Safety at Work 6 E Part 13 ppsx

Fire precautions 695 4.2.7 Fixed fire-fighting equipment Fixed fire-fighting equipment is permanently fixed in a building and is designed to work automatically in the event of a fire. Essentially it comprises a system of fixed pipes with discharge heads or points for the extinguishing medium at predetermined positions. The positioning of the discharge heads is determined by the type of building, its contents, the fire risk and the type of extinguishant and is normally to standards developed by fire insurers. Once installed and commissioned fixed fire- fighting equipment must be kept in a state of instant readiness. Sprinkler systems have the advantage that only the discharge heads in the immediate vicinity of the fire rupture, thus limiting the extent of water damage to areas in the immediate vicinity of the outbreak. In older wet systems that drew their water supply from ponds and rivers, the system was kept pressurised by air pressure above the water in a storage tank. This provided an immediate supply of water to a fractured head which continued until the main pumps cut in. The flow of water actuated a hydraulic alarm gong. In modern sprinkler systems (shown diagrammatically in Figure 4.2.10) water is supplied at pressure from the town mains which charges a pressure tank. When a sprinkler head ruptures, the loss of water pressure Figure 4.2.10 Diagram of the layout of a typical sprinkler system (Manual of Firemanship. Courtesy the Controller, Stationery Office) 696 Safety at Work in the supply pipe triggers the alarm valve. The alarm is actuated by the alarm valve either by diverting part of the water flow to a hydraulic gong or by actuating an electrical alarm. The pressure tank acts as a buffer to absorb any water hammer effects and to provide a temporary water supply if the mains flow is interrupted. Gas systems contain an extinguishant gas at high pressure supplied from gas cylinders. Fixed fire fighting systems have the advantages that they can: 1 detect the fire; 2 raise the alarm; 3 attack the fire; and 4 prevent the fire from spreading; even when the building is not occupied. The most common type of fixed installation uses water as the extinguishant. However, in situations where water could present a hazard or do unacceptable damage an alternative extinguishant can be used. The different types of systems are described below. 4.2.7.1 Sprinkler systems Water sprinkler systems were first developed in the mid-19th century and the original designs used a discharge head sealed by a fusible soldered strut. These have been superceded by glass bulb sprinkler heads which, by selecting particular bulbs, can be made to rupture at a range of temperatures. The main type of sprinkler systems currently in use are: wet – where all pipes are permanently filled with water; dry – where the pipes above the main control valve is filled with compressed air that holds back a pressurised water supply. On the actuation of a sprinkler head the compressed air is released allowing water to enter the pipes and discharge through the broken head onto the fire; alternate – are used in areas where the installation is liable to freeze. The system is normally wet but is temporarily drained during winter and converted to a dry system; pre-action – systems are normally dry but are linked to an automatic fire detection system. On actuation of the detection system water enters the supply pipes and the system becomes a wet one, but water does not discharge until a sprinkler head breaks. In the UK, sprinkler systems are installed in accordance with the Loss Prevention Council (LPC) Rules 13 which incorporate Part 2 of BS 5306 10 . Further requirements are contained in Part 1 of BS EN 12259 14 . During 2002 the Fire Protection Association (FPA) produced a new set of Fire precautions 697 Sprinkler Rules based on the contents of the new BS EN standard. The LPC Rules together with the Comit´e Europ´een des Assurances (CEA) Rules 15 are now being considered with a view to producing a European standard for sprinkler installations. This may become a requirement of the Construction Products Directive, Interpretative Document for Safety in Case of Fire 16 . In the USA the National Fire Protection Association (NFPA) has revised its sprinkler rules and produced the new NFPA 13 Sprinkler Code 17 . 4.2.7.1.1 Sprinklers in the protection of buildings Fire prevention arrangements in buildings include a requirement to ‘compartmentise’ the building with at least one hour fire separation between compartments. In buildings fitted with sprinklers an Approved Document B 18 allows some relaxations of this requirement. For example, office, shop, commercial, assembly, recreation, industrial, storage and other non-residential premises a 30 minute reduction in the fire separation is allowed. Other requirements of this document include the fitting of sprinklers in all buildings over 30 metres high and sprinkler protection in all new single storey buildings having a retail floor area of 2000 m 2 or more. 4.2.7.1.2 Sprinklers for life safety Traditionally sprinkler systems were installed to protect buildings and contents rather than save life. However, in 1979 a fire occurred in a retail store in Manchester in which 10 people died. One of the recommenda- tions from the investigation into the cause of the fire was that if sprinklers had been installed the life loss may have been reduced or eliminated. At that time, while sprinklers had been well proven in the protection of building structures, there was no evidence that their installation had any effect on life safety. Research, subsequently undertaken into the role of sprinklers in saving life, has resulted in official recognition of a fire engineering approach to fire prevention in buildings. This allows a sprinkler system to be part of the overall fire safety measures in buildings to which the public have access as well as in workplaces. 