Fire poses a serious risk to any home or business. Here at B&B Electrical contractors Ltd we aim to save lives and reduce the risks associated with fire. Using the latest in fire systems equipment we can provide 1st class protection.
With our knowledge and practical expertise and access to cutting-edge technology, B&B Electrical can help protect your site or premises from the material and financial damage caused by fire.
This guide should be read in conjunction with, but never as a substitute for current BS Standards. The full fire safety system specification shall be agreed between the responsible persons, which may include the local fire authority, the fire safety consultant, health and safety officer, system installer and the insurance company.
Risk Assessment
Further to recent changes to the fire act, fire officers will no longer issue fire certificates for buildings. Ensuring that a building is safe for the occupants is now the responsibility of the employer. Insurance companies may refuses to insure buildings that have not had a risk assessment carried out. Fire officers are planning to carry out spot-checks on buildings without giving prior notice. As the new requirements are backed by criminal law, failure to have carried out risk assessments or operating in an unsafe environment may render the employer liable to court action, heavy fines and possibly imprisonment.
Zone requirements
- Only one zone is required if the total floor area is not greater than 300m²
- The total area of a zone must not exceed 2000m² (Dependent on the risk present)
- The maximum search distance for a zone fire shall not exceed 60m
- Where stairwells or similar extend beyond one floor but are in one fire compartment, the stairwell shall be a separate zone
- If the zone covers more than one compartment, the zone boundaries shall follow compartment boundaries
- If the building is split into several occupancies, no zone shall be split between two occupancies
Classification(Property or Life)
Category P systems
Category P systems are automatic fire detection systems where the objective is to protect property. Categories are subdivided into the following systems:
P1
The objective of a category P1 system is to reduce the time from the discovery of a fire to the arrival of the fire brigade to a minimum. P1 systems should have fire detectors installed throughout all areas of the building.
P2
Category P2 systems are intended to provide an early warning of fire in areas of high hazard, or to protect high-risk property. Automatic fire detection should be installed in defined areas of a building.
Category L Systems
Category L systems are automatic fire detection systems where the objective is to protect life. Categories are subdivided into the following systems:
L1
This is the highest category for the protection of life and is intended to give the earliest possible notification of a fire in order to allow maximum time for evaluation. Automatic and manual fire detection should be installed throughout all areas of the building with smoke detectors employed wherever possible to protect rooms in which people are expected to be present. All alarm signals given in a category L system must be sufficient to warn people for whom the alarm is intended to allow time for an evacuation.
L2
Intended to offer early notification of a fire allow evacuation before escape routes becomes smoke filled. Automatic fire detection should be specified in defined areas in addition to L3 and additional protection should be provided in rooms at higher risk.
L3
As with L2, category L3 is intended to offer early notification of a fire to allow evacuation before escape routes become smoke filled. Smoke or heat detectors should be installed in escape routes and in rooms opening onto escape routes.
L4
Category L4 is designed to offer protection to the escape routes from a building and should comprise category M plus smoke detectors in corridors and stairways.
L5
Category L5 is a non-prescriptive system in which the protected areas are designed to satisfy a specific fire risk objective other than that of L1 to L4. Within the building, certain areas defined but the fire system specification are protected by automatic fire detection in order to reduce risk to life. Category L5 may also include manual fire protection.
Category M Systems
Category M systems are reliant on human intervention and use only manually operated fire detection such as break glass call points. category M systems should only be employed if there are no persons sleeping in the building and if a fire is likely to be detected by people before escape routes are affected. Any alarm signals given in a category M system must be sufficient to ensure that any persons within the alarm areas are warned of a fire condition.
Break glass call point positioning
- Break glass call points shall be located on exit routes and in particular on the floor landings of stairs cases and at all exits to the open air
- Dependent upon the risk, break glass call points shall be located so that no person needs to travel more than 45m from any position
- General call points shall be fixed 1.4m above the floor in easily accessible, well-illuminated and conspicuous positions clear of any obstruction
- Detection devices may be installed on the same system, though it is advisable to install call points on separate zones where automatic detection needs to be delayed
Alarm sounders
- A minimum sound level of 65dBA or 5dBA above any background noise likely to persist for longer than 30 seconds is required at any point in an occupied building
- If the alarm systems is to used in buildings such as hotels, a minimum sound level 75dBA at the bed head is required in order to wake a sleeping person.
