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The risk of carbon monoxide poisoning from domestic gas appliances

Quantitative Risk Assessment February 2012

Report to the Department of Resources, Energy and Tourism

The Allen Consulting Group ii

Allen Consulting Group Pty Ltd

ACN 007 061 930, ABN 52 007 061 930

Melbourne

Level 9, 60 Collins St Melbourne VIC 3000 Telephone: (61-3) 8650 6000 Facsimile: (61-3) 9654 6363

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Online

Email: [email protected] Website: www.allenconsult.com.au

Disclaimer: While the Allen Consulting Group endeavours to provide reliable analysis and believes the material it presents is accurate, it will not be liable for any claim by any party acting on such information. © Allen Consulting Group 2012

Q R A O N T H E R I S K O F C O P O I S O N I N G

The Allen Consulting Group iii

Acknowledgments

The authors wish to acknowledge the assistance of Mr Stephen Brook, VIPAC and the Gas Technical Regulators Committee in preparing this report.


The Allen Consulting Group iv

Contents

Executive summary vi Consequences of CO poisoning vi Risk factors vi Mitigating the risks of CO poisoning viii

Chapter 1 1 Quantifying the risk of gas appliances 1

1.1 Basis for the QRA 1 1.2 The health risks of CO poisoning 2 1.3 Requirements for CO poisoning 3

Chapter 2 5 Framework for the QRA 5

2.1 Factors leading to CO production and spillage 5 2.2 Risk ratings 8 2.3 Data requirements and sources 9 2.4 Risk factors 10

Chapter 3 17 Quantifying the baseline risk 17

3.1 Top-down approach 18 3.2 The bottom-up approach 21

Chapter 4 29 Risk mitigation strategies 29

4.1 Risk mitigation strategies for assessment in the QRA 29 4.2 Strategies to reduce appliance risk 30 4.3 Strategies to reduce installation risk 31 4.4 Strategies to reduce operation risk 33

Chapter 5 35 Impact of risk mitigation strategies 35

Chapter 6 40 Conclusions 40

Appendix A 42


The Allen Consulting Group v

Probability tree 42

Appendix B 43 Carbon monoxide poisoning in recreational vehicles 43

References 45


The Allen Consulting Group vi

Executive summary

This Quantitative Risk Assessment (QRA) has been undertaken to assess the level of risk of carbon monoxide (CO) poisoning from gas appliances in Australian households and recreational vehicles. It is part of a two-phase work program to be undertaken by the Allen Consulting Group. The second phase is to produce a Regulation Impact Statement (RIS) on potential options to reduce the incidence and harm of CO poisoning in households and recreational vehicles.

This review was undertaken to address the risk of CO poisoning from gas appliances to further the work undertaken by the Gas Technical Regulators Committee (GTRC) in the Gas Appliance (Carbon Monoxide) Safety Strategy (Safety Strategy). The Safety Strategy outlined a range of mitigation strategies to address the key risks in associated with the common use of gas appliances in domestic settings in Australia. The QRA is designed to assess key risks posed by different appliances that are widely used in the community and the extent to which different risk mitigation strategies can be used to address these risks. A RIS will follow this QRA. The RIS will examine feasible risk mitigation strategies, addressing the costs and benefits of potential mitigation strategies.

This report focuses on the current risk of CO poisoning from gas appliances. Consultations with the GTRC have raised concerns that the potential exists for these risks to increase in coming years as a result of improved building sealing requirements necessary to satisfy higher energy efficiency requirements in the Building Code of Australia.

Consequences of CO poisoning

Exposure to CO has the potential to cause serious permanent injury and in some cases, death. Certain demographic groups — such as children, the elderly and those with existing heart problems — are likely to be more susceptible to CO poisoning.

In Australia, CO poisoning causes, on average, 1 reported death per annum. Using available UK data it is estimated that a further 21.3 injuries each year are also attributable CO poisoning.

Risk factors

The QRA has focussed on a number of common gas appliances found throughout Australian households. This includes heaters (natural draught, balanced flued and flueless), internal domestic hot water systems and cooktops. Gas appliances in recreational vehicles — which also pose a concern — were largely unable to be quantified due to data limitations.


The Allen Consulting Group vii

Although the consequences of CO poisoning are severe, the risks of CO poisoning are low. CO poisoning requires both burner disruption and the unsafe discharge of combustion products, and the probability of these two incidents jointly occurring is rather low. Furthermore, a variety of significant and stringent safety measures are already in place to prevent CO injuries from occurring. These safety measures relate to regulation, inspection, appliance standards, appliance approvals processes, gas installation standards, gasfitters training, installation certification and Building Code standards.

Australian houses are different to those in Europe. It is common in Australia to have 2 or more bathrooms. Likewise modern rangehoods now used in residential kitchens are often fitted with powerful exhaust fans with 200 Watt motors not uncommon. Therefore the opportunity to create negative pressures in 5 or 6 star houses is becoming more likely in Australia than in Europe.

Some appliances are inherently more prone to risk than others. The level of baseline risk associated with each appliance was estimated by first identifying the factors that could lead to either burner disruption or unsafe discharge of combustion products; and then estimating the likelihood of those events occurring. Internal open flued water heaters and natural draught space heaters are associated with most risk factors. Accordingly, the associated risk of injury from these two appliances is 4.8 and 4.9 per million respectively. It should be noted that the number of internally mounted water heater is reducing and the actual total number is only around 50,000.

It is important to note that the majority of the risk associated with CO poisoning from gas appliances in Australia arises from the use of natural draught space heaters. In fact, 98 per cent of the risk of CO poisoning is attributed to this type of appliance which is in line with overseas experiences.

The estimated baseline risk associated with each appliance type is summarised in the following table.

Table ES 1.1

RISK POSED BY APPLIANCE TYPE

Appliance Risk factor Population Estimated number of injuries from CO

poisoning per year

Injuries per million

exposed

Natural draught heater

4.9 x 10-6 4,524,120 22.1 4.9

Balanced flue heater

1.8 x 10-9 1,900,130 0 0

Flueless heater

8.1 x 10-8 678,618 0.1 0.1

Cooktops 1.0 x 10-8 9,862,582 0 0

Internal domestic hot water services

4.8 x 10-6 45,241 0.2 4.8

Total 13,775,945 22.5 1.63

Source: The Allen Consulting Group


The Allen Consulting Group viii

Estimated total risk of injury per million exposed reflects the exposed population per gas appliance. Individual risk will depend on the cumulative risk of all gas appliances to which an individual is exposed. As 5 and 6 star homes become more prevalent, it is likely that the risks of CO injuries may increase.

Mitigating the risks of CO poisoning

Strategies to reduce the risk of CO poisoning were assessed by the degree to which they addressed certain risk factors. Eleven strategies were developed based on earlier consultation between members of the Ministerial Council on Energy and GTRC, and these strategies were assessed in terms of their ability to mitigate the risk of CO poisoning. These strategies targeted risks factors relating to appliances, installation and operation and are summarised in Table ES 1.2.

Table ES 1.2

SUMMARY OF RISK MITIGATION STRATEGIES

Nature of risk

Risk mitigation strategy name

Summary

Appliance CO alarms (rental) Mandatory installation of CO alarms in rental properties and RVs only.

Appliance CO alarms (all) Mandatory installation of CO alarms in all residential properties and RVs.

Installation Improved training Improving training requirements for tradespeople, educating the public about using licensed gas fitters.

Installation Ventilation for appliance operation

Ensure adequate adventitious air or install permanent ventilation openings.

Installation Ventilation for removal of products of combustion (flueless)

Mandate the installation of permanent ventilation openings for flueless heaters

Installation Ventilation design of extraction systems

Design housing ventilation to ensure that negative pressures do not develop*

Installation Phase out / major engineering improvements to natural draught appliances

Mandate use of room sealed appliances in new installations or subject natural draught appliances to material engineering changes

Installation Timers inserted into exhaust fans

Retrofitting timers to all exhaust fans to limit the time they can be in continuous use, thus decreasing the possibility for extended periods of negative pressure.

Operation Public awareness Raise public awareness of CO hazards, importance of maintenance.

Operation Appliance maintenance (rental)

Mandatory maintenance of appliances every two years in rental properties and RVs only.

Operation Appliance maintenance (all)

Mandatory maintenance of appliances every two years in all residential properties and RVs.

* For the proper operation of extraction systems in 5 or 6-star buildings, this will require adequate design to ensure the star rating is achieved, this may involve motorised dampers and or push pull systems. AS 1668 will require amendments to achieve these performance standards

Source: The Allen Consulting Group.


The Allen Consulting Group ix

In general, this analysis shows that strategies addressing the risk of adverse flow and insufficient air for combustion were the most successful at reducing the risk of CO poisoning. This was due to these being the dominant risk factors for spillage and combustion disruption respectively.

The most successful mitigation strategy involved improved ventilation design of extraction systems, which was shown to remove almost half of the risk. Currently, the effect of retrofitted exhaust fans on the room air pressure is generally not considered in residential premises. In combination with the increasing air tightness of dwellings to comply with higher energy efficiency ratings, the potential for adverse flow from the use of exhaust fans is exacerbated. These ventilation systems (typically bathroom and kitchen exhaust systems) require openings either permanent or motorised to operate correctly. Negative pressure and inadequate extraction are both alleviated by better ventilation design and installation. One option is for push-pull ventilation; another option is for motorised openings linked to extraction fans; yet another, simpler, option is to allow for permanent air vents, although the last option may compromise the energy efficiency rating of a dwelling.