4.2.7.2 Drencher or deluge system These systems are usually employed to protect high risk installations such as above ground storage tanks for highly flammable liquids or chemicals. A common arrangement, shown in Figure 4.2.11, is for the system to comprise a series of open drencher discharge heads arranged in a pattern to ensure that all parts of the installation are drenched. A second system of conventional dry sprinkler heads is interspersed with the drencher heads. The conventional system is pressurised by air which also retains the main drencher water valve in the closed position. In the event of a fire, a conventional sprinkler head will rupture releasing the air pressure and allowing the main drencher valve to open resulting in the installation being drenched. 698 Safety at Work 4.2.7.3 Water mist systems A development to replace halon systems has been water mist systems in which a system of open discharge heads is used. The system is actuated by smoke detectors located within the area to be protected. Operation of one detector raises the alarm and it requires a second detector to be actuated before the water is released into the discharge pipework. Water for the system is stored in cylinders at high pressure and the discharge heads are designed to produce a fine water mist. Water mist systems use significantly less water than a sprinkler system and extinguish fires by: Figure 4.2.11 Diagram of a typical drencher (deluge) system (Manual of Firemanship. Courtesy the Controller, Stationery Office) Fire precautions 699 1 cooling – fine droplets of water create large cooling surface area. Air entrained in the fire plume assists in the penetration of water droplets into the fire; 2 radiant heat suppression – high density of water mist and water vaporisation create a condition for high heat absorption and provide a screen to reduce radiant heat transfer; 3 oxygen level reduction – when water droplets vaporise, they expand about 1700 times and displace the air with its oxygen, thus inhibiting growth of the fire at the flame base. 4.2.7.4 Foam systems There are several different types of foam systems which can either use a traditional sprinkler pipework system employing a proportional-tank mechanical foam installation, shown in Figure 4.2.12, in the supply line to the sprinkler heads or have their own alarm system and discharge pipework incorporating a pre-mix foam installation, shown in Figure 4.2.13. Installations using high expansion foam are used to protect large areas such as aircraft hangars. In these installations a number of foam generators, each producing foam with expansion ratios of between 200 and 1200 to 1, can be connected together. For areas containing oil or Figure 4.2.12 Diagram of a proportional-tank mechanical foam installation (Manual of Firemanship. Courtesy the Controller, Stationery Office) 700 Safety at Work flammable liquids, foam inlets are provided on the exterior of the building to which the fire brigade can connect their foam-making branch pipe. Fixed piping transports the foam to the area being protected. 4.2.7.5 Dry powder systems A dry powder system comprises a container in which the powder is stored and which is connected to pipework leading to discharge nozzles in the protected area. On actuation of the system the powder is fluidised in the expellant gas (an inert gas such as nitrogen or carbon dioxide) and is conveyed to the nozzles. These systems are suitable for fires involving flammable liquids, electrical equipment or where water damage must be kept to a minimum. They are not suitable in situations where there is likely to be a heat sink such that re-ignition could occur. Standards which cover dry powder systems are contained in BS EN 12416–2:2001 19 . Figure 4.2.13 Diagram of a pre-mixed foam installation (Manual of Firemanship. Courtesy the Controller, Stationery Office) Fire precautions 701 4.2.7.6 Gas systems Gas systems are used to protect sensitive equipment such as computer suites and electrical equipment and also areas where water damage is not acceptable, such as archive stores. The gases used depend on the application but fall into three main categories: Figure 4.2.14 Diagram of battery of CO 2 cylinders supplying a small gas installation (Manual of Firemanship. Courtesy the Controller, Stationery Office) 702 Safety at Work 1 inert gases such as argon, carbon dioxide and nitrogen; 2 chemically produced gases; 3 halon gases which are now strictly controlled and the only permitted use is in specialist military and aerospace applications. The gas, at high pressure, is stored in cylinders (Figure 4.2.14) which are usually located outside the area being protected. Actuation of the system is by automatic fire detectors. Because the gases present a health hazard when installed in a workplace area, discharge is initiated in two stages. A pre-discharge alarm is sounded when the first detector operates allowing any staff present to evacuate the area. Gas discharge occurs only when the second detector is actuated. BS ISO 14520 20 series of standards covers gas fire-extinguishing systems with each part dealing with a different extinguishant. General requirements can be found in part 1 of this series. 