Element 2 - Principles Of Fire And Explosion Flashcards
What are the components of a fire triangle
Fuel
Oxygen
Heat
Endothermic reaction
Absorbs heat from the surroundings. Requires energy for the reaction to take place.
Exothermic reaction
Releases energy in the form of heat light or sound.
Causes increase in temperature.
Can occur spontaneously.
May produce heat quickly and can cause explosions.
Combustion is an exothermic reaction
Stages of combustion
- Induction - vapours mix with air.
- Ignition
- Fire growth - direct, convection, conduction, radiation.
- Steady state
- Decay - fuel or oxygen consumed.
Flashpoint
The lowest temperature at which a liquid gives off sufficient vapour to form of flammable vapour/ air mixture.
Fire point
The temperature at which a fuel will continue to burn after ignition for at least 5 seconds
Ignition point
The temperature to which a material has to be heated for sustained combustion to be initiated by pilot source
Auto ignition temperature
The lowest temperature at which a substance will ignite without any additional ignition source
Vapour density
The mass of vapour per unit of volume.
Relative vapour density
The density of the Vapour relative to the density of some standard material, usually air.
Vapour pressure
The Pressure exerted by vapour when the liquid and vapour are equilibrium. example: such as in a closed vessel
Minimum ignition energy
The minimum energy that will ignite a flammable fuel/ air mixture.
Safe storage of LPG cylinders
In a well-ventilated place in open air.
Away from occupied buildings, boundaries and sources of ignition and heat
Properly secured and uprights.
Safe storage of LPG in bulk pressurized tanks
- Sufficient distance between them and buildings or sources of ignition
- Sufficient ventilation
- Tanker access from a dedicated flat parking area
- Security to protect from unauthorised access.
- Impact protection for motorway traffic.
- Emergency arrangements for leakage or fire.
Classification of fires
Class A: solids Class B: liquids Class C: flammable gases Class D: metals Class f: high temperature cooking oils and fats
Causes of Fire growth and spread
- Fuel characteristics - Ease of ignition, Heat of combustion, Fluidity of liquid.
- Fuel seperation
- Containment - open or in building.
- Room dimensions
Structural Factors that influence fire growth rates and smoke movement
Building Design - gaps in doors, ceilings walls
Insulated core panels - Fire rated insulation.
Internal linings.
Construction materials - brick, steel, timber.
Ventilation levels - natural or forced.
Contents of the premises - furnishings
Methods of heat transfer
Conduction.
Convection
Radiation
Direct burning
Categories of explosion
Detonation - supersonic
Deflagration - subsonic
Gas and vapour explosions
Confined vapour cloud explosion.
Unconfined vapour cloud explosion.
Boiling liquid expanding vapour explosion.
Classifications under EU CLP regulations (No. 1272/ 2008)
- Flammable liquid - flashpoint 23°C - 60°C.
- Highly flammable - flash Point below 23°C and boiling point above 35°C.
- Extremely flammable - flash point below 23°C boiling point less than 35°C.
Flammable (explosive) limits
Lower flammable (explosive) limit - minimum concentration of fuel in air. Upper flammable (explosive) limit - maximum concentration of fuelled air.
Methods of preventing or controlling the ignition
Equipment designed for use inflammable atmospheres.
Plant designed to maintain vapours below LFL.
Proper storage of flammable and combustibles.
Good Housekeeping.
Information instruction and training.
Safe systems of work.
Inerting.
Lining material properties that might increase fire spread.
Ignitability.
Right surface flame spread and Heat release.
Amount of smoke produced when ignited.
Tendency to produce flaming droplets.
Properties that lining material should have to limit spread of Fire
Resistance to ignition. Resistance to spread of Fire. Low smoke production. Slow rate of Fire growth Examples: exposed brick/ blockwork, mineral fibreboard, plasterboard and skim, concrete and stone.
Conditions required for a gas explosion to occur
- Presence of a combustible gas becoming airborne mixing with air.
- Concentration of gas lies between the flammable limits.
- Atmosphere contains sufficient oxygen to support combustion.
- Ignition source with sufficient heat energy.
Preventing explosions
Good Housekeeping. Ventilation. Safe storage and handling of explosive material. Control of detonation sources. Cooling.
Rules for safe storage and handling of explosive material.
Identification of explosive and potentially explosive chemicals.
Correct labelling.
Keep explosives away from ignition sources.
Designated area for explosive chemical use.
Periodic checking of chemicals that could be come over pressurised.
Ensuring workers are thoroughly trained.
Venting systems to prevent explosion
Pressure relief valves.
Bursting discs.
Venting panels.
Preventing Dust explosion
Sealing joints to prevent escape of dust. Exhaust ventilation on dust filters. Regular maintenance plant equipment. High standard of housekeeping. Insulating hot surfaces. Using intrinsically equipment. Bonding to Earth.
