Selection and Location of Fire Detectors
General
Fire detectors are designed to respond at an early stage to one more of the four
major characteristics of combustion, heat, smoke, flame or gas.
No single type of detector is suitable for all types of premises or fires. Refer to the
attached table for general recommendations of type of detector and location.
Detectors should be chosen for the best response to the effects of fires, as well the
need to minimise unwanted false alarm activations.
Detectors should be located where the early stages of fire will be detected, and
ensure they are placed at regular intervals on the ceiling. The issue of unwanted fire
alarm activations from environmental conditions must also be considered
Heat detectors
Heat detectors respond to the temperature rise associated with a fire.
A fixed temperature heat detector is designed to operate when the temperature at the
detector exceeds a predetermined value. A rate of rise detector is designed to
operate when the rate of temperature rise at the detector exceeds a predetermined
value.
Smoke detectors should be preferred to heat detectors where detection of visible
smoke or smouldering fire is required. Rate of rise detectors should be avoided
where
rapid temperature fluctuations are expected.
Ionisation Smoke detectors
Ionisation smoke detectors respond to very small smoke particles a wide range of
responses. They are most sensitive to hot fast burning fires, and less sensitive to
slow smouldering fires. Don’t locate them near cooking area’s, or in locations subject
to high air velocity.
Photo-electric smoke detectors
Photo-electric smoke detectors measure the scattered light from smoke particles.
They are most sensitive to larger, cooler, smoke particles typical of smouldering fires
such as plastics. Don’t locate in area’s subject to steam to prevent unwanted false
alarms Often called optical or photo-optical detectors.
Linear beam smoke detectors
Linear beam smoke detectors measure the reduction of intensity of a beam of light
due to the presence of smoke particles. They have broad response to a wide range
of smoke types, and are particularly useful for detection applications in large spaces.
Require careful installation.
Aspirated smoke detectors
Aspiring-type systems eg (Vesda Systems) are more effective in detecting smoke
than point type detectors in many applications. The sensitivity of the actual ‘sampling
points’ is dependent on the sensing chamber sensitivity and the design of the
aspiring pipe network.
Physical or electronic filtration of the air drawn through the sensing chamber and
processing of the output signals has been shower to reduce spurious alarms caused
by pollution, smoking and dust particles.
Carbon Monoxide (CO) fire detectors
CO fire detectors respond to the presence of carbon monoxide (CO) in fires
involving carbon based materials. CO is produced due to incomplete combustion
during smouldering or slow burning fires. Not suitable for the detection of slow
burning fires. Currently should not be used as a sole detector for early warning, but
used in combination with other early warning detectors as part of a fire engineering
design. Ongoing tests are being carried out to improve these type of detectors.
Combination( multi-criteria ) detectors
These type of detectors are available as part of an analogue addressable fire alarm
system. They vary of the type of combination, and can involve up to 4 separate
sensing elements, such as CO, Infra- Red Sensing, Optical and Heat detection.
The integration of continual monitoring of all the major elements of a fire allows a
quick response to any fire and the reduction of nuisance alarm activations (false
alarms)
Discuss the type of detector required with your fire alarm company to ensure the
most suitable detector for the location. A combination of detectors ensure the
property has the best coverage for the detection of fire.
Battery Smoke Alarms
Are available in ionistaion and photo-electrical. Refer to comments above including
suitable location
Hard wired smoke alarms
Are available in ionistaion and photo-electrical and are connected to a 240w power
source, such as a lighting circuit. A battery back up ensures when power is shut off a
working smoke alarm exists as long as the battery is in working order.
Suitable to be linked to other smoke alarms
Note: A smoke alarm is a unit which gives early warning of fire and is powered by a
9 volt battery or 240 v. The alarm sounder is within the unit.
A smoke detector is a unit which is powered by a fire alarm system. The alarm
comes from a sounder installed in the location of the room where the detector is
located
Special considerations
The location of smoke detectors should take into
consideration areas where false operation or no-operation is likely.
