call points are used to give a manual indication of a fire. These are normally
protected by means of a glass/plastic cover that needs to be broken in order to
trigger the alarm.
must be clearly recognisable and should all be identical in type when installed
on the same system. The person operating this device must be made aware of the
success of the operation by an audible and sometimes a visual alarm. Certain
types of manual call points are reset able and these must not have a delay of
more than 3 seconds before triggering an alarm. On conventional systems manual
call points within an area connected to a specific zone can be included on that
zone, but it must be remembered that people will not always trigger the call
point closest to the fire. For this reason manual call points are often all on
one zone reserved for this purpose.
of manual calls points.
call points should be located on all exit routes, in particular on floor
landings or stairways and at exits to the open air. They should be located so
that no person in the premises should need to travel more than 30m to trigger a
manual call point. If it is difficult to travel at normal speed in certain areas
than this should be taken into account and the manual call points should be
closer than 30m. In areas where potentially hazardous conditions exist then
these should also be mounted closer than 30m
There are various types of fire detectors, the main types are;
is essential that the correct type of detector be installed in the correct
Smoke Detectors detect visible smoke particles in a dark chamber. A light source
is projected into the chamber out of view of a light sensitive receiver. When
smoke enters the chamber, the visible smoke particles reflect this light onto
the light sensitive receiver and trigger the smoke detector.
Optical smoke detectors are more efficient at detecting denser smoke
produced by smoldering materials, like those found in homes or general offices
where furniture is found. Optical detectors are far better at detecting
polyurethane foam than ionization detectors, which can be insensitive to larger
smoke particles. Optical smoke detectors are more prone to false alarms in dusty
areas. Due to environmental storage concerns optical detectors are becoming more
and more popular. Lately this technology has improved at a rapid rate.
Detectors detect small invisible smoke particles when these enter the chamber.
These smoke particles reduce the normal ionisation current flow, created by a
small radioactive source, causing the detector to trigger. lonisation Detectors
are more efficient at detecting fast burning flaming fires and are less likely
to false alarm in areas with tobacco smoke. Diesel exhaust fumes, certain
chemicals (like ether), high humidity and wind are more likely to cause false
alarms with lonisation Detectors. While lonisation Detectors give off less
radiation than the human body, sufficient quantities when stored together, can
create harmful amounts of radiation. For this reason European authorities are
phasing this type of detector out.
type of smoke detector "breathes" the air at intake points before
pumping this air through a filter and then into an extremely sensitive chambers
which is far more sensitive than the standard smoke detectors chamber. The air
is then exposed to an intense light source and analysed for a smoke to air
ratio. This information is converted into an electronic signal and the signal is
then compared to algorithms. This type of detection is expensive but highly
accurate and less susceptible to false alarms. One of these types of detectors
can have many sampling points reducing the cost of equipment dramatically. With
this type of system it is essential that piping from each sampling point to the
detector be installed exactly according to the manufacturers specifications.
Beam Smoke Detectors use an active beam to detect visible smoke between the
transmitter and the receiver. Certain modules can also detect the turbulence
from a fire by detecting the refraction of the beam. If any part of the beam is
obscured by smoke an alarm will be triggered. Optical Beam Smoke Detectors are
ideal for protecting areas such as churches and certain factory warehouses as
the detection area can be up to a 100m (or more depending on the make and
model), directly between the transmitter and the receiver. This type of smoke
detector can be mounted up to 25m high, far higher than any other smoke
detector. This type of smoke detector can go into a state of false alarm due to
birds or bats obstructing the beam, or due to bright light sources like sunlight
or flash bulbs.
There are two types of Heat Detectors: Fixed Temperature Heat Detectors & Rate of Rise Heat Detectors. These can also be combined into one detector to provide more sensitivity using logic with an "or gate", or less sensitivity using logic with an "and gate". Both of these types of heat detection are also available in two configurations. The "Point" type configuration determines the heat at a specific place, while the "Line" type heat detector determines heat at any place along the detector length. "line" type detectors either compare heat in one area compared to the rest of the length or by comparing the heat at any point of the detector against a pre-programmed temperature or rate of rise.
Temperature Heat Detectors are designed to trigger when a specific
pre-determined temperature is reached, often 60°C or 80°C. Fixed Temperature
Heat Detectors are normally once off devices and have to be replaced after
triggering. These normally have a substance that melts at the specified
temperature separating the contacts. When this substance melts the contacts
close and an alarm is triggered. Fixed Temperature Heat detectors are more
reliable than rate of rise heat detectors and combinations of the two are
normally required to have an "or gate". Fixed temperature
detectors can false alarm where ambient temperatures have not been adequately
taken into account, either due to direct sunlight or heating elements being
of Rise heat detectors are designed to trigger when the ambient temperature
rises faster than a specific rate. This often operates using two types of metal
with different expansion rates. If the temperature increases slowly, as it would
on a warm day, the expansion of the one metal will slowly catch up with that of
the second metal, which would not create an alarm. If the temperature were to
increase rapidly the first metal would expand faster than the second metal,
resulting in contact between the two metals to create an alarm. Rate of Rise
Heat Detectors are less likely to respond to slow burning fires, and may not be
used in escape routes.
detectors can false alarm where low temperatures are increased to normal room
temperature by closing outside loading bay doors, etc in a cold climate. Heat
detectors are normally used in areas where there may be smoke present, like
generator rooms, etc and are unlikely to trigger until flames reach up to the
ceiling. They should be avoided in areas where small fires can create
unacceptable losses like computer rooms.
Flame detectors detect ultra violet and/or infra red radiation.
flame detectors detect ultra-violet radiation emitted from flames and normally
restrict this to specific bandwidth that are not common in solar radiation due
to the ozone layer. Flame detectors are often used for outside fire detection
and are often the best method of detection for fires where smouldering is
unlikely such as liquid fuel or gas fires. Normally, if these are used indoors
the areas are also covered with smoke or heat detectors. These must be installed
within line of sight of the protected areas.