Principles of auto fire detection

Question 1

The types of detector are

Answer 1

Smoke
Heat
Flame
Line

Question 2

Category M systems

Answer 2

manually
operated systems and therefore do
not incorporate automatic detectors.

Question 3

Category L systems are

Answer 3

automaticfire detection systems intended for
the protection of life. Category L
systems are sub-divided into five
types:
L1, L2.L3,L4 and L5

Question 4

What are category P systems

Answer 4

Category P systems are automatic
fire detection systems designed for
the protection of property.
Category P systems are divided into two types.

Question 5

In the classification of detectors, what is an Analogue detector

Answer 5

A detector which is part of a system where the output
signal representing the value of the sensed fire
phenomena is analysed, either at the detector or
within the control equipment. The purpose of the
analysis is to identify conditions that are not representative
of fire, which may result in a false alarm
from a ‘two state’ alarm system.

Question 6

In the classification of detectors what is a two state detector

Answer 6

A ‘two state’ fire detector is one which is only
capable of indicating two output states, ‘normal’
and ‘fire’ conditions

Question 7

In the classification of detectors what is a multi state detector

Answer 7

A multi state detector is one capable of indicating
more than two output states, which include
‘normal’, ‘fire’ and other abnormal conditions.
Multi state detectors are less likely to give false
alarms of fire.

Question 8

when classifying detectors what are the 3 classifications

Answer 8

Analogue
two state
multi

Question 9

Generally, products of the fire will be transported
to the detector and they will be ‘checked’ against
the prevailing environment. When the detection
system is sufficiently ‘sure’ that what it is detecting
is not an ‘environmental fluctuation’ it will
‘decide’ that a fire exists and raise the alarm. All
this appears straightforward but there are many
ways in which an AFD system could fail. For
example

Answer 9

(i) Wind or draught fluctuations causing a false
temperature reading.
(ii) Obstructions to smoke travel heat or flame
radiation preventing the detector from acting
quickly enough
(iii) The detector may be unable to detect the
products of that particular fire.
(iv) A fault in the system may have made the
detector inoperative.
(v) The system may be switched off for servicing
(more strictly a maintenance system failure).
(vi) The detector may be prone to false alarms, so
that a genuine alarm may be ignored until a
late investigation is made.
(vii) In certain areas at certain times insects
invading detectors may trigger false alarms

Question 10

Products from fire will travel either by radiation or

by physical movement of the atmosphere. Discuss

Answer 10

Radiation is fast moving in straight lines, physical
movement is slower but more flexible. A broad
term used for physical transport is ‘mass transport’
and it is by this means that most smoke and heat
detectors work. Flame detectors use radiation

Question 11

What is mass transport

Answer 11

A broad term given to the physical movement of the products of fire .