One of the least effective strategies (from a pure efficacy point of view) was increased training. Mandatory appliance maintenance and the mandatory installation of CO alarms in rental properties were also found to be relatively ineffective, given the relatively low proportion of rental dwellings and issues regarding the efficacy of alarms.

Table ES 1.3

EFFECT OF INTERVENTION STRATEGIES ON CO POISONING RISK

Intervention Injury frequency rate (per million exposed)

Per cent reduction

Status quo (bottom-up estimate) 1.63 na

CO alarms (rental) 1.58 3.02

CO alarms (all) 1.44 11.31

Improved training 1.61 0.01

Ventilation for appliance operation 0.88 45.72

Ventilation for removal of products of combustion (flueless)

1.63 0.00

Ventilation design of extraction systems

0.85 47.71

Phase out / major engineering improvements to natural draught appliances

0.81 after 10 years 50 after 10 years

Timers inserted into exhaust fans 1.47 9.54

Public awareness 1.59 2.43

Appliance maintenance (rental) 1.62 0.01

Appliance maintenance (all) 1.59 2.44



The Allen Consulting Group 1

Chapter 1

Quantifying the risk of gas appliances

This Quantitative Risk Assessment (QRA) has been undertaken to assess the level of risk of carbon monoxide (CO) poisoning from gas appliances in Australian households and recreational vehicles. It has been commissioned by the Department of Resources, Energy and Tourism (the Department) following a motion passed by the Federal Parliament requesting the Ministerial Council on Energy work with the Gas Technical Regulators Committee (GTRC) to explore issues related to carbon monoxide (CO) poisoning from gas appliances and recreational vehicles and develop the Gas Appliance (Carbon Monoxide) Safety Strategy, which examines the issue of carbon monoxide poisoning in residences and the most effective options to mitigate the risk of poisoning.

The document is part of a two-phase work program to be undertaken by the Allen Consulting Group. The second phase is to produce a Regulation Impact Statement on potential options to reduce the incidence and harm of CO poisoning in households and recreational vehicles.

The QRA first explores the health effects arising from CO poisoning before investigating the risk of carbon monoxide poisoning in the community from domestic household gas appliances. Once relative risks have been identified and quantified this information can be used to determine the overall level of risk of CO poisoning in the community in absolute terms and costs.

1.1 Basis for the QRA

A QRA is designed to determine the level of risk of an adverse event in the community. It involves an assessment of the population susceptible to the risk and an estimation of the likelihood of an event occurring to determine the affected population. This QRA is designed to quantify the current risk of CO poisoning in residences and to what extent risk mitigation options are likely to lower the risk, either in isolation or in combination. The QRA also quantifies the residual risk following Government intervention.

Gas appliances are also commonly used in recreational vehicles (RVs), however a lack of available data has limited the analysis of CO poisoning incidents in RVs. CO poisoning in RVs is further discussed in Appendix B.

This QRA is based on the probability tree highlighted in the Gas Technical Regulators Committee’s Gas Appliance (Carbon Monoxide) Safety Strategy (see Appendix A), as well as additional concerns highlighted in stakeholder discussions and research.

Gas appliances vary with regard to their design and operational elements and, as such, have different risks of CO release from various forms of appliance or unsafe discharge.



Historically, space heaters and internal domestic water heaters have posed the highest risk of CO poisoning to the household sector (Energy Safe Victoria 2010). New appliances such as cooktops with increased fuel burning capacity, and the 5-star and more recently 6-star thermal efficiency requirements for new and substantially renovated houses requiring better building sealing, as well as the encouragement of retrofitted weather sealing for increased energy efficiency, potentially pose an increased risk of CO poisoning. Due to these changes the risk of CO poisoning in Australian homes has the potential to increase.

1.2 The health risks of CO poisoning

CO is an invisible, odourless and tasteless gas that can cause significant health problems at very low atmospheric concentrations. CO binds more strongly to haemoglobin than oxygen, with exposure to CO resulting in a reduction in an individual’s blood oxygen-carrying capacity.

Exposure to CO can lead to flu-like symptoms at low doses (including headaches, tiredness and nausea) and permanent injury and death in higher doses (FASTS 2002). Table 1.1 shows a range of health effects that result from CO poisoning, in terms of the percentage of carboxyhaemoglobin (COHb) in the blood.

Table 1.1

HEALTH EFFECTS OF COHB BLOOD LEVELS ON HEALTHY ADULTS

% COHb Effects

0.3–0.7 Normal range in non-smokers due to endogenous CO production

0.7–2.9 No proven physiological changes

2.9–4.5 Cardio-vascular changes in cardiac patients

4–6 Usual values observed in smokers, impairment in psychomotor tests

7–10 Cardio-vascular changes in non-cardiac patients (increased cardiac output and coronary blood flow)

10–20 Slight headache, weakness, potential burden on foetus

20–30 Severe headache, nausea, impairment in limb movements

30–40 Severe headache, irritability, confusion, impairment in visual acuity, nausea, muscular weakness, dizziness

40–50 Convulsions and unconsciousness

60–70 Coma, collapse, death

Source: UK Department for Communities and Local Government 2009.

Some groups in society are more susceptible to the health effects of CO poisoning, particularly children, the elderly and individuals with existing heart problems (Solid Fuel Association UK, 2007). People in these groups are likely to experience more severe effects from CO poisoning at lower carboxyhaemoglobin concentrations.



Mortality and morbidity rates from CO exposure are dependent on both concentration of CO and time of exposure. Lower concentrations of CO are increasingly harmful as exposure time is prolonged. The relationship between CO concentration and exposure time is represented in Figure 1.1 below. It is important to note that this represents a model case, with significant variation surrounding the health consequences of different CO exposures amongst individuals.

Figure 1.1

EXPOSURE TIME AND CO CONCENTRATION – IMPACTS ON HEALTH

Source: Underwriters Laboratories 1996.

1.3 Requirements for CO poisoning

A build up of excess CO in an occupied space requires both:

• burner disruption leading to the production of CO by a gas appliance; and

• the failure to discharge combustion products from the dwelling.



Whilst burner disruption leads to negative consequences such as increased fuel costs and reduced appliance performance, burner disruption alone will not cause CO poisoning provided combustion products are effectively removed from an appliance and vented externally. Likewise, the failure to discharge combustion products alone is not sufficient to cause CO poisoning. CO poisoning requires two independent events – burner disruption and unsafe discharge – to occur simultaneously for CO to be released internally and potentially reach dangerous concentrations.

Limited empirical data of actual incidents is available on the rate of CO release by appliances in common states of fault. However a forensic examination of a CO poisoning scene undertaken by Sedda and Rossi (2006) reported that a faulty flueless internal hot water system, combined with a light two knot breeze, resulted in the concentration of CO in the 26m3 shower cabin increasing to 9000 ppm after 40 minutes of continuous hot water heater usage. As Figure 1.1 demonstrates, there is a high risk of a fatality occurring after a short period of exposure to CO at this concentration.

Factors leading to the production and unsafe discharge of CO are explored in detail in Chapter 2.



Chapter 2

Framework for the QRA

The QRA was undertaken to assess the level risk of CO poisoning in Australian households and recreational vehicles. The QRA has been developed according to the steps outlined in Figure 2.1. This chapter outlines the framework and data sources that form the basis of the QRA analysis.

Figure 2.1

STAGES IN DEVELOPMENT OF THE QRA


2.1 Factors leading to CO production and spillage

CO can be produced as a result of complications with appliances, problems regarding the installation of gas appliances, and problems with the operation of appliances. CO poisoning can result from either an individual problem that leads to both burner disruption and unsafe discharge (such as a blocked flue) or from a combination of factors (such as burner disruption leading to CO production and adverse flow leading to unsafe discharge).

Each of these factors are summarised in Table 2.1 and discussed individually in the sections below.



Table 2.1

FACTORS THAT CAN LEAD TO CO PRODUCTION AND SPILLAGE

Appliance Installation Operation

Appliance failure Poor appliance/flue connection

Flue obstruction/blockage

Appliance modification Downdraughts (due to ambient conditions)

Flue dilapidation

Adverse flow (due to operation of exhaust fans)

Burner disruption

Inappropriate gas supply Unvented rooms

Inappropriate location for the installation of the appliance

Insufficient air supply for appliance operation

Insufficient ventilation for the removal of combustion products


Gas is commonly used for cooking, space heating and water heating. Each type of appliance poses its own unique set of CO poisoning risks. The risk posed by different appliance types is outlined Box 2.1 below.



Box 2.1 RISK OF CO POISONING POSED BY DIFFERENT APPLIANCE TYPES

Aspects of the design and functionality of different gas appliances result in different levels of CO poisoning risk posed by different appliance types. The risks of CO poisoning posed by domestic gas appliances are outlined below. • Cooking appliances — Gas cooking appliances such as ovens and stove tops are

thought to pose a lesser threat of CO poisoning when used correctly. This is because the appliance has a large area from which to draw oxygen for combustion and is often associated with dedicated air extraction systems.

