LPS 1265 Issue 1.1 Requirements and testing procedures for the LPCB approval and listing of carbon monoxide fire detectors using electrochemical cells.
Carbon monoxide (CO) is a known product of the combustion of carbon-based materials. It is an invisible and odourless gas which, unlike smoke, cannot be detected by humans. When present in the atmosphere in sufficient quantity, CO can seriously impair the ability of people to react in a fire situation and can eventually lead to their death. In certain conditions, in which the fire is starved of oxygen and develops slowly, a dangerous concentration of CO may be present in the atmosphere before other fire detectors are able to operate. This can make CO fire detectors suitable for certain applications for the protection of life.
Although there are many techniques for sensing and detecting the presence of CO, not all of the available sensor types are suitable for use in fire detectors. One sensor, the electrochemical cell, has proven suitable for fire detection applications, and is being used in commercially available products. The electrochemical cell does however have known weaknesses. These include sensitivity to substances other than CO that may be present in the atmosphere. In addition, cell performance may be degraded by long-term exposure to very low or very high humidity.
This standard has been drafted to allow the evaluation of detectors using electrochemical cells and includes tests specifically intended to demonstrate that the electrochemical cell used has adequate performance for fire detection applications. Other types of CO sensor may be suitable for use in fire detectors. However, the tests in this standard may not be sufficient to demonstrate the robustness of any other type of sensor.
The test schedule included in this standard also recognises certain strengths and weaknesses in the application of CO fire detectors. For example, it is noted in BS 5839-1:2002 that CO detectors are best suited for the detection of smouldering fires and can be relatively insensitive to free burning fires supported by a plentiful supply of oxygen. In recognition of this, the test schedule includes only the smouldering fires, TF2 and TF3, from EN 54-7: 2000. These are supplemented by one other fire representing deep-seated combustion.
A particular strength of electrochemical cells is that they do not respond to a short- term exposure to steam or condensation, and can therefore be used in some applications in which smoke detectors would be unsuitable. To verify this strength, a cyclic damp heat operational test is included in the standard.
Because this standard has been drafted specifically for CO fire detectors using electrochemical cells, great care must be used in interpreting the results of these tests if applied to detectors using other sensing technologies.
Response threshold value
The CO concentration in the proximity of the specimen at the moment that it generates an alarm signal, when tested as described in 5.1.5.
Individual alarm indication
Each detector shall be provided with an integral red visual indicator, by which the individual detector that released an alarm, can be identified, until the alarm condition is reset. Where other conditions of the detector can be visually indicated, they shall be clearly distinguishable from the alarm indication, except when the detector is switched into a service mode. For detachable detectors, the indicator may be integral with the base or the detector head. The visual indicator shall be visible from a distance of 6 m directly below the detector, in an ambient light intensity up to 500 lux.
Connection of ancillary devices
Where the detector provides for connections to ancillary devices (e.g. remote indicators, control relays), open- or short-circuit failures of these connections shall not prevent the correct operation of the detector.
Monitoring of detachable detectors
For detachable detectors, a means shall be provided for a remote monitoring system (e.g. the control and indicating equipment) to detect the removal of the head from the base, in order to give a fault signal.
Manufacturer’s adjustments
It shall not be possible to change the manufacturer’s settings except by special means (e.g. the use of a special code or tool) or by breaking or removing a seal.
On-site adjustment of response behaviour
If there is provision for on-site adjustment of the response behaviour of the detector then:
- for each setting at which the manufacturer claims compliance with this standard, the detector shall comply with the requirements of this standard, and access to the adjustment means shall only be possible by the use of a code or special tool or by removing the detector from its base or mounting;
Rate-sensitive response behaviour
The response threshold value of the detector may depend on the rate of change of CO concentration in the vicinity of the detector. Such behaviour may be incorporated in the detector design to improve the discrimination between ambient CO levels and those generated by a fire. If such rate sensitive behaviour is included then it shall not lead to a significant reduction in the detector’s sensitivity to fires, nor to a significant increase in the probability of false alarm.
Additional requirements for software controlled detectors
To enable correct operation of the detectors, this data should describe the requirements for the correct processing of the signals from the detector. This may be in the form of a full technical specification of these signals, a reference to the appropriate signalling protocol or a reference to suitable types of control and indicating equipment etc.
The manufacturer shall submit documentation which gives an overview of the software design. This documentation shall be in sufficient detail for the design to be inspected for compliance with this standard and shall include at least the following:
Design detail
The manufacturer shall have available detailed design documentation, which only needs to be provided if required by the testing authority. It shall comprise at least the following:
Software design
In order to ensure the reliability of the detector, the following requirements for software design shall apply:
- the software shall have a modular structure;
- the design of the interfaces for manually and automatically generated data shall not permit invalid data to cause error in the program operation;
- the software shall be designed to avoid the occurrence of deadlock of the program flow.
