Ei Professional Smoke Alarms and Smoke Detectors

Specifiers Guide

• 1. Scope - what dwellings are covered
• 2. Risk Analysis
• 3. Design Considerations
• 4. Grades of System
• 5. Level of Protection
• 6. Choice of System
• 7. Types of Detector
• 8. Location/Siting/False Alarms
• 9. Audibility

1. Scope - what dwellings are covered

The recommendations apply to both new and existing dwellings and cover:-

• Houses and Bungalows
• Multi-Storey Houses
• Flats and Maisonettes
• Sheltered Housing
• Bedsits
• Mobile Homes
• NHS Housing
• Houses In Mulitple Occupation

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2. Risk Analysis

Risk analysis is identified as critical and the design of a fire detection installation should take into account the level of protection and type of system best suited for the particular type of property.

In assessing the fire risk, the following should be considered:-

• The presence of smoke in escape routes is the greatest impediment to safe escape in the event of fire and therefore smoke alarms should be installed in the circulation areas.
• Approximately 46% of domestic fires start in kitchens and it is essential that a smoke alarm be sited in any adjacent circulation space.
• Fires started by smokers' materials are the most common cause of fatalities, therefore, occupants known to smoke should have smoke alarms fitted in living rooms, dining rooms and bedrooms.
• Heating appliances are the second most common cause of fire deaths and particular consideration should be given to installing smoke alarms in the relevant rooms.
• Fires caused by electrical appliances and faulty wiring account for about 14% of fires and the use of electric blankets, by high risk groups such as the elderly justify fitting smoke alarms in bedrooms.
• Arson is a growing problem and if a significant possibility, the level of protection should be high, especially around the vicinity of entrance doors if malicious ignition is considered a significant threat.
• The elderly, over 80 years and children under 5 years are at greater risk and should be protected to an appropriately high level.
• Socially deprived and low income occupants have an increased risk from fire and replacement of smoke alarm batteries can be a low priority - in these cases mains power is essential.
• People with impaired mobility require more time to escape and special consideration should be given.
• Occupants in Hmo's are also a high risk group.
• In all cases, the risk is greater during sleep and it is essential that the smoke alarms are capable of arousing occupants from normal sleep.

Balance between fire risk and system reliability and sucess rate

3. Design Considerations

Battery-operated smoke alarms
These are low cost and simple to install but the battery is vulnerable to removal and therefore the ability of these smoke alarms to detect a fire some years after initial installation is not considered to be high.

Mains-powered smoke alarms
Potentially more reliable than battery-operated ones, because they require less attention by the user, they are more costly themselves to install. Also, they suffer the disadvantage that there is no protection when the supply is interrupted. In view of this they should be supplied from a dedicated circuit and not a lighting circuit as this could be at risk from fire damage.

Mains-powered smoke alarms with back up
This is the best option especially if reliability of the mains supply is not high or disconnection is likely. Also, this type of alarm can be connected to a lighting circuit. RCDs are not recommended unless on a lighting circuit already.

Consideration should be given to the difficulty of disabling when permanently in alarm due to fault, without isolating the lighting.

Relative frequency of fires in rooms within dwellings

Room	Proportion Of Fires
Kitchen	46%
Bedroom, Bedsit	15%
Living Room, Dining Room	14%
Access Area	5%
Ashpit, Refuse Area	4%
Store	2%
Bathroom, Cloakroom, WC	2%
Roof Space	1%
Laundry	1%
Airing Cupboard	1%
Misc & Unknown	9%

Deaths in Fires

Room	Proportion Of Fires
Living Room/Dining Rooms	50%
Bedrooms	30%
Kitchens	15%

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4. Grades of System

This covers many types of alarms, differing widely in cost, complexity and reliability, and groups system into 6 grades.

Grade A     A BS 5839 Part 1 and Part 4 System.

Grade B     Detectors other than smoke detectors but complying to BS 5839 Part 4.

Grade C     System of detectors from mains supply with some central control.

Grade D     One or more mains smoke alarms with standby supply.

Grade E     One or more mains smoke alarms with no standby supply.

Grade F     One or more battery-operated smoke alarms.

Recommended grade and type of system in typical dwellings

BUNGALOW, FLAT OR OTHER SINGLE STOREY UNIT
GRADE: E	LEVEL: LD2
OWNER-OCCUPIED MAISONETTE OR HOUSE
GRADE: E	LEVEL: LD2
RENTED HOUSE OR MAISONETTE
GRADE: D	LEVEL: LD2

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5. Level of Protection: types of system

A system is usually installed to protect life and the level of protection should be related to the fire risk.

Systems for the protection of life (type LD) have detectors installed in the following subdivisions:

LD1     Throughout the dwelling.

LD2     Escape routes and high risk rooms.

LD3     Escape routes only.

Systems for the protection of property (type PD) are subdivided into:

PD1     Throughout the dwelling.

PD2     Defined rooms or areas.

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6. Choice of System

The grade of system considered depends on the nature of the dwelling, the level of fire risk and characteristics of the occupants.

Two examples, the Standard states:

Grade F systems, comprising one or more battery-operated smoke alarms, are the least reliable in the long term because of the need for battery replacement.

With occupants at risk due to being deprived of power through non payment of bills, mains powered smoke alarms with standby should be installed.

Because of the greater fire risk in HMOs these are considered separately from single family dwellings.

With regard to sheltered housing, smoke alarms should normally form part of a social system. Where this is not possible, mains smoke alarms should be installed and any fire signal relayed to the warden.

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7. Types of Detector

There are two types of smoke detectors commonly used:

Ionisation   Operate on the principle that electrical current flowing between electrodes in an ionization chamber is reduced when smoke particles enter.

They are particularly sensitive to the smoke from fast flaming fires containing small particles.

Optical   Operate by detecting the scattering of light by smoke particles and are sensitive to optically dense smoke.

Where the Standard recommends the use of smoke alarms, either type is generally suitable, but the type of fire that may be expected and the need to avoid false alarms, should be taken into account.

Heat   Only fixed temperature type (point) is recommended for most dwellings. They should be installed where ambient temperatures are likely to fluctuate rapidly over short periods, e.g. kitchens.

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8. Location/Siting/False Alarms

For most single-family dwellings a type LD3 system will provide a reasonable standard of protection, i.e. smoke alarms sited in the circulation areas ( hallways and staircases).

In houses of four or more storeys, a LD2 system with heat detector in each kitchen is recommended.

Location:

• one detector between bedroom and kitchen/living room.
• in circulation areas, no door should be further than 7.5m from nearest detector.
• in a single storey dwelling, with one detector, it should be as close as possible to the living accommodation.

False alarms:

false alarms are common in domestic fire systems, and accordingly, installation design should aim to minimize false alarms.

• most common cause is fumes from the kitchen, therefore, fit optical type nearest kitchen.
• if people smoke in living and dining rooms, then fit ionisation type.
• heat detectors should be fitted in kitchens, laundry rooms and boiler rooms.

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9. Audibility

Smoke alarms only work if they are capable of arousing the sleeping occupants and a sound level of 85 dB should be achieved at the open doorway to each bedroom and 75 dB at the bedhead in each bedroom with the door shut.

In single-family dwellings, a lower sound level is acceptable in other areas of the house, with no minmium sound level recommended.

For people with severe impaired hearing, a visual alarm and underpillow vibrating disc linked to a smoke alarm is recommended.

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