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Fire Extinguisher, Classes, Types, Selection Criteria and its Inspection Explained

You must have seen a red colored small cylinder hanging on a wall place at highly identifiable location in your school, college, office or any workplace. That red cylinder is called fire extinguisher, these are mandatory safety equipment to keep in places of potential fire hazards, in the hands of a rightly trained man fire extinguishers can save people and property from fire in its early stages. If you are an engineer or a safety office you might know about this piece of equipment but most of us don’t know much details about the widely used fire extinguishers, types of fire extinguishers, selection of fire extinguishers and its inspection requirements.

What is a Fire Extinguisher?

A fire extinguisher is a small, portable, movable and active piece of equipment use to extinguish or prevent small accidental fires. Fire extinguisher can control small fires in emergency conditions however, they shouldn’t be used on out of control fires. A fire extinguisher is a small cylindrical vessel containing a special material that can extinguish of control the fire when that material is directed onto the fire. This substance has an ability to control a fire that is spread on a small area. Fire Extinguisher is like a first aid against accidental fires. A personal can easily operate this device. Non cylindrical fire extinguishers are very less common.

Parts of a Fire Extinguisher

Almost all the fire extinguishers are consisting of similar type of parts, although the extinguishing agent which is filled inside the fire extinguisher may differ depending upon the type of fire and fire origin. Common parts are:

  • A cylindrical pressurized vessel that contains the fire extinguishing agent.
  • A release mechanism consisting of a squeeze and release handle, valve assembly, pressure gauge.
  • A safety mechanism consisting of a seal and a safety pin.
  • A hose with a nozzle for directing extinguishing agent to fire.
Fire Extinguisher Parts

Classes of Fire Extinguisher

Before selecting or installing a fire extinguisher it is very important to know about its characteristics, different types of fires require different type of extinguishing agents. So, on this bases fire extinguishers are classified into 6 categories.

Class A

These fire extinguishers are used to put out Class A fires like ordinary combustible materials such as wood, cloth, paper, fabric, rubber and many plastics.

Class B

These fire extinguishers are used to put out Class B fires in flammable and combustible liquids, petroleum greases, tars, oils, oil-based paints, solvents, lacquers, alcohols.

Class C

These fire extinguishers are used to put out Class C fire hazards that involve fires caused by combustion of gases such as methane, propane, hydrogen, acetylene, natural gas and city gas.

Class D

These fire extinguishers are used to put out Class C fire in combustible metals, such as magnesium, titanium, zirconium, sodium, lithium, and potassium.

Class E

These fire extinguishers are used to put out Class E fires that involve energized electrical equipment. However, in many countries it is termed as Electrical fire class not Class E and was formally classified as Class C.

Class F

Class F fire extinguishers find their use to extinguish class F fires characterized by fires from combustible cooking media such as cooking oils, vegetable oils, fats, butter, etc. In some standards it is termed as Class K rather than Class F.

Note that, the above fire extinguisher classes may slightly differ from country to country. The comparison is tabulated below for guidance:

Comparison of Classes of Fire according to International Standards

Types of Fire Extinguishers

Depending on the type of extinguishing content in inside the vessel, 7 types fire extinguishers are available.

These are:

  • ·     Water Fire Extinguisher
  •     Foam Fire Extinguisher
  •     Powder Fire Extinguisher
  •     Carbon Dioxide (CO2) Fire Extinguisher 
  •     Wet Chemical Fire Extinguisher
  •     Dry Chemical Fire Extinguisher
  •     Clean Agent Fire Extinguisher

Water Fire Extinguisher

Water is used as primary extinguishing liquid in these types of fire extinguishers with other additives. This is the most economic and simplest fire extinguisher amongst all. These are suitable to control and putt off class A type fires, they have bright red label on them. Water fire extinguishers are widely used in homes, shops, offices, retail stores, schools, warehouses and hospitals etc. A drawback of these water fire extinguishers is that it cannot be used in freezing conditions.

Water type fire extinguishers are of four types.

  •         Water Jet Extinguishers
  •         Water Spray Extinguishers
  •         Water Extinguishers with additives
  •         Water mist Extinguishers

Water jet extinguisher throws a water jet at the burning medium forcing the material to cool down. Water spray extinguishers uses a fine spray such that it suspends in the air around the fire preventing from further expansion. A foaming chemical is added in the water fire extinguishers with additives that help in effective soaking into the burning materials. Water mist fire extinguisher applies fine droplets of fog or mist. Due to this mist these droplets have more surface area hence covering more burning area, quickly evaporating and removing the heat energy from the fire.

