Aico Residential Fire Detection RFD - Manual (Page 11)

SYSTEM PLANNING
BS 5839: Pt.6 quite reasonably points
out that, no matter how good the
system is, people will only have an
adequate chance of escape if there
are enough detectors installed and if
the alarms can successfully rouse them
from sleep.
SILENCING & DISABLEMENT
The Code is very aware of the grave
danger posed by tampering with
alarms and their wilful disablement. It
acknowledges that false alarms are a
major reason why householders disable
alarms, and looks at practical steps to
help prevent this. Foremost among
these recommendations is a built-in
method by which alarms can be
silenced without the use of a tool of
any kind, for example a “Hush” or False
Alarm Control button.
The Code stresses the role of
specifying “good quality equipment”
in reducing false alarms, and makes
helpful distinctions between alarm
sensor types in reducing sensitivity to
environmental factors liable to cause
false alarms, such as cooking
vapours.
However, the need to avoid false
alarms should never take priority over
the need for early fire detection.
The 2004 Code says that the high rate
of false alarms in dwellings makes it
‘generally inappropriate’ to connect
domestic smoke alarms direct to a fire
and rescue service. However, it
acknowledges that vulnerable people
such as the disabled might benefit
from such a connection.
11
MAINS POWERED SMOKE
ALARMS - GRADE E
The Code states that mains powered
smoke alarms are potentially more
reliable and are recommended to
be installed in existing dwellings
occupied by people who are unlikely
to be able to change a smoke
alarm’s battery.
However, mains powered systems
have their drawbacks; power cuts or
the termination of supply for
whatever reason disables them
totally. They can also be rendered
useless by the tripping of a protective
device, or even - in some cases - by
the fire itself. Householders may also
disable them at the mains all too
easily if false alarms are a problem.
MAINS POWERED SMOKE
ALARMS WITH STAND-BY
SUPPLY - GRADE D
The problems outlined above can
be overcome by using alarms that
incorporate, within each alarm, a
stand-by supply such as a primary
or rechargeable battery.
This sort of system should be
considered, says the Code, if the
reliability of the mains supply is not
high, or if the fire risk is likely to be
high during periods of failure or
disconnection of the mains supply
to the dwelling. In new build and
tenanted two storey properties this
type of alarm is now considered
essential.
This begs a simple question of
landlords - can they be sure that
their tenants are paying their
electricity bills? Given that many
tenants may have low incomes (in
many local authorities, 70% or
more of all tenants are on
subsidised incomes), they may
well experience periods of
disconnection - and yet the
landlord could well be liable if the
alarm fails to sound because the
tenant has not paid his or her bills!
Unfair or not, as the law stands, it
obviously makes good
commercial sense to ensure that
a reliable, high quality back-up
battery facility is in place.
The minimum back-up duration
recommended is 72 hours, and the
Code acknowledges that there
could well be circumstances where
a longer stand-by period is justified
e.g. tenants’ inability to pay their
electricity bill.
FIRE DETECTORS
SUPPLIED WITH
POWER FROM A
COMMON POWER
SUPPLY UNIT
Beyond this, more expensive high
specification systems can offer
connection of all fire detection
devices to a common power supply
via low voltage transformers, or
interlinked fire and security systems.
Again, a minimum 72 hour back-up is
recommended by the Code.
OTHER SYSTEMS
For larger applications, such as
mansions and HMOs, or for areas
with a high risk of fire, higher grade
systems are recommended.