• Heaters — Heating is a major contributor of CO poisoning risk in the Australian context. Space heaters caused 78 per cent of CO poisoning deaths in Victoria between 1997-98 and 2009-10 (Energy safe Victoria 2010), and is responsible for 95 per cent of CO poisoning deaths in the US (Glenergy Consulting 2004). There are 3 major types of heating appliances, each of which has a different risk profile for CO poisoning. – Natural draught or open flue heaters — Natural draught or open flue heaters

draw oxygen for combustion from the internal environment and expel combustion products through a flue to the external environment. Natural draught heaters rely on the pressure differences caused by the chimney effect to expel combustion products. Natural draught or open flue heaters are thought to pose a significant CO poisoning risk due to their susceptibility to blockages and to adverse flow conditions. This type of appliance includes a down draught diverter designed such that the combustion process isn’t affected by a downdraught or adverse flow condition cause by the effect of outside wind. Testing for the ability for the appliances to cope with negative pressures does take place as part of the checks for compliance to relevant standards. The standards requiring 7.5 Pa are considered inadequate. In addition, single story housing (and thus short chimneys) in Australia, combined with generally windy conditions, further diminishes the opportunity to bring about robust chimney effects.

– Balanced flue heaters — Balanced flue heaters (also known as room sealed heaters) both draw oxygen for combustion and expel combustion products from/to the external environment typically through separate, concentric pipes. The combustion products from balanced flue heaters are sealed from the internal environment preventing spillage of combustion products internally. This reduces the risk of CO poisoning from these appliances.

– Flueless heater — Flueless heaters are portable gas appliances that draw oxygen for combustion and release combustion products into the internal environment. At face value this increases the risk of CO poisoning posed by these appliances, as any combustion failure resulting in the production of CO will lead to the release of CO internally. However work in the early 90’s to overcome NOx issues meant that improvements in burner technology of these appliances and introduction of Oxygen Depletion Sensors have resulted in very low incident rates. No CO related deaths have been recorded as a result of using flueless space heaters, connected to the Natural Gas Network at all The Australian Standards for flueless heaters have much more stringent emission requirements for CO and other noxious gases. In some States there are additional ventilation requirements for flue gas dispersion.

• Gas fired water heaters — Internal domestic gas fired water heaters can potentially release CO into the internal environment and cause injury. Regulations in some states now prevent the installation of internal domestic gas fired water heaters in traditionally small rooms such as bathrooms and toilets. Natural draught or open flue internal gas fired water heaters are thought to pose a significant risk of CO poisoning, with balanced flued internal hot water systems posing a much lower threat. Water heaters were responsible for 22 per cent of CO deaths in Victoria (Energy Safe Victoria 2010) and 5 per cent of CO poisoning deaths in the US (Glenergy Consulting 2004)




As well as domestic settings, gas appliances are also used in recreational vehicles. Commonly used appliances in recreational vehicles include gas heating, gas hot water services, gas refrigeration and gas cooking. CO poisoning risks in recreational vehicles are discussed in Appendix B.

Appliances are likely to produce CO in cases where they are used in ways they were not designed for. This is referred to as gross misuse. Gross misuse of appliances is beyond the scope of this QRA. What constitutes gross misuse of appliances is outlined in Box 2.2.

Box 2.2 GROSS MISUSE OF APPLIANCES

Regulatory approaches can reduce risk, but it is very difficult for regulation to totally eliminate risk. Residual risk remains in the case of gross misuse of appliances. With respect to gas appliances, gross misuse refers to cases where the appliance is used in a manner for which it was not designed. This can include: • using appliances designed for external use only in an internal environment; • using appliances designed for cooking as space heaters; and • using appliances with different fuels than what they are designed for.


2.2 Risk ratings

Baseline risk has been calculated using available data, with data sources listed in Section 2.3. Where data was unavailable risk ratings have been assessed using the scale outlined in Table 2.2 below. As an example, the risk of a poorly maintained flue developing a blockage is considered low, whilst the risk of spillage of combustion products from a modified appliance is considered high.



Table 2.2

RELATIVE RISK POSED BY EACH FACTOR

Risk Rating

Probability Explanation

Nil 0 There is no risk posed

Negligible 1 x 10-6 Adequate controls ensure the event poses almost no risk in cases of regular use

Minimal 1 x 10-5 Event is possible but risk will only develop in extremely rare cases

Low 1 x 10-4 Event is unlikely, however it will develop given the presence of a number of plausible circumstances

Moderate 1 x 10-3 The event is one of a number of potential outcomes that will occur with low frequency under regular use

High 1 x 10-2 Given the presence of the right set of conditions, this event will be expected to occur in a low number of cases

Extreme 1 x 10-1 This event will result in a large number of cases

Certain 1 The event will occur


2.3 Data requirements and sources

The QRA relies on a number of data sources as well as some assumptions in cases where data is not available. Data sources used in this QRA are outlined in Table 2.3 below. Assumptions regarding the probability of events where data is unavailable are outlined in Section 2.4.



Table 2.3

DATA SOURCES FOR THE QRA

Data Source Abstract

Households with gas connections

Australian Bureau of Statistics (ABS 2011a)

The ABS provides data on the proportion of households with gas connections in their publication “Environmental issues: Energy use and conservation”.

Gas appliances ABS 2011a The ABS provides data on the proportion of households who use gas for cooking, heating and hot water in their publication “Environmental issues: Energy use and conservation”.

Unauthorised appliances No data available Use of unauthorised or improperly modified appliances would be expected to be low.

Faulty installation Plumbing Industry Commission 2011

The PIC audits around 5 per cent of certified plumbing work each year, including simple domestic gas installations. The PIC has found that between 10 and 11 per cent of plumbing work, including gas fitting, fails the audit process. Other data sources indicate that Perth metropolitan rates for gas fitting only are 11.5 per cent for 2010/2011 and 9.25 per cent for 2009/2010.

Houses that have undergone renovations leading to significant changes to the sealing or the extraction capabilities of a building

ABS 2011d and Allen Consulting Group calculations

ABS data outlined the proportion of houses that have undergone renovations in the last ten years. Assuming no change to the rate of renovations since this survey was undertaken, the proportion of renovations since the introduction of 5 star standards was estimated. Finally, it was estimated that one quarter of these renovations resulted in significant changes to building weather sealing and/or extraction leading to the potential to develop negative pressures.

Gas appliances installed by a licensed gas fitter

MacGregor Tan Research for SA

A survey of 300 SA households by MacGregor Tan Research indicated that almost all (98 per cent) survey respondents would use a licensed gas fitter when having gas appliances installed.

Gas users awareness of and attitudes to gas appliance maintenance

MacGregor Tan Research for SA

Only 29 per cent of respondents said they service their gas appliance at least every two years as recommended.


2.4 Risk factors

For each source of risk — appliance, installation and operation — risk factors that can lead to the production of CO or the incomplete removal of combustion products have been identified. These risk factors are outlined below.

Appliances

Gas appliance standards are underpinned by state regulation. All relevant state and territory technical regulators recognise the product certification of domestic gas appliances and components against the following Australian Standards (AS) outlined in Table 2.4 below.



Table 2.4

GAS APPLIANCES AND CORRESPONDING STANDARDS

Appliance Australian Standard

Domestic gas cooking appliances including for recreational vehicles

AS 4551

Water heaters AS 4552

Space heating appliances AS 4553

Indirect gas-fired air heaters AS 4556

Decorative gas appliances AS 4558

Source: Tasmania Department of Justice 2011.

Certification to these standards ensures that appliances commonly sold for domestic use on the Australian market meet stringent requirements regarding appliance and component safety. These testing requirements ensure that Australian domestic gas appliances are safe when correctly installed and maintained.

Unauthorised or modified appliances are not protected by gas appliance standards. As a result, the risk of carbon monoxide poisoning posed by these appliances is increased. The installation of unauthorised or modified appliances needs to be considered when determining the contribution of appliance malfunction to the risk of carbon monoxide poisoning.

Unauthorised appliance modification can increase the risk of burner disruption and the production of carbon monoxide. The rate of unauthorised appliance modification will need to be considered when determining the level of risk attributable to appliances.

The table below identifies the key appliance-based risks of CO poisoning and the probability that these factors will result in the production or release of CO.



Table 2.5

APPLIANCE-BASED RISK FACTORS

Nature of risk Risk factors Risk rating estimate Notes

Appliance failure Installation of appliances that do not meet Australian Standards

Low 10-4 The risk of appliance failure associated with age and lack of appliance servicing is captured under “Operation”. Appliance failure here refers to manufacturing faults.

Appliances produce unacceptable levels of CO

Extreme 10-1

Appliance modification Unauthorised people modify own gas appliance

Low 10-4 Rates of unauthorised appliance modification are unknown but expected to be low. Modification leads to burner

disruption Extreme 10-1

Modification leads to spillage of combustion products

High 10-2

Source: The Allen Consulting Group in consultation with the GTRC

Installation

Gas regulators mandate that gas appliances be installed by an appropriately licensed gas fitter. Requiring that only properly trained individuals undertake work to install gas appliances minimises the risk of faulty installation. Proper regulation and training:

• reduces the risk of a faulty connection between an appliance and its flue, which can potentially lead to the spillage of combustion gases internally.

