Apollo ORB-RB-10004-APO Product Manual - Page 5

Browse online or download pdf Product Manual for Security Sensors Apollo ORB-RB-10004-APO. Apollo ORB-RB-10004-APO 16 pages. Orbis series
Also for Apollo ORB-RB-10004-APO: Product Manual (17 pages)

Print Page

Should I use optical detectors to detect

smoke in all applications?

Optical detectors have long been

recommended as good general purpose

smoke detectors. Laboratory tests

have been carried out to compare the

performance of optical detectors in

the standard test fires described in the

European standard EN54.

The results of these tests are given in

Fig 1. The graph shows the acceptable

response in terms of smoke density which

is given as 'm' on the y axis. Detectors

must respond before the end of test which

is an 'm' = value of 2. The performance

of Orbis detectors is given as a solid line

which shows how evenly the optical

detectors respond to the test fires.

If detectors respond too quickly (the lower

shaded portion of the graph) they may be

too sensitive and hence likely to generate

false alarms.

If detectors respond too slowly (the upper

shaded portion) they are in danger of not

changing to the alarm state before the

end of test.

An even response in the centre is the

ideal response.

Orbis Optical detector response to Test Fires

2.00

1.50

1.00

0.50

0.00

TF2

TF3

Figure 1

2.00

1.50

1.00

0.50

When would I use a multisensor?

Multisensor smoke detectors have a heat

sensing element which makes them more

sensitive if a fire develops heat as well as

smoke. This speeds up the response of

the detector in certain fires where heat is

generated rapidly, for instance in test fire

TF5, which is an open, flaming liquid fire

in which n-heptane is burned.

Multisensor smoke detectors are

recommended for open flaming fire risks.

If there is any doubt as to whether an

optical detector or a multisensor smoke

detector should be used it is wise to fit a

multisensor smoke detector.

Where would there be a need to install

heat detectors?

Heat detectors should be used if it is not

possible to use smoke detectors. This

will be the case for example in kitchens

and smoking areas and where normal

industrial processes produce substances

which could be mistaken for smoke by

a smoke detector, eg, flour mills, textile

mills or loading bays with diesel-engined

vehicles.

The type of substance encountered here

would cause frequent false alarms if

smoke detectors were fitted, so a heat

detector is used instead.

Poor

Acceptable

values

Too sensitive

TF4

TF5

Test Fires

Poor

TF5

Acceptable

values

CONVENTIONAL DETECTORS

How are heat detectors classified?

EN54 classifies heat detectors according

to the ambient temperature in which

they will be working and according to

whether they may be tested as 'static'

detectors (changing to alarm at a preset

temperature) or 'rate-of-rise' (changing to

alarm at a preset increase of temperature).

Heat detectors may also be marketed

without either classification; but then the

detection characteristics are unknown.

All Orbis heat detectors are tested and

classified as either static or rate-of-rise.

So what is the best way to choose a heat

detector?

To make things easier we have produced

a flow chart which is shown on page 10.

2.00

1.50

1.00

0.50

0.00

TF2

TF3

Test Fires

Comparisons of response between

Orbis Optical & Multisensor

2.00

1.50

1.00

0.50

0.00

Orbis Optical

Test Fires (TF5)

Figure 2

Poor

Acceptable

values

Too sensitive

TF4

TF5

Poor

TF5

Acceptable

values

Too sensitive

Orbis Multisensor