- Audible warning devices should have a similar sound and distinct from alarms used for other purposes, and noisy areas may require high output sounders
- To prevent alarm sounds from exceeding comfortable levels, the use of a greater number of quieter sounders, should be considered
- Two sounder installed on two independent circuits must be used be used on a fire system so that a failure on one circuit does not cause a total failure of all sounders
- Most standard doors will cause a 20dB drop in sound levels. Fire doors will cause a drop of 30dB
- For P systems, a red external sounder marked 'FIRE ALARM' is required
- When mains voltage sounders are used in addition to 24V DC sounders, the mains sounder supply must be monitored
Smoke detectors
- Optical smoke detectors are designed to rapidly detect visible and invisible smoke particles, in the range of 0.2µm to 60µm. An optical arrangement is located within a light proof chamber, which triggers the detector when smoke enters the chamber
- Smoke detection devices have an individual coverage of 7.5m radius. However, these radii must overlap to ensure there are no 'blind spots'. Therefore, the individual coverage can be represented by a square measuring 10.6m x 10.6m giving an actual area coverage of 112m² per device
Heat/Rate Rise of Detectors
- Fixed temperature heat detectors are suitable in environments where there is a high ambient temperature or in areas where sudden changes in the ambient temperatures are common e.g. boiler rooms, drying rooms, kitchens
- Rate of rise detectors are designed to detect a fire as the temperature increases. They incorporate a fixed upper temperature limit if the rate of temperature increase has been too slow to trigger the detector earlier. These detectors are suitable where the ambient temperature is stable and a fast to sudden temperature increase is required, for example, areas unsuitable for smoke detection due to dust or other contamination
- Heat detection devices have an individual coverage of 5.3m radius. However these radii must overlap to ensure there are no 'blind spots'. Therefore individual coverage can be represented by a square measuring 7.5m x 7.5m giving an actual coverage of 56-25m² per device
Detector Selection
| Type of Detector | Ideal Application | Unsuitable |
| Ionisation Smoke Detector | General Purpose. Ideal for fast flaming fires | Unsuitable for areas, subjected to smoke, steam dust or dirt during normal use |
| Optical Smoke Detector | General Purpose. Ideal for smoldering fires | Unsuitable for areas, subjected to smoke, steam dust or dirt during normal use |
| Combined Optical Smoke/Heat Detector | General Purpose. Ideal for both fast flaming and smoldering fires | Unsuitable for areas, subjected to smoke, steam dust or dirt during normal use |
| Optical Beam Smoke Detector | Large and high rooms | Unsuitable for areas, subjected to smoke, steam, dust or dirt during normal user |
| Rate of Rise Heat Detector | Areas subjected to smoke, steam, dust or dirt during normal use | Unsuitable for areas, subjected to temperatures of over 43°C and rapid changes of temperature |
| 58°C Fixed Heat Detector | Areas subjected to smoke, steam, dust or dirt and rapid changes of temperature during normal use | Unsuitable for areas, subjected to temperatures of over 43°C |
| 78°C Fixed Heat Detector | Areas subjected to smoke, steam, dust or dirt and temperatures over 43°C during normal use
| Unsuitable for areas, subjected to temperatures of over 70
|
Maximum ceiling heights for Detectors
| Type of Detector | Maximum ceiling height |
| EN54-7 Smoke Detector | 10.5m |
| EN54-5 Class A1 58°C Heat Fixed Detector | 9m |
| EN54-5 Class B 78°C Heat Fixed Detector | 6m |
| Optical Beam Smoke Detector | 25m
|
The sounder device should give a minimum sound level of 65dB(A) or 5dB(A) above any background noise lasting more than 30 seconds. It shall operate at 500Hz to 1000Hz
A person searching a zone for a fire should not have to travel more than 60m to identify the source of a fire. A person should not have to travel more than 45m to reach a manual call
Manual Callpoints should be positioned1.4m (/-200mm) from floor level. Any non-mechanically protected cable medium should have additional protection up to 2m from floor level.
Cabling to the sound device should be arranged so in the event of a fault occurring during a fire condition, at least one sounder device will remain operational. Any metallic parts of fire systems including cabling and conduit should be well separated from any lighting protection system.
Smoke detection devices have an individual coverage 7.5m radius. However, these radii must overlap to ensure there are no 'blind spots'. Therefore, the individual coverage can be represented by a square measuring 10.6m x 10.6m giving an actual area coverage of 112m² per device.
Heat detection devices have an individual coverage of 5.3m radius. However, these radii must overlap to ensure there are no 'blind spots'. Therefore, the individual coverage can be represented by a square measuring 7.5m x 7.5m giving an actual area coverage of 56.25m² per device.
For ceilings that feature an apex, if the height of the apex is less than 150mm from the rest of the ceiling for heat detectors and 600mm from the rest of the ceiling for smoke detectors, they can be treated the same as flat ceilings. For higher apexes, a device should be installed at the highest point. The distance to adjacent devices can be increased by 1% per1 degree of the angle of the roof. Up to a maximum of 25%
Limits of ceiling heights
For areas where people are sleeping, sounder devices should produce a minimum of 75dBA at the bed-head with all doors shut.
Decibel loss occurs through doors: -20dBA through a normal door, -30bDA through a fire door.
In corridors less than 2m wide, the horizontal spacing of detectors may be increased. The areas of coverage need not overlap as in the case of a room.
Any corridor over 2m wide is deemed a room and device spacing should follow the standard for rooms.
Do not site detectors less than 1m from air inlets or air conditioning units.
Detectors should not be mounted within 500m of any obstruction. If the opt of a solid partition is less than 300mm from the ceiling, it should be treated as a wall. Similarly, ceiling obstructions such as beams should be treated as walls if they are deeper than 10% of the ceiling height.
Fire resistant cabling is required within the whole fire alarm system including the mains supply cables. The user of non-fire resisting cables will no longer comply with BS5839.
Never mount detectors closer than twice the depth of luminaire
Voids less than 800mm in height need not have independent coverage, unless fire or smoke is able to spread from one area to another through the void or this risk assessment shows an AFP (Automatic Fire Protection) to be necessary.
Vertical shafts like lifts and stairways should have a detector mounted within 1.5m of any opening. Enclosed stairways should have a detector on each main landing.
The sensing element of a heat detector (Themistor) should not be less than 25mm below the ceiling and not greater than 150mm below the ceiling.
The sensing element of a smoke detector (Photoelectric chamber) should not be less than 25mm below the ceiling and not greater than 600mm below the ceiling.
