CONTRACT RESEARCH REPORT 360/2001Technotrend CO-350.....49 Appendix 18. CO Alarm Field Trial.....50...

HSEHealth & Safety

Executive

Joint industry project on carbonmonoxide issues: Long-term reliability

of domestic CO alarms

Prepared by Advantica Technologies Ltd

for the Health and Safety Executive

CONTRACT RESEARCH REPORT

360/2001

HSEHealth & Safety

Executive

Joint industry project on carbonmonoxide issues: Long-term reliability

of domestic CO alarms

Advantica Technologies LtdAshby Road

LoughboroughLeicestershire

LE11 3GR

This report describes a work programme to investigate the long-term reliability of domestic carbonmonoxide (CO) alarms, initiated as part of a joint industry project (JIP) on carbon monoxide issues. Alarge number of commercially available models, covering a range of detector technologies, wereinitially assessed using laboratory test equipment designed for the purpose. From the results, asuitable number were selected for further long-term field trials. After one year of service, only one ofthese models is both currently available with the UK and still performing satisfactorily. Severalappropriate recommendations are made.

This report and the work it describes were jointly funded by BG Group, the Department of Trade andIndustry (DTI) and the Health and Safety Executive (HSE). Its contents, including any opinions and/orconclusions expressed, are those of the author(s) alone and do not necessarily reflect HSE or DTIpolicy.

HSE BOOKS

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© Crown copyright 2001Applications for reproduction should be made in writing to:Copyright Unit, Her Majesty’s Stationery Office,St Clements House, 2-16 Colegate, Norwich NR3 1BQ

First published 2001

ISBN 0 7176 2085 9

All rights reserved. No part of this publication may bereproduced, stored in a retrieval system, or transmittedin any form or by any means (electronic, mechanical,photocopying, recording or otherwise) without the priorwritten permission of the copyright owner.

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Foreword by HSE This report sets out the results of a two-year project on the long-term reliability of CO alarms, which has been jointly funded by BG plc, the Department of Trade and Industry and the HSE, and which formed part of a wider Joint Industry Programme on Carbon Monoxide issues. The report and the work it describes should not be construed as a comprehensive product survey of all CO alarms on the market. Rather the studies were intended to provide an assessment, from a representative sample of alarms and sensor types currently available within the UK, of the stability and longer-term reliability of such devices, as a basis for further work. Some models were kitemarked to the relevant British Standard, BS 7860: 1996 ‘Specification for Carbon Monoxide detectors (electrical) for domestic use’, or purported to be BS compliant. Others were not. However, neither the current BS nor a proposed European (CENELEC) standard give a guarantee of long-term service reliability. The only long-term test of sensor reliability is limited to three months and is not carried out in conditions representative of a domestic environment. Therefore, assessment of the long-term reliability of CO alarms over a period of one year in domestic premises was included in this project. Various types of alarm, covering the range of sensor technologies currently available within the UK, were subjected to initial laboratory screening, based on the BS, with a smaller number being selected for a one-year field trial for reliability. Therefore, not all the CO alarms available were subjected to a full field trial, and it should not necessarily be inferred from the results of the project that those not selected would have performed similarly. It should also be noted that some manufacturers of models tested have disputed some of the findings. As the health and safety regulator, HSE’s interest in this area will be to focus on work to address possible deficiencies in the current standards criteria and test protocol, with a view to the development of an agreed standard covering long-term sensor reliability. This would be consistent with recommendation 33 in the HSC report “Fundamental Review of Gas Safety Regime: Proposals for Change” on the question of encouraging wider use of CO alarms in domestic premises, and the issue of possible future mandatory requirements in this area. While acknowledging the limitations in the project as outlined above and the fact that improvements in sensor technology have taken place since the work was completed, the HSE is publishing this report in the public interest, as a contribution to the wider debate on the potential of CO alarms to assist in achieving the target for improved gas consumer safety set out in the HSC’s Fundamental Review recommendations.

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Joint Industry Project on Carbon Monoxide Issues

Long-Term Reliability of Domestic CO Alarms

CONTENTS 1. BACKGROUND...........................................................................................1 2. TEST METHODOLOGY ...........................................................................2

2.1 Alarm Set Levels........................................................................................................2 2.2 Further Considerations...............................................................................................3 2.3 Test Equipment ..........................................................................................................3

3. PERFORMANCE ASSESSMENT.............................................................5

3.1 Initial Specimens and Results ....................................................................................5 3.2 Later Developments ...................................................................................................6

4. FIELD TRIAL ..............................................................................................8

4.1 Testing and Results ....................................................................................................8 4.2 Sensor Summary ........................................................................................................9

5 DISCUSSION AND OBSERVATIONS...................................................10 6 CONCLUSIONS.........................................................................................12 7 RECOMMENDATIONS...........................................................................13 REFERENCES..................................................................................................14 Table 1. Summary of Domestic CO Alarm Models Considered.........17 Table 2. Results of Initial Checks on Field Trial Units .........................18 Table 3. Feedback from Field Trial Participants ....................................19 Table 4. Location of Installed Field Trial Units ......................................20 Table 5. CO Sensors Summary ..................................................................21 Table 6. Summary of Domestic CO Alarms and Sensors Tested .....22

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Figure 1. Performance Requirements.......................................................23 Figure 2. Schematic of Special Test Chamber .......................................23 Figure 3. General View of Test Rig ............................................................24 Figure 4. Close-up View of Special Test Chamber................................24 Figure 5. General View of Test Rig Instrumentation ............................25 Figure 6. Build-up of CO in Special Test Chamber ...............................25 Figure 7. Testing Results Sheet .................................................................26 Figure 8. Siting of Field Trial Units............................................................27 Figure 9. SF330KM Field Trial Results .....................................................28 Figure 10. Dicon CO805B Field Trial Results .........................................29 Figure 11. Schlumberger XH-443B Field Trial Results ........................30 Figure 12. Kidde Nighthawk Field Trial Results ....................................31 Appendix 1. Anglo Nordic 570 1200 ..........................................................32 Appendix 2. BRK CO1000BE.......................................................................33 Appendix 3. BRK FDC3EC ...........................................................................34 Appendix 4. BRK WICOE..............................................................................35 Appendix 5. Detecta 9 ...................................................................................36 Appendix 6. Dicon CO805 & CO810 ..........................................................37 Appendix 7. EI 225 .........................................................................................38 Appendix 8. GasGuard G 021 CO ..............................................................39 Appendix 9. Gas Maestro GSS 2002 .........................................................40 Appendix 10. GasWatch 200 .......................................................................42 Appendix 11. Monox.....................................................................................43 Appendix 12. Nighthawk Basic 900-0081.................................................44 Appendix 13. Nighthawk Deluxe 900-0089 ..............................................45 Appendix 14. Schlumberger XH-443B ......................................................46 Appendix 15. Senco model ONE ................................................................47 Appendix 16. SF330KM.................................................................................48 Appendix 17. Technotrend CO-350 ...........................................................49 Appendix 18. CO Alarm Field Trial ............................................................50 Appendix 19. Domestic CO Alarm Installation Questionnaire...........55 Appendix 20. GRI Report 96/0055 ..............................................................57

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SUMMARY

The health effects of carbon monoxide (CO) on the human body are well documented, but there has recently been an increasing awareness and interest amongst the general public. The traditional view within the gas industry has been that proper installation and maintenance of gas appliances should obviate the risk of significant CO build-up inside a home from that particular source. However, the use of domestic CO alarms may become appropriate as a further safety assurance to consumers, provided that adequate long-term behaviour can be assured.

The crucial first step in assessing CO detectors is to decide on suitable alarm levels relevant to the domestic environment, and those specified in BS 7860 are considered to be entirely appropriate for making objective comparisons. Unfortunately, BS 7860 does not include long-term testing, which is the purpose of this programme. The North American standards covering domestic CO alarms have been revised recently, to address the problems that are being experienced with long-term reliability of such devices. However, it is believed that current UK and draft European documents are inherently superior.

A test rig has been built and commissioned, and suitable procedures devised, to enable specimens to be subjected to different concentrations of CO, under a wide range of ambient temperatures, humidities and mains supply voltages, as appropriate. Commercially available models of domestic CO alarm were identified as potentially compatible with the aims of this programme, and these have been assessed using the test rig. Based on the results, models have been selected for further investigation by field trial, to check their long-term performance in typical domestic premises

A table has been produced, which summarises all the work carried out under this project. Results of earlier testing have also been included, where appropriate, with the different CO alarms being categorised by the sensing technology employed. Of the models selected for field trial and currently available within the UK, only the SF330KM has been found to be still satisfactory after one year in service.

It is concluded that the best indication of adequate initial performance by domestic CO alarms, is a kitemark to BS 7860. Unfortunately, this does not necessarily guarantee long-term reliability. Furthermore, the results of tests carried out suggest that claims by some manufacturers of product compliance to BS 7860 in advertising and other literature, and on the products themselves, are not always justified.

It is recommended that pressure should be maintained within Cenelec, to ensure that the draft European standard for domestic CO alarms, prEN 50291, becomes as close as possible to BS 7860. In addition, clear and simple rules for the siting of domestic CO alarms should be generated for the draft European guidance document, prEN 50292, which should also address the future likelihood of combined CO, smoke and/or natural gas alarms.

Recommendations are made that the existing field trial should continue, in order to further evaluate the SF330KM and Schlumberger XH-443B. The Kidde Nighthawk Basic 900-0081 and Dicon CO805B should be withdrawn, due to excessive drifting in alarm calibration levels. In addition, samples of new models should be obtained for initial assessment and longer-term testing if appropriate. A programme of testing for possible interferant effects of household substances should be performed, including the products of cooking and smoking.

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1. BACKGROUND The health effects of carbon monoxide (CO) on the human body are well documented (Reference 1) but there has recently been an increasing awareness and interest amongst the general public. One reason has been a number of well-publicised incidents, stimulating media interest in the subject.

It has long been recognised that incomplete combustion, for whatever reason, can create hazardous levels of CO. The traditional view within the gas industry has been that proper installation and maintenance of gas appliances (Reference 2) should obviate the risk of significant CO build-up inside a home from that particular source, and this is reflected in current Government (DTI and HSC/E) advice to consumers. However, it is also accepted that domestic CO alarms have a role to play as a further safety assurance to consumers, provided that adequate long-term behaviour can be assured, and this is the subject of the present programme, commencing in April 1998.

