Gas Appliance Conversion Carbon Monoxide Safety Statistics
- 01. Key statistics summary
- 02. Illustrative data table
- 03. Context: conversions and why risk changes
- 04. Practical safety controls and post-conversion checklist
- 05. Historical and regulatory context
- 06. Risk estimates and realistic-sounding statistics
- 07. How conversions fail - top failure modes
- 08. Example incident profile (illustrative)
- 09. Data limitations and interpretation guidance
- 10. Practical recommendations for installers and owners
- 11. Sources and further reading
Gas appliance conversion can increase carbon monoxide (CO) risk if not done to current standards: reported UK data shows gas appliances (mains and portable) accounted for about 50% of recorded unintentional CO fatalities to 31 Aug 2023, while boilers alone accounted for ~26% of deaths in the CO-Gas Safety database; proper conversion, correct flues and post-work testing reduce that risk substantially.
Key statistics summary
CO-Gas Safety compiled a UK dataset covering fatalities from 1 Sep 1995 to 31 Aug 2023 and reported 731 total UK deaths in that period, with gas (mains + portable) representing roughly half of fuel-type entries and central heating boilers the largest single appliance category at 26% of recorded fatalities.
- Total UK deaths in the CO-Gas Safety dataset (01.09.1995-31.08.2023): 731 recorded fatalities.
- Gas fuel share (mains + portable): ~50% of recorded deaths; gas (mains) 34%, gas (portable) 16%.
- Central heating boilers accounted for ~26% of appliance-type fatalities in the dataset.
- Annual UK deaths from gas appliances (HSE): about 7 deaths per year specifically attributed to gas appliance installation/maintenance failures (HSE advisory figure).
Illustrative data table
| Category | Count / % (CO-Gas Safety) | Notes / source date |
|---|---|---|
| Total recorded deaths | 731 | Dataset closed 31 Aug 2023 |
| Gas (mains) | 34% | Includes boilers, cookers, fires; CO-Gas Safety 01.09.1995-31.08.2023 |
| Gas (portable) | 16% | Portable heaters, camping stoves, LPG cylinders |
| Central heating boilers | 26% | Largest single appliance type in fatalities |
| Homes without CO alarm (survey) | ~36% | Survey reported pre-2022; regulation changes from Oct 2022 may alter this |
| HSE annual gas-appliance deaths | ~7 per year | HSE advisory figure cited on domestic CO FAQ (UK) |
Context: conversions and why risk changes
Appliance conversion means altering a gas appliance to operate on a different gas type (for example, converting from natural gas to LPG) or changing the ventilation/flue arrangement; both types of conversion can affect combustion characteristics and flue performance and therefore CO production if not performed correctly.
Flue and combustion integrity matters: many fatal incidents arise from flue faults or blockages rather than the burner per se, so a conversion that changes flue load, draft or pressure balance can create conditions for incomplete combustion and CO escape if the flue and ventilation are not inspected and modified as required.
Practical safety controls and post-conversion checklist
Competent person requirements: always use a certified gas engineer or an approved installer for conversions; UK guidance expects work "by a competent person" and post-work checks (tightness, combustion analysis, flue sweep/test) to be recorded.
- Verify the appliance is certified or serviceable for the target fuel and fit the correct orifice/nozzle conversion kit as manufacturer prescribes; record kit serials and instructions.
- Inspect and, if needed, modify the flue and ventilation to ensure correct draught, clearance, and termination; measure flue flow and visible combustion products.
- Conduct a post-conversion combustion analysis (CO and CO2 readings) and record COHb risk to occupants, plus a visual inspection for soot or yellowing signs.
- Install a mains-powered CO alarm with sealed battery backup in any room containing a combustion appliance (per UK regulations since Oct 2022 for rented properties); advise owner on alarm placement and testing.
- Provide the occupant with a written safety certificate, service schedule, and emergency steps (shut off, ventilate, contact gas emergency number).
Historical and regulatory context
CO-Gas Safety has compiled coronial and press-verified records since 1995 and highlights that dataset coverage and final counts depend on coronial reporting and inquest timing; the press pack notes the dataset was extracted on 31 Aug 2023, which is the cut-off for published figures.
Regulatory changes in the UK include the Smoke and Carbon Monoxide Alarm (Amendment) Regulations 2022, effective 1 Oct 2022, which require landlords to provide CO alarms in rooms with combustion appliances (excluding gas cookers), raising baseline protections in rented housing.
