(Material correct at 1/11/2011)

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1 NEBOSH International Diploma in Occupational Health & Safety Unit IC INTERNATIONAL WORKPLACE AND WORK EQUIPMENT SAFETY element IC3 WORKPLACE FIRE RISK ASSESSMENT Sample material (Material correct at 1/11/2011) RRC Training St George s Road London SW19 4DS United Kingdom T +44 (0) F +44 (0) info@rrc.co.uk Skype ID rrctraining

2 Fire Detection and Alarm Systems and Procedures Key Information All buildings should have provision for detecting fire and sounding an alarm in the event of fire. The type of detection/alarm system used will be determined by the type of occupancy and escape strategy. A fire detector identifies physical changes in the protected environment indicative of the development of a fire condition such as combustion products, visible smoke, flame/illumination or temperature rise. The types of detector designed to identify these conditions are: Ionisation smoke detectors. Optical detectors. Radiation detectors. Heat detectors. Manual alarm systems are suitable for small workplaces and include rotary gongs, hand strikers, handbells, whistles, air-horns. An automatic fire alarm system may be designed to respond to heat, smoke and the products of combustion and flames and may incorporate a facility for additional functions, such as closing down ventilation or air conditioning plant, or activating automatic door releases. Common Fire Detection and Alarm Systems and Procedures Fire Warning Signal Design and Application of Fire Detection and Alarm Systems As a basic provision, workplaces should have arrangements for: Sounding an alarm in the event of fire. Evacuating staff to safe fire assembly points using means of escape routes. Fighting the fire. In order to determine the most suitable type of detection/alarm system for a particular building, it is necessary to establish the type of occupancy and escape strategy: If the escape strategy is based on simultaneous evacuation then activation of a manual call point or detector should cause all fire alarm sounders to operate. If the escape strategy is based on phased evacuation (large organisations such as college and university campuses where full evacuation is often not necessary) a staged alarm system might be more appropriate (one tone for alert, another for evacuate). The provision for detecting fire will depend on the nature of the building, use and occupants and should be considered in the fire risk assessment. In simple cases detection might be by people either observing or smelling the fire and verbal warning of fire sufficient to raise the alarm or a rotary gong. In more extensive premises buildings would need electrically operated fire alarms and a fire-warning signal distinct from other signals in use. Regular tests of an alarm system will check the circuits and help staff to identify the alarm tone. RRC Training Unit IC Element IC3 3-5

3 Principal Components of Alarm Systems Detection and Signalling A fire detector identifies one or more physical changes in the protected environment which indicate the development of a fire condition. Detectors can be activated by smoke or heat/light radiation arising: After ignition has occurred and the invisible products of combustion are released. When visible smoke is produced. When the fire produces flame and a degree of illumination. When the temperature in the vicinity of the fire rises rapidly or reaches a predetermined value. Smoke Detector The types of detector designed to operate in this way are: Ionisation smoke detectors. Optical detectors. Radiation detectors. Heat detectors. The final choice depends on the risk to be protected and the individual circumstances of each case (see the following table). Unit IC Element IC3 3-6 RRC Training