The storage of programs and data
The program necessary to comply with this standard and any pre-set data, such as manufacturer’s settings, shall be held in non-volatile memory. Writing to areas of memory containing this program and data shall only be possible by the use of some special tool or code and shall not be possible during normal operation of the detector.
Site-specific data shall be held in memory which will retain data for at least two weeks without external power to the detector, unless provision is made for the automatic renewal of such data, following loss of power, within 1 h of power being restored.
TEST METHODS
Atmospheric conditions for tests
Unless otherwise stated in a test procedure, the testing shall be carried out after the test specimen has been allowed to stabilize in the standard atmospheric conditions for testing as described in IEC 60068-1:1988+A1:1992 as follows
Operating conditions for tests
If a test method requires a specimen to be operational, then the specimen shall be connected to suitable supply and monitoring equipment with characteristics as required by the manufacturer’s data. Unless otherwise specified in the test method, the supply parameters applied to the specimen shall be set within the manufacturer’s specified range(s) and shall remain substantially constant throughout the tests. The value chosen for each parameter shall normally be the nominal value, or the mean of the specified range. If a test procedure requires a specimen to be monitored to detect any alarm or fault signals, then connections shall be made to any necessary ancillary devices (e.g. through wiring to an end-of-line device for conventional detectors) to allow a fault signal to be recognised.
Mounting arrangements
The specimen shall be mounted by its normal means of attachment and in its normal orientation in accordance with the manufacturer’s instructions. If these instructions describe more than one method of mounting, or more than one acceptable orientation, then the method considered to be most unfavourable shall be chosen for each test.
Tolerances
Unless otherwise stated, the tolerances for the environmental test parameters shall be as given in the basic reference standards for the test (e.g. the relevant part of IEC 60068).
If a requirement or test procedure does not specify a tolerance or deviation limits, then deviation limits of ± 5 % shall be applied.
Measurement of response threshold value
The specimen, for which the response threshold value is to be measured, shall be installed in the CO tunnel, described in annex A, in its normal operating position, by its normal means of attachment. The orientation of the specimen, relative to the direction of airflow, shall be the least sensitive orientation, as determined in the directional dependence test, unless otherwise specified in the test procedure.
Before commencing each measurement, the CO tunnel shall be purged to ensure that the tunnel and the specimen are free from CO.
The air velocity in the proximity of the specimen shall be (0.35 ± 0.15) m s-1 during the measurement, unless otherwise specified in the test procedure.
Unless otherwise specified in the test procedure, the air temperature in the tunnel shall be (23 ± 5) °C and shall not vary by more than 5 K for all the measurements on a particular detector type.
The specimen shall be connected to its supply and monitoring equipment as described in 5.1.2, and shall be allowed to stabilise for a period of at least 15 min, unless otherwise specified by the manufacturer.
CO shall be introduced into the tunnel such that the rate of increase of CO concentration is between 1 ppm min-1 and 6 ppm min-1. For detectors whose response is rate sensitive, the manufacturer may specify a rate of increase within this range to ensure that the measured response threshold value is representative of the static response threshold value of the detector.
The rate of increase in CO concentration shall be similar for all measurements on a particular detector type.
The CO concentration at the moment that the specimen gives an alarm shall be recorded as c (ppm). This shall be taken as the response threshold value.
Provision for tests
The following shall be provided for testing compliance with this standard:
- For detachable detectors: twenty-four detector heads and bases;
For non-detachable detectors: twenty-four specimens;
- The data required in 4.9.
NOTE 1: Detachable detectors comprise at least two parts; a base (socket) and a head (body). If the specimens are detachable detectors, then the two, or more, parts together are regarded as a complete detector.
The specimens submitted shall be representative of the manufacturer’s normal production with regard to their construction and calibration.
NOTE 2: This implies that the mean response threshold value of the twenty-four specimens, found in the reproducibility test should also represent the production mean, and that the limits specified in the reproducibility test should also be applicable to the manufacturer’s production.
The specimens shall be tested according to the following test schedule (see Table 1). After the reproducibility test, the four least sensitive specimens (i.e. those with the highest response thresholds) shall be numbered 21 to 24, and the others shall be numbered 1 to 20 arbitrarily:
- Repeatability
- Object
To show that the detector has stable behaviour with respect to its sensitivity even after a number of alarm conditions.
The response threshold value of the specimen to be tested shall be measured as described in 5.1.5 six times.
