BS 54-20:2006 pdf download – Fire detection and fire alarm systems — Part 20: Aspirating smoke detectors
5 Requirements5.1Compliance
To comply with this standard the detector shall meet the requirements of this clause,which shall beverified by inspection and engineering assessment,and,when tested in accordance with the testsdescribed in Clause 6, shall meet the requirements of the tests.
5.2Individual visual alarm indication
Each aspirating smoke detector shall be provided with integral red visual indicator(s), visible fromoutside the aspirating smoke detector, by which the individual smoke sensing element(s)(see 3.1),which released an alarm, can be identified, until the alarm condition is reset. Where other conditionsof the detector may be visually indicated,they shall be clearly distinguishable from the alarmindication.
5.3Connection of ancillary devices
The detector may provide for connections to ancillary devices (e.g.remote indicators, control relays),but open- or short-circuit failures of these connections shall not prevent the correct operation of thedetector.
5.4 Manufacturer’s adjustments
lt shall not be possible to change the manufacturer’s settings except by special means (e.g. the use ofa special code or tool) or by breaking or removing a seal.
5.5On site adjustment of response behaviour
NOTE1 The effective response behaviour of an aspirating smoke detector is dependent upon both thesensitivity settings of the smoke sensing element and the design of the sampling device.Many types of aspiratingsmoke detectors therefore have facilities to adjust the smoke sensing element sensitvity to suit the applicationand sampling device etc.
lf there is provision for field-adjustment of the sensitivity of the smoke sensing element then:
a) access to the means of adjustment shall be limited by the need for the use of tools or a special code;
b) it shall be possible to determine what sensitivity settings have been selected and to relate these to documentation which describes the sensitivity settings required for different sampling devicesand applications;
NOTE2 These adjustments may be made at the detector or at the control and indicating equipment.
NOTE3 Changing sensitivity settings may affect the classification of the installed ASD – see Clause 7.
c)if it is possible to configure the detector(including the sampling device and the sensitivity
settings) in such a way that the detector does not comply with this standard, it shall be clearlymarked on the detector or in the associated data that,if such configurations are used,thedetector does not comply with this standard.
5.6 Response to slowly developing fires The provision of “drift compensation” (e.g. to compensate for sensor drift due to the build up of dirt in the detector), and/or the provision of algorithms to match a detector to its environment, shall not lead to a significant reduction in the detector’s sensitivity to slowly developing fires. Because it is not practical to make tests with very slow increases in smoke density, an assessment of the detector’s response to slow increases in smoke density shall be made by analysis of the circuit/software, and/or physical tests and simulations. Where such algorithms are used, the detector shall be deemed to meet the requirements of this sub- clause if the documentation and assessment shows:
a) how and why a sensor drifts,
b) how the compensation technique modifies the detector response to compensate for the drift,
c) that suitable limits to the compensation are in place to prevent the algorithms/means being applied outside the known limitations of the sensor and to ensure ongoing compliance with the clauses of this standard,
d) for any rate of increase in smoke density R, which is greater than A/4 per hour (where A is the detector’s initial uncompensated response threshold value), the time for the detector to give an alarm does not exceed 1,6 × A/R by more than 100 s,
e) the range of compensation is limited such that, throughout this range, the compensation does not cause the response threshold value of the detector to exceed its initial value by a factor greater than 1,6.BS 54-20 pdf download.