• limits potentially hazardous situations — Trained gas fitters could also identify situations where certain gas appliances may be incompatible with building conditions. This includes ensuring that appliances are suitable for the type of gas to which they will be connected.

• covers issues regarding insufficient ventilation and the development of negative pressure situations that will potentially increase risk as the thermal efficiency of newly built and renovated houses improve.

Training however, will only address these issues at the time of installation of the gas appliance and will provide no protection for adverse flow arising from retrofitted extraction fans or increased weather sealing.

Some states have specific requirements on the use of flueless heaters, limiting the types of rooms and buildings in which they may be installed. The current regulatory framework is summarised in Table 2.6 below.



Table 2.6

GAS APPLIANCE REGULATIONS BY STATE

State Regulation title Short summary

NSW Gas Supply (Consumer Safety) Regulation 2004

Only certified gas appliances to be installed. All installations to be done by a qualified gasfitter according to AS 5601.

Vic Gas Safety (Gas Installation) Regulations 2008

Gasfitting work must comply with AS 5601. A person cannot install a flueless space heater or a connection device for a flueless space heater as a new installation in residential premises (including caravans and boats). However a person can replace an existing LPG flueless space heater with a new LPG flueless space heater provided it meets specific NOx and CO/CO2 emission requirements. Flueless heaters cannot be installed in hospitals and other health centres, educational institutions or childcare centres.

Qld Petroleum and Gas (Production and Safety) Act 2004 and Petroleum and Gas (Production and Safety) Regulation 2004

All gas appliances must be approved and certified by an approving authority approved by the Chief Inspector. A person must not carry out gas work on gas appliances unless the person holds a license to carry out the work The safety requirement for gas work is AS/NZS5601 Regulations relating to the quality of gas, specifications and testing of meters, and construction of mains. Gas installations in premises, caravans and vessels must be certified.

SA Gas Regulations 1997 Gasfitting work must comply with AS/NZS 5601 and be undertaken by a licensed gas fitter. The regulations also have provisions about gas supply, residential energy efficiency, price regulation and gas quality.

WA Gas Standards (Gasfitting and Consumer Gas Installations) Regulations 1999

Gas appliances must be installed by a gasfitter with a current gasfitting licence applicable to the appliance in question. Appliance must be flued if installed in bedroom or any type of bathroom, unless the room has a volume greater than 30 m3 and has 2 ventilation openings (satisfying specific requirements) and the installation is approved by an inspector. A gas space heating appliance that is not fitted with a flue must not be installed in a private dwelling unless the appliance is fitted with an approved oxygen depletion sensing system. Flueless space heaters cannot be installed in schools or childcare centres in any location where children may be exposed to combustion products for anything longer than short periods of time. In marine craft a gas appliance cannot be installed in an unventilated space or a space that contains explosive or highly combustible materials. If natural ventilation is insufficient, it must be augmented by mechanical means. Gas water heaters may only be installed in the galley and must be approved by an inspector.

TAS Gas (Safety) Regulations 2002

Gasfitting must comply with AS/NZS 5601. Provisions about gas quality. Gas plant safety plans and management. Gas appliances must be installed by a licensed gasfitter. The gasfitter must demonstrate correct operation of the appliance to the consumer after installation. A certificate of compliance may be needed for some complex installations.

NT N/A

ACT Gas Safety Regulation 2001

Gasfitting work must be carried out by licensed gasfitters. Only certified appliances to be used.

Source: State and Territory legislation, Allen Consulting Group analysis.



Installation-based risk factors include:

• poor appliance/flue connection resulting in the escape of combustion products;

• inappropriate gas supply, for example LPG instead of natural gas, being used to fuel an appliance designed for another gas type;

• inappropriate location of a gas appliance increasing the risk of CO poisoning; and

• inadequate ventilation.

These installation-based risk factors are further explored in Table 2.7 below.



Table 2.7

INSTALLATION-BASED RISK FACTORS

Nature of risk Risk factors Risk estimate Notes

Poor appliance/flue connection

Faulty appliance plumbing 10 per cent (Plumbing Industry Commission 2010)

Plumbing Industry Commission (Vic) data indicates that 10 per cent of plumbing work fails a work quality audit. Perth metropolitan rates for gas fitting only are; 11.5% for 2010/2011 and 9.25% for 2009/2010.

Fault relates to appliance/flue connection

High 10-2

Fault leads to internal release of combustion products

Extreme 10-1

Downdraughts due to ambient conditions

Down draughts Negligible 10-6 Downdraughts are transient events The downdraught diverter is typically in-built in the appliance and likely ensures continued correct combustion during a downdraught

Adverse flow due to operation of exhaust fans

Current estimate of renovated houses which have significant changes to extraction capacity or weather sealing

4.3 per cent (Allen Consulting Group, based on data from ABS)

Will develop in well-sealed houses with open flued appliances and extraction fans. Risk is predominantly in houses that have retrofitted exhaust fans and/or improved weather sealing.

Houses develop conditions leading to adverse flow

Extreme 10-1

Inappropriate gas supply Users do not use a licenced gas fitter to install appliances

3 per cent (McGregor Tan Research)

Minimised by installation by licenced gas fitters

Users who install the wrong appliance for their gas supply

Minimal 10-5

Inappropriate location of gas appliances

Water heaters installed in bathroom, toilets or bedrooms

Low 10-4 Regulations proscribe a 40MJ/hr energy limit on gas fired water heaters in bathrooms and toilets. Licensed gas fitters would be aware of these regulations

Users who get their gas appliances serviced less than once every two years


Flue develops a blockage Low 10-4

Insufficient air supply for appliance operation

Well sealed houses may not supply adequate air for combustion and produce CO

Extreme 10-1 – new house Moderate 10-3 – existing houses

Relevant to appliances without ODS, such as open flued Existing Australian house designs typically have sufficient leakage, 6 star house will most likely not

Insufficient ventilation for flueless heaters

Flueless heater is used without adequate ventilation

Moderate 10-3 The use of flueless gas appliances in unvented rooms can potentially result in the build up of dangerous combustion products.

Source: The Allen Consulting Group in consultation with the GTRC



Operation

The performance of gas appliances can deteriorate with age, and it is recommended that appliances are serviced by a licensed gas fitter as per the manufacturer’s recommendations, or at least every two years (Energy Safe Victoria, undated).

Prolonged periods without servicing can increase the risk of a number of potential problems with gas appliances. This includes poor burner calibration, flue obstruction/blockage and/or the build up of lint and dust at the burner leading to burner disruption and the production of carbon monoxide. A lack of maintenance of gas appliances can also lead to the discharge of combustion products into living areas as the result of a blocked flue or flue dilapidation.

Other operation issues that could potentially lead to the accrual of dangerous concentrations of carbon monoxide include operating flueless appliances with insufficient ventilation to prevent the potentially dangerous build up of combustion products.

Another operational issue of concern is the creation of negative pressure gradient through the operation of extraction fans, resulting in adverse flow from conventionally flued appliances. This matter is further complicated by:

• the fact that the Building Code of Australia refers to AS1668 which does not set out any requirements for ventilation in residential buildings; and

• that the installers of extraction fans do not install gas appliances and may be unaware of the implications.

Operation-based risk factors are outlined in Table 2.8 below.

Table 2.8

OPERATION-BASED RISK FACTORS

Nature of risk Risk factors Risk estimate Notes

Flue obstruction/ blockage Users who get their gas appliances serviced less than once every two years


The probability of a flue becoming blocked or obstructed is increased for poorly maintained flues

Flue develops a blockage Low 10-4

Flue dilapidation Users who get their gas appliances serviced less than once every two years


A small hole in a flue will suck in outside air. Spillage will only occur if the hole is very large.

Flue develops a hole or leak Negligible 10-6

Burner disruption due to build up of contaminants

Users who get their gas appliances serviced less than once every two years


The build up of dirt and dust at a burner can lead to burner disruption and the production of carbon monoxide. Contaminants cause burner

disruption Low 10-4

Source: The Allen Consulting Group in consultation with GTRC.



Chapter 3

Quantifying the baseline risk

CO poisoning requires both burner disruption leading to the production of CO and the failure to extract combustion products allowing them to accumulate internally. The conceptual basis of the QRA is outlined in Figure 3.1 below.

Figure 3.1 CONCEPTUAL BASIS FOR THE QRA


In most cases, the probabilities of each of these factors occurring are independent of each other, such that the probability of one event occurring is not affected by another event having occurred.

The probability of a CO release incident has been estimated assuming a gas appliance is present in a dwelling (as opposed to the risk of poisoning across the entire population). The probability was calculated according to the formula below:

Pr(CO release) = Pr(burner disruption) × Pr(unsafe discharge)

The probability of the various CO poisoning risk factors identified in Chapter 2 differs according to the appliance type. For example, balanced flue heaters pose no risk of CO poisoning from adverse flow. As such, the probability of CO poisoning is dependent on the type of appliance in question.

In sum, the overall probability of CO poisoning in the community is dependent on:



• the type of gas appliances that are in use; and

• the rate of both burner disruption and unsafe discharge.