The CO alarms considered in this project are shown in Table 1, categorised according to the sensing technology used. A number of sensing techniques can be utilised for detecting CO, but only three have had significant impact in the domestic application so far, as described below;

Reagent Gel: Also referred to as "colourimetric", this system relies on a colour change affecting the passage of a light beam. It is claimed to mimic the action of the human body in terms of taking in and expelling CO, and hence is sometimes called "biomimetic". However, the main drawback in terms of the CO alarm application is the very slow recovery time. This criticism also applies to non-alarming indicator cards which are cheaply available, but which additionally suffer from cross-sensitivity and poisoning problems.

Semiconductor: Usually based on a metallic oxide, with various dopants and/or catalysts added to improve sensitivity and selectivity. The sensing material normally needs to be heated to a working temperature of 300°C to 400°C, which often necessitates mains voltage supplies to provide the power requirements. Semiconductors have been used in this application for many years and, whilst by no means ideal, they have previously been well characterised and are relatively inexpensive. New sources of semiconductor sensors are becoming available, especially from the Far East, which are claimed to give improved long-term stability.

Electrochemical Cell: Well-established technology, but only recently targeted at this application, due to previous concerns over cost and longevity. New models have been developed which are much smaller, and promise high accuracy together with low power requirements, enabling operation with dry-cell batteries. However, service lifetime may still be a potential problem.

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2. TEST METHODOLOGY

2.1 Alarm Set Levels

The crucial first step in assessing CO detectors is to decide on suitable alarm levels relevant to the domestic environment. There are many (usually conflicting) aspects to be considered, as detailed in Reference 1. It is a complex problem, because the health effects depend upon time of exposure, as well as CO concentration in the ambient air. Other important factors are;

� the rate at which CO accumulates in the blood as carboxyhaemoglobin (COHb),

� the rate of CO concentration change, both before and after alarming, and

� the susceptibility of the CO detector to false alarms, for whatever reason.

Figure 1 shows a curve for 5% COHb, taken from Reference 1, assuming typical physiological features (eg. body weight and blood volume) and physical activity levels, for the domestic application. Two alarm bands were proposed, taking into account all the various technical and medical considerations, and these were accepted as the basis for the relevant British Standard (ie. BS 7860:1996, Reference 3). These alarm bands are;

� under normal conditions of CO accumulation:

100±50 ppm CO within 30 minutes, but not less than 10 minutes, and

� for conditions of rapidly rising CO concentration:

250±100 ppm CO within 6 minutes.

BS 7860 covers all aspects of design and construction, but the requirements relating specifically to alarm performance were devised partly with a view to keeping the costs of obtaining certification approval within reasonable limits. To comply with the British standard, domestic CO alarms need to meet the following specification, over a wide range of environmental conditions;

� no alarm within one hour at 45 ppm CO,

� alarm within 30 minutes but not less than 10 minutes at 150 ppm CO,

� alarm within 6 minutes at 350 ppm CO, and

� recovery from the alarm state within 6 minutes in clean air.

After due consideration (see Section 2.2) it was decided that these criteria should form the basis of all performance testing for the present investigations.

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2.2 Further Considerations As noted above, BS 7860 specifies alarm levels for domestic CO detectors derived from medical considerations, but also taking into account technical feasibility and likely cost implications. It is specifically not applicable to people who are particularly vulnerable to CO, for whatever reason, but is intended to give adequate protection to the vast majority of the general public. It is therefore believed to be a good basis for comparing the performance of domestic CO alarm units. Unfortunately, BS 7860 does not include long-term tests, so there is no guarantee of service lifetimes, even for models that have been kite-marked by BSI.

Alternatives to BS 7860 have been proposed (References 4, 5 & 6) but are considered unsuitable for various reasons. The Japanese draft standard (Reference 4) is similar in principle, but includes hydrogen at 50% of the CO level. The North American standard (UL2034, Reference 5) has serious flaws, not least of which is the lack of an alarm recovery requirement. The fact that numerous problems have been reported with false alarms in the USA supports this viewpoint, and extensive revisions to UL2034 have not addressed the cause of these problems. Equally, the latest draft European standard (prEN 50291, Reference 6) has been criticised, and efforts are being made to revise the alarm level requirements before it progresses further towards publication.

2.3 Test Equipment A test facility has been established, designed to assess the performance of domestic CO alarm units. This consists of a purpose-built transparent chamber, housed inside a Sanyo/Gallenkamp (ex. Fisons) FE80H/FM environmental cabinet. The cabinet has a wide working range of temperature and humidity, with a special capability for achieving very low humidities. A solenoid valve arrangement allows the chamber to be either purged with conditioned air from within the cabinet, or supplied with test gas. Possible contamination of the laboratory air is avoided by actively venting the chamber to outside atmosphere, as shown schematically in Figure 2.

Figures 3 and 4 give the general arrangement of the chamber inside the cabinet, with the associated instrumentation shown in Figure 5. This includes a Claude Lyons TS voltage stabiliser and Fluke 8840A digital multimeter, to smooth and measure electrical power supplies to test specimens energised from the mains. There is also a Regavolt 404 variac to alter this supply, as necessary. In addition, a standard laboratory rotameter allows adjustment of the required test gas flow rate, and a Siemens Ultramat 21P gas analyser enables the actual concentration of CO within the chamber to be monitored.

This equipment is not claimed to precisely reproduce the temperature extremes of BS 7860 test conditions, because the available instrumentation is not thought to be absolutely stable at temperatures as high as 40°C and as low as 0°C. However, representative assessment testing is still possible over a wide range of realistic service conditions, covering those of most interest to the vast majority of UK consumers, as follows;

� ambient temperatures from 5°C to 35°C,

� ambient humidities from 30% RH to 70% RH, and

� mains supply voltages up to 255 volts AC.

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The procedure adopted for evaluating CO alarm units is to position the test specimen within the special chamber, after energising for at least one hour, and wait for a suitable period for conditions to fully stabilise. Test gas is then applied, and the time taken for the unit to alarm is measured using a standard stopwatch. The CO concentration in the chamber needs a finite time to reach the desired level, and Figure 6 shows that, typically, 95% of the final figure is achieved within two minutes. This time lag is acceptable, because a gradual build-up is more representative of practical situations, and is easier to control than a sudden concentration change. Also, the lag can easily be taken into account when comparing responses of different specimens and, in any case, the specified response times do not require a high degree of measurement accuracy.

Another important factor is the time taken to recover from the alarm condition when exposed to clean air. This is measured from the point at which the analyser indicates that the gas concentration in the special chamber has purged below 10 ppm CO. At lease one hour is allowed between consecutive tests, and all relevant measurements are noted on the results sheet shown in Figure 7.

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3. PERFORMANCE ASSESSMENT

3.1 Initial Specimens and Results A standard procedure has been developed for use with the test rig described in Section 2.3, whereby one specimen is examined thoroughly, and then a small number of nominally identical units are tested less extensively to check for any variability. The rig has previously been used to evaluate the behaviour of a wide range of different models of domestic CO alarm, and this has established confidence in both the equipment and the BS 7860 alarm levels. The present project has allowed the market situation to be reviewed, so that suitable models available within the UK can be compared objectively on a common basis. Note that this does not purport to be an exhaustive market survey.

A number of models were identified as being potentially compatible with the aims of this programme, as summarised in Table 1. Note, however, that some of these models were not commercially available at the appropriate time. A more detailed description, and a summary of the results obtained for the full range of models actually evaluated during the project, appears in Appendices 1 to 17. Six of these were initially found to be worth consideration in the long-term reliability investigation, viz.

� Dicon CO805/CO810 (Appendix 6) � EI 225 (Appendix 7) � Nighthawk Basic 900-0081 (Appendix 12) � Nighthawk Deluxe 900-0089 (Appendix 13) � Schlumberger XH-443B (Appendix 14) � SF330KM (Appendix 16)

Some of these models were considered to be sufficiently similar as to represent a duplication of sensing technologies. It was therefore proposed to dispense with the EI 225 and the Nighthawk Deluxe 900-0089 (these two models would be represented by the Nighthawk Basic 900-0081 and SF330KM, respectively) so that numbers of the remaining models used for the next phase of testing could be increased appropriately.

The Nighthawk Basic 900-0081 originally assessed used the Figaro TGS 203 semiconductor sensor, but this was subsequently changed to a proprietary electrochemical cell. The revised version was externally very similar to the original, and was also certified to BS 7860. Samples of this version were obtained for assessment, and were found to perform at least as well as the earlier version, which was being withdrawn from production. It was therefore decided to include the newer model in the planned longer-term investigations. However, it was still thought useful to have samples with the TGS 203 sensor, as being representative of previous technology, so a few of the original Nighthawk Basic and EI 225 (Appendix 7) models were included along with the other field trial specimens.

Hence, five mains-powered models and one battery-powered model, covering four different types of sensor, were carried forward to the next phase of the programme. For models which were claimed to satisfy BS 7860, but which were found to be unsuitable for further investigation, efforts were made to ascertain the manufacturer's future intentions.

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3.2 Later Developments A number of changes have occurred in the UK domestic CO alarm market since the project started, as follows;

Kidde Nighthawk: Changes to the Nighthawk range of CO alarms (subsequent to those described in Section 3.1) came to light from a widely publicised product recall. Various reasons have been proposed for the cause of the problem, but the latest information points to out-gassing from adhesives used during final assembly, poisoning the electrochemical sensor. The manufacturer intends to reduce the possibility of such incidents in the future, by incorporating an activated charcoal filter. However, this highlights another potential problem, in that there currently appears to be ambiguity between different Nighthawk model numbers (ie. mains or battery powered, with or without digital displays) utilising different types of sensing technologies.

BRK FDC3EC: This new design of CO alarm (Appendix 3) became available through retail outlets within the UK, and samples were procured for evaluation. However, tests showed that performance was identical to the BRK model CO1000BE (Appendix 2) based on the same sensing technology, and which had been found to be unsatisfactory from previous testing.

Gas Maestro: As with the GasWatch (previously tested and found to be unsatisfactory, see Appendix 10) the Gas Maestro (Appendix 9) is intended for use with safety shut-off systems linked to gas detectors. Despite claims of conformity to the appropriate standards (including BS 7860) performance was found to be unsatisfactory, highlighting that the gas sensor is the single most critical component of these systems.

Senco Model ONE: This new design of CO alarm is understood to incorporate a proprietary electrochemical sensor, and test samples were obtained for assessment. Appendix 15 indicates satisfactory performance, so the unit could be considered for field trials in the future.

Monox Electrochemical Cell: This new sensor on the market is claimed by the manufacturer to be capable of meeting the performance requirements of BS 7860, and test samples have been obtained and subjected to the same assessment procedures described previously. Results are summarised in Appendix 11, but any further testing depends on the availability of suitable CO alarm specimens, rather than the test bed provided so far.

