Chapter 8: Fire Detection And Warning
305. A fire warning system allows occupants to be alerted and the emergency fire action plan to be implemented. In some small premises, a fire may be obvious soon after it starts. In such cases and where travel distances are short, a shouted warning of 'fire' or a simple manually operated device that can be heard throughout when operated from any single point within the building, may be all that is needed.
306. In larger premises, particularly those with more than one floor or that are multi occupied, where a shout or warning sounded from a single point will not be heard throughout, an electrical fire alarm system incorporating sounders and manually operated call points is likely to be required. In large or complex premises, particularly those accommodating large numbers of people, a more sophisticated fire alarm system may be required.
307. Information on maintenance and testing of fire warning systems is in Chapter 4. Guidance on the design, installation and maintenance of fire detection and warning system is contained in BS 5839: Part 1.
308. Where an electrical fire alarm system is considered necessary, a fire warning system in accordance with the guidance in BS 5839: Part 1 for a category M system is likely to be appropriate for many premises. A category M system is operated by manual call points only.
309. Where automatic detection of fire is necessary for life safety, the system will be designated as a category L system, within which there are subdivisions L1 to L5.
- L5 is a system designed to achieve a specific fire safety objective;
- L4 is a system which provides warning of smoke within escape routes;
- L3 is a system designed to give a warning before escape routes are impassable;
- L2 is a system designed to give warning before escape routes are impassable but with enhanced coverage in specified areas; and
- L1 is a system installed throughout all areas of the building.
310. In areas where an explosive atmosphere could result from the presence of flammable gases, vapours, mists, or dusts, an electrical fire alarm system will require the same consideration as would other electrical equipment in respect of protection to prevent the potential for ignition.
311. An enclosed shopping centre, will have a category L1 automatic fire detection and alarm system. The system should also actuate upon the operation of the sprinkler system. alerted using a voice alarm system however, individual shops may have conventional sounders.
312. Manual call points, often known as 'break-glass' call points, enable a person who discovers a fire to operate the fire warning system and immediately raise the alarm to warn other people in the premises. Manual call points are normally positioned at exit doors. They should be conspicuous and positioned no higher than 1.4 m from the floor, but may be reduced to make accessible to wheelchair users. Building occupants should not have to travel more than 45 m to reach the nearest call point. Where there is particularly high hazard equipment or activity, it may be desirable to have a call point located in close by to allow early warning to be given.
313. A hinged cover on the call point can be a deterrent where there is the potential for malicious operation or accidental damage.
314. In some premises, such as assembly or entertainment premises where there is high potential for malicious operation, call points may be sited in positions readily accessible only to staff, such as behind bar counters or in box offices, if these positions are staffed at all material times.
315. Conventionally sited call points that operate a general alarm are not desirable in supervised transport premises due to the potential for malicious or accidental operation which may promote unnecessary evacuation. Alternative arrangements will be appropriate.
Automatic Fire Detection
316. Existing fire warning systems may have automatic fire detection incorporated for the purpose of property protection, or speculatively because the end use of the building was unknown, or just to have a very high specification. However, the inclusion of automatic fire detection in a fire warning system is only required under fire safety law when it is needed to safeguard life on the basis of risk. Examples of the use of automatic fire detection for life safety in non-residential premises are:
- To ensure an early warning of fire in situations where a fire could develop and affect escape routes before a building could be evacuated;
- To operate smoke control systems or door release devices; and
- To ensure early warning of fire where this is necessary to allow the use of phased or staged evacuation.
317. Where the layout of the premises is such that a fire could develop to the extent that escape routes could be affected before the fire is discovered, it may be necessary for the fire alarm system to incorporate automatic fire detectors to ensure an early warning. This may be the case where there are unoccupied areas or circulation areas in multi-occupied buildings or where people work alone and might not see a fire; but the need for the provision of automatic fire detection will be influenced by the means of escape available.
318. Automatic fire detection may be necessary in the rooms and napping areas which accommodate young children in childcare premises, to ensure an early warning of fire. This will be influenced by the level of adult supervision and the layout of the premises.
319. The choice of automatic fire detector type depends on the nature of the hazard and the balance between the speed of system response and the need to avoid false alarms. The common types of automatic fire detector are:
- Heat detectors which operate when a fixed temperature is reached (and may also respond to abnormal rate of rise of temperature). Heat detectors have a good performance in respect of false alarms but are not appropriate where the detection of smoke is required (such as in escape routes);
- Smoke detectors which detect the presence of smoke (either ionisation or optical type). They give a speedier response to most fires than heat detectors but have greater potential to generate false alarms. (Smoke detectors within corridors and stairs should be the optical type);
- Combustion gas detectors which respond to the gases produced in a fire such as Carbon Monoxide. They can be sensitive to smouldering fires, respond to many fires faster than heat detectors and have a good false alarm performance in the presence of dust, steam and cigarette smoke; and
- Multi-sensor detectors contain a combination of heat, smoke or combustion gas detection. These sensors enhance system performance and have a low potential for false alarm actuations.
