EVASAFE FIRE SYSTEMS
FREQUENTLY
ASKED QUESTIONS ABOUT FIRE ALARMS
DISCLAIMER: NOTE THAT THIS
IS A UK SITE AND THE INFORMATION GIVEN BELOW MAY WELL NOT APPLY
IN OTHER COUNTRIES.
- When is a fire alarm required in a
building?
ANS. Although
it is often not a legal requirement, it may be considered that
a fire alarm should be provided wherever more than a few people
are employed; it is normally, in the UK at least, a legal requirement
to have "a satisfactory means
of warning in case of fire"
(i.e. a fire alarm) for most offices, shops, railway premises,
hotels and larger guest houses, factories and houses in multiple
occupation (HMOs). There are other special categories of building
that also have legal requirements.
- What is meant by "satisfactory"?
ANS.
Normally this means a system meeting the relevant national standards.
In the UK these are BS5839 Part 1:1988 for systems in buildings,
and various component parts should meet the relevant other parts
of BS5839 - e.g. Control Panels should meet part 4 requirements.
Anyone needing detailed information on fire alarm systems and
components would be well advised to read these standards.
- How loud should a fire alarm be?
ANS.
Normally sufficiently loud to be heard clearly above any ambient
noise. For normally quiet areas a minimum sound level of 65dBA
is specified. For noisier areas, at least 5dBA above any ambient
noise level, and for bedrooms where there are no permanent night
staff to wake sleeping persons, the sound level should be 75dBA
at the bed head. This normally means an alarm sounder/bell in
each bedroom.
- Are smoke and heat detectors a requirement
of a fire alarm?
ANS.
Not necessarily. For smaller premises a simple "manual"
system is often adequate. However, where an early warning of
fire is needed for the safety of life, automatic detectors should
be used to complement the manual activation of an alarm. There
are normally 3 levels of protection, type L3 is the protection
of escape routes, type L2 is the protection of vulnerable areas,
and type L1 is total coverage. In most cases smoke detectors
will be required, except for areas such as kitchens where fumes
are often produced, where heat detectors would normally be used.
If detectors are required for the protection of property, there
are two levels of protection, level P1 giving total coverage,
and P2 where low risk areas are not covered.
A special case is fire protection of computer centres, which
has its own British Standard, BS6266, which offers much advice
on fire protection in general, and fire detection in detail,
for such areas.
- What are the requirements for cabling
a fire alarm?
ANS.
Normally cabling must be fire resistant, assuming operation is
needed during a fire. This can be achieved by using Fire resistant
cables, e.g. MICC or FP200 types, or, by running pvc cables in
conduit, or by being buried in walls etc. Mechanical protection
is also needed in some cases, to give protection from impact,
abrasion or attack by rodents. Cabling would normally meet the
requirements of the IEE Wiring Regulations, 16th Edition (also
known as BS7671:1992)
It should also be noted that there are systems not requiring
cables which use radio. These systems are much cheaper to install,
but the equipment is much more expensive! They are sometimes
the only type acceptable to a client where the site is historical,
heritage, prestige etc. A mixed system of conventionally wired
and radio is sometimes a more cost-effective solution, since
often the less prestigious areas do not require a radio system.
- How is a building divided up - i.e.
how is the location of any fire determined?
ANS.
Any but the smallest building will normally be divided into a
number of zones, each of which will have a separate indication
on the fire alarm panel. Zones should not normally exceed 2000
square metres in area, nor cover more than a single floor. Often
systems will have more than the minimum number of zones in order
to give a more precise location. There are also systems called
Analogue Addressable systems, where each and every device (call
point, smoke and heat detector etc.) can indicate its state and
location. These are normally used in larger premises where the
detailed information is of more use, and the extra cost of this
type of equipment may be justified.
- How do I know that a system meets the
required standard?
ANS. Any
competent installation company should be willing to issue a commissioning
certificate showing that the system meets the required standards.
This is obviously only of use for newly installed systems, but
companies such as ours will readily inspect existing systems,
and issue a report, or certificate if one is justified. However,
in many instances, it may not be possible to adequately inspect
a system to ensure it meets all present requirements, so there
may be some provisos or exceptions listed on any certificate
for previously installed systems.
- How often should an alarm be tested?
ANS.
Normally once a week, with a DIFFERENT
device being tested every
week - not the same call point next to the panel, as is often
the case! Further inspections of the system are required after
any fire, and at monthly, quarterly, annual and five yearly intervals.
The quarterly, annual and five yearly inspections should be carried
out by a competent company.
- Will my alarm work if the mains fail?
ANS.
In nearly all cases it should! However, unless the system has
been checked for correct stand-by operation in the event of mains
failure, this may not happen. Often the stand-by batteries have
not been checked, and need replacement or topping up if of the
wet variety, so that in the event of mains failure, the system
would only work for a few minutes or less. Systems are intended
to operate for at least 24 hours without a mains supply, and
sometimes for up to 72 hours.
- Why do we get so many false alarms?
ANS.
Often so called "False" alarms are in fact strictly
unwanted alarms, where the system is in fact operating correctly,
but where, for instance, a smoke detector is being triggered
by some-one making toast where they should not, or where, perhaps,
a heat detector would be more appropriate. Although smokers may
occasionally trigger smoke detectors, this is not common as most
detectors have a built-in delay to prevent triggering by passing
smokers. This may not function adequately in a dedicated smoking
room though, due to the continued presence of smoke.
In some cases smoke detectors have been fitted where fumes are
sometimes emitted, such as engine or boiler rooms - in such cases
a dramatic reduction in alarms can be achieved by changing the
detectors to heat type.
One possible cause of unwanted alarms from heat detectors is
if they are placed directly above ovens in a kitchen, and when
the oven door is opened, the rapidly increasing temperature causes
the "Rate-of Rise" element of the detector to operate,
whereas the normal operating temperature of the detector has
not been reached.
Another common reason for false alarms is dirty detectors, which
makes some types very prone to operate intermittently - in many
cases the dust etc. can be easily blown out, but in severe cases
the detectors may need cleaning by the manufacturers. It is sometimes
the case that detectors are placed in an air stream which causes
rapid dust build-up - the answer there is to move them out of
the air-stream if this is practicable.
Where an analogue addressable system is in use, it is often possible
to obtain a readout of the state of each detector, and so to
arrange cleaning before they cause any problems. Sometimes on
these systems dirty detectors will cause pre-alarm indications
to be given initially, which also allows preventative action
to be taken.
- IF YOU HAVE ANY MORE QUESTIONS YOU
WOULD LIKE ANSWERED, PLEASE ASK - WHY NOT E-MAIL HERE TO info@evasafe.co.uk
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THIS PAGE LAST UPDATED 8th November 2006