Existing risk factors were analysed to determine the baseline case against which mitigation options were compared. A number of considerations were taken into account to ensure accuracy, such as:

• latent risk (e.g. non-fatal poisoning);

• attribution of certain illnesses to poisoning;

• under-reporting, particularly of non-fatal poisoning; and

• future trends towards more air-tight residences and increased use of exhaust fans.

Combining the probability of CO poisoning from appliances with the rate of appliance use we were able to calculate the risk of CO poisoning in the community. The results of this calculation are outlined in Section 3.2 below.

Baseline risk was assessed two ways, using both a top-down and bottom-up approach. This provides a reasonable cross check of the estimated risk.

3.1 Top-down approach

The top-down approach estimates the risk of CO poisoning at the aggregate level. This approach does not address incidents at the appliance level or risk factor level as is required for the assessment of the regulatory options (this is undertaken through the bottom-up approach). The top-down approach, however, acts as an important tool to ensure the bottom-up approach determines a reasonable level of risk that reflects the rate of CO poisoning in the community.

The top-down approach relies on international data regarding CO deaths and injuries. Data regarding unintentional CO poisoning deaths and injuries is more readily available in international jurisdictions such as the UK and the United States. Regulation and usage of gas appliances, as well as building standards and other factors, differ greatly between Australia and other countries. As a result, international appliance failure data or poisoning frequency data cannot be extrapolated directly to an Australian setting. To illustrate this, Figure 3.2 below outlines the fatal accident frequency rate (FAFR) for deaths from natural gas usage in all settings across a number of international jurisdictions. The table demonstrates that gas usage in Australia is safer than almost all other countries.



Figure 3.2 THE FATAL ACCIDENT FREQUENCY RATE RESULTING FROM GAS USAGE ACROSS DIFFERENT JURISDICTIONS

Note: The FAFR is calculated as the number of fatalities per year, divided by the number of people at risk in gas supply households.

Source: Glenergy Services 2004, based on a 5-year average of gas accidents between the years of 1994 and 2002.

There were substantial differences in gas usage and building regulations that led to different rates of gas-related fatalities across different national jurisdictions (Enhealth 2007). However, there is no evidence that there are differences in the physiological responses to CO across races or nationalities. Likewise, whilst evidence indicates that there is a difference in the rate of CO poisoning across different countries, it is reasonable to assume that there is no difference in the relative distribution of the severity of these poisoning events. That is, the ratio of CO poisoning deaths to non-fatal poisonings is consistent between Australia and other jurisdictions. This assumption has been used to undertake the top down estimation of the risk of CO poisoning in Australia.

The climatic effect on gas usage is considerable. For example, the rate of gas usage in households in Canada can be 3 to 10 times higher than those in Australia. Additionally, in other jurisdictions nearly all gas appliances are located inside the premises, a vast contrast to the situation in Australia.

Cases of fatal CO poisoning in Australia are well documented, mainly through the work of various gas regulators. The rate of non-fatal cases of CO poisoning in Australia, however, is less well defined due to a lack of data, misdiagnosis and under-reporting.1 The most comprehensive body of research into non-fatal CO poisoning has been undertaken in the UK and, to a lesser extent, the US. An analysis of UK data is summarised in Table 3.1 below.

1 The most relevant Australian data available surrounds hospital admissions for CO poisoning. The AIHW (2011)

reports that there were 397 hospital admissions for CO poisoning in 2009-10. This figure, however, includes intentional CO poisonings, CO poisonings in all settings and CO poisonings from the combustion of all types of fuel, limiting the utility of this data in this QRA.



Table 3.1

INCIDENCE OF FATAL AND NON-FATAL CO POISONING IN THE UK

Year CO fatalities CO injuries CO injuries per fatality

2006-07 10 184 18.4

2007-08 13 191 14.7

2008-09 15 289 19.3

2009-10 9 292 32.4

2010-11 14 343 24.5

Average 12.2 259.8 21.3

Source: Health and Safety Executive 2011,

An injury, for the purposes of this QRA, is defined as any event that results in a non-fatal exposure to CO, and can include symptoms such as headaches, dizziness, breathlessness, nausea, chest pains and loss of consciousness.

Using this data, a ratio of fatal to non-fatal CO poisoning cases from the US and the UK was further extrapolated to the Australian context. Over the last 10 years, Australia has had on average one CO poisoning fatality per year (GTRC 2011). This has been extrapolated to 21.3 unintentional, non-fire related CO poisoning injuries per year.

Whilst there are marked differences in the gas appliance stock and gas usage in the UK compared to Australia, it is reasonable to assume a similar distribution of the severity of internal CO accumulation and similar physiological responses across the two populations. These assumptions have enabled the exploration of UK data regarding CO injury rates to estimate the injury rate in Australia.

Given that 60.9 per cent of homes in Australia are connected to either mains gas or bottled LPG (ABS 2011a), and assuming that household size is not different between households connected to gas or not, then the population living in a dwelling with a gas connection is 13,775,945 (ABS 2011b). The resulting expected injury rate is 1.55 injuries per million exposed population.

Table 3.2

TOP DOWN BASELINE RISK ESTIMATE

Estimate Result

Deaths per year 1

Injuries per year 21.3

Deaths per million exposed population 0.073

Injuries per million exposed population 1.55




Although the injury rate of 1.55 per million does not identify the appliance types that cause the risk, like in the UK the injury rate in Australia also comes predominantly from natural draught heating devices used for space heating.

Another source of variability in these figures is the low number of fatalities, especially in Australia. This variability has been managed by using UK fatalities and injuries from the last 5 years and Australian fatalities from the last 10 years to estimate the rate of non-fatal CO poisoning in Australia. In the absence of better reporting and monitoring of non-fatal CO poisoning in Australia, this is the best estimation possible of the scale of unintentional, non-fire related CO poisoning that could be developed for Australia.

3.2 The bottom-up approach

The second approach taken was to determine risk by appliance type and possible risk factors. This approach is necessary before further modelling can be undertaken to estimate the expected change in the risk of CO poisoning from various proposed interventions. The outcome of the top-down approach will act to calibrate the bottom-up approach.

The bottom-up approach examined 5 different appliance types with different risk factor profiles:

• natural draught space heaters;

• balanced flue space heaters;

• flueless space heaters;

• internal domestic hot water services with a natural draught flue; and

• cooktops.

The risk factor profile for each of these appliances is provided below:



Table 3.3

RISK FACTOR PROFILES FOR EACH APPLIANCE TYPE

Risk factor Natural draught heaters

Balanced flue

heaters

Flueless heaters

Internal domestic hot water systems

Cooktops

Appliance failure

✓ ✓ ✓ ✓ ✓

Appliance modification

✓ ✓ ✓ ✓ ✓


✓ ✓ ✓

Down Draughts (ambient conditions)

✓ ✓

Adverse flow (exhaust fan)

✓ ✓

Inappropriate gas supply

✓ ✓ ✓ ✓ ✓

Inappropriate location

✓ ✓

Insufficient air supply

✓ ✓ ✓

Insufficient ventilation

✓ ✓

Flue obstruction

✓ ✓

Flue dilapidation

✓ ✓

Burner disruption

✓ ✓ ✓


The risk attributable to each appliance is outlined below.

Natural draught space heaters

Natural draught heaters have no engineering controls in place that prevent combustion products entering the internal environment in cases of flue blockage or other failures to safely discharge combustion products. As such, natural draught heaters will be expected to pose a relatively high risk of CO poisoning.

An assessment of the risk posed by natural draught heaters has been undertaken as outlined in Chapter 2. The risk of CO poisoning posed by natural draught heaters is summarised in Table 3.4 below.



Table 3.4

EXPECTED RISK OF CO POISONING FROM NATURAL DRAUGHT SPACE HEATERS

CO production risk factors

Probability Unsafe discharge risk factors

Probability

Appliance failure 1 x 10-5 Appliance modification

1 x 10-6

Appliance modification 1.1 x 10-5 Poor flue/appliance connection

1 x 10-4


3 x 10-7 Down draughts 1 x 10-6

Combustion disruption*

7.1 x 10-5 Flue dilapidation 7.1 x 10-6

Insufficient air for combustion

1 x 10-3 Adverse flow due to exhaust fans**

4.3 x 10-3

Total category risk 1 x 10-3 4.5 x 10-3

Total risk 4.9 x 10-6

*This risk may increase with older, unmaintained heaters and it is conceivable that they may reach an order of 10-3. ** This risk will develop in well-sealed houses with open flued appliances and extraction fans. Risk is predominantly in houses that have retrofitted exhaust fans and/or improved weather sealing. Source: The Allen Consulting Group in consultation with GTRC.

The risk posed by natural draught flued heaters was calculated as outlined at the beginning of this Chapter. The probability of CO release from natural draught space heaters was calculated at 4.9 x 10-6. The two major components that make up the risk for these appliances are issues of adverse flow and a lack of air for combustion.

This risk has been calculated for current market conditions. Consultations with the GTRC have raised concerns that this risk may increase in coming years. This is a result of improved building sealing in order to satisfy higher energy efficiency requirements in the Australian Building Code.

Balanced flue space heaters

Due to the room sealed nature of balanced flue space heaters, the number applicable risk factors for these appliances is greatly reduced. These risks, and their determined probabilities, are outlined in Table 3.5 below.



