Class of Laboratory Fires and Fire Extinguishers
Different types of fires and the extinguishers approved to fight them.
Rating, classification, and uses of fire extinguishers.
Related links :
Safety in the chemistry laboratory
Laboratory waste management
Classification of Fires
Fires are classified according to the materials they burn. They are coded with the capital letter of the alphabet A, B, C, D, F, etc.. with the word 'Class' placed in front of each letter. Example Class A fires, Class B fires, Class C fires etc..
Class A Fires Fires involving combustibles such as : wood, paper, boxes, plastic, packing material etc..
Class B Fires Ignition of flammable liquids such as : solvents, kerosene, gas, grease etc..
Class C Fires Fires arising from electrical equipment such as : AC outlets, wiring, appliances, flammable gases etc..
Class D Fires Combustible metal fires such as : Mg, K, Na, Al, Titanium, Lithium (includes powders and swarfs).
Class E Fires Electrical fires : Fires involving electrical apparatus.
Class F Fires Fires involving coking oils and Fats : burning hot oil, cooking oil, lard.
Class K Fires Fires in cooking utensils and appliances caused by oils and fats.
- There is no class E or class F fires in the US system of classification. Class E is equivalent to class C and class F is equivalent to class K.
- Class E is no longer applicable because when power is turned off, electrical fires can fall into any category.
Classification of Fire Extinguishers
Fire extinguishers are classified according to 'class' of fires they are made to put out. An ABC extinguisher can be used to put out a Class A, Class B, or Class C fire.
An AB extinguisher is used to out a Class A or Class B fire.
And a D extinguisher can be used to extinguish a Class D fire only.
Fire Extinguisher colors
There is no official standard for color in the US classification. Red is the preferable color except
Class D yellow
Water mist white
Fire Extinguisher Ratings
The Numerical Rating of Fire extinguishers is a measure of the Fire Power of the extinguisher.
For example, a class ABC rating is given as 5-A :10-B:C
The No. in front A gives the number of gallons of water the extinguisher is equivalent to.
One (1) unit is equal to 1.25 gallons of water. Hence, 5A = 5 × 1.25 which is equal to 6.25 gallons of water.
The No. in front B gives the number of square feet of fire it can extinguish. In the example, this will be 10 sq. ft.
The No. in front C. There is no number in front of C, which means that the extinguisher does not have a rating and the extinguishing agent is non conductive.
Class D extinguishers have no numerical rating and is non conductive.
Summary of Fires and Fire extinguishers
||Type of Fire
||Examples of Fire type
||Class A only
||Ordinary materials, paper, wood, boxes, plastics, packings etc...
||Not recommended for lab or electrical fires; leaves area water-logged|
Where possible class C hazard exists.
|Hospital environments, books, clean-rooms, MRI and NMR rooms
||Misting nozzle provide safety from electrical shock and reduce scattering of burning material|
|Dry chemical (powder)
• BC - Na or K carbonate
• ABC - ammonium phosphate
Combustible liquids, solvents and gases.
Electrical fires, appliances
|Overlaying powder reduces re-ignition|
Leaves sticky or corrosive residue that can damage electrical equipment
Isolate gas supply first for gas fires
Disconnect power for electrical fires
|Dry metal powder
• Copper agent
• NaCl agent
|Class D only
||Combustible metal fires :
(Cu) Metal and lithium alloys
(Nacl) Mg, Na, K, Uranium and Al
|(Cu) Powder adhere to vertical surfaces |
(NaCl) Cakes over surface, excludes air, dissipates heat
|Every day combustible materials
Flammable solvents and electrically charged equipment and appliances
|Leaves no harmful residue, but may re-ignite with class A fires|
Disable gas and electricity supply if necessary
Caution! Reacts with class D fires
|Not recommended but safer than water if inadvertantly used on electrical fires|
|Wood, paper, fabrics etc..
Fats, Lard, vegetable oils
Animal oil, cooking oil, butter
|Flash prevention spray|
Soapy foam prevents re-ignition
Emergency numbers :
• Fire Department Emergency Dial 990 (T&T Fire Services)
• UWI Fire Safety 662 4707
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