EI 204 and 205: Externally very similar to the EI 225 (Appendix 7) but incorporating the MIDI 40 electrochemical cell from SF Detection Ltd. They are battery-powered, with digital displays, and one has a “memory” feature. Initial assessment indicates a performance very similar to the SF330KM (Appendix 16) already on field trial.

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SF340: A mains powered model with battery backup, which also has an optional output signal to operate an ancillary device. Samples for assessment are not yet available.

Dicon 1100B: Battery-powered, but not yet available in the UK.

Another new development is the introduction of combined alarms for both CO and natural gas. Such units have been available for some time in Japan, using separate sensors for the two gases, but a new sensor is now being introduced which is capable of detecting both species. The FiS SB-95 has been used in the Simecon Prevent PG-21D (which is available in certain South American countries) and also in the Fagor BG (which is expected to be available shortly within the UK). The latter is intended for use with security systems via a telephonic gateway, which is increasingly an area of potential interest as CO, smoke and/or natural gas alarms become more widely used. Potential drawbacks to such combined alarms are;

� Appropriate siting, taking into account the likely differences in physical behaviour of the species actually detected, and

� Possible confusion of consumer reaction, depending on different output signals produced by the alarm unit.

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4. FIELD TRIAL

4.1 Testing and Results Appropriate numbers were obtained of those models of domestic CO alarm identified in Section 3.1 as suitable for field trial. Performance of all these specimens was then compared with the requirements of BS 7860, using the test rig as described previously, but with the following changes to reduce testing time for the large number of specimens involved;

a) Checks were performed under ambient temperatures and humidities (generally within 17° to 23° C and 50% to 70% RH) rather than being controlled to a high level of accuracy. Results from assessment testing indicated that, for the models selected, this would not significantly affect alarm performance.

b) Checks for non-alarming were performed for a minimum of 30 minutes duration at 50 ppm CO, instead of 60 minutes at 45 ppm CO. Again, assessment testing had indicated that this change would be a satisfactory alternative, by significantly reducing the duration of testing without having any detrimental effect on the selected models.

As expected, these changes did not create any behavioural differences in the field trial specimens during testing. Table 2 summarises the results of these tests, and it can be seen that performance varied from the ideal in a few cases. However, it was considered that this variation was insufficient to inhibit the trial, although two units with defective audible alarms were thought suitable for testing only under laboratory conditions. Of more concern, were instances when alarms triggered correctly on Dicon CO805 units, but the alarm then stopped operating after a further time period.

For convenience, and to retain adequate control, it was decided to ask BG Technology staff to participate in the field trial, and a suitable number of volunteers offered to install specimens in their homes. Appendix 18 shows the documentation that was generated and supplied to these participants, to explain the requirements of the trial and to give guidance on installation. It can be seen from the final page that it was thought necessary to give extra guidance to those participants who were allocated the Dicon CO805 unit, in addition to the instructions given by the manufacturer.

One aspect of the trial, which was considered to be an important source of information, was the opportunity for feedback from the participants. This feedback covered comments on both installation and siting, as summarised in Tables 3 and 4, and Figure 8 gives additional details of mounting heights, both by the model of alarm and by room type. It can be seen that most of the mains-powered models raised problems with siting. This was usually due to positioning of the cable, but several participants also commented that, at 1.85 m, the Dicon CO805 cable was too short. Several comments related to the usefulness of the manufacturer's instructions, which were sometimes considered too lengthy or difficult to follow. The majority of installations were in a lounge, or similar room, but a significant proportion of battery-powered models were located in kitchens.

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The field trial specimens have now been recalled for alarm calibration checks, after approximately one year in the homes of participating BG Technology staff. These checks were carried out in the same way as initially, so that comparisons can be made with earlier data and with the requirements of BS 7860 given in Section 2.1. The results for the four CO alarm models representing current sensing technologies, and tested in significant numbers, appear in Figures 9 to 12. These are bar charts, showing alarm performance as received and after one year in service, at both 350 ppm CO and 150 ppm CO. It can be seen that the SF330KM has hardly changed at all, and the Schlumberger XH-443B has drifted but by only a moderate amount. The Dicon CO805B has drifted to a greater extent, whilst the Nighthawk Basic 900-0081 has drifted most of the four. The remaining specimens on field trial are insufficient in number to be worth presenting graphically, but similar checks have been performed to show that calibration drift varied from very little to significant amounts.

The Kidde Nighthawk Basic 900-0081 has changed due, presumably, to the problem described in Section 3.2, and there seems little value in continuing the field trial on these specimens. The Dicon CO805B has also changed quite dramatically, and could possibly be withdrawn from the trial. The Schlumberger XH-443B does not at first appear to have drifted much, but note that the initial calibrations were set more sensitive than specified by BS 7860, thereby increasing the total change. The relevant manufacturers have been contacted and asked to comment on these results, but responses have not yet been received.

In addition to the drift in alarm performance, there have been a number of component failures observed in the field trial samples, as follows;

• SF330KM: One complete buzzer failure and one intermittent, plus one low battery indication.

• Schlumberger XH-443B: Two buzzer failures.

• Kidde Nighthawk Basic 900-0081: One transformer failure.

4.2 Sensor Summary Table 1 describes the models of domestic CO alarm investigated for this project, from which it appears that three types of sensor are generally suitable, based on cost and reliability considerations (see Section 1). Other technologies (eg. non-dispersive infra-red) may become popular in time, but are not presently practicable for the application. It had been intended as part of the project to develop a method of accelerating the natural ageing process of one or more of these types, so that representative tests could be performed under controlled laboratory conditions. However, an extensive literature search, combined with other sources of information (Reference 7) has failed to identify a suitable basis for such tests.

From knowledge currently available, it is possible to summarise the different models of sensor used in domestic CO alarms, and their known behaviour, as detailed in Table 5. This enables some useful general comparisons to be drawn, but it also highlights the lack of adequate long-term data in the majority of cases.

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5 DISCUSSION AND OBSERVATIONS

Table 6 summarises all the work carried out under this project, comprising initial assessment and field trials. Results of earlier testing based on the same procedures have also been included, where appropriate, with the different CO alarms being categorised by the sensing technology employed. It can be seen that, of the models investigated and currently available within the UK, only the SF330KM has been found to be satisfactory after one year in service. Most of the models that passed the initial assessment have since exhibited significant calibration drift during field trials representing typical in-service usage, which was the main concern of this particular project.

It is worth noting that a few of the older designs of CO alarm (mostly using the Figaro TGS 203 semiconductor sensor) have actually drifted much less than some more recent models. It is thought possible that this may be due to the requirement in BS 7860 for a delay period before alarming at 150 ppm CO, forcing manufacturers to operate at a different point on the calibration curve, with consequent changes in long-term drift behaviour.

From the available literature, it is obvious that the long-term behaviour of domestic CO alarms is becoming of increasing interest, especially within the USA. A number of investigators have examined the performance of units (References 8 to 10) and many of the commercially available models were found to be unsatisfactory in practice. A variety of in-service issues (but not actual siting) have also been identified (References 11 to 14) as contributing to the complex, and sometimes bizarre, situation presently surrounding the use of these devices in North America. The authorities have responded by making the performance requirements more severe (References 15 and 16) and incorporating a range of additional tests, as detailed in Appendix 20 which summarises Reference 17. However, it is believed that the additional tests, whilst considerably increasing the cost of obtaining certification approval, will not be effective in achieving long-term reliability. The reason is that the two fundamental flaws have not been addressed; ie. no alarm recovery time is specified, and no guidance is given on correct siting within the home.

The lack of an alarm recovery time in the North American standards for domestic CO alarms is believed to be primarily due to the relatively slow response of the product that has the major market share. The lack of guidance on siting is more difficult to understand, since much information is already available (Reference 18) and more is being produced as part of the joint industry programme (References 19 and 20). There are more than sufficient data available on medical effects (Reference 21) to be able to use this information in a sensible manner. As an example, simple siting instructions are included as an Informative Annex to BS 7860, and more detailed guidance is intended to accompany the European standard in a parallel document (prEN 50292, Reference 22).

The correct siting of domestic CO alarms is considered to be a major influence on the likelihood of protecting consumers in practice. Section 4.1 gave an indication of the observed variability in location for the field trial units. In each case, instructions given by the manufacturer for siting the alarms are based on the guidance given in Annex B of BS 7860. Nevertheless, there are some obvious differences between models, and these are believed to be due mainly to individual design features, such as the length of power cables. It is believed that the variability likely to prevail in service will exceed that observed in the field trial, with consequent impact on the levels of protection afforded to consumers.

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There have been significant developments in the European standards arena recently, with a revised draft performance standard for domestic CO alarms (prEN 50291) being circulated by Cenelec for voting. The UK national committee still had strong reservations on the technical content compared with BS 7860, and therefore entered a negative vote. Italy and Spain also submitted negative votes, and this was sufficient to halt publication in its present form. Hence, there will be a further delay before it can be issued, and the final version is likely to be even more akin to BS 7860. The companion guidance document (prEN 50292) has been circulated for comment, and may be issued at the same time as the performance standard. It contains much good advice to the installer and/or supplier of domestic CO alarms, including guidance on siting.

Siting has already been highlighted as being of major importance to the correct performance of domestic CO alarms, and the need for definitive rules is a main recommendation. Additional information has recently become available (Reference 23) which might be used to address the situation, although data being generated both here and in other parts of the joint industry programme (References 24 and 25) give further insight into actual conditions in single and multi-room situations. All these sources will hopefully be used in producing the final version of prEN 50292, which should also address combined gas alarms as described in Section 3.2.

Although BS 7860 covers an extensive range of specification requirements, it does not guarantee the longer-term behaviour of domestic CO alarms, since the longest test is only three months. The latest North American requirements have introduced specific reliability tests but, as noted previously, these are not currently considered appropriate for the UK. There may be, however, an argument in favour of including more extensive interferant testing than presently appears in BS 7860. A significant feature of North American test requirements for CO alarms is the long list of interferant substances (see Appendix 20) that must be considered, even though some of these compounds are not believed to be relevant to the domestic environment. In comparison, many substances that might be thought to be more relevant have been omitted.

It was not possible to infer any relationships for substances such as the products of smoking or cooking from the field trial results, because;

a) The number of field trial households containing smokers is very small, compared to the total, and

b) SF330KM units were mounted in kitchen areas in greater numbers than any of the other field trial units and, since this is the only type not severely affected by drifting, the results are not statistically useful.

Table 6 provides a summary of all the results from the present programme of work, but it is evident that new models of domestic CO alarm are still coming onto the UK market. It would therefore be beneficial for funding to be made available for a continuation of the project, but on a reduced scale. This would enable the latest models to be evaluated on a comparable basis, as well as more information to be gathered on the long-term behaviour of new and existing designs. It is obvious that there are increasing levels of concern and interest being shown within the UK and elsewhere (References 26 and 27) with CO issues playing a large part in the research programme for the National Air Quality Strategy and the HSE Gas Safety Review (Reference 28).