Table 3.5

EXPECTED RISK OF CO POISONING FROM BALANCED FLUE SPACE HEATERS



Probability

Appliance failure 1 x 10-5 Appliance modification

0

Appliance modification 1 x 10-7 Poor flue/appliance connection

1 x 10-4


3 x 10-7 Flue dilapidation 7.2 x 10-5

Total category risk 1 x 10-5 1.7 x 10-4



The resulting probability of CO poisoning from balanced flued space heaters was calculated at 1.8 x 10-9.

Flueless space heaters

Flueless space heaters release combustion products into the rooms in which they are being operated. These combustion products will accumulate internally unless the room is adequately ventilated. Given that heaters will be operated in cool months, we have assumed that the operation of flueless gas heaters will only occur in unvented rooms in order to prevent the inflow of cold air. As a result, combustion products from flueless gas heaters will accumulate internally in all cases.

Table 3.6

EXPECTED RISK OF CO POISONING FROM FLUELESS SPACE HEATERS



Probability

Appliance failure 1 x 10-5 Adventitious ventilation

1 x 10-3

Appliance modification 1 x 10-7


3 x 10-7

Combustion disruption 7.1 x 10-5

Total category risk 8.1 x 10-5 1 x 10-3


Source: The Allen Consulting Group in consultation with GTRC. Note this level of risk is only for installations without ventilation openings, installations in WA and SA have reduced risk levels due to mandatory ventilation requirements.



The resulting probability of CO poisoning from flueless space heaters was calculated at 8.1 x 10-8. This is further validated because no recordings are available for deaths resulting from flueless heaters that comply with the strict engineering standards for these appliances that have been in place since 1986, such as mandatory oxygen depletion sensors. In new 5 and 6-star houses ventilation requirements would need to be adapted to ensure that adequate air for combustion is available; however, engineering controls ensure that vitiation of these heaters will not lead to CO production. This extra ventilation would be required to control levels of nitrogen oxides and other emissions that can lead to chronic health issues.

Internal domestic water heaters (open flue)

Natural draught internal domestic water heaters have the same risk factors as natural draught space heaters, as well as the potential risk associated with inappropriate installation in bathrooms and toilets. CO poisoning risk factors associated with natural draught internal domestic water heaters are outlined in Table 3.7 below.

Table 3.7

EXPECTED RISK OF CO POISONING FROM NATURAL DRAUGHT INTERNAL DOMESTIC WATER HEATERS



Probability

Appliance failure 1 x 10-5 Appliance modification 1 x 10-6


1 x 10-7 Poor flue/appliance connection

1 x 10-4


3 x 10-7 Down draughts 3 x 10-6

Combustion disruption

7.1 x 10-5 Flue dilapidation/obstruction

7.2 x 10-5


1 x 10-3 Adverse flow* 4.3 x 10-3

Sub totals 1.1 x 10-3 4.5 x 10-3


* This risk will develop in well-sealed houses with open flued appliances and extraction fans. Risk is predominantly in houses that have retrofitted exhaust fans and/or improved weather sealing. However, the use of natural draught domestic water heaters in new buildings and retrofitted buildings is on the decline. Source: The Allen Consulting Group in consultation with GTRC

The risk of CO poisoning for natural draught internal domestic hot water services is estimated at 4.8 x 10-6.

Cooktops

Cooktops are effectively flueless gas appliances and can potentially release CO into domestic living areas. CO poisoning risk factors from cooktops are outlined in Table 3.8.



Whilst cooktops are considered flueless appliances they are generally operated in concert with rangehoods to extract combustion products. It is in unvented rooms, however, where the risk of cooktops increases in significance.

Table 3.8

EXPECTED RISK OF CO POISONING FROM COOKTOPS



Probability

Appliance failure 1 x 10-5 Unvented rooms 1 x 10-3


1 x 10-7


3 x 10-7

Sub total 1 x 10-5 1 x 10-3

Total risk 1 x 10-8


The probability of CO poisoning from cooktops is estimated at 1 x 10-8. This aligns well with historical evidence as no known fatalities have occurred from cookers.

Other cooking appliances such as grillers and ovens have increased risks, however since they are used less frequently are not considered here any further.

Calculation of risk

Data was obtained for the prevalence of gas appliances in terms of heaters, cooktops and hot water services. Estimates were made to determine the breakdown of heaters by flue system and hot water services by location. This data is provided in Table 3.9 below.

Table 3.9

HOUSEHOLDS WITH VARIOUS GAS APPLIANCES

Appliance Percentage of households Exposed population

Heaters 31.4

Natural draught 20 4,524,120

Balanced flue 8.4 1,900,130

Flueless 3 678,618

Cooktops 43.6 9,862,582

Hot Water Services 37.2

External 37 8,369,622

Internal 0.2 45,241

Total population in households with gas connections

60.9 13,775,945

Source: ABS 2011a and the Allen Consulting Group



The bottom-up analysis calculated the expected number of CO release injuries. The CO risk posed by appliance type is summarised in Table 3.10 below. This table reports the estimated number of injuries per year by appliance type and the expected rate of injuries per million residents exposed. For example, it estimated that the number of CO poisonings from natural draught heaters each year is 22.1. Around the country, over 4.5 million residents are exposed to the risks associated with this appliance. This implies that the risk of injury from natural draught heaters is about 4.9 per million exposed persons.

Table 3.10

EXPECTED RISK POSED BY APPLIANCE TYPE

Appliance Risk factor Population Estimated number of injuries from CO

poisoning per year

Injuries per million

exposed

Natural draught heater

4.9 x 10-6 4,524,120 22.1 4.9

Balanced flue heater

1.8 x 10-9 1,900,130 0 0

Flueless heater

8.1 x 10-8 678,618 0.1 0.1

Cooktops 1.0 x 10-8 9,862,582 0 0

Internal domestic hot water services

4.8 x 10-6 45,241 0.2 4.8

Total 13,775,945 22.5 1.63


It is important to note that the majority of the risk associated with CO poisoning from gas appliances in Australia arises from the use of natural draught space heaters. In fact, 98 per cent of the risk of CO poisoning is attributed to this type of appliance, which is in line with overseas experience.

The vast majority of new houses do not have natural draught heaters installed given the risk posed by adverse flow in 5 and 6-star thermal efficient buildings. The risk posed from natural draught heaters is predominantly in houses that are renovated and retrofitted with additions to limit draughts from doorways, windows and other parts of the house, and/or have high-powered extraction fans installed in the house.

The risk from retrofitted sealing and/or extraction fans is expected to rise as more house owners improve the weather sealing in response to increased energy efficiency awareness.

The top down and bottom up approaches both estimate the same events across the same population, and as such it is appropriate that the two approaches deliver a similar estimate of CO risk in the community. The bottom up approach is necessary to provide a framework to estimate the impact of proposed mitigation strategies.



Strategies to reduce this risk of CO poisoning are explored in Chapter 4.



Chapter 4

Risk mitigation strategies

The QRA assesses eleven potential risk mitigation strategies, including two non-regulatory options. These options address appliance risk, installation risk and operation risk. This chapter provides further detail regarding the options that are to be considered in the QRA.

4.1 Risk mitigation strategies for assessment in the QRA

The QRA assesses eleven main risk mitigation strategies, including two with sub- options. The strategies address appliance risk, installation risk and operation risk, and include, among other things, better training for tradespeople and requirements for appliance maintenance. Table 4.1 provides a summary of each risk mitigation strategy, with each risk mitigation strategy discussed in further detail below.



Table 4.1

SUMMARY OF RISK MITIGATION STRATEGIES

Nature of risk

Risk mitigation strategy name

Summary

Appliance CO alarms (rental) Mandatory installation of CO alarms in rental properties.

Appliance CO alarms (all) Mandatory installation of CO alarms in all residential properties.

Installation Improved training Improving training requirements for tradespeople, educating the public about using licensed gas fitters.

Installation Ventilation for appliance operation

Ensure adequate adventitious air or install permanent ventilation openings.

Installation Ventilation for removal of products of combustion (flueless)

Mandate the installation of permanent ventilation openings for flueless heaters.

Installation Ventilation design of extraction systems

Design housing ventilation to ensure that negative pressures do not develop*.

Installation Phase out / major engineering improvements to natural draught appliances

Mandate use of room sealed appliances in new installations or subject natural draught appliances to material engineering changes.

Installation Timers inserted into exhaust fans

Retrofitting timers to all exhaust fans to limit the time they can be in continuous use, thus decreasing the possibility for extended periods of negative pressure.

Operation Public awareness Raise public awareness of CO hazards, importance of maintenance.

Operation Appliance maintenance (rental)

Mandatory maintenance of appliances every two years in rental properties.

Operation Appliance maintenance (all)

Mandatory maintenance of appliances every two years in all residential properties.


4.2 Strategies to reduce appliance risk

The key strategy to reduce appliance risk was the compulsory installation of CO alarms in residential premises containing gas appliances. The requirement may apply to all homes or just rental properties only.

CO alarms

CO alarms would have to be installed in all rooms with gas burning appliances and certain rooms without gas appliances, according to manufacturers’ instructions and maintained at set intervals to ensure proper operation.