4.2.8 Fire safety signs The posting of fire safety signs has been a legislative requirement for many years. Their primary purpose is to ensure that the occupants and users of buildings are aware, not only, of escape routes and exits but also of any hazards and dangers that may be present. 4.2.8.1 Current legislation The EU identified the need to have a unified system of signs and symbols that could be recognised throughout the Union and introduced the Safety Signs Directive 21 that has been implemented in the UK in Regulations 22 which require the provision and maintenance of appro- priate signs to: 1 warn workers of any risk to their health and safety; 2 indicate safe exit routes; 3 identify the location of fire-fighting equipment. The signs specified in these Regulations also satisfy the requirements for fire safety signs required by other legislation (such as the Fire Precautions Act 1971, The Fire Precautions (Workplace) Regulations 1997 (as amended)). The signs required by these Regulations are pictograms of specified shapes, colours and patterns that give the appropriate information. The pictograms may be supported by a written caption but written notices on their own are not acceptable as fire safety signs. The object of using pictograms is to make them understandable to all regardless of knowledge of the local language. Thus, the words FIRE EXIT on their own are not permitted but the words FIRE EXIT used in conjunction with a pictogram is allowed. To prevent confusion with other safety signs, all Fire precautions 703 safety signs relating to fire alarm and fire-fighting equipment are square or rectangular in shape with a white pictogram on a red background. The signs used on fire escape routes are the same as emergency exit signs, i.e. square or rectangular with a white pictogram on a green background. Typical examples are shown on the inside covers of this book. The appropriate fire safety signs should be used to indicate the location of fire-fighting equipment and fire alarm call points which should be on fire escape routes. If equipment and call points are located together they can be mounted on a panel to form a Fire Point. In crowded and irregular shaped work areas high level signs can make the location of fire exit routes and fire-fighting equipment easier to identify. 4.2.9 Means of escape in case of fire The principle aim in establishing a means of escape in case of fire is to provide a safe escape route that everyone who may be on the premises can follow by their unaided efforts regardless of where the fire occurs. When designing escape routes consideration must be given to the abilities and needs not only of the fit but also of the old, the young, the infirm and the disabled. The factors to be taken into consideration when assessing means of escape include: 1 an assessment of the fire risk; 2 the construction and surface finish of walls, floors and ceilings in workplaces and on escape routes; 3 the likely maximum number of occupants in the building; 4 the ability of the occupants to respond to the fire alarm and make their way to safety; 5 the distance of travel to a place of safety; 6 the degree of fire protection provided by escape corridors and staircases; 7 the provision of information and guidance such as exit, directional signs, emergency lighting, etc. Certain types of equipment that are not officially recognised as means of escape include: 1 lifts (except for a specially designed lift for evacuation of disabled persons); 2 portable ladders and throw-out ladders; 3 manipulative apparatus and appliances such as fold-down ladders, chutes, self-rescue and lowering devices. 4.2.9.1 Assessment of the fire risk When assessing the risk to the occupants of a premises from fire and the safety of the means of escape, account must be taken of the type and 704 Safety at Work materials of construction of the building, the type and condition of the contents and particularly its flammability, the likely rapidity of spread of smoke and flames and the use to which the building is being put. Fire risk assessments are dealt with in detail in section 4.2.13. 4.2.9.2 Construction and surface finish of walls, floors and ceilings The construction and surface finish of escape routes are important factors in the degree of protection provided in the event of a fire. In general, the fire resistance of escape routes should be at least 30 minutes but in high risk buildings a higher standard of protection may be necessary. Regulations 23 require that circulation spaces and escape routes should be Class O (the highest standard), rooms (except small rooms) Class 1 and small rooms and small areas other than rooms Class 3 (see also Table 4.2.4). These latter two classifications are determined by reference to criteria given in a standard 24 . These documents also cover the fire resistance of walls, floors and doors. Additional information is given in a guide 25 . 4.2.9.3 Occupancy of a building The rated occupancy of a building is the maximum number of persons, including staff, visitors or customers, that can safely be accommodated in a building at any one time. Occupancy rates can be calculated using floor space factors detailed in the documents referred to above and range from 0.3 m 2 per person for standing spectator areas to 30 m 2 per person for warehouse and storage areas. 