The specimen’s orientation relative to the direction of airflow is arbitrary, but it shall be the same for all six measurements.
The maximum response threshold value shall be designated cmax, the minimum value shall be designated cmin.
Directional dependence
To confirm that the sensitivity of the detector is not unduly dependent on the direction of airflow around the detector.
The response threshold value of the specimen to be tested shall be measured eight times as described in 5.1.5, the specimen being rotated 45° about its vertical axis between each measurement, so that the measurements are taken for eight different orientations relative to the direction of air flow.
The maximum response threshold value shall be designated cmax , the minimum value shall be designated
Reproducibility
To show that the sensitivity of the detector does not vary unduly from specimen to specimen and to establish response threshold value data for comparison with the response threshold values measured after the environmental tests.
Long term stability
To confirm that the detectors are stable over long periods of time.
Connect the detector to suitable supply and monitoring equipment and place it in an environment free of CO and atmospheric contaminants. Measure the response threshold value, as described in 5.1.5, at 28 days, 56 days and 84 days from the start of the test. Designate the highest of the values measured in this test and that measured for the same detector in the reproducibility test as cmax. Designate the lowest of the values measured in this test and that measured for the same detector in the reproducibility test as cmin.
Variation in supply parameters
To show that, within the specified range(s) of the supply parameters (e.g. voltage), the sensitivity of the detector is not unduly dependent on these parameters.
The response threshold value of the specimen shall be measured as described in 5.1.5, at the upper and lower limits of the supply parameter (e.g. voltage) range(s) specified by the manufacturer.
The maximum response threshold value shall be designated cmax and the minimum value shall be designated
Air movement
To show that the sensitivity of the detector is not unduly affected by the rate of the airflow.
Dry heat (operational)
To demonstrate the ability of the detector to function correctly at high ambient temperatures appropriate to the anticipated service environment.
The specimen to be tested shall be installed in the CO tunnel described in annex A, in its least sensitive orientation, with an initial air temperature of (23 ± 5) °C, and shall be connected to its supply and monitoring equipment.
Cold (operational)
To demonstrate the ability of the detector to function correctly at low ambient temperatures appropriate to the anticipated service environment.
The specimen to be tested shall be installed in the CO tunnel described in annex A, in its least sensitive orientation, with an initial air temperature of (23 ± 5) °C, and shall be connected to its supply and monitoring equipment.
Damp heat, cyclic (operational)
To demonstrate the ability of the detector to function correctly at high relative humidities (with condensation), which can occur for short periods in the anticipated service environment.
The test apparatus and procedure shall be as described in IEC 60068-2-30:1980 +A1:1985, using the Variant 1 test cycle and controlled recovery conditions, and as described below.
The specimen shall be mounted as described in 5.1.3 and shall be connected to supply and monitoring equipment as described in 5.1.2.
The following severity of conditioning (IEC 60068-2-30 Severity 1) shall be applied:
Damp heat, steady state (endurance)
To demonstrate the ability of the detector to withstand the long term effects of humidity in the service environment. (e.g. changes in electrical properties of materials, chemical reactions involving moisture, galvanic corrosion, dilution and expansion of cell electrolyte etc.)
The test apparatus and procedure shall be as described in IEC 60068-2-56:1988 Test Cb or IEC 60068-2-3:1969+A1:1984 Test Ca, and as described below.
The greater of the response threshold value measured in this test and that measured for the same specimen in the reproducibility test, shall be designated cmax , and the lesser shall be designated cmin
5.12 Low humidity, steady state (endurance)
To demonstrate the ability of the detector to withstand long periods of low humidity in the service environment. (i.e. to evaluate its resistance to the drying out of electrolyte in the electrochemical cell.)
The specimen shall be mounted as described in 5.1.3 but shall not be supplied with power during the conditioning.
The following conditioning shall be applied:
Temperature: (25 ± 3) °C
Relative Humidity: (11 ± 1) %
Duration: 21 days
Sulphur dioxide SO2 corrosion (endurance)
To demonstrate the ability of the detector to withstand the corrosive effects of sulphur dioxide as an atmospheric pollutant.
The test apparatus and procedure shall be as described in
IEC 60068-2-42:1982 Test Kc, except that the conditioning shall be as described
below.
The specimen shall be mounted as described in 5.1.3. It shall not be supplied with power during the conditioning, but it shall have untinned copper wires, of the appropriate diameter, connected to sufficient terminals, to allow the final measurement to be made, without making further connections to the specimen.
Shock (operational)
To demonstrate the immunity of the detector to mechanical shocks, which are likely to occur, albeit infrequently, in the anticipated service environment.
The test apparatus and procedure shall be as described in IEC 60068-2-27:1987 Test Ea, except that the conditioning shall be as described below.