12

6 CONCLUSIONS

� Alarm levels specified in BS 7860 are entirely appropriate for comparing the

performance of domestic CO alarm units. A test rig has been built and commissioned, and suitable procedures devised, to allow such comparisons to be made objectively.

� Commercially available models of domestic CO alarm were identified as possibly being

appropriate to the aims of this programme, and have been assessed using the test rig described. A number of these were selected for further investigation, so as to include different sensing technologies without duplication. Only one type selected for this further investigation and currently available in the UK still performed within specification after one year in service, viz. the SF330KM from SF Detection Ltd.

� Initial feedback from participants in the field trial of domestic CO alarms has highlighted

a number of design features that have caused concern. The most frequent comments have related to the length and routing of mains electrical cables, and manufacturer’s instructions, which have been found too lengthy or difficult to follow. This has often resulted in units being installed in locations that are less than ideal, although it is likely that this will be the case in many households anyway, with consequent impact on the levels of protection afforded by alarm units.

� A summary of existing CO sensors has highlighted the lack of long-term data, as well as

the possible significance of cross-interference by substances commonly found in the domestic environment.

� The best indication of adequate initial performance by domestic CO alarms is a kitemark

to BS 7860. Unfortunately, this does not necessarily guarantee long-term reliability. The results of tests suggest that some manufacturers may be making unsubstantiated claims of product conformity to BS 7860 in advertising and other literature, and on the products themselves. Some older designs have been found to give better long-term behaviour than newer models, but they were not designed to conform to the performance requirements of BS 7860.

� The North American standards covering domestic CO alarms have been revised recently,

to address the problems that are being experienced with long-term reliability of such devices in the USA. However, there has been no attempt to incorporate either alarm recovery times or guidelines on correct siting. It is therefore believed that current UK and draft European documents are inherently superior.

13

7 RECOMMENDATIONS

� The current field trial should continue, yielding good quality data on the long-term

behaviour of domestic CO alarms. � Manufacturer's intentions should be ascertained over the future of models claimed to

comply with BS 7860, but which were found to perform unsatisfactorily. � Every effort should be made to produce clear and simple guidelines for the siting of CO

alarms in domestic premises, giving adequate protection for consumers against potential hazard.

� Pressure should be maintained within Cenelec, to ensure that the draft European standard

for domestic CO alarms (prEN 50291) follows BS 7860 as closely as possible. � The draft European guidance document (prEN 50292) should also address the future

likelihood of combined CO, smoke and/or natural gas alarms. � Samples of new models of domestic CO alarm should be obtained for initial assessment

and longer-term testing if appropriate. � A programme of testing should be performed, to establish the possible interferant effects

of a range of household substances, including the products of cooking and smoking.

14

REFERENCES 1. Allen J D Domestic Carbon Monoxide Alarms and Safety Shut-off Systems British Gas Plc Position Paper

BSI document 93/213675, September 1993. 2. - Health and Safety Commission Approved Code of Practice and

Guidance: Safety in the Installation and Use of Gas Systems and Appliances, based on;

Gas Safety (Installation and Use) Regulations 1998. 3. - Specification for Carbon Monoxide Detectors (Electrical) for Domestic

Use. British Standard BS 7860:1996, 4. - Institute for Safety of High Pressure Engineering, March 1994.

Japanese Technical Requirements, Test methods and Judgments for Incomplete Combustion Detectors. 5. - Underwriters Laboratory UL2034, Third Edition, October 1997,

Standard for Single and Multiple Station Carbon Monoxide Detectors. 6. - Electrical Apparatus for the Detection of Carbon Monoxide in Domestic Premises: Test Methods and Performance Requirements. Draft European Standard prEN 50291, 1999. 7. Bartlett P N Electrochemical Carbon Monoxide Sensors. & Webb B C University of Southampton Electrochemistry Group, November 1998. 8. - Carbon Monoxide Alarm Performance Testing Phase 1: Basic Performance, Task 1: Steady-State CO Concentration Tests GRI Topical Report 95/0220, ETL Testing Labs Inc, August 1995 9. - Chamber Tests of Residential CO Alarms GRI Final Report 98/0140, GARD Analytics Inc, May 1998 10. - Performance Testing of Residential CO Alarms GRI Final Report 98/0284, Mosaic Industries Inc, December 1998 11. - Carbon Monoxide Response Surveys Analyses: Suburban Chicago Data - Interim Report GRI Topical Report 95/0335, Resource Strategies Inc, October 1995 12. - Carbon Monoxide Response Surveys Analyses: Utility Data - Interim Report GRI Topical Report 95/0468, Resource Strategies Inc, February 1996

15

13. - Residential Carbon Monoxide Study: Population Estimates and Methodologies for Acquiring Demographic Data and Verifying Detector Performance GRI Topical Report 98/0175, Scientific Applications Int Corp, August 1998 14. - Residential Carbon Monoxide Alarm Population: Four Cities Study GRI Topical Report 98/0273, Resource Strategies Inc, December 1998 15. - IAS US Requirements for Carbon Monoxide Alarms for Residential Use International Approval Service - US No. 6-96, June 1998 16. - Residential Carbon Monoxide Detectors and Alarms National Standard of Canada CAN/CGA-6.19-M93, March 1993. Including Technical Information Letter No. R-03, September 1998. 17. - Test Protocols for Residential Carbon Monoxide Alarms, Phase 1 GRI Draft Topical Report 96/0055, Mosaic Industries Inc, February 1996. 18. Persily A K Carbon Monoxide Dispersion in Residential Buildings: Literature Review and Technical Analysis. US Department of Commerce, NISTIR 5906, undated. 19. Bullman S J, An Analysis of Full Scale Data to Assess Factors Affecting Vitiation Hill R W Associated with Gas Appliances. & Pool G BG Technology Report GRTC R2412, March 1999. 20. Bullman S J The Siting of Domestic CO Alarms: & Pool G An Analysis of Full Scale Vitiation Tests. BG Technology Report GRTC R2951, May 1999. 21. Dayan A D Health Effects of Carbon Monoxide, & Pool G with Particular Reference to Indoor Air. Review of the Literature from January 1995 to June 1998. BG Technology Report GRTC R2453, September 1998. 22. - Electrical Apparatus for the Detection of Carbon Monoxide on Domestic Premises: Guide for Selection, Installation, Use and Maintenance. Draft European Standard prEN 50292, 1999. 23. Ross D Carbon Monoxide Detectors. BRE Good Building Guide GBG 30, April 1999. 24. Bullman S J The Siting of Domestic CO Alarms: & Pool G Analysis of Full-Scale Vitiation Tests. GRTC Report R2951, May 1999. 25. Bullman S J Development of a Model to Predict CO Build-up in a Single Room

GRTC Preliminary Report, 1999.

16

26. Dayan A D, Health Effects of Carbon Monoxide, Marks S T with Particular Reference to the Indoor Air. & Pool G Review of the Literature from July to October 1998. GRTC Report R2827, May 1999. Review of the Literature from October to December 1998. GRTC Report R2828, May 1999. Review of the Literature from January to April 1999. GRTC Report R2996, May 1999. Review of the Literature from April to December 1999. GRTC Report R 3527, March 2000. 27. Lefebvre L & Natural Gas Technologies and Applications: Horizon 2015. Lefebvre L A Ecole Montreal BRCDT, June 1999. 28. - Gas Safety Review: Options for Change. HSC Discussion Document, 1999.

17

Table 1. Summary of Domestic CO Alarm Models Considered

NOTE: BS 7860 denotes kite-marked approval * Denotes ambiguity between model numbers.

Sensing Technology

Sensor Maker

Sensor Reference

CO Alarm Make And Model

BS 7860

Comment

BRK CO1000BE X

BRK FCD3EC X New unit

COSTAR 9L-I X No longer available

Reagent Gel Quantum Gel cell

Dicon CO1100B Yes New unit

SF310 X No longer available

SF320 X No longer available

Pama GHD-2010 X No longer available

EI 225C Yes

TGS 203

Nighthawk 900-0081 * Yes Production halted

TGS 822 BRK WICOE Yes

Figaro

TGS 2440 Gas Maestro GSS 2002 X

SP-31 GasAlert X

New Age CO200 X No longer available

Dee Detecta 7 X Development unit

SB-50

Dee Detecta 9 X

SC-50 Dicon CO805B Yes

Simecon PG-21D X Unavailable in UK

FiS

SB-95

Fagor BG X New unit

Anglo-Nordic 570 1200 X ScimArec AF22C

GasGuard G021CO HW X

Semiconductor

New Cosmos CH-C Schlumberger XH-443B Yes

Unknown 2M003 Technotrend CO350 X No longer available

3E/7E GasWatch 200 X City

- AIM SAS-IDR BS X Unavailable in UK

SF330KM Yes

SF340 Yes New unit

Nighthawk 900-0089 * Yes Production halted

SF Detection MIDI 40

EI 204 & 5 Yes New units

N/hawk 900-0081 & 2 * Yes New units Kidde -

N/hawk 900-0089 & 90* Yes New units

Monox - S-Tech test bed X Prototype unit

Electro-chemical

Senco - Model ONE X New unit

18

Table 2. Results of Initial Checks on Field Trial Units Numbers of observed defects [compared to specified requirements]

Alarm Model Numbers Tested

50 ppm CO [>30 mins]

150 ppm CO [10 to 30 mins]

350 ppm CO [<6 mins]

Other Remarks

SF330KM

20 1 <30 mins 0 0 1 buzzer unserviceable

Dicon CO805

20 0 2 >30 mins 2 alarm stops

0 0

Schlumberger XH-443B

20 0 14 <10 mins 0 1 buzzer# unserviceable

EI 225

4 0 0 1 >6 mins 0

Nighthawk Basic

4 0 0 2 >6 mins 0

Nighthawk (BS)

14 0 0 0 0

All Types

82 1 18 3 2

Note: # This unit also alarmed early at 150 ppm CO

50 ppm CO <30 minutes150 ppm CO <10 minutes150 ppm CO >30 minutes150 ppm CO alarm stops350 ppm CO >6 minutesCalibration to BS 7860

Calibration Failure ModesBreakdown of Overall Numbers

19

Table 3. Feedback from Field Trial Participants (based on replies received from 73 field trial participants)