Some typical locations where the use of smoke detectors should be carefully
evaluated are as follows:
(a)
In the vicinity of certain materials, such as polyvinyl chloride (PVC), which
when smouldering produce mainly large particles to which optical detectors
are more responsive.
(b)
Areas where gases may be present from exhausts and normal manufacturing
processes.
(c)
Kitchens and other areas subject to cooking fumes. Photoelectric detectors
are more suitable for these areas, however not in the actual kitchen
(d)
Near openings, such as doors, windows, or other inlets, where the
introduction of outside industrial gases or products of combustion may be
possible.
(e)
Areas where the detector is subject to movement and excessive vibration in
particular where beam detectors are used.
(f)
Dusty areas or in areas where particulate matter, such as aerosols, could
enter the detector.
(g)
In areas subject to high velocity air currents, a sampling type detection
system may be more suitable.
(h)
In areas where high concentrations of tobacco smoke are expected,
ionization detectors are less susceptible to false operation.
(i)
In areas where steam or condensation vapour is expected, ionization
detectors are less susceptible to false operation.
Flame
Specific fire engineering
✓
✓
ok
ok
✓
ok
ok
ok
ok
Offices, shops
✓
✓
ok
ok
✓
✓
ok
ok
ok
Auditoriums/clubs (theatrical smoke)
x
x
x
x
✓
✓
ok
ok
✓
Autoclave/sterilizer areas
x
x
x
x
✓
✓
x
ok
ok
Bathrooms/laundries
x
x
x
x
ok
✓
x
ok
ok
Boiler/furnace rooms
x
x
x
x
x
✓
x
x
ok
x
x
ok
x
xx
✓
✓
ok
ok
Ceiling or roof voids with access
ok
ok
ok
ok
ok
✓
ok
ok
ok
Ceiling or roof voids difficult access
x
x
ok
ok
x
✓
ok
ok
✓
Cleaners’/understair cupboards
x
x
x
x
x
✓
✓
ok
ok
x
x
x
ok
x
ok
✓
ok
✓
Electrical risers
✓
✓✓
x
ok
x
✓
ok
ok
ok
Electrical switchrooms/cupboards
✓
✓✓
ok
ok
x
✓
ok
ok
ok
✓✓
✓
ok
ok
x
✓
ok
✓
ok
x
✓
ok
ok
ok
✓
ok
ok
✓
x
x
x
x
x
✓
✓
ok
✓
High/difficult access ceilings
ok
ok
✓
✓
ok
ok
ok
✓
HVAC duct sampling
ok
✓
ok
ok
x
x
x
x
✓
ok
x
ok
ok
ok
✓
✓
ok
ok
Car parking
1
Cool rooms/freezers
2
Flammable liquid hazard areas
3
Forced air flow/draughts
Fume cupboards
Ice rinks
3
1
Aspirated smoke
Linear beam smoke
Ionisation smoke
Location
Carbon monoxide (CO)
Bedrooms/sleeping areas
Photoelectric smoke
Rate of rise thermal
Fixed temperature Thermal
Recommended fire detectors for different applications
✓✓
x
x
x
x
ok
✓
x
x
ok
Kitchen extract ducts
1
xx
xx
xx
xx
x
✓
x
x
ok
Paint spray booths(s)
3
x
x
x
x
x
✓
ok
ok
ok
✓
✓
ok
✓
ok
ok
ok
ok
x
x
ok
x
✓
✓
ok
ok
ok
xx
✓
ok
ok
xx
✓
ok
ok
ok
x
x
x
ok
✓
✓
x
ok
✓
Kitchens
Service shafts
Stables
1
Warehouse with vehicles and / or nonelectric forklift
<1.8m from rooms containing bath, shower,
or steam source
KEY -
✓✓strongly recommended
X not advised
✓
✓recommended
xx do not use
ok may be used
NOTE –
(1) Environmental protection may also be required.
(2) Cold rooms and freezers can be difficult to reliably protect and will usually need special
engineering including heaters to prevent ice build-up on detectors, manual call points and
alerting devices.
(3) Hazardous area.