Questions still remain over the efficacy of CO alarms. Ryan and Arnold’s (2011) recently found that half of the CO alarms tested either alarmed before CO concentrations had reached dangerous levels, or failed to alarm at potentially dangerous concentrations of CO. Further, most CO alarms installed would be expected to be run on battery power. A NSW survey of smoke alarm use indicated that 9.5 per cent of households tested their smoke alarm less than once a year, with this trend expected to be replicated in CO alarms. CO alarms also require proper installation procedures to be followed to ensure correct functioning.

The installation of CO alarms may reduce the risk of CO poisoning associated with appliance failure, although they will not prevent the appliance failure itself.

4.3 Strategies to reduce installation risk

Incorrect or faulty installation of gas appliances can increase the risk of adverse flow occurring in residential premises. The mitigation strategies aimed at reducing the risks associated with appliance installation include:

• improved training;

• increased ventilation to ensure sufficient combustion/dilution air;

• room sealed and forced draught appliances;

• timers inserted into exhaust fans; and

• mandated ventilation for flueless appliances.

Improved training reduces installation risk through enhanced training of those who install gas appliances, while increased ventilation diminishes the possibility of adverse flow that may be caused by incorrect installation of appliances. By requiring new gas appliance installations to either be room sealed or have a forced draught conventional flue, the risk of adverse flow is reduced. Similarly, requiring that timers be inserted into exhaust fans may, in some cases, prevent the build up of combustion products internally due to adverse flow.

Improved training for gasfitters and plumbers

This risk mitigation strategy would enhance the training of gasfitters/plumbers, electricians, builders and other tradespeople who may be involved in the installation and operation of gas appliances. The additional training would focus on the risks of CO build-up, especially in situations of negative pressure.

This strategy will reduce the risk of poor appliance flue connection, downdraughts and adverse flow by improving the quality of flue connections and flue design. Improved training may also reduce the risk of gas appliances being installed in inappropriate locations such as bathrooms.

Ventilation for appliance operation

Gas appliances require adequate sources of air for combustion. The absence of sufficient air for combustion results in vitiation and the production of CO.

This strategy requires adequate adventitious air or, alternatively, ventilation openings to allow for proper combustion by gas appliances.




Flueless appliance release combustion products internally. This increases the risk that, should a flueless space heater produce CO, the people inside will likely be exposed to CO.

States such as WA and SA already require permanent ventilation openings for flueless heaters. This mitigation strategy requires all states adopt these standards.


The effect of exhaust fans on the room air pressure is currently not considered in residential premises. In combination with the increasing air tightness of dwellings to comply with higher energy efficiency ratings, the potential for adverse flow from the use of exhaust fans is exacerbated. These ventilation systems (typically bathroom and kitchen exhaust systems) require openings either permanent or motorised to operate correctly.

Negative pressure and inadequate extraction are both alleviated by better ventilation design and installation. One option is for push-pull ventilation; another option is for motorised openings linked to extraction fans; yet another, simpler, option is to allow for permanent air vents, although the last option may compromise the energy efficiency rating of a dwelling.


The use of room sealed appliances would either eliminate or greatly reduce the risk of a number of CO poisoning risk factors. This option requires all new gas appliance installations to either be room sealed balanced flue appliances or for natural draught appliances to require material engineering change.

Over time, this would lead to the phasing out of internal, open flue natural draught appliances. Assuming a 20 year life span for appliances, the number of natural draught appliances will decrease by five per cent of the current total each year, until the stock of natural draught appliances have been fully replaced after 20 years.

This strategy will gradually reduce the overall risk as higher risk natural draught appliances are phased out over time.

Timers inserted into exhaust fans

This risk mitigation strategy requires timers to be installed in all exhaust fans. The timers would allow the exhaust fan to operate for a maximum of ten minutes at a time, before requiring the user to manually turn them on again. It is also possible to require that an exhaust fan remain switched off for a period of time before the fan can recommence operation.

By limiting the amount of time an exhaust fan can be used continuously, the risk of a dangerous build-up of products of combustion due to adverse flow is reduced. However, the exhaust timers may be seen as a nuisance by users and may be ineffective in some cases.



4.4 Strategies to reduce operation risk

Reducing operation risk involves undertaking precautionary measures to reduce the risk of CO spillage due to faults or deterioration in the functioning of the gas appliance. Two strategies to reduce operation risk include:

• public awareness; and

• appliance maintenance.

Public awareness campaigns involve educating owners of gas appliances about risks associated with negative pressure in spaces where a natural draught open flued appliance is operating. Appliance maintenance can be undertaken to reduce the risk of appliance malfunction such as combustion disruption.

Public awareness

Instead of pursuing regulatory options to limit or remove the potential for negative pressure and adverse flow to occur, it is also possible to take a non-regulatory approach by engaging in a public awareness campaign. Such a campaign would educate owners and users of gas appliances about the risks associated with negative pressure in spaces where a natural draught open flued appliance is operating. In particular, it could point out the risks of operating exhaust fans simultaneously with open flued gas appliances (as well as appliances burning other fuels) and recommend they not be used together. In addition, the campaign would educate consumers on the use of licensed tradespeople and the importance of regular maintenance of all gas appliances, as well as the importance of ventilation in areas where gas appliances operate.

The education campaign could take the form of flyers distributed through gas providers, TV and radio advertising, and warning labels attached near exhaust fan switches or gas appliances.

This strategy will reduce the risk of adverse flow by increasing awareness of the effects of exhaust fans, as well as reduce the risk of appliance failure by increasing the frequency of maintenance. Increased maintenance will also reduce operation-based risk factors such as flue obstruction and blockage, flue dilapidation and combustion disruption because these things will be checked as part of regular servicing.

Appliance maintenance

Under this risk mitigation strategy appliances must be serviced according to the appliance manufacturer’s instructions, or at least once every two years. There are two sub options:

• limit the maintenance requirement to rental properties and RVs only; and

• require all gas appliances in all residential properties and RVs to be serviced at least once every two years.

This strategy will reduce the risk of appliance failure, as well as the risks associated with flue obstruction and blockage, flue dilapidation and combustion disruption.



Implementation of this mitigation strategy will require a substantial shift in community attitudes to gas appliance maintenance. Gas appliance servicing will need to be considered a maintenance requirement for appliances, rather than only for repair of failed appliances.



Chapter 5

Impact of risk mitigation strategies

This chapter examines the impacts of various options outlined in Chapter 4 on sources of CO poisoning risk.

The various options outlined in Chapter 4 are designed to address one or more of the appliance-based, installation-based and/or operation-based CO risk factors that were outlined in Section 2.4.

Each proposed regulatory option addresses at least one risk factor identified in Section 2.4, with the exception of regulating the use of CO alarms. CO alarms are a post-failure intervention, alerting the occupants of a dwelling of the presence of potentially dangerous levels of CO; however their use does not reduce the risk of these potentially dangerous CO events from occurring. As such, the impact of mandating the installation of CO detectors needs to be considered in a different manner to the other CO poisoning interventions. Table 5.1 demonstrates how each proposed regulatory option acts to reduce the risk of CO production and/or unsafe discharge.



Table 5.1

IMPACT OF OPTIONS ON CO RISK

Mitigates the risk of

Option burner disruption due to unsafe discharge due to

Status quo None None

CO alarms None None

Improved training Appliance modification Inappropriate gas supply

Appliance modification Poor flue/appliance connection Flue obstruction/blockage Flue dilapidation


Insufficient air for combustion None


Insufficient air for combustion (flueless)

Unvented rooms (flueless)


None Adverse flow


None Downdraughts Adverse flow


None Adverse flow

Public awareness Burner disruption Flue obstruction/blockage Flue dilapidation


Burner disruption Flue obstruction/blockage Flue dilapidation


The baseline risk of CO poisoning was calculated in Chapter 2. The reduction in risk resulting from each intervention strategy was determined according to Table 5.2 below.



Table 5.2

EFFECTS OF INTERVENTION STRATEGIES ON RISK FACTORS

Reducing likelihood of risk

Intervention Reduces the risk of from to

CO alarms (rental only)

CO poisoning following internal release of CO gas

1 0.97

CO alarms (all dwellings)

CO poisoning following internal release of CO gas

1 0.89

Improved training


1 x 10-4 5 x 10-5



1 x 10-3 5 x 10-4

Ventilation for removal of combustion products (flueless)

Combustion disruption (flueless)

1 x 10-4 7.1 x 10-6


Adverse flow events 4.3 x 10-3 2.2 x 10-3


Prevalence of natural draught appliances (excluding cooktops) reduced by five per cent per year

20 per cent of households now (Natural draught

heaters) 0.2 per cent of

households now (natural draught

internal water heaters)

10 per cent of households in 10

years (Natural draft heaters)

0.1 per cent of households in ten

years (natural draught internal

water heaters)


Adverse flow events 4.3 x 10-3 3.9 x 10-3

Public awareness

Burner disruption Flue obstruction/dilapidation

7.1 x 10-5

7.17 x 10-5

5 x 10-5

5 x 10-5


Burner disruption Flue obstruction/dilapidation

7.1 x 10-5

7.17 x 10-5

5 x 10-5

5 x 10-5

Source: The Allen Consulting Group in consultation with the GTRC.