Alarm Model Siting Problems

Fixing Problems

Cable Problems

Test Button Obtrusive No Problem

SF330KM

- - N/A 1 1 17

Dicon CO805

4 5 5 5 2 3


2 1 3 N/A# - 12

EI 225

- 1 - - - 2

Nighthawk Basic

- - - - 1 2

Nighthawk (BS)

3 - 5 - - 5

All Types

9 7 13 6 4 41

Percentage (of 73)

12% 10% 18% 8% 5% 56%

Note: # This model does not have a Test button, but is provided with a gas testing kit, which had been used successfully by four participants

Siting Fixing Cable Test Obtrusive None0

10

20

30

40

50

60

Per

cent

age

of P

artic

ipan

ts

Overall Breakdown of Reported Problems

20

Table 4. Location of Installed Field Trial Units (based on replies received from 73 field trial participants)

Alarm Model

Lounge (+ Study or

Diner)

Kitchen

Hallway

Landing

Bedroom

Other

Total

SF330KM

10 7 1 0 1 0 19 (of 19)

Dicon CO805

13 5 1 0 0 0 19 (of 19)


12 3 1 0 0 1 17 (of 19)

EI 225 and Nighthawk Basic

1 2 0 0 3 0 6 (of 6)

Nighthawk (BS)

7 3 0 1 1 0 12 (of 13)

All Types

43 20 3 1 5 1 73 (of 76)

LoungeKitchen

HallwayLanding

BedroomOther

Overall Breakdown by Room Type

21

Table 5. CO Sensors Summary

Sensing

Technology Sensor

Manufacturer Model

Numbers Remarks and

Reported Behaviour Known

CO Alarm Users Reagent Gel Quantum biomimetic Significant temperature

dependence, slow recovery BRK, First Alert, COStar

PH Products indicator card No output, short lifetime, interferant-prone, PdClx

PH, EI

Semiconducting metal oxide

Figaro TGS 203 Well known & popular, SnO2 SF, EI, Nighthawk plus many others

TGS 822 Not intended for CO BRK

TGS 2440 New generation, but may be affected by interferants

Gas Maestro

FiS SB-50 Low drift Dee, New Age

SB-95 SnO2 material, detects both CO and CH4

Fagor, Simecon

SC-50 Similar to SB-50 Dicon

SP-31 Not intended for CO Gas Alert

ScimArec AF22C Reported to be affected by interferants

Anglo-Nordic, Gas Guard

New Cosmos CH-C SnO2 material, with In2O3

dopant Schlumberger

Capteur GS07/GL07 CrTiOx material Gas Guard (p/t)

Nemoto NAP-11A Long-term drift reported Anglo-Nordic (p/t)

NAP-70A Catalytic pellistor may be unreliable in service

Nemoto (p/t)

Microchemical Systems

MiCS 1110 Ex-Motorola product, SnO2 material

none known

Electrochemical cell

City Technology 3E/7E Reliable but relatively expensive

GasWatch, Safeair

domestic Self-calibrating feature, temperature dependence

AIM

Sixth Sense MIDI 40 H2SO4 electrolyte SF, Kidde

Kidde proprietary Nafion/water electrolyte Nighthawk

Monox proprietary H2SO4 electrolyte S-Tech (p/t)

MSA proprietary Electrolyte leakage reported none known

Note: (p/t) indicates a prototype CO alarm unit

22

Table 6. Summary of Domestic CO Alarms and Sensors Tested NOTE: “Test” denotes initial assessment testing. “Trial” denotes extended field trialling.

* Denotes ambiguity between model numbers. ? Denotes results slightly below “Pass”.

Sensing Technology

Sensor Maker

Sensor Reference

CO Alarm Make And Model

Test Trial Comment

BRK CO1000BE Fail None

BRK FCD3EC Fail None

COSTAR 9L-i Fail None Earlier testing

Reagent Gel Quantum Gel cell

Dicon CO1100B None None New product

SF310 ? ? Earlier testing

SF320 ? ? Earlier testing

Pama GHD-2010 ? Fail Earlier testing

EI 225C Pass Fail Significant drift

TGS 203

Nighthawk 900-0081 * Pass Pass Old product

TGS 822 BRK WICOE Fail None

Figaro

TGS 2440 Gas Maestro GSS 2002 Fail None

SP-31 GasAlert Fail None Earlier testing

New Age CO200 ? None Earlier testing

Dee Detecta 7 Pass None Old product

SB-50

Dee Detecta 9 Fail None

SC-50 Dicon CO805B Pass Fail Significant drift

Simecon PG-21D ? None Earlier testing

FiS

SB-95

Fagor BG Pass None New product

Anglo-Nordic 570 1200 Fail None ScimArec AF22C

GasGuard G021CO HW Fail None

Semiconductor

New Cosmos CH-C Schlumberger XH-443B Pass ? Moderate drift

Unknown 2M003 Technotrend CO350 Fail None

3E/7E GasWatch 200 Fail None City

- AIM SAS-IDR BS Fail None Earlier testing

SF330KM Pass Pass Low drift

SF340 None None New product

Nighthawk 900-0089 * Pass None See SF330KM

SF Detection MIDI 40

EI 204 & 5 Pass None See SF330KM

N/hawk 900-0081 & 2 * Pass Fail Massive drift Kidde -

N/hawk 900-0089 & 90* Pass None See 0081 & 2

Monox - S-Tech test-bed Pass None Prototype

Electro-chemical

Senco - Model ONE Pass None New product

23

Figure 1. Performance Requirements

Figure 2. Schematic of Special Test Chamber

(healthy 55kg woman, light work, 0.1% background CO2)

NORMAL - alarm between 10 and 30 minutes at 150 ppm CO

HIGH - alarm within 6 minutes at 350 ppm CO

NONE - no alarm within 60 minutes at 45 ppm CO

1 10 100 1000

Exposure Time (minutes)

10

100

1000

CO

Con

cent

ratio

n (p

pm)

NB. Alarm recovery within 6 minutes in clean air

BS 7860 CO Alarm Bands(compared with 5% COHb curve)

Vent to atmosphere

Purge from cabinet

Test gas conditioned fortemperature and humidity

perforated plate supports test unit and allows uniform gas mixing, without high velocities.

Maximum internal dimensions 200mm x 200mm x 100mm

Cables and piping fed through ports inthe side of the environmental cabinet

Tight-fitting perspex lidwith cut-out for cable entry

COanalyser

Test Unit

Fan

24

Figure 3. General View of Test Rig

Figure 4. Close-up View of Special Test Chamber

25

Figure 5. General View of Test Rig Instrumentation

Figure 6. Build-up of CO in Special Test Chamber

26

Figure 7. Testing Results Sheet

PERFORMANCE ASSESSMENT OF DOMESTIC CO ALARMS

Make, Model and Serial Number

Date and Time Temp'ture (degC)

Humidity (%RH)

Supply (volts)

Concent'n (ppm CO)

Alarming (minutes)

Recovery (minutes)

Remarks

Notes.

27

Figure 8. Siting of Field Trial Units

Lounge Kitchen Hallway Landing Bedroom Other0

5

10

15

20

25

Num

ber

in C

lass

<1.0 m1.0 to 1.5 m1.6 to 2.0 m>2.0 m

All CO Alarm Field Trial UnitsMounting Height by Room Type

Lounge Kitchen Hallway Landing Bedroom Other0

5

10

15

Num

ber

in C

lass

SFDiconSchlumKidde

All CO Alarm Field Trial UnitsModel Location by Room Type

28

Figure 9. SF330KM Field Trial Results Comparison of performance as received (0) and after one year in service (1)

NOTE. BS 7860 requires alarm and recovery both within 6 minutes.

NOTE. BS 7860 requires alarm between 10 and 30 minutes; recovery within 6 minutes.

0 1 2 3 4 5 6 7

Alarm or Recovery Time (minutes)

0

5

10

15

Num

ber

in C

lass

Alarm(0)Recover(0)Alarm(1)Recover(1)

Alarm Performance at 350 ppm CO

0 5 10 15 20 25Alarm or Recovery Time (minutes)

0

5

10

15

Num

ber

in C

lass



29

Figure 10. Dicon CO805B Field Trial Results Comparison of performance as received (0) and after one year in service (1)

NOTE. Recovery from the alarm state achieved by pressing the RESET button.

NOTE. BS 7860 requires alarm within 6 minutes.

NOTE. BS 7860 requires alarm between 10 and 30 minutes.

0 3 6 9 12 15 18 21 24


0

1

2

3

4

5

6

7

Num

ber

in C

lass

Alarm(0)Alarm(1)


0 3 6 9 12 15 18 21 24Alarm or Recovery Time (minutes)

0

1

2

3

4

5

Num

ber

in C

lass

Alarm(0)Alarm(1)


30

Figure 11. Schlumberger XH-443B Field Trial Results Comparison of performance as received (0) and after one year in service (1)



0 4 8 12 16 20


0

5

10

15

Num

ber

in C

lass



0 3 6 9 12 15 18 21 24Alarm or Recovery Time (minutes)

0

5

10

15

Num

ber i

n C

lass



31

Figure 12. Kidde Nighthawk Field Trial Results Comparison of performance as received (0) and after one year in service (1)



0 4 8 12 16 20 24 28


0

5

10

15

Num

ber

in C

lass



0 4 8 12 16 20 24 28Alarm or Recovery Time (minutes)

0

5

10

15

Num

ber

in C

lass



32

Appendix 1. Anglo Nordic 570 1200

Manufacturer and Contact Details Anglo Nordic Burner Products Ltd, 12/14 Island Farm Avenue, West Molesey, Surrey, RT8 2UZ. Brian Lelliott, Managing Director. Tel. 0181 979 0988 Fax. 0181 979 6961 Description and Detail of Specimens Flimsy plastic case, bearing the inscription "BS 7860", with green "power" and red "alarm" LEDs, plus "test" button. Output function available as an option. No visual or audible indications during 4 minute warm-up. Test button activates quiet buzzer, but not red LED. Powered by 12 volt DC mains transformer, which also acts as battery back-up. Sensor is ScimArec AF22C semiconductor. 6 specimens purchased at the list price of £36.00 each. Summary of Performance Assessment Alarm time at 350 ppm CO was 12 to 16 minutes, but this reduced with lower ambient temperatures. Performance at 150 ppm CO was variable, sometimes not alarming within 30+ minutes, and also susceptible to variations in ambient temperature. The manufacturer has promised that references to BS 7860 will be removed.

