Portable Fire Extinguisher Flashcards
Definition of Portable Fire Extinguishers
- An appliance for use by occupants of a building to fight fires whilst it is still in its early stage of development.
- Designed to be carried & operated by hand & should have a mass of not more than 20 kg.
- Contains an extinguishing medium, which is expelled by internal pressure and can be directed at fire.
Provision of Portable Fire Extinguishers
Are to be provided for every floor of all buildings except:
- Purpose Group I: private houses
- Purpose Group II: flats, apartments & condominiums (residential
floors) - Car parking areas in standalone car parks or mixed-use residential buildings
Limitations of Portable Fire Extinguishers
- Limited amounts of extinguishing medium & hence limited discharge time of extinguisher
- Limited range of discharging medium
- Extinguishing medium must be suitable for specific risk application
Classes of fires
- Class A
- Class B
- Class C
- Class D
- Class F
Class A Fire
combustible organic solids like paper, wood, rubber, plastics and cloth.
Class B Fires
flammable liquids such as petrol, kerosene, alcohol, solvents and paints.
Class C Fires
flammable gases such as propane and butane.
Class D Fires
combustible metals such as magnesium & lithium.
Class F fires
cooking oils and fats such as olive oil, maize oil, lard & butter.
Electrically energized fires
- Not classified as electricity by itself does not burn but can cause fires in class A, B, C, D and F materials.
- Extinguishers that contain a non-conductive medium such as CO2 can be used on fires involving energised electrical equipment.
Types of Portable Fire Extinguishers
- water
- carbon dioxide
- dry powders
- foam
- wet chemical
- vaporising liquids
Extinguishing Media: Water
- An effective cooling agent, with high specific heat capacity absorbing heat from fire.
- Especially effective on Class A fires. As water is heavy, its force can knock out a fire.
- Capable of penetrating into deep seated fires putting out any smouldering embers.
- Ordinary water extinguishers w continuous jet discharge are not safe for use on other classes of fire, cuz will spread Class B fire, conduct electricity from energised equipment, release explosive hydrogen from Class D fires & will explosively boil over on Class F fires.
Foams
- Detergent/protein-based compounds added to water to produce a film or froth that can float over the surface of Class B fires forming a vapour-proof seal that smothers a fire.
- Effective on Class A & B fires
- Allows extinction of a liquid fire & prevents re-ignition.
- Foams cannot be used on Class D fires.
- Cannot use on Class F fires as tremendous heat of burning fat destroys the foam blanket rendering it ineffective.
Dry Powders: BC Powder
- Prevent chemical reaction between heat, fuel & oxygen, thus extinguishing fire.
Most common types of powder extinguisher used are
- BC Powder
- designed for Class B & Class C fires and it does not conduct electricity.
ABC powder
- Consisting of compound that melts & flows to seal & smother Class A fires in addition to its chemical inhibition properties used on Class B & Class C fires.
- Does not conduct electricity.
- However, mono-ammonium phosphate compound causes corrosion.
Powder
- Almost multipurpose & knock down most fires in seconds but got drawbacks.
- Do not cool, reducing effectiveness on Class A fires
- Discharge is very messy & obscures vision and on Class B fires flames will flashback if the whole fire is not extinguished in one go or if an ignition source remains (unlike foam which is not affected either way).
- Enclosed electrical equipment is difficult to tackle & powder will damage electronic components by corrosion.
- ABC powder ineffective on Class F as heat of the oil causes flashback once extinguisher is empty.
- BC Powder can have a limited effect.
Carbon Dioxide (CO2)
- Non-conductive gaseous agent that displaces oxygen to smother a fire.
- Can use on live electrical equipment as it penetrates & floods enclosures & leaves no residue.
- However, once gas dissipates, fire can re-ignite, especially if equipment remains live.
- Effective on small indoor Class B fires, however, re-ignition of hot liquid is possible.
- Ineffective against Class A, D or F fires.
- Cannot use in small rooms, as the risk of CO2 poisoning is significant.
- 4% CO2 concentration is enough to cause symptoms of CO2 poisoning.
- 8% is enough to kill a person.
Wet Chemical
- Alkaline water-based solution of that reacts with burning fat of Class F fire to saponify it & turn surface into a soapy crust, sealing it from the air, allowing it to cool & preventing re-ignition.
- Produces gentle but highly effective spray and helps prevent hot oil splashing onto user.
Vaporising Liquids
- Complex chemical compounds that extinguish fires by chemical inhibition.
- Most common chemical blend used is HCFC-123 which is safe, effective and environmentally acceptable.
- Mixed with tetrafluoromethane and argon as propellants.
Class A Fire use what
- Water
- Dry powder
- Foam
- Vaporising liquids
Class B Fire use what
- Dry powder
- Foam
- Carbon Dioxide
- Vaporizing liquid
Class C Fire use what
ABC Dry powder
Class D Fire use what
Depends on type of metal
Class F Fire use what
Wet Chemical
Not Classified Fire use what
Carbon dioxide
Colour Coding of Water Fire Extinguishers
Red
Colour Coding of Foam Fire Extinguishers
Cream
Colour Coding of Dry Powder Fire Extinguishers
Blue
Colour Coding of CO2 Fire Extinguishers
Black
Colour Coding of Wet Chemical Fire Extinguishers
Yellow
Colour Coding of Vaporising Liquids Fire Extinguishers
Green
Methods of expelling Medium from Extinguisher Body
- Pressure Gauge
- Gas Cateidge
Stored pressure
- Cylinder is permanently pressurised with propellant gas, usually nitrogen.
- Upon operation a valve is opened allowing pressurised contents to be pushed out.
- Pressure gauge fitted to indicate pressure inside cylinder.
- Used for water, dry powders, foam & wet chemical fire extinguishers.
- CO2 extinguishers also operate using this method with CO2 stored as a liquid under its own vapour pressure.
- Exception is that CO2 extinguishers don’t have pressure gauge.
Gas cartridge pressure
- Internal cartridge of compressed CO2 is screwed into head cap inside main extinguisher body.
- Upon operation cartridge seal is pierced allowing CO2 inside to pressurise main body & expel contents.
Classification of Occupancy Hazards and Size of Fires
- Premises in building are classified according to severity of their hazards.
- Severity of the hazard will determine rating of fire extinguisher used in premises.
Categories of how buildings are classified according to severity of their hazards
- Low hazard
- Medium hazard
- High hazard
size of small hazard fire
- small fire expected
- consist of quantities of Class A combustibles and/or total quantity of Class B flammables expected to be less than 5 litres
examples of small hazard fire
offices, classrooms, places of worships, domestic kitchens etc
size of medium hazard fire
- Moderate size fires expected.
- Consist of Class A combustible
materials beyond anticipated furnishings, and/or total quantity of Class B flammables expected from 5 litres to 20 litres.