Foam Fire Extinguisher

AFFF (aqueous film-forming foam) and FFFP (film-forming fluoroprotein) fire extinguishers are rated for use on both Class A and Class B fires. Foam fire extinguishers blanket the fire with a foam generated when the spray hits the air. This blanket of foam prevents the fire from further spread and vapors reaching the air, also the water in the foam acts as a cooling agent to minimize the possibility of re-ignition. Foam fire extinguishers carry a cream label.

Powder Fire Extinguisher

Power fire extinguishers are multi-purpose and are commonly known as ABC extinguishers as they can be utilized in the event of a class A, B or C fire scenario. However, this type of extinguisher should not be used in an enclosed space. This is because the powder can be easily inhaled and is very difficult to clean up after the fire has been extinguished.

Fine chemicals in powder form as extinguishing agents are released by the powder extinguishers to blanket the fire and suffocate it. The common powder is mono-ammonium phosphate. Powder fire extinguishers carry a blue label.

Carbon Dioxide (CO2) Fire Extinguisher

Carbon dioxide (CO2) fire extinguishers are used for electrical hazards. The principal advantage of Carbon Dioxide (CO2) fire extinguishers is that the agent does not leave a residue after use. This can be a significant factor where protection is needed for delicate and costly electronic equipment. Carbon dioxide extinguishers are listed for use on Class B and Class C fires.

Carbon dioxide fire extinguishers blanket the fire by cutting off the air supply which in turn removes oxygen, required for fire to continue. CO2 fire extinguishers carry a black label.

Wet Chemical Fire Extinguisher

The wet chemical extinguishers are highly efficient extinguishers and ideal for fire hazards
involving cooking oils and vegetable fats (Type F or type K fire class). The liquid agent has a PH of 9.0 or less. They contain a potassium solution that rapidly knocks the flames out, cools the hot oil, and seals the liquid surface with a thick soap-like substance generated by a chemical reaction. This soap-like substance prevents re-ignition. Wet chemical fire extinguishers can also be used for class A fires and they carry a yellow label.

Clean Agent Fire Extinguisher

Clean fire extinguisher is a gaseous fire suppression system. The extinguishing agent is stored as a liquid in the cylindrical vessel but it converts to an eco-friendly, non-conductive, gas when it comes in contact with the air. This gas then makes a blanket around the fire reducing the oxygen levels. These fire extinguishers are widely used for Class B and E-type fire.

The following table will provide an overview of fire extinguisher type chart:

Fire Extinguisher Types Chart

Selection of Fire Extinguisher

While selecting a fire extinguisher, the engineer must identify the reason of fire and its origin so that class of the fire could be determined. If the fire hazard is a mix of 2 or 3 fire classes, it is important to select a fire extinguisher that can drop off all the present hazards. 

The manufacturers provide the rating for the extinguisher and that is specified on the product label affixed to the extinguisher. The main factors that should be considered while selecting a fire extinguisher are:

  • Fire Extinguishers of certain fire hazard types may not be effective against fires of a different hazard class. Even, it may increase the fire severity if not selected carefully. 
  • Extinguishers intended for certain types of hazards can increase personnel hazards for users when used against different hazard class fires. 
  • Extinguishers rated for multiple fire hazards may have different levels of effectiveness for each hazard. 
  • Fires involving metals are controlled by class D extinguishers. Note that, an extinguisher that may be highly effective in one type of metal fire, may be dangerous on other types of metallic fires. 
  • Class F (K) fire extinguishers for controlling kitchen fire exposures may not be suitable for conventional usage.

Fire Extinguisher Inspection

NFPA 10 provides guidelines for the inspection requirements of fire extinguishers, to get to know if fire extinguisher will work properly during fire events. This inspection is carried out by certified safety professionals, performing an inspection is the easiest thing you can do to ensure your extinguisher can be used reliably and effectively in an emergency. At a minimum, inspection needs to consist of the following steps:

  • Availability: Make sure it is located at designated place and can be easily accessible, and visible. 
  • Physical State: Make your fire extinguisher is physically intact, there is no damage, clogged nozzle, handle is operational, tamper seal in unbroken, locking pin is intact, and operating instructions are visible. 
  • Pressure Gauge & Weight: Inspect the pressure gauge and weight of the fire extinguisher by ensuring that the gauge is at operable range and vessel is full. For wheeled extinguishers check the wheels on the trolley, nozzle and hose. 
  • Inspection Tag: Ensure that inspection tag on fire extinguisher is filled and extinguisher is being properly inspected.

Any observation should be informed to the concerned person for necessary action and a report must be prepared indicating the date of inspection. Such fire extinguisher inspection reports must be maintained for at least 12 months. Depending on the type of extinguisher, an internal examination of fire extinguishers must be conducted within 1-6 year intervals.

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