33

Appendix 2. BRK CO1000BE

Manufacturer and Contact Details BRK Brands Europe Ltd, Fountain House, Canal View Road, Newbury, RG14 5XF. Original contact left company, and company believed to have changed ownership. Description and Detail of Specimens Circular in shape, and previously marketed under the "FirstAlert" brand. A "test" button incorporates a flashing red combined power and alarm LED. A sliding drawer holds a replaceable combined battery/sensor module, and sensing uses colourimetric technology, as devised by the Quantum Corporation. Two specimens purchased at a preferential price of £19.87 each. Summary of Performance Assessment No alarm within 30+ minutes at 150 ppm CO, but low-level alarm in 29 minutes. Alarm between 9 and 14 minutes at 350 ppm CO, with low-level alarm between 6 and 10 minutes. Alarm recovery required operation of the reset button, but there was a tendency to re-alarm at low temperature, after resetting in clean air. No compliance with BS 7860 is claimed for this product.

34

Appendix 3. BRK FDC3EC

Notes on BRK CO1000BE (Appendix 3) are applicable, except that this unit incorporates a separate replaceable battery.

35

Appendix 4. BRK WICOE

Manufacturer and Contact Details BRK Brands Europe Ltd, Fountain House, Canal View Road, Newbury, RG14 5XF. Original contact left company, and company believed to have changed ownership. Description and Detail of Specimens Attractive design, kite-marked to BS 7860, but with a specialist power connection fitting, probably aimed at the new housing market. Green "power", yellow "warning" and red "alarm" LEDs, plus button labelled "test/silencer". Green LED flashes during 4-minute warm-up, after which holding down the test button activates loud buzzer and alternating red and yellow LEDs. Sensor is believed to be Figaro TGS 822, which is not normally used for the CO application. Six specimens purchased at a preferential price of £30.10 each. Summary of Performance Assessment Alarm triggered between 2 and 5 minutes at 350 ppm CO, but between 5 and 20 minutes at 150 ppm CO. The buzzer generally reset automatically within about 2 minutes in clean air, but recovery of the red LED required the unit to be switched off and on again. The effects of environmental changes were not investigated.

The manufacturer has not yet commented on these findings.

36

Appendix 5. Detecta 9

Manufacturer and Contact Details Dee Electronics Ltd, Parkway, Deeside Industrial Park, Deeside, Flintshire, CH5 2NS. Clive Rowlands, Development Manager.Tel. 01244 288606 Fax. 01244 289031 Description and Detail of Specimens Compact size, with "BS 7860" on front of casing. Unmarked test button activates red "alarm" LED and loud buzzer. Green "power" LED flashes during 40 second warm-up, but is extremely small, as is yellow "fault" LED. Sensor is FiS SB-50 semiconductor. Output function is fitted as standard, and battery back-up option is available. Six specimens purchased at a preferential price of £23.90 each. Summary of Performance Assessment Unit failed to alarm within 30 minutes at 150 ppm CO, and performance was variable at 350 ppm CO, with increased ambient temperature giving an increased speed of response. The manufacturer does not accept that these findings are valid.

37

Appendix 6. Dicon CO805 & CO810

Manufacturer and Contact Details Dicon Safety Products (UK) Ltd, PO Box 15, Cheltenham, Gloucestershire, GL51 9UD. Jason Perrins, Standards & Approvals Director. Tel. 01242 516242 Fax. 01242 222935 Description and Detail of Specimens Fairly compact units, kite-marked to BS 7860, except for the 9 volt DC mains adapter on the CO805 model, which has been recently changed. Green "power" and red "warning/alarm" LEDs, plus "test/reset" button which is rather stiff to use. The reset button must be used each time, to recover from the alarm state. Alarm signal is flashing LED accompanied by triple beeps, and this occurs every 2.5 minutes during low-level alarm. Sensor is FiS SC-50 semiconductor. Six hard-wire and two plug-in specimens purchased, at preferential prices of £18.00 and £22.45 each, respectively. Summary of Performance Assessment Some variation was apparent between specimens, indicating slight differences in calibration setting. However, these differences were not sufficient to inhibit functionality of the units in practice. Full alarm triggered within 6 minutes at 350 to 400 ppm CO, and after 20 minutes at 100 to 150 ppm CO, for all conditions. In every case, alarm recovery was immediate on pressing the reset button in clean air.

Recommended for further consideration.

38

Appendix 7. EI 225

Manufacturer and Contact Details EI Company Ltd, Shannon Airport, Shannon, Ireland. Michael Byrne, Engineering Director. Tel. 0035361-471277 Fax. 0035361-471053 Description and Detail of Specimens Largish unit, kite-marked to BS 7860 and provided with green "power", red "alarm" and yellow "fault" LEDs, plus "test/hush" button. Alarm signal is red LED plus triple beeps. Sensor is Figaro TGS 203, and output function is available as an option. Six specimens purchased at a preferential price of £27.00 each. Summary of Performance Assessment Five of the six units alarmed at 6 minutes with 350 ppm CO, but the other one alarmed at 11 minutes. All units alarmed at about 20 minutes with 150 ppm CO, and recovered within 2 minutes in clean air. No effects were observed due to variations in temperature, humidity or voltage supply.


39

Appendix 8. GasGuard G 021 CO

Manufacturer and Contact Details Applecroft Technologies Ltd, Chelworth Lodge, Cricklade, Swindon, Wiltshire, SN6 6HB. Supplied by PP Controls Ltd, Cross Lances Road, Hounslow, Middlesex, TW3 2AF. Bill Sanderson, Managing Director. Tel. 0181 572 3331 Fax. 0181 572 6219 Description and Detail of Specimens Compact unit, which is claimed by the manufacturer to satisfy BS 7860. Provided with about 1.5 metre power cable, green "power", amber "alert" and red "alarm" LEDs and "test/hush" button. 2 hour warm-up with flashing red LED, after which test button operates satisfactorily. Output option provided, with additional yellow "reset" LED and button, which must be used each time to recover from the alarm state. Sensor is ScimArec AF22C semiconductor. One specimen supplied free of charge. Summary of Performance Assessment Unit gave low-level warning, but failed to fully alarm within 10 minutes at 350 ppm CO or within 30+ minutes at 150 ppm CO. Environmental effects were not investigated.

The manufacturer has promised to provide new specimens.

40

Appendix 9. Gas Maestro GSS 2002

Background The Gas Maestro consists of a master controller, and a range of optional modules for remote or stand-alone sensing, viz. GSS 1202G main control GSS 1301G gas detector GSS 1501 tilt detector (not tested) GSS 1701M CO detector GSS 2000 gas valve GSS 2002 CO detector Two sets of test samples were provided, one from Glowmoor Technologies (Europe) Ltd and another more recently from Safety Systems (International) Ltd. It is understood that the intermediate contact in both cases was British Gas Services.

41

Description and Detail of Specimens The controller unit is powered by 9 volts DC via a mains adapter, and is provided with a green/red LED and a RESET button. A switched output to the manually-resetting gas valve is achieved via screw terminals, and the sensor connections are via standard telephone-style jack sockets. One of these has an internal ten second delay function, which could be useful for reducing false alarms. The sensor units can be connected to the controller or, in the case of the tilt and CO detectors, be powered separately by the mains adapter and used in the stand-alone mode. The supplied instructions claim compliance with a range of performance standards, including BS 7348 and BS 7860 for domestic gas and CO alarms, respectively. The GSS 1701M is the same size and shape as the control unit, and incorporates two sensors. One is a KE-50 from the Japanese Storage Battery Co Ltd, and is assumed to be for oxygen. The other (presumably for CO) is marked P020-5972, and is of unknown manufacture. The GSS 2002 is more compact in size, of white rather than grey plastic, and utilises a Figaro TGS 2440 semiconductor sensor. Both models have a TEST/RESET button, and give warning beeps on energisation and de-energisation. The GSS 2002 additionally provides a digital LED display beneath a hinged cover, giving an ambient temperature reading when no CO is detected. Summary of Performance Assessment The GSS 1701M failed to alarm at even 450 ppm CO, and so no further testing was undertaken on that module. The GSS 2002 was found to alarm at between 6 and 10 minutes at 350 ppm CO, and between 13½ and 17½ minutes at 150 ppm CO. However, these times were significantly increased at low temperatures (5°C) whilst high temperatures (35°C) led to an increase at low humidity and a decrease at high humidity. Automatic alarm recovery was achieved within 3 minutes, in every case, and the audible alarm could be muted by operation of the RESET button. An indication of the actual sensor output could be gained from the digital display, which was updated every 12 seconds. However, it was apparent that the sensor calibration was very non-linear, giving relative errors greater than ±100 ppm CO, depending on the rate of change, as well as the absolute CO concentration. In addition, sensor output decreased markedly with time at steady-state conditions, so the display could give misleading information in practice.

No response has yet been received on these results.

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Appendix 10. GasWatch 200

Manufacturer and Contact Details GasWatch Safety Systems Ltd, Regent House, 291 Kirkdale, London, SE26 4QE. Jennifer Wildey, Account Manager. Tel. 0181 659 5575 Fax. 0181 659 7710 Description and Detail of Specimens Standard commercial plastic box, with no provision for cable access. Electrochemical sensor is CityCell LoCO3, and output function relays are fitted as standard. Green "power" LEDs, red "alarm" LEDs and a "reset/test" button on front face. Five minute warm-up indicated by green LEDs flashing 1 second on and 1 second off, after which green LEDs blink 5 seconds on and 0.5 second off. Test button activates red LEDs and buzzer, but buzzer seems quiet. Complex alarm sequence of flashing and steady red LEDs, and intermittent and continuous buzzer. Unit must be reset after alarm is triggered. Two specimens purchased, at the list price of £155.00 each. Summary of Performance Assessment Alarm triggered within 5 minutes at 350 ppm CO, but not within 30+ minutes at 150 ppm CO. Sensitivity decreased with ambient temperature.

No compliance with BS 7860 is claimed for this product.

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Appendix 11. Monox

Manufacturer and Contact Details

Monox Ltd, Rutland House, Hargreaves Road, Goundwell Industrial Estate, Swindon, SN2 5AZ. Piers Hubbard-Miles, Managing Director. Tel. 01793 747718 Fax. 01793 747701 Description and Detail of Specimens

Proprietary electrochemical sensor, mounted in a test-bed (manufactured by S-Tech in Canada) to provide an alarm configuration suitable for initial assessment purposes. An alternative test vehicle had very low battery life.

Summary of Performance Assessment

Alarm after about 5 minutes at 350 ppm CO, and about 21 minutes at 150 ppm CO. No observed effect of temperature, humidity or other interferants.

Recommended for further consideration when production units become available.