4 Type Smoke Ionisation Sensitive in the early stages of a fire when smoke particles are small. Sensitivity tends to drop as particles grow in size. Optical Most effective in situations where the protected risk is likely to give rise to dense smoke (i.e. large particles). Radiation Infra-red Rapid detection because of almost instantaneous transmission of radiation to the detector head. This is dependent, however, on the detector having a clear view of all parts of the protected area. Ultra-violet As for infra-red. Heat Fusible alloys Alloys will need replacing each time detector operates. Expansion of metal, air and liquid Generally self-resetting. Electrical effect Not widely installed. Some specialist use. Note for all types of heat detectors May be used as point or line detectors and are designed to operate at a pre-selected temperature ( fixed-temperature type) or on a rapid rise in temperature ( rate-of-rise type) or both. With all heat detectors (particularly fixed-temp types), thermal lag needs to be considered when choosing the operating temperature. Detectors vary in suitability and a combination of different detectors may be required: Smoke and heat detectors are suitable for most buildings. Radiation detectors are particularly useful for highroofed buildings, e.g. warehouses, and situations in which clean-burning flammable liquids are kept. Laser infra-red beam detectors appear to have advantages where there are tall compartments or long cable tunnels, for example. Automatic Fire Detectors Suitability Areas having a controlled environment, i.e. free from airborne dust, etc., and generally housing complex equipment of a high intrinsic value, e.g. computer installations. Normally used as point detectors but have been developed to form zone sampling systems by monitoring air samples drawn through tubes. Warehouses or storage areas, etc. Detectors are available which can scan large open areas and will respond only to the distinctive flame flicker. Can be used to detect certain chemical fires. The ultra-violet detector tends to be used mainly for specialised purposes. Areas of general risk where vapour and particles are normally present. Cost is relatively low compared to other types of detectors. Both fixed-temp and rate-of-rise are equally efficient but fixedtemperature types are preferred in areas where a rapid rise in temperature is a likely result of the normal work processes. Rate-of-rise types will compensate for gradual rises in ambient temperature and are more efficient than the fixed-temperature type in low-temperature situations. ( Rate-of-rise detectors generally incorporate a fixed-temperature device.) Selection will also need to consider the nature of the risk to be protected in order to establish: Reliability required (a more robust detector is necessary in an industrial setting than is required for hotel purposes, since dusty or damp atmospheres will affect some detectors more than others). The sensitivity required. The location of detectors in the best possible place to perform their function. RRC Training Unit IC Element IC3 3-7

5 Manual and Automatic Systems Manual Systems Manual systems are suitable for small workplaces. They involve the use of the following basic devices: Rotary gongs sounded by turning a handle around the rim of the gong. Hand strikers such as iron triangles suspended from a wall accompanied by a metal bar which is used to strike the triangle. Handbells. Whistles. Air-horns. They are normally found on the walls of corridors, entrance halls and staircase landings, in a situation where they are readily available to anyone who may need to raise an alarm. Such systems give an alarm over a limited area, and are inadequate for giving a general alarm throughout the premises. As a person is required to operate manual systems a continuous alarm cannot be guaranteed for as long as may be necessary. Manual/Electric Systems These systems are set in motion manually but operate as part of an electrical alarm circuit. Call points in a manual/electric system are usually small wall-mounted boxes designed to operate either: Automatically, when the glass front is broken, or When the glass front is broken and the button pressed in. Automatic Systems Automatic systems may be designed to alarm on detection of: Heat. Smoke. Products of combustion and flames. They may incorporate automatic facilities to: Close down ventilation or air conditioning plant. Activate automatic door releases. All alarm systems should be maintained and tested regularly and the results recorded. Any faults discovered should be corrected and the system rechecked. Staff should know how to raise the alarm and what to do when the fire alarm sounds. Revision Questions 3. Name the four types of detector commonly used in buildings. 4. Explain the benefits of regular testing of fire alarms. 5. For what types of workplaces are manual alarm systems suitable? (Suggested Answers are at the end of Unit IC.) Unit IC Element IC3 3-8 RRC Training

6 Fire-Fighting Equipment Key Information Fixed ( passive ) fire-fighting systems fall into four main categories: sprinklers, drenchers, total flood systems and deluge systems. The main types of extinguishing agent used in fixed installations are: water, foam, carbon dioxide, halon and dry powder. Fires are classified as follows: Class A - Solid materials Class B - Flammable liquids and liquefied solids Class C - Gases and liquefied gases Class D - Flammable metals Class F - High temperature cooking oils Each class has can be extinguished using different agents. Extinguishing a fire is based on removing one or more sides of the fire triangle: Removing the fuel by starvation. Removing the oxygen by smothering. Removing the heat by cooling. Fire-fighting equipment should be sited in an easily seen and reached position, regularly inspected and maintained, and persons required to use it suitably trained. Design and Application of Fixed Fire- Fighting Systems and Equipment Fixed fire-fighting systems fall into four main categories. Sprinklers Independent, sealed sprinkler heads which rupture in the immediate vicinity of the fire (limiting water damage). Have a rating ranging from LH (light hazard) through OH (ordinary hazard) to HH (high hazard). Drenchers Designed to protect adjacent buildings or facilities from the effects of radiated heat. Provide a curtain of water over parts of a building (or openings). Commonly used to protect large gas storage tanks. Total Flood Systems Render the atmosphere inert by dilution or flame interference (CO 2 or halon). Dangerous to occupants and therefore a safe system (manual lock off) must be employed. Danger of re-ignition when protected area is opened up. Deluge Systems All the discharge heads open but the flow of extinguishing agent is controlled by a single deluge valve (which may be activated by a pilot sprinkler system). Often used for high risk cases such as flammable liquid storage tanks. Fixed fire-fighting systems consist of pipework which delivers and releases an extinguishing medium when activated directly by heat or indirectly by the warning/ alarm system. Systems are likely to be installed in large buildings where: There is a high risk. Access is difficult. Equipment or stock is valuable. The main types of extinguishing agent used in fixed installations are: Water Generally used in sprinkler systems. Foam Low expansion foam is suitable for flammable liquid fires. High expansion foam is useful in inaccessible areas such as cable tunnels and basements. RRC Training Unit IC Element IC3 3-9