4.2.9.4 Ability of occupants to respond Account must be taken of the types of occupants likely to be in an area or premises and of the proportion who may experience difficulties in responding to the sounding of an alarm. People in wheelchairs or who walk with sticks or crutches have an obvious disability and may well need physical assistance to evacuate the building, while people with poor sight or those suffering from hearing loss have a less obvious disability but may still need assistance in an emergency. Elderly people or young children will also need special consideration. In hospitals and other care premises the patients who are bedridden will be totally reliant on assistance to escape. Guidance on the means of escape provisions for disabled people is given in Part M of the Building Regulations 23 and also in a Code of Practice 26 . The concept of refuges and the use of evacuations lifts are covered but the most important aspect is the need for the effective management of any evacuation. All premises that are likely to contain people who are not able to respond immediately or quickly to a fire evacuation should have an emergency plan that makes special provisions [...]... high temperatures, on this occasion caused by the ignition of aviation fuel 4.2.12 Legal requirements For many years, premises of all types have been subject to legislative requirements to have adequate fire precautions These requirements 712 Safety at Work were often enforced through the Fire Authority’s powers to issue fire certificates However, recent legislation has shifted the emphasis of the responsibility... requirements from the EC Framework Directive35 and the Workplace Directive 36 In doing so these Regulations were extended to include vehicles, offshore installations, tents or moveable structures as workplace premises, but do not include those premises already covered by or that have applied for a Fire Certificate They place obligations on the employer or persons who have control of premises to meet the... any one time or more than 10 elsewhere than on the ground floor A fire certificate is also required for factories storing or using highly flammable or explosive materials regardless of how many people are working in the premises Fire Authorities have the power to exempt premises from the requirement to have a fire certificate if they consider the fire risk to be low and there are adequate fire safety. .. available to the designer and user of modern equipment What is not dealt with is the other vital element in the interface – the operator – and the training necessary to ensure his/her safety and how it matches the equipment, the culture and the working methods of the particular organisation Essentially the term work equipment encompasses any equipment used in the course of work However, in this chapter work. .. the effectiveness of the control measures and review the risk assessment at regular intervals The records made of each fire risk assessment should be used as the basis for monitoring the effectiveness of the measures taken 4.2 .13. 1 Fire risk categories For ease of application it is convenient to categorise the fire risk in each defined area as either high, medium or low The criteria used for determining... fire extinguishing systems such as sprinklers, drenchers or gas systems operate when the heat of the fire in the region of a detector head reaches predetermined levels and cause the seal in the detector head to fracture releasing the extinguishant These systems can incorporate a facility to raise the alarm 4.2.11.1.5 Active fire protection and smoke stop doors Pedestrian and vehicular movement between... specific requirements in respect of fire, fire prevention, or fire precautions are contained in the Health and Safety at Work etc Act although under s 78, FPA was extended to include places of work 4.2.12.2.1 Fire certificates Section 1 of the FPA authorises the designation of those premises that are required to have a Fire Certificate Only two Designating Orders have been made in respect of: 1 hotels and... Precautions (Workplace) Regulations 1997, The Stationery Office, London (1997) European Council Directive no 89/391/EEC, On the introduction of measures to encourage improvements in the safety and health of workers at work (the Framework Directive), EU, Luxembourg, (1989) European Council Directive no 89 /65 4/EEC, concerning the minimum safety and health requirements for the workplace (the Workplace Directive),... fire matters It is the findings of a fire risk assessment that will determine the type and number of fire extinguishers to be provided Under the Fire Precautions (Workplace) Regulations 1997 the findings of a fire risk assessment must be recorded The fire risk assessment should cover a defined area of the workplace In small premises the defined area could be the whole premises whereas for larger places... themselves known to the relevant services before an emergency arises; 6 appoint area wardens whose duties will include ensuring their area of responsibility has been evacuated; 7 make arrangements to ensure the safe evacuation of any staff who need special assistance, e. g disabled person; 8 train all employees in the emergency plan procedures The emergency plan should be in writing to prevent any ambiguity . adjacent areas and be linked automatically to the local fire brigade. They have the advantage that they give protection even when the premises are unoccupied. Between these two extremes are the. extinguishing systems such as sprinklers, drenchers or gas systems operate when the heat of the fire in the region of a detector head reaches predetermined levels and cause the seal in the detector head to fracture. people are working in the premises. Fire Authorities have the power to exempt premises from the requirement to have a fire certificate if they consider the fire risk to be low and there are adequate