictions for identified classes of vehicles. Under NFPA 10, all commercial vehicles must carry at least one fire extinguisher (size/UL rating depending on type of vehicle and cargo, ie. fuel tankers typically must have a 20lb. when most others can carry a 5lb.).

A fire extinguisher fitted to the passenger seat of a car.

Varying classes of competition vehicles require fire extinguishing systems, the simplest requirements being a 1A10B.C.E. hand-held portable extinguisher mounted to the interior of the vehicle.

Types of extinguishing agents

Dry Chemical:

  • Ammonium phosphate, used on class A, B, and C fires. It receives its class A rating from the agent's ability to melt and flow at 350 degrees to smother the fire. More corrosive then other dry chemical agents.
  • Sodium bicarbonate, used on class B and C fires. Interrupts the fire's chemical reaction.
  • Potassium bicarbonate (aka Purple-K), used on class B and C fires. About two times as effective on class B fires as sodium bicarbonate. The preferred dry chemical agent of the oil and gas industry. The only dry chemical agent certified for use in AR-FF by the NFPA.

Foams:

  • AFFF (aqueous film forming foam), used on A and B fires and for vapor suppression.
  • AR-AFFF (Alcohol-resistant aqueous film forming foams), used on fuel fires containing alcohol. Forms a membrane between the fuel and the foam preventing the alcohol from breaking down the foam blanket.
  • FFFP (film forming fluoroprotein) contains naturally occurring proteins to create a foam blanket that is more heat resistant than the synthetic AFFF foams.
  • CAFS (compressed air foam system) Any APW style extinguisher that is charged with a foam solution and pressurized with compressed air. Generally used to extend a water supply in wildland operations. Used on class A fires and with very dry foam on class B for vapor suppression.
  • FireAde, a foaming agent that emulsifies burning liquids and renders them non-flammable. It is able to cool heated material and surfaces similar to CAFS. Used on A and B (said to be effective on some class D hazards).
  • Wet Chemical (potassium acetate) extinguishes the fire by forming a crust over the burning oil. Generally class A and K only.

Water:

  • APW (air pressurized water) cools burning material by absorbing heat from burning material.
  • Water Mist uses a misting nozzle to break up a stream of distilled water to the point of not conducting electricity back to the operator. Class A and C rated.

Clean Agents:

  • Halon, a gaseous agent that smothers the fire. Classes A, B, and C. Banned from new production; replaced by Halotron.
  • CO2, a gaseous agent that smothers the fire. Classes B and C.

Class D:

  • Sodium Chloride and Copper forms a crust over the burning metal and performs like a heat sink to draw heat away from the burning material, also smothers to a degree.

Maintenance

An empty fire extinguisher which was not replaced for years.

Most countries in the world require regular fire extinguisher maintenance by a competent person to operate safely and effectively, as part of fire safety legislation. Lack of maintenance can lead to an extinguisher not discharging when required, or rupturing when pressurized. Deaths have occurred, even in recent times, from corroded extinguishers exploding.

There is no all-encompassing fire code in the United States. Generally, most municipalities (by adoption of the International Fire Code) require inspections every 30 days to ensure the unit is pressurized and unobstructed (done by an employee of the facility) and an annual inspection by a qualified technician. Hydrostatic pressure testing for all types of extinguishers is also required, generally every five years for water and CO2 models up to every 12 years for dry chemical models.

Recently, the National Fire Protection Association and ICC voted to allow for the elimination of the 30 day inspection requirement so long as the fire extinguisher is monitored electronically. According to NFPA, the system must provide record keeping in the form of an electronic event log at the control panel. The system must also constantly monitor an extinguisher’s physical presence, internal pressure, and whether an obstruction exists that could prevent ready access. In the event that any of the above conditions are found, the system must send an alert to officials so they can immediately rectify the situation. Electronic monitoring can be wired or wireless.

In the UK, three types of maintenance are required:

  • Basic Service: All types of extinguisher require a basic inspection annually to check weight, correct pressure (using a special tool, not just by looking at the pressure gauge) and for signs of damage or corrosion (the powder used in Dry Powder type fire extinguishers tend to settle, the technician is unable to physical confirm this and is forced to open the extinguisher); Tests conducted by SABS in South Africa have proven that by adding "powder indicators," steel balls would give the technician or owner the opportunity to first shake the dry-powder fire extinguisher to physically hear/feel the movement of the indicating balls thus confirming the condition of the powder. These indicators can be further used to test the different types of powders presently available.
  • Extended Service: Water, Wet Chemical, Foam, and Powder extinguishers require a more detailed examination, including a test discharge of the extinguisher, and recharging if satisfactory, every five years;
  • Overhaul: CO2 extinguishers, due to their high operating pressure, are subject to pressure vessel safety legislation and must be hydraulic pressure tested and date stamped every 10 years.


Notes

  1. Australian Department of the Environment and Heritage, Halon Disposal: Ozone Protection. Retrieved October 29, 2007.

References

  • National Fire Protection Association. 2003. Sudbury, MA: Nfpa Guide to Portable Fire Extinguishers. Sudbury, MA: Jones & Bartlett Publishers. ISBN 0877654786
  • National Fire Protection Association. 1992. Portable Fire Extinguishers: Fighting Small Fires. Quincy, MA: National Fire Protection Association. ISBN 0877653852
  • National Fire Protection Association. 1994. Standard for Portable Fire Extinguishers. Quincy, MA: National Fire Protection Association. ISBN 0317630407

External links

All links retrieved April 10, 2017.


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