For example, when calculating the reduction in CO poisoning risk from natural draught heaters following strengthened appliance maintenance requirements, risk levels associated with the risk factors addressed were adjusted to reflect the post-intervention scenario. Using these revised ratings for the affected risk factors, new risk ratings were calculated and the resulting risk of injury was estimated.



The exceptions to this method were calculations associated with CO alarms and the phasing out of natural draught appliances.

For CO alarms, the likelihood of a CO release event was the same as the status quo option. However, a properly functioning alarm reduced the risk of injury by alerting residents to the risk posed by the CO release. A recent study showed that fifty per cent of alarms tested did not alarm at the appropriate CO concentration (Ryan and Arnold 2011). Further, UK gas safety register inspectors reported that 25 per cent of alarms were inappropriately deployed – for example positioned incorrectly – limiting the effectiveness of the alarms in detecting CO (HSE 2011b). Using smoke-alarm data as a proxy, given the rate of alarm testing undertaken we can expect that nine and a half per cent of installed alarms will be disabled due to battery issues (NSW Dept of Health 2008). Thus, these issues reduce the effectiveness of CO alarm installation in both the all dwellings and rental dwellings only options.

Natural draught appliances were assumed to have a 20-year lifespan, implying that in any one year five per cent of appliances will be replaced. Over a ten-year period half of the existing stock of higher risk natural draught appliances will be replaced with lower risk balanced flue appliances.

Revised risk levels resulting from each intervention option are outlined in Table 5.3 below.

Table 5.3

EFFECT OF INTERVENTION STRATEGIES ON CO POISONING RISK

Intervention Injury frequency rate (per million exposed)

Per cent reduction

Status quo (bottom-up estimate) 1.63 na

CO alarms (rental) 1.58 3.02

CO alarms (all) 1.44 11.31

Improved training 1.61 0.01

Ventilation for appliance operation 0.88 45.72


1.63 0.00


0.85 47.71


0.81 after 10 years 50 after 10 years

Timers inserted into exhaust fans 1.47 9.54

Public awareness 1.59 2.43

Appliance maintenance (rental) 1.62 0.01

Appliance maintenance (all) 1.59 2.44




Of the proposed intervention strategies, only those that addressed the risk factors of adverse flow events and insufficient air for combustion lead to a significant reduction in the risk of a CO release incident. This is because these two risk factors were the most prominent unsafe discharge and burner disruption risk factors respectively.



Chapter 6

Conclusions

This QRA has quantitatively assessed the current baseline risk associated with gas appliances in the home and the extent to which these risks could be mitigated through appropriate measures. The risks associated with gas appliances in recreational vehicles — which also pose a real concern — were not directly quantified due to data limitations.

Gas appliances are a prominent feature of many Australian homes. Over 65 per cent of Australian households (including 92 per cent in Victoria) have natural gas or LPG powered appliances including water heaters, space heating and cooktops.

Exposure to CO has the potential to cause serious permanent injury and in some cases, death. Certain social groups — such as children, the elderly and those with existing heart problems — are likely to be susceptible to more severe poisoning symptoms at lower levels of CO exposure.

Although the consequences of CO poisoning are severe, the risks of CO poisoning are relatively low. CO poisoning requires both burner disruption and unsafe discharge and a variety of significant, stringent safety measures are already in place to prevent CO injuries from occurring. These safety measures relate to regulation, inspection, appliance standards, appliance approval processes, gas installation standards, gasfitter training, certification and Building Code standards.

On average, CO poisonings have been responsible for about 1 fatality per annum across the country over the last decade. It is estimated that a further 21.3 injuries each year are also attributable CO poisoning. This equates to a rate of 1.55 injuries per million persons exposed.

This analysis has demonstrated that some appliances are inherently riskier than others. The level of baseline risk associated with each appliance was estimated by first identifying the factors that could lead to either burner disruption or unsafe discharge; and then estimating the likelihood of those events occurring.

Natural draught space heaters were found to have more associated risk than any other appliance. Natural draught heaters are exposed to the most risk factors (with the exception of open flued internal water heaters). Further the population exposed to these risks, 4.5 million persons, makes up about a third of all gas customers in the country. The risk of CO poisoning from this appliance was estimated at about 4.5 per million persons and accounts for 98 per cent of the risk of all CO poisonings in the country.

The main sources of risk in the household are from insufficient air for combustion and adverse flow. These are the dominant risk factors for combustion disruption and spillage respectively. Generally speaking, the most effective mitigation strategies addressed these risk factors.



Strategies to reduce the risk of CO poisoning were assessed by the degree to which they limited exposure to certain risk factors. A total of eleven mitigation strategies were assessed. These strategies targeted risks factors relating to appliances, installation and operation.

The most successful mitigation strategy involved improved ventilation design of extraction systems, which was shown to remove almost half of the risk. Currently, the effect of retrofitted exhaust fans on the room air pressure is generally not considered in residential premises. In combination with the increasing air tightness of dwellings to comply with higher energy efficiency ratings, the potential for adverse flow from the use of exhaust fans is exacerbated. These ventilation systems (typically bathroom and kitchen exhaust systems) require openings either permanent or motorised to operate correctly. Negative pressure and inadequate extraction are both alleviated by better ventilation design and installation. One option is for push-pull ventilation; another option is for motorised openings linked to extraction fans; yet another, simpler, option is to allow for permanent air vents, although the last option may compromise the energy efficiency rating of a dwelling.

A phase out (or undertaking significant engineering changes) of natural draught appliances was also found to be effective. Requiring the use of room sealed appliances, or significantly reengineered natural draught appliances, would either eliminate or greatly reduce the risk of a number of CO poisoning risk factors. This strategy, however, will take time to become effective.

CO alarms were identified as a relatively effective mitigation strategy and could reduce the overall risk of CO poisoning by an estimated 11.3 per cent. CO alarms, unlike other mitigation strategies are able to reduce the risks associated with a range of factors, albeit after the event. This analysis has considered criticisms of the effectiveness of CO alarms as a strategy and acknowledges that there are a number of factors that may impact on their performance and success. Moreover, CO alarms address the symptoms of the problem, not the cause — they do not reduce the risk of a CO release event from a gas appliance from occurring.

The least effective strategies (from a pure efficacy point of view) included mandatory maintenance in rental dwellings and increased training for gas fitters. Given the stringency that already applies to appliance safety standards and gasfitter/plumber accreditation it was unlikely that suggested increases would have a material effect. Moreover, these strategies did not address the key sources of risk. The mandatory installation of CO alarms in rental properties was also found to be relatively ineffective, given the relatively low proportion of rental dwellings and issues regarding the efficacy of alarms.

Importantly, this QRA has assessed how various interventions might mitigate the risk of CO poisoning — without regard to how cost effective those interventions might be. This report is part of a work program to assist in the development of Gas Appliance (Carbon Monoxide) Safety Strategy. The next step in this work program will be to produce a regulation impact statement to assess the net economic impact conferred by each regulatory option.



Appendix A

Probability tree

Below is the probability tree developed in the GTRC’s Gas Safety (Carbon Monoxide) Strategy.

Figure A.1

PROBABILITY TREE FROM GAS SAFETY (CARBON MONOXIDE) STRATEGY

Source: GTRC 2011



Appendix B

Carbon monoxide poisoning in recreational vehicles

Recreational vehicles (RVs) containing gas or other fuel burning appliances are a potential source of CO poisoning risk in the community. RVs pose an increased risk of CO poisoning due to the small area within which gas appliances operate. As a result, faulty appliances can rapidly increase the CO concentration in RVs to potentially dangerous levels. Gas is commonly used in RVs to fuel space heating, water heating, cooking and refrigeration devices, however no data is available as to the prevalence of these gas appliances in RVs.

In 2011, there were a total of 50,653 motor homes and caravans registered in Australia (ABS 2011c). This is an increase of four per cent from 2010, and a 22 per cent increase from the 41,520 registered recreational vehicles in 2006. As shown in the graph below, Queensland, Victoria and New South Wales have the highest number of registered campervans, followed by Western Australia and Tasmania.

Figure A.2 REGISTERED RVS BY STATE

Source: ABS 2011c

Further data estimating the number of RVs with gas appliances installed is not publically available.

There is no data publically available that records the number of CO poisoning incidents in recreational vehicles.



Statistics on broader gas incidents in relation to recreational vehicles are sparse, with Victoria the only jurisdiction with comprehensive publically available reporting of its gas-related incidents in RVs. This data, however, does not separate CO poisoning incidents from other gas-related incidents. A total of 30 caravan/camping gas incidents were reported, resulting in four deaths, 23 injuries requiring medical attention and three injuries that did not require medical attention (see table below).

Table B.1

DOWNSTREAM GAS INCIDENTS FOR CARAVAN CAMPING AREA IN VICTORIA, 1997-98 TO 2009-10

NG LPG Others TOTAL

Deaths - 4 4

Injuries, Medical Attention - 22 1 23

Injuries, No Medical Attention - 2 1 3

Total incidents for caravan/camping - 28 2 30

Source: Energy Safe Victoria 2010

In the United Kingdom the Health Protection Agency recommends that caravan owners should have their appliances serviced by registered engineers (the UK equivalent to licensed gas fitters), as well as having an audible carbon monoxide alarm (Health Protection Agency 2008).



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