7 Carbon Dioxide Suitable for hazardous or valuable plant such as electrical equipment, computer areas, control rooms and sensitive materials. Halon Used in similar situations to carbon dioxide (but its use is strictly controlled for environmental reasons - alternatives to the use of halon include water mist). Dry Powder Suitable for: Flammable liquids. Electrical equipment. Situations where water damage must be kept to a minimum. Not suitable where re-ignition may occur. For water-based systems the supply of water is from two basic systems: Wet riser systems: These remain filled with water at fire mains pressure. They are subject to frost damage in unprotected areas and/or water leaks. Dry riser systems: Water is only available at the outlets when the system is connected to the fire mains or to a pumped reservoir or supply. The system is not subject to frost damage, and may be used in cold stores. Wet and dry riser sprinkler systems have independent, sealed sprinkler heads designed to open under fire conditions (through fusible solder links). Water is only directed to those heads which have been activated, since they are all independent. Deluge systems are designed for high-risk areas: They consist of pipework with open heads, the water being held back by a deluge valve. A fire-detection device trips the deluge valve and water is discharged from every head. Portable Fire-Fighting Equipment Classification of Fires Provision of portable fire-fighting equipment should be matched to the nature of the risk. The table below shows the types of extinguishing agent that would be suitable for various fire situations. Unit IC Element IC RRC Training

8 Nature of Risk Class Description Examples Extinguishing Agent A B C D Solid materials usually of organic origin (containing carbon based compounds) Flammable liquids and liquefied solids Gases and liquefied gases Flammable metals Miscible with water (capable of being mixed). Immiscible with water. Wood, paper, fibres, rubber, etc. Alcohol, acetone, methyl acetate, etc. Petrol, diesel, oil, fats and waxes Natural gas, liquefied petroleum gases (butane, propane) Potassium, sodium, magnesium, titanium F High temperature cooking oils - Gas fires can be difficult to deal with; whilst dry powder and carbon dioxide may be used to knock the flame down there is a risk of build up of gas if it cannot be turned off. In some situations it may be better to allow the fire to continue and to call the fire services. Extinguishing Media and Mode of Action Extinguishing a fire is based on removing one or more sides of the fire triangle: Removing the Fuel - Starvation. Achieved by: Taking the fuel away from the fire. Taking the fire away from the fuel. Reducing the quantity or bulk of fuel available. Removing the Oxygen Smothering. Achieved by: Allowing the fire to consume all the available oxygen. Preventing the inward flow of any more oxygen. Adding an inert gas to the mixture. Most usual method - use of a blanket of foam or a fire blanket. Removing the Heat Cooling. Achieved by: Cooling with water (absorbs heat thereby reducing the heat input into the fire). Water Foam Dry powder (ABC) Dry powder Specialist foam CO 2 Dry powder Foam Turn off the supply Liquid spills may be controlled by dry powder Special powders (m28 or l2) Dry sand or earth Graphite powder Sodium carbonate and salt and/or talc Specialist wet chemical Fire blanket (minor fire only) Types of Extinguishing Media Water Applied as a pressurised jet or a spray. Most effective means of extinguishing Class A fires. May also be used, as a spray, on Class B fires involving liquids and liquefied solids which are capable of mixing with water (methanol, acetone). May be used to cool leaking gas containers. Should never be used on: Fires involving electricity. Non-miscible liquid fires. Foam A special mixture that forms a smothering blanket over the fire, cutting off the supply of oxygen. Can be used: On Class A and B fires (some restrictions regarding Class B fires since certain types of foam break down on contact with alcohols). Dry Chemical Powder Sprayed as a cloud over the fire. Acts to smother the supply of oxygen. Can be used on Class B fires and on small liquefied gas fires (within Class C). Specialised dry powders using inert substances are also used on Class D fires, where they form RRC Training Unit IC Element IC3 3-11

