Element 7: Principles of Fire Initiation & Spread & Fire Risks Caused by Construction Activities. Flashcards
What are five classifications of fires according to fuel type?
1) Class A - Solid materials, paper, wood, coal, packaging material & textiles.
2) Class B - liquids or liquefiable solids, petrol, diesel, paraffin, oil, grease.
3) Class C - Gases, methane, propane, butane, acetylene & mains gas.
4) Class D - Metals, eg. Aluminium, magnesium.
5) Class F - High temperature fat.
What are 4 basic principles of heat transmission & fire spread?
• Convection - Hot gases from fire rise up & ignite combustible materials. Outdoors convection currents carry hot embers which can carry fire to another location.
• Conduction - Heat transmitted through solid materials.
• Radiation. Infrared waves travelling in straight lines can pass through transparent surfaces.
• Direct burning- Flame spreads through material on fire til all consumed.
Identify 3 ways of stopping a fire.
• Remove oxygen - smother (fire blanket, foam, dry powder).
• Remove heat - cool with water or carbon dioxide
• Remove fuel - turn off gas/electricity/oil supply
What 3 topics should a fire risk assessment address?
1) A site plan
2) The fire hazards & their level of risk
3) Fire control & evacuation measures
What considerations should be made when identifying fire hazards in risk assessment?
Looking around construction site, including existing buildings being worked in & temporary accommodation for sources of heat, fuel & oxygen which together might lead to fire.
What should site emergency plan cover & where should it be kept?
Location of all main fire hazards & protective measures on site.
Kept in Construction Phase Plan.
Precautions identified will become part of site induction.
How might you minimise risk of fire in woodworking area?
Ensuring that wood shavings & dust are cleared regularly & ignition sources such as sparks from electrical equipment do not come in to contact with combustible materials.
What precautions should be taken when using flammable liquids?
• Volume minimised (up to 250l usual).
• Held in appropriate (usually metal), correctly labelled containers with secure lids.
• Decanting from one container to another minimised reducing risk of spillage.
• Storage area well ventilated.
• Drip trays & proper handling aids provided.
• Method for dealing with spillages & disposal of empty containers & contaminated waste required.
What are hazards associated with LPG?
LPG is colourless liquid which evaporated into gas to form flammable or explosive mixture. Heavier than air can collect in drains gullies cellars & excavations where it can accumulate & lead to possible asphyxiation. Not easily detected by smell.
Can cause frost/ cold burns to skin & risk of fire or explosion especially in unventilated places.
Cylinders vulnerable to impact from equipment near. Leaks from faulty valves & pipe connections.
Cylinder give rise to manual handling problems & proper risk assessment required.
What are requirements for safe storage of LPG?
• Cylinders should be stored upright (unless designed otherwise- LPG fuelled forklift trucks)
• Stored in suitable containers with valves uppermost, open air position protected from sunlight & falling material.
• Storage areas Suitably signed, warning sign where explosive atmosphere can occur.
• LPG storage is classified as hazardous place, i.e. in zonal classification.
• Not stored beneath beneath overhead cables or in path of falling materials.
• Planning- to ensure no. Of cylinders kept small as reasonable.
• Clearly marked “Highly flammable LPG, with design pressure & temperature.
• Correct regulators used & pipe colour coded orange.
• Not stored next to oxygen or other flammable gases, e.g. Acetylene or oxidising agents, or near any cellars, drains, excavations.
• Full stored separately to empty & separate from bulk containers.
• Suitable fire extinguishers available in event of accident (foam/powder).
- Upon what does fire resistance for
Timber depend?
Four T’s
• Thickness (cross sectional)
• Tightness of any joints involved.
• Type of wood
• Treatment received
Upon what does fire resistance for reinforced concrete depend?
• Type of aggregate used.
• Thickness concrete over reinforcing rods.
Upon what does fire resistance for a brick wall depend?
• Thickness
• Applied Rendering/plastering
• Load bearing or not.
• Perforations/cavities within bricks
Describe affects of fire on unprotected steel beam.
Describe how flame retardant paint protects covered timber.
Bubbles rather than burns thereby giving added protection
Describe conditions that determine 3 zones used to identify hazard areas (UK DSEAR)
• Zone 0 - explosive atmosphere present continuously or for long periods.
• Zone 1 - explosive atmosphere likely to occur in normal operation.
• Zone 2 - explosive atmosphere not likely to occur in normal operation, if it does, it is only short time.
What are limitations of manual alarm system & how May they be overcome?
• Only raise alarm limited area for limited time.
• Overcome with means for person raising alarm to make it more widespread - Phone, public address system, manual/ electric system.
Identify the 3 ways in which fire may be detected and state the types of automatic detector associated with each.
• Smoke/Fumes by ionisation or optical smoke detector.
• Flames by ultraviolet & infrared radiation detector.
• Heat by fusion or expansion heat detectors.
Identify classes of fire for which water is suitable.
Water - Class A
Identify classes of fire for which carbon dioxide gas is suitable.
Carbon dioxide Gas - Class B & electrical fires).
Identify classes of fire for which Dry powder is suitable.
All classes except F
Identify classes of fire for which foam is suitable.
Foam- Class A&B (Specialist foams for elec fires)
Identify classes of fire for which Fire Blankets are suitable.
Classes B & F
State colour coding requirements for portable fire extinguishers.
• Water - white lettering.
• Carbon dioxide - black.
• Foam - Cream.
• Dry powder - Blue.
• Halon - Green (rare)