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Appendix 12. Nighthawk Basic 900-0081

Manufacturer and Contact Details Kidde Safety (UK) Ltd, Hollins Road, Oldham, Lancashire, OL8 3DX. Paul Holland, Marketing Manager. Tel. 07801 473434 Fax. 01844 218489 Description and Detail of Specimens Sturdy-looking unit, kite-marked to BS 7860 and provided with 2.5 metre mains lead and 3 amp fused plug. Green "operate" and red "alarm" LEDs, plus "test/reset" button. Loud buzzer and clear indicators, with easy to use button. Good instruction booklet. Sensor is Figaro TGS 203, and it is understood that improvements in calibration procedures are to be implemented shortly by the manufacturer. Five specimens provided free of charge. Summary of Performance Assessment Alarmed between 4 and 8 minutes at 350 ppm CO and about 20 minutes at 150 ppm CO. Some variation caused by temperature and voltage changes, but not sufficient to inhibit functionality in service. Recovery within 3 minutes in clean air in every case.


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Appendix 13. Nighthawk Deluxe 900-0089

Manufacturer and Contact Details Kidde Safety (UK) Ltd, Hollins Road, Oldham, Lancashire, OL8 3DX. Paul Holland, Marketing Manager. Tel. 07801 473434 Fax. 01844 218489 Description and Detail of Specimens Circular unit with hinged casing, which seems rather flimsy. Powered by three replaceable dry batteries, and understood to be approved to BS 7860. Green "operate" and red "alarm" indicators, with "test/reset" button. Also provided with digital display and "peak hold" button. Sensor is replaceable Zellweger electrochemical cell, with a claimed lifetime of 4 years. One specimen provided free of charge. Summary of Performance Assessment

Alarmed within 5 minutes at 350 ppm CO, and within 15 to 25 minutes at 150 ppm CO, for all temperature and humidity variations. Recovery within 3 minutes in clean air in every case. Digital

display took about 8 minutes to give steady reading, and battery lifetime may be a problem. Recommended for further consideration.

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Appendix 14. Schlumberger XH-443B

Manufacturer and Contact Details Schlumberger Electricity and Gas, Industrial Estate, Port Glasgow, PA14 5XG. Roger Hunt, Sales Director. Tel. 01475 745131 Fax. 01475 744567 Description and Detail of Specimens Sturdy-looking unit, kite-marked to BS 7860, and provided with green, yellow and red LEDs and symbology for power, fault and alarm, respectively. Two-stage alarm, with loud intermittent buzzer. Sensor is semiconductor, possibly made by New Cosmos, and relay for an output function is included as standard. A CO test kit is included, which involves the use of a gas cigarette lighter, but which appears to work satisfactorily. The instruction leaflet is rather brief in comparison to other models. Six specimens provided free of charge, one of which was accidentally damaged during testing. Summary of Performance Assessment Alarm triggered at 2 minutes in 350 ppm CO. With 150 ppm CO, low-level alarm occurred after 2 minutes, with full alarm after 16 to 17 minutes. Alarm recovered within 1 minute in clean air for every case. There was no apparent effect from variations in temperature, humidity or voltage supply, but the unit could be more sensitive on initial energisation.


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Appendix 15. Senco model ONE

Manufacturer and Contact Details

Senco Sensors Inc. 1335 Matheson Boulevard East, Mississauga, Ontario, Canada. Mario Zanon, VP Engineering. Tel. 905-282-9908 Fax. 905-282-1506

Description and Detail of Specimens

Compact unit with hinged back, which can be used either for wall locations or as a stand. Battery-powered and available in BS 7860 configuration, although approval has not been sought. Red LED flashes once per minute, and digital display provides CO concentration plus other information. Reset button must be operated following alarm, to remove warning icon. Proprietary electrochemical cell is claimed to have lifetime of 7 years. Six specimens obtained at $30 each.

Summary of Performance Assessment

Alarm after about 5 minutes at 350 ppm CO, and about 21 minutes at 150 ppm CO. No observed effect of temperature, humidity or other interferants. Digital display reads slightly low, but within 10%.


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Appendix 16. SF330KM

Manufacturer and Contact Details SF Detection Ltd, 4 Stinsford Road, Nuffield Industrial Estate, Poole, Dorset, BH17 0RZ. Michael Fleck, General Manager. Tel. 01202 645577 Fax. 01202 665331 Description and Detail of Specimens Compact unit, kite-marked to BS 7860, with a single red LED which flashes at about 50 second intervals during normal operation. Test button to rear of unit activates LED and buzzer in novel alarm signal, comprising repeated CO in Morse code. However, the button was stiff and prone to sticking inside the casing on one unit. Low-level warning is a flash plus beep once every 5 seconds. Sensor is Zellweger electrochemical cell. Neither battery nor sensor are replaceable, although 5 year lifetime is claimed for normal usage. Eight specimens purchased at the list price of £34.99 each. Summary of Performance Assessment Alarmed after about 2 minutes at 350 ppm CO. Low-level alarm triggered after about 8 minutes at 150 ppm CO, and full alarm within 17 minutes. Recovery in clean air was within 2 minutes in

each case. No significant variations were observed with changes in temperature or humidity. Recommended for further consideration.

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Appendix 17. Technotrend CO-350

Manufacturer and Contact Details Supplied by Advanced Power Conversion Ltd, Unit B5, Armstrong Mall, Southwood Summit Centre, Farnborough, Hants, GU14 0NR. David Roberts, Commercial Director Tel. 01252 373242 Fax. 01252 373440 Description and Detail of Specimens Attractive casing, provided with 4 metre mains lead and 3 amp fused plug, green "power" and red "alarm" LEDs, together with "test/reset" button. Alarm state is red LED plus loud double beeps from buzzer. Sensor is a semiconductor of unknown origin, marked 2M003, possibly a variant of the Figaro TGS 203. Six specimens purchased at the list price of £49.95 each. Summary of Performance Assessment No alarm within 10 minutes at 350 ppm CO, nor within 30+ minutes at 150 ppm CO. Effects of environmental changes were not investigated. No compliance with BS 7860 is claimed for this product. The unit is no longer included in the supplier's product range.

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Appendix 18. CO Alarm Field Trial

Guidelines for Participants Background A number of different models of domestic CO alarm are being compared in this trial. Each of these has been type tested and approved to the relevant British Standard (BS 7860) but we need to obtain extra information on long-term behaviour under real conditions in the home. Installation of Specimens It is impossible to give absolute rules for siting CO alarms, because every household will have individual differences in internal layout, as well as personal life-style of the occupants. The choice of location will therefore depend on your own needs and preferences. The instruction leaflet supplied by the manufacturer should give advice based on Annex B to BS 7860 but the following points should also be taken into consideration;

a) Any room in regular use (eg. a sitting room) would be a suitable choice for a CO alarm, if it contains a fuel-burning appliance. b) Any room used for sleeping would also be suitable, if it is near to or contains a fuel-burning appliance. c) In a bed-sitting room, the CO alarm should be located away from any cooking appliances (because of the likelyhood that interferant substances will be produced during cooking) but close to the sleeping area. d) To avoid possible false alarms during cold start-ups, a CO alarm should be at least 2 metres away from a fuel-burning appliance. e) To give adequate protection to people whether standing, sitting or lying down, a CO alarm should be sited 1½ to 2 metres above floor level. f) If the fuel-burning appliance is in a room not normally used (eg. a boiler room) then a location just outside the room would be suitable, so that the alarm can be heard more clearly.

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Do not locate a CO alarm in any of the following positions;

- outside the building. - at floor level. - where it could be easily knocked or damaged. - inside or below a cupboard, wardrobe or other enclosure. - anywhere obstructed by curtains or furniture. - where dirt or dust is likely to block any air gaps. - next to a door, window, or anywhere affected by draughts. - where the temperature could be below -5°C or above 40°C. - in a damp or humid area, or where condensation occurs. - close to or directly above a sink or cooker. - in an area where chemicals or solvents may be used. - where it could be accidentally turned off or removed.

Once the CO alarm is installed, please complete the details requested on the attached sheet [I], including a sketch plan of the chosen location. This sheet should then be forwarded to the field trial organiser, for record purposes. Routine Procedures For mains-powered CO alarms, electrical supplies should be maintained at all times except, perhaps, when the premises are left vacant for long periods. Note that there is a warm-up period after first energisation, or re-energisation, when the unit may not give maximum protection. Some of the alarm units incorporate a test and/or reset facility, and the manufacturer's instructions will indicate how and when these should be used. It is not the intention of this field trial to deliberately interfere with normal operation of the units, but please be aware that they may react to a range of everyday compounds. Any instance of alarming (other than routine testing) should be recorded on one of the attached sheets [II]. The completed sheet should then be forwarded to the field trial organiser, when the unit is returned for calibration checks. It would be prudent to treat any unexpected alarming as a possible emergency, and follow the advice given in the manufacturer's instructions, or Annex B to BS 7860. However, if there is reason to believe that the CO alarm has stopped working correctly, please return it to the field trial organiser, along with a description of the defect.

YOUR PARTICIPATION AND CO-OPERATION IN THE SMOOTH-RUNNING OF THIS FIELD TRIAL

IS GREATLY APPRECIATED

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FIELD TRIAL OF DOMESTIC CO ALARMS

I. Details of Installation Unit Type: Serial No. Name of Participant: Date of Installation: Address of Installation: Initial Comments: Sketch plan of installed location of the alarm, giving height above floor level, and including major features, such as fuel-burning appliances, and approximate overall dimensions:

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FIELD TRIAL OF DOMESTIC CO ALARMS

II. Reporting Form for Instances of Alarming

Unit Type: Serial No. Please include a copy of this form each time the unit is returned for calibration checks, even if there have been no instances of alarming. Date and Time Comments and Probable Cause of Alarming (if known)

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CO Alarm Field Trial

Additional Information Regarding Dicon CO805 Units During evaluation testing, the following points have come to light, and may be found useful by field trial participants; Backing Plate The instruction leaflet does not refer to releasing the unit from the backing plate, which is held in place by a catch on a plastic arm. Use a small screwdriver (or similar) to lever the plastic arm away from the backing plate. The plate can then be removed by sliding it downwards. Install the plate in the desired location, using the screws provided. The unit can then be positioned, by placing the cutouts in the rear over the backing plate lugs, and sliding downwards until the catch engages again. Test Button The test/reset button may seem stiff to operate, and comments on this aspect will be welcomed. Note that, if the alarm triggers, this button must be depressed to cancel the alarm signal.

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Appendix 19. Domestic CO Alarm Installation Questionnaire

Please complete one of these forms (both sides) each time that a CO alarm is installed, or found to be installed, during an inspection of domestic premises. 1. Description of Location Postcode of Premises: _________________ House Type (tick one): o-Flat o-Maisonette o-Bungalow o-Terraced o-Semi-detached o-Detached o-Caravan o-Boat Room Type (tick one): o-Bed-sit o-Bedroom o-Landing o-Hallway o-Lounge o-Kitchen o-Cellar o-Outhouse Sketch plan of installed location of the alarm, giving height above floor level, and including major features, such as fuel-burning appliances, and approximate overall dimensions: Is the siting generally in accordance with the recommendations of BS 7860 (Yes/No)? Any additional remarks on the location?