9 a crust over the burning metal and exclude the oxygen. Also effective on fires involving electricity. Carbon Dioxide Gas Smothers the supply of oxygen. Effective on: Class B fires. Electrical fires. Vaporising Liquids Produce a heavy vapour which extinguishes the fire by excluding oxygen. Safe to use on Class A and B fires. Effective on fires involving live electrical equipment. Halons, widely used in portable fire-fighting equipment, have been banned in many countries since 1994, and are being phased out in others. Identification of Fire Extinguishers It is important to be able to identify the different types of fire extinguisher in use and colour coding is widely used to indicate the type of extinguishing agent inside. In Europe the harmonised standard BS EN3: 1996 specifies that all fire extinguishers should be red in colour but a zone of up to 5% of the external area may be coloured to indicate the type of extinguishing medium. The following table illustrates this colour coding system: Colour Coding for Fire Extinguishants Fire extinguisher content Water Foam Dry Powder Carbon Dioxide Wet Chemical Colour of body or label/band Red Cream Blue Black Yellow Siting of Extinguishers The correct type of extinguisher should be available for the risk it is going to protect against. The fire-fighting equipment should be sited in an easily seen and reached position, usually by an escape route. The location should be marked and should not be further than 30 metres from an alternative equipment location (see the following figure). Unit IC Element IC RRC Training

10 The location should be: Conspicuous. Readily visible on escape routes. Properly mounted. Accessible (less than 30 metres from any fire). Special extinguishers close (but not too close) to risk. Sited to avoid temperatures beyond the operating range and corrosive environments. Siting of Extinguishers Maintenance Regular inspections and examinations should be carried out on fire extinguishers by a suitably qualified technician. These will vary for different types of extinguisher but best practice is indicated below. Water Extinguishers Stored-Pressure Check that: Pressure is correct. Hoses and nozzles are not blocked. There is no corrosion. RRC Training Unit IC Element IC3 3-13

11 Discharge annually and check: Internally for corrosion. Free working of operating mechanism. Gas-Cartridge Open annually: Check the working parts and contents. Weigh the gas cartridge to check for losses. Discharge every five years. Foam Extinguishers Open annually and check that: No clogging has occurred. All the working parts are in good order. Weight of gas cartridge - loss in excess of 10% requires replacement. Discharge every two years. Dry Powder Extinguishers Annual examination. Discharge every five years. Carbon Dioxide Extinguishers Annual examination: Check contents by weighing. Examine working parts and check horn for freedom of movement. Vaporising Liquid Extinguishers Annual working order check by weighing the contents. Check by discharge every five years. Wet Chemical Extinguishers Same maintenance requirements and procedures as for foam extinguishers. Training Requirements It is very important that all personnel are familiar with the fire-fighting equipment and are able to use it correctly. The following points form a general scheme for training in the use of fire-fighting equipment: General understanding of how extinguishers operate. The importance of using the correct extinguisher for different classes of fire. Recognition of whether the extinguisher has to be used in the upright position or in the upside-down position. Practice in the use of different extinguishers (with or without a practice fire). Understanding that evacuating the building must take precedence over fighting a fire if the condition demands immediate evacuation. When, and when not, to tackle a fire (if the fire is small and has not involved the building structure, then portable extinguishers can generally be used but always see that a means of escape is maintained). When to leave a fire that has not been extinguished (as a general rule, once two extinguishers have been discharged, the fire requires specialist assistance). When leaving an unextinguished fire, try to close all doors and windows to help contain the fire. Revision Questions 6. Describe the five basic classes of fire. 7. With reference to fire extinction describe what is meant by starvation. 8. Explain why gas fires may be difficult to deal with. (Suggested Answers are at the end of Unit IC.) Unit IC Element IC RRC Training