The greater of the response threshold value measured in this test and that measured for the same specimen in the reproducibility test, shall be designated cmax , and the lesser shall be designated
Impact (operational)
To demonstrate the immunity of the detector to mechanical impacts upon its surface, which it may sustain in the normal service environment, and which it can reasonably be expected to withstand.
The test apparatus shall consist of a swinging hammer incorporating a rectangular-section aluminium alloy head (Aluminium alloy Al Cu4 Si Mg complying with ISO 209-1:1989, solution treated and precipitation treated condition) with the plane impact face chamfered to an angle of 60° to the horizontal, when in the striking position (i.e. when the hammer shaft is vertical). The hammer head shall be (50 ± 2.5) mm high, (76 ± 3.8) mm wide and (80 ± 4) mm long at mid height as shown in Figure E.1. A suitable apparatus is described in annex C.
The specimen shall be rigidly mounted to the apparatus by its normal mounting means and shall be positioned so that it is struck by the upper half of the impact face when the hammer is in the vertical position (i.e. when the hammerhead is moving horizontally). The azimuthal direction and position of impact, relative to the specimen shall be chosen as that most likely to impair the normal functioning of the specimen. The specimen shall be connected to its supply and monitoring equipment as described in 5.1.2.
Vibration, sinusoidal, (operational)
To demonstrate the immunity of the detector to vibration at levels considered appropriate to the normal service environment.
The test apparatus and procedure shall be as described in IEC 60068-2-6:1995+Corr.: 1995 Test Fc, and as described below.
The specimen shall be mounted on a rigid fixture as described in 5.1.3 and shall be connected to its supply and monitoring equipment as described in 5.1.2. The vibration shall be applied in each of three mutually perpendicular axes, in turn. The specimen shall be mounted so that one of the three axes is perpendicular to its normal mounting plane.
Vibration, sinusoidal (endurance)
To demonstrate the ability of the detector to withstand the long term effects of vibration at levels appropriate to the service environment.
The test apparatus and procedure shall be as described in IEC 60068-2-6:1995+Corr.: 1995 Test Fc, and as described below.
The specimen shall be mounted on a rigid fixture as described in 5.1.3, but shall not be supplied with power during conditioning. The vibration shall be applied in each of three mutually perpendicular axes, in turn. The specimen shall be mounted so that one of the three axes is perpendicular to its normal mounting axis.
Electromagnetic Compatibility (EMC), Immunity tests (operational)
The following EMC immunity tests shall be carried out, as described in EN 50130-4:1995+A1:1998:
- Electrostatic discharge;
- Radiated electromagnetic fields;
- Conducted disturbances induced by electromagnetic fields;
- Fast transient bursts;
- Slow high energy voltage surges.
Fire sensitivity
To show that the detector has adequate sensitivity to a range of fire types known to produce potentially dangerous levels of CO and which a detector would be required to detect for application in fire detection systems for buildings.
The specimens are mounted in a standard fire test room and are exposed to a series of test fires designed to produce smoke and CO.
Assessment of exposure to high concentrations of carbon monoxide
To demonstrate the ability of the detector to withstand exposure to high levels of carbon monoxide which may be encountered during a fire condition.
The specimen shall be mounted as described in 5.1.3 and shall be connected to supply and monitoring equipment as described in 5.1.2.
The specimen shall be subjected to an atmosphere containing 500 ppm ±10% carbon monoxide for a period of 1 h.
The specimen shall be monitored to detect any alarm or fault signals.
During the last five minutes of the conditioning the detector shall be reset in accordance with the manufacturers’ instructions.
After a recovery period of between 1 h and 2 h at the standard laboratory conditions, the response threshold value shall be measured as described in 5.1.5.
The greater of the response threshold value measured in this test and that measured for the same specimen in the reproducibility test, shall be designated cmax , and the lesser shall be designated cmin .
The detector shall remain in the alarm condition during the conditioning and shall generate an alarm signal within 1 min of being reset at the end of the conditioning period.
CO measuring instrument
The response threshold of CO fire detectors is characterized by the concentration of CO in air measured in the proximity of the detector, at the moment that it generates an alarm signal.
The instrument used for the measurement of CO in the tunnel shall have a measurement error not exceeding 3 ppm + 5% of the measured CO concentration, for concentrations up to 300 ppm. The response time of the instrument shall be such that it does not cause a measurement error at the highest rate of increase used for tunnel measurements greater than 5 ppm.
Obscuration meter
The obscuration meter shall have characteristics as defined in EN54-7:2000, annex C.
- grooved hot plate
- temperature sensor
- wooden sticks