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2. Description of CO Alarm Manufacturer: ________________________ Model Number: ________ Power Source (tick one): o-Mains o-Mains Adapter o-Dry Battery o-Other Battery Does the unit claim approval to BS 7860 (Yes/No)? Approximate Age (unless new): ______ years Serial Number or Production Date Code: ___________ Any additional comments on the appearance, etc? 3. History and Experience Is there a known history of CO-related problems at these premises (Yes/No)? Has the CO alarm triggered (Yes/No)? If so, are the reasons known (Yes/No)? Has the CO alarm been tested on a regular basis (Yes/No)? If so, was this by pressing a TEST button (Yes/No)? Why was the CO alarm originally installed? Was the occupier involved in the selection/supply (Yes/No)? If so, was BS 7860 a consideration (Yes/No)? Any other comments or information given by the occupier? 4. Contact Details Please provide the Inspector's CORGI Reference Number, and a telephone number in case any further information is needed. Ref No: ___________ Tel No: _________________ Date: _______________

YOUR CO-OPERATION IN THIS PROGRAMME IS GREATLY APPRECIATED

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Appendix 20. GRI Report 96/0055

Test Protocols for Residential Carbon Monoxide Alarms Phase 1, February 1996

Overview This Draft Topical Report has been prepared for GRI by Paul Clifford and Michael Dorman of Mosaic Industries, in response to the reported poor reliability of domestic CO alarms in the USA. It examines the strengths and weaknesses of current sensor technologies, and the potential influence of indoor environmental pollutants. Changes are suggested to the quality assurance and performance tests specified in UL2034, aimed at improving performance in service. Introduction Reasons for the increased usage of CO detectors are reviewed, together with the high numbers of false alarms, especially in the Chicago area. A breakdown of these false alarms is given for the different sensor types, with the main contributor being the colourimetric device, as used by BRK in their First Alert product. False alarm costs are estimated, together with the likelyhood of "negative alarms", ie. no alarm triggered in hazardous conditions. Despite the lack of any real data, it is suggested that negative (but un-reported) alarms are just as likely as false alarms, even for semi-conductor sensors. The existing US standard (UL2034) is blamed for this situation, by not including credible reliability criteria, nor addressing false alarm immunity or long-term performance. The stated aim of the report is to develop effective tests, applicable to all the different CO detection technologies. Background The need for CO alarms is reviewed, in the light of a steady decline in CO-related deaths. It is emphasised that the majority of these are due to motor vehicle exhausts, with some also due to liquid and solid fuels, and only a minority due to natural gas. Physiological effects of CO exposure are considered in detail, with the emphasis on two factors;

- variation in susceptibility by different sectors of the population, with some people being particularly vulnerable, and - variation in physical activity level, with UL2034 implicitly assuming sustained heavy work.

By comparison with US and Japanese standards, it is suggested that an allowable threshold limit of 10% COHb is appropriate, together with a table of exposure times and concentrations to mimic the curve published in UL2034. [NOTE: Only steady-state exposures are considered, rather than the more practical situation of steadily rising CO concentrations]

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Environmental Factors Although CO detectors can be made to perform various functions, it is suggested that the main purpose of a domestic CO alarm is to warn of acute hazards. The problem of setting alarm levels is discussed in relation to possibly high background CO levels, whilst still allowing a reasonable reaction time. It is suggested that the main consumer requirements are reliability and ease of use, at an affordable price. The report then presents a very informative and useful examination of probable (US) indoor pollutants, by chemical category. Likely sources are listed for each one, and the possible concentrations are estimated. Lifetime exposures are tabulated, giving the following order of ranking;

- carbon dioxide, carbon monoxide, methane, nitric oxide, ammonia, formaldehyde, acetic acid, hydrogen, isopropanol and acetone, plus many more!

Available Technologies This quite extensive section assesses the different types of sensor most likely to be used in domestic CO alarms. It includes descriptions of the detection mechanisms, together with the historical background and any associated advantages or disadvantages. These are briefly summarised; a) Colourimetric: Inherent manufacturing variations lead to different reaction rates, particularly affecting sensor reversibility. They are sensitive to temperature and humidity, plus poisoning by hydrogen sulphide and possibly ammonia, as well as oxides of nitrogen. Lifetimes are un-proven, but the devices are fairly cheap and many units are now in service within the USA. b) Semi-Conductor: These are inexpensive and very popular, especially the Figaro TGS 203. Inherently un-selective in response, they are prone to temperature and humidity variations, and can have poor long-term stability. Much research worldwide has failed to reduce hydrogen and ethanol cross-sensitivities, or poisoning by nitrogen oxides. New developments promise to decrease power requirements. c) Electro-Chemical: Relatively expensive, and presently of limited lifetimes, new developments promise to reduce size and cost, and extend service life. Essentially accurate and stable, they can be significantly affected by both humidity and temperature, outside certain limits. Hydrogen and hydrogen sulphide are the major cross-sensitivities. d) Non-Dispersive Infra-Red: Potentially extremely stable and selective, such sensors are presently far too large and costly for this application. However, miniaturised and much cheaper devices are promised. [NOTE: The report does not mention the obvious adverse effects of moisture interference] e) Catalytic: Slightly more expensive than semi-conductors, pellistors exhibit most of the same drawbacks, unless they are recalibrated regularly. Once again, improvements are promised, to reduce power and increase sensitivity.

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The Role of Standards The reliability of a CO alarm is defined as its effectiveness in preventing CO poisoning. It is suggested that this can best be specified in terms of allowable failure rates, both at the time of manufacture and after a particular period in service. Taken together, these are intended to address the areas of design certification, manufacturing quality assurance and lifetime compliance. The success of UL2034 in meeting these requirements is reviewed, and several shortcomings are highlighted, viz.

- blood COHb levels are not explicitly specified. - unrealistically high initial reliability levels are specified for the alarm unit excluding the sensor, but with no test requirement. - the most critical item (ie. the sensor itself) is only assessed by small numbers of tests. - no minimum lifetime is specified, nor any final reliability level. - exposure-related lifetime testing is not addressed. - there is no requirement for repeatability. - 100% production testing is unjustifiable.

[NOTE: Not all of these criticisms are considered valid, and the greatest flaw in UL2034 (ie. the lack of a realistic alarm recovery time) is ignored] Reliability Specification and Testing It is suggested that detailed information is needed in three main areas, in order to develop a standard for domestic CO alarms;

- relevant reliability data, - the physiological effects of CO exposure, and - characterisation of the indoor environment.

From this, performance tests can be devised, in addition to those presently specified in UL2034. Appropriate failure rates are given as 1% initially and 16.5% after three years, both at a confidence level of 90%. The report discusses target values of mean time between failure (MTBF) and how these might be derived for models already in service. The numbers of test specimens needed to ensure statistical verification are also considered. For example, 90% confidence of a failure rate less than 1% would require 230 units to be tested, with no failures!

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Alarm set levels are also discussed extensively, but the concentration and exposure levels presently used in UL2034 are retained, with extra checks on non-alarming. Additional interference and exposure tests are recommended, based on the analysis in section 3. Tests after a 24 hour interval are also included, to check on repeatability. [NOTE: A single passing reference incorrectly states that a draft British standard includes a lifetime test. A list of all the proposed extra testing follows this summary] Conclusions and Recommendations It is concluded that available sensor technologies all have distinct limitations, and that existing CO alarms suffer from both false alarms and false negatives, as well as poisoning and long-term drift. The main reason for this situation is the inadequate reliability requirements of UL2034, and the influence of indoor pollutants typically found in the domestic environment. Additional performance testing and quality assurance procedures are needed to rectify this. Detailed tests are proposed, in addition to those presently specified in UL2034. Further recommendations include a survey of CO alarm installation rates, reliability testing of newly purchased units and a programme of field retrieval and testing. References A total of 426 direct references are included, most of which relate to semiconductor sensors, plus 83 other references.

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Table 6.5 of GRI Report 96/0055

Comprehensive Tests for CO Detectors Target reliability: Detectors must pass tests 1 to 6 with a cumulative failure rate of less than 1% at a 90% confidence level. Detectors must pass test 8 with a cumulative failure rate of less than 3.7% at a 90% confidence level. 1. Alarm Level Purpose: Consistently alarm at exposures producing 10% COHb, or less. Method: Alarm within 90 mins @ 100 ppm CO, 35 mins @ 200 ppm CO and 15 mins @ 400 ppm CO, at various temperatures and in sufficient numbers. 2. Low Concentration Immunity Purpose: Non-alarm on long-term exposure at ambient CO levels. Method: No alarm within two weeks @ 20 ppm CO. 3. Surge Immunity Purpose: Non-alarm to short duration exposures producing less than 2% COHb. Method: No alarm within 30 minutes @ 50 ppm CO. 4. Sensitivity Distribution Purpose: Check that the within-batch variation is less than the specified tolerance. Method: Subject sufficient units to tests 1 & 2. 5. False Negatives Purpose: No non-alarms in the presence of oxidant gases. Method: Repeat the alarm level test whilst exposed to 1 ppm each of NO and Cl2.

6. False Positives Purpose: Non-alarm in the presence of reducing gases. Method: No alarm within 2 hours @ each of; 500 ppm methane, 300 ppm butane, 500 ppm heptane, 200 ppm ethyl acetate, 200 ppm isopropyl alcohol, 1000 ppm carbon dioxide, 100 ppm ammonia, 200 ppm ethylene, 200 ppm ethanol, 200 ppm toluene and 200 ppm trichloroethane. 7. Repeatability Purpose: Remain fully functional after several alarms. Method: Pass test 1 without replacement, then repeat tests 1 & 3 one day later. 8. Accelerated Lifetime Exposure Purpose: Remain functional throughout the stated lifetime. Method: Pass tests 1 to 6 in sufficient numbers, after exposure (in ppm-days) to; iso-butane (700), ethylene (350), ammonia (650), toluene (70), trichloroethane (200), ethanol (900), formaldehyde (1000), acetone (500), acetic acid (600), hydrogen (550), hydrogen chloride (143), sulphur dioxide (41), nitric oxide (1400), hexamethyldisiloxane (10), chlorine (40) and hydrogen sulphide (33).

Printed and published by the Health and Safety ExecutiveC30 1/98

Printed and published by the Health and Safety ExecutiveC2.5 08/01

CRR 360

£25.00 9 780717 620852

ISBN 0-7176-2085-9

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