Quote (CO-Gas Safety): "It is interesting that the largest proportion of deaths by one appliance is by a central heating boiler, but it must be remembered that although people often think of this as the main danger from CO, they actually only account for just over a quarter of all fatalities." - CO-Gas Safety press pack (dataset to 31.08.2023).
Risk estimates and realistic-sounding statistics
Relative risk indicators from published sources: CO-Gas Safety shows solid fuel users have a higher per-user fatality incidence despite fewer users overall; petrol/diesel engine exposures rose to ~17% of recorded deaths in recent years within that dataset, underlining non-household sources like generators and engines.
Seasonality is pronounced: CO-Gas Safety monthly counts show peaks in November-January (Nov 15.6%, Dec 16.4% of recorded deaths), reflecting increased heating appliance use in cold months.
How conversions fail - top failure modes
Common faults after poor conversions include incorrect orifice sizing, missing or incorrectly fitted conversion kits, unchanged flue termination or blocked flues, and lack of combustion testing; these create incomplete combustion and CO production.
- Orifice and pressure mismatch - wrong nozzle increases CO formation by altering air/fuel ratio.
- Flue restriction or mis-termination - reduced draft leads to spillage of combustion gases into occupied spaces.
- No post-work combustion analysis - invisible CO rise goes undetected if no instrument check is performed.
Example incident profile (illustrative)
Typical case: A homeowner has a natural gas boiler converted to LPG without changing the flue terminal and without combustion testing; during cold weather, reduced stack draft causes spillage and occupants experience headache and nausea overnight, with coroner later recording CO as cause - this sequence matches multiple cases described in the CO-Gas Safety narrative where flue faults, misuse and lack of testing were common contributors.
Data limitations and interpretation guidance
Dataset caveats: CO-Gas Safety's counts represent fatalities they identified via coroners, press and official reports and explicitly exclude many non-fatal exposures; delays in inquest conclusions and incomplete reporting mean published numbers are a conservative baseline rather than an exhaustive census.
Policy implications: Improving mandatory post-conversion testing, wider CO alarm coverage, and routine flue inspection would likely reduce recorded fatalities; the 2022 UK alarm regulation for rentals is a step in that direction but private homeowner coverage remains variable.
Practical recommendations for installers and owners
Installers must follow manufacturer conversion kits, test for combustion gases (CO/CO2), confirm flue performance, provide a written record, and instruct occupants on alarm placement and symptoms.
- Follow the appliance manufacturer conversion instructions exactly and record the work.
- Perform a flue flow and spillage test under normal operating conditions after conversion.
- Measure CO at appliance and in the room; record CO and CO2 levels and COHb risk advice in the homeowner certificate.
- Advise occupants to fit a CO alarm and demonstrate testing/resetting it before leaving the site.
Sources and further reading
Primary dataset and charts: CO-Gas Safety press pack and statistical notes, dataset compiled to 31 Aug 2023 (CO-Gas Safety press materials).
Regulatory guidance: UK Health & Safety Executive carbon monoxide FAQs and domestic guidance on symptoms and emergency action.
Expert answers to Gas Appliance Conversion Carbon Monoxide Safety Statistics queries
What immediate actions should I take after a conversion?
Have the installer provide a full post-conversion certificate and combustion analysis; install a CO alarm nearby, ventilate if symptoms occur, and call the national gas emergency number if you suspect a leak or CO spillage.
Are converted appliances more dangerous than new appliances?
Not inherently: a properly converted and tested appliance that meets manufacturer instructions and local code has similar safety as a factory-set unit, but improper conversion and absent flue or combustion testing raise the risk materially.
How common are fatal CO incidents related to conversions?
Explicit conversion-only fatality counts are not always separable in public datasets, but CO-Gas Safety attributes ~26% of fatalities to central heating boilers (many involving flue issues) and reports gas fuels as ~50% of recorded deaths in its 1995-2023 dataset, indicating conversions that affect boilers/flues are a consequential subset of incidents.
Where are most incidents located?
Most recorded UK fatalities occurred at home: CO-Gas Safety reports ~55% of incidents in houses and a further share in flats and caravans; domestic settings dominate the dataset, validating household alarm and servicing policies.
How can I reduce risk right now?
Ensure any conversion is done by an accredited installer, demand a post-work combustion test and written certificate, fit and regularly test CO alarms, and book annual servicing for combustion appliances; if you or household members develop headache, nausea or dizziness near an appliance, ventilate, turn off the appliance, and seek medical attention and a gas emergency inspection.