Automatic fire detection systems Radio based systems

Question 1

What are the safeguards

Answer 1

Used to prevent electronic interference

Zoned
repeaters

Radio systems should only be installed after a
radio survey is undertaken to confirm that:
(i) There are no other sources of radio transmission
which could interfere with the system;
(ii) There is no possibility of interaction
between the system and other radio linked
systems.
(iii) There is adequate strength of signal between
components.

Question 2

The advantages of a radio system

are. List

Answer 2

(i) It is quick to install with no wiring and,
therefore, there is no requirement to redecorate,
which, in turn, means little disturbance.
(ii) The risk of wiring damage, which could isolate
several detectors, is avoided.
(iii) The location of the detectors is flexible, e.g.
they can be installed in buildings under construction
or areas where partitions are frequently
moved.
(iv) Radio links will function even in a fire situation,
so there is no need for special fire-protected
cabling.
(v) Extra zones can easily be connected to the
main receiver, or remote indicator panels set
up.

Question 3

Disadvantages of a radio based system are. List.

Answer 3

(i) The initial capital cost of radio system equipment
is relatively high.
(ii) Temporary screening may occur, although
frequent ‘report-ins’ will indicate this fairly
quickly.
(iii) The system has to be designed very carefully
to avoid clashes of frequencies and interference
either into or from the system (see
Section 15.2 above).
(iv) There may be a significant delay between
occurrence of a fault and its indication on the
control equipment. This arises because limitations
of allowed frequency spectrum can
lead to interference between simultaneous
signals at very frequent intervals. BS 5839
suggests that radio links be monitored so that,
if signals are not received from any remote
component, the failure will be indicated at the
central control and indicating equipment
within two hours of the fault occurring.
(v) Frequent tests or fire drills can seriously
reduce fire alarm sounder battery life

Question 4

BS 5839 recommends the types of power supplies
for detectors, manual call points and sounders
forming part of a radio interconnected system

Answer 4

(i) The normal mains supply plus a reserve battery
(primary or continuously charged secondary).
(ii) A primary battery plus a reserve second primary
battery. The primary battery used for
the normal supply should have an operational
life of at least one year.
(iii) Power supplies having one or more primary
batteries are required to give at least 30 days
warning of impending failure of any primary
battery.
(iv) Where the power supplies to any radiolinked
component can maintain the component
in operation for no more than seven
days, or 30 minutes in the alarm condition, a
warning should be given.