320. Sounders are provided to alert building occupants. The type of warning signal and sound level should be appropriate for the premises, the characteristic of the occupants, the fire action plan, and staffing arrangements A coded staff alert may be desirable in some circumstances to initially warn only staff.
321. It may be necessary to provide tactile and/or visual alarms for staff in high noise level areas or where there are occupants or staff with hearing impairment to the extent that the sounders cannot be perceived.
322. As an alternative to conventional sounders, a voice-alarm facility that provides an automatically broadcast verbal warning of fire, may be suitable for some premises. Voice alarm systems can provide benefits in terms of reduced response time and improved information dissemination. A new voice alarm system should comply with the guidance in BS 5839: Part 8. In considering the areas to be provided with a voice alarm system, the desirability of providing occupants with information regarding the fire and factors such as background noise levels need to be taken into account. The wording of the message on a voice alarm system needs to be clear and precise.
323. In certain types of premises, for example sports grounds/stadia, theatres, cinemas or nightclubs, a conventional audible warning via a fire alarm sounder may provide insufficient information for the patrons to take appropriate action. A fire warning that initially alerts staff members only, by means of lights, a pager or another form of audible or coded alarm at permanently staffed points in the premises. In the case of major sports grounds and stadia, the indication of the fire warning and its location should be given to a central control point.
324. Areas of buildings to which only staff have access could have a conventional audible warning of fire provided, if such an alarm cannot be heard within public areas.
325. The provision of a combined public address/voice alarm system is appropriate for some transport premises, and can allow the use of coded messages for staff investigation where this is part of the pre-planned response to activation of the fire alarm.
326. A control and indicating panel provides facility for indication of fire or fault signals and manual controls such as silencing and resetting. Where a control and indicating panel is installed, it should be sited at a location which is appropriate both for staff and for the arriving Fire and Rescue Service.
327. The provision of a suitable fire detection and warning system should be accompanied by suitable staff training so that staff know how to operate the system and how to respond to system operation. A schematic plan should be displayed adjacent to the control panel to allow staff to quickly identify and locate the source of an actuation. If the fire warning system has detection zones, these zones should be shown on a zone plan in a simple and unambiguous way.
328. The evacuation strategy for premises may require the source of actuation to be quickly identifiable. The building should be divided into detection zones so that the actuation can be located quickly. The allocation of detection zones needs to take into account the layout of the building and should facilitate the emergency fire action plan. Detection zoning should comply with the recommendation in BS 5839-1, and should not be determined purely for the convenience of the system installer.
329. An addressable fire warning system is one where individual detectors and call points can be identified at the control and indicating equipment. Addressable systems are of great advantage in some premises as they reduce the time taken to identify the location of a fire. Where an addressable system is installed, zone indication is also necessary.
330. Certain fire safety measures are designed so that they operate when the fire warning system operates; examples are:
- Automatic release of door hold-open devices;
- Automatic closure of self-closing doors which are fitted with swing free arms;
- Automatic opening facility disabled on swing doors with automatic opening;
- Electronically powered locks on doors returning to the unlocked position; and
- Automatic opening of some exit doors.
331. In entertainment and assembly premises, where the sound pressure level of amplified music exceeds 80 dB(A) then the music should be muted automatically when the fire alarm signal is given.
332. If an automatic life safety fire suppression system is installed, the fire warning should actuate if the suppression system operates.
333. In the case of enclosed shopping centres, on the operation of the fire alarm:
- escalators would come to a controlled halt and lifts should return to the exit level;
- amplified music systems within the mall or shops are silenced; and
- subject to the pre-determined delay, shutdown of air-moving and other systems in the relevant smoke reservoir.
334. With remote monitoring, the actuation of the fire warning system causes a signal to be transmitted automatically to a remote alarm receiving centre ( ARC). On receipt of a signal, the ARC then calls the Fire and Rescue Service.
Reducing False Alarms
335. False alarms from automatic fire detectors or manual call point actuation are a major problem causing disruption to the running of premises and many unwanted calls to the Fire and Rescue Service. If frequent false alarms occur in the premises, members of staff may become complacent and may not respond correctly to a warning in the event of a real fire.
336. A record log of system actuations should be kept. Each false alarm should be investigated to try to establish the cause. Remedial action may be needed, such as re-positioning a detector head or changing a detector to a different type. A fire warning system should not be disabled, if it is posing a problem, specialist advice should be sought.
337. Steps can be taken to discourage inappropriate or accidental call point use such as the provision of a protective hinged cover on the call point, with or without a tamper alarm. In cases where there is the potential for objects to collide with a call point, then side impact protection could be provided.
338. Where a call point is sited close to a green box or button for door control, the door control feature should be clearly signed, to avoid unintentional actuation of the fire alarm.
339. Where a fire warning system is connected to an alarm receiving centre, robust arrangements need to be in place to take the system off-line during tests or for notification of the ARC.
Email: Richard Hastings, Richard.Hastings@scot.gov