Requirement J3: Warning of Release of Carbon Monoxide – A Critical Analysis

Mike Hartley BSc (Hons) ACABE ACIAT MCIHT

Published in the February 2019 edition of the Chartered Association of Building Engineers (CABE) Building Engineer journal.


On 30th April 2018, the government announced that it would be reviewing the legislation of carbon monoxide alarms to see if the legislation was still fit for purpose.  The review will consider whether there should be a blanket requirement to install alarms for all methods of heating, including both gas and oil.

A consultation was carried out previously to review the Smoke and Carbon Monoxide Alarm (England) Regulations 2015 which yielded 170 responses; 27% of which indicated that the regulations should be expanded to cover gas appliances.  The government did not make any recommendations on the back of this consultation.

On 26th October 2018, the Ministry of Housing, Communities and Local Government published the guidance on the upcoming Carbon Monoxide Alarms Requirements Review: Terms of Reference.  The focus of the review will consider the following evidence:

  • Improvements to and the falling cost of carbon monoxide alarms.
  • Any new evidence on the number of carbon monoxide incidents that the emergency services attend.
  • Any new research that shows whether carbon monoxide poisonings are wrongly diagnosed as something else and so under-reported by statistics.
  • Any new research on the effects of prolonged low-level carbon monoxide exposure on health.

The aim is to submit the outcome of the review to ministers for consideration in December 2018.  Consultation on any proposed changes will likely be in early 2019.

A Brief History of Carbon Monoxide Alarms in The Building Regulations.

The building regulations, in their current form, came into force on 1st October 2010 and have been amended numerous times since then, most recently in 2015.  However, there has been no significant change to the requirements for carbon monoxide alarms since the further amendments in 2010.

Carbon monoxide was first introduced to the building regulations in the 2002 Edition of Approved Document J, although even then it was mentioned only once under provision 4.2, when recommending that open-flued oil-fired appliances should not be installed in rooms such as bathrooms and bedrooms where there is an increased risk of carbon monoxide poisoning.

In the 2010 Edition, a section titled ‘Warning of release of carbon monoxide’ was introduced under requirement J2A, which gave guidance on the provision of carbon monoxide alarms where solid fuel appliances are installed.  The requirement states:

‘Where a fixed combustion appliance is provided, appropriate provision shall be made to detect and give warning of the release of carbon monoxide.’

The limits of this application are that requirement J2A applies only to fixed combustion appliances located in dwellings.

It should be noted that whilst the requirement is non-specific as to the fuel type of the fixed combustion appliance, Section 1: Provisions which applies generally to combustion installations states under provision 1.1 that, in the Secretary of State’s view, requirements J1 to J4 will be met if the building provisions for the safe accommodation of combustion appliances incorporate an appropriate means of warning of the release of carbon monoxide for fixed appliances that burn solid fuels.

A note has been included which states that, for the purposes of requirement J2A, it is considered appropriate to require carbon monoxide alarms only with solid fuel appliances, however such alarms can still reduce the risk of poisoning from other types of appliance.

The document goes on to provide guidance on the type of alarm, as well as its positioning.

It is worth noting that provision 4.2 from the 2002 Edition of the regulations still recommends that open-flued oil-fired appliances should not be installed in rooms such as bathrooms and bedrooms.

Further 2010 amendments reflected a regulation number change as a result of re-ordering and so, requirement J2A became requirement J3.  There are no other changes regarding carbon monoxide alarms although, interestingly, the note in provision 1.1 still references requirement J2A.

Why do we need warning of the release of carbon monoxide?

Carbon monoxide is a poisonous gas which is odourless, tasteless and colourless.  It is produced when fuels such as gas, oil, coal and wood do not burn fully and, for this reason, can be produced by more than only appliances which burn solid fuels.

Carbon monoxide can also be caused by incorrectly installed, poorly maintained or poorly ventilated household appliances.  Blocked chimneys and flues can also prevent the gas from escaping the property.

Carbon monoxide is responsible for approximately 50 deaths per year and up to 4,000 hospital visits in England and Wales, according to the Department of Health (2011).  Breathing the gas in can result in symptoms similar to flu or food poisoning and can even lead to unconsciousness and death if a person is exposed to high levels or has a prolonged exposure to the gas.  Due to its characteristics, it is known as ‘the silent killer’.  Early warning is vital.

The Guidance – A Critical Analysis

Paragraph J3 of Schedule 1 states that “Where a fixed combustion appliance is provided, appropriate provision shall be made to detect and give warning of the release of carbon monoxide”.  Whilst it applies only to those combustion appliances located in dwellings, the requirement states that carbon monoxide alarms are required where fixed combustion appliances are provided.

Conflicting with this, the guidance states that, in the Secretary of State’s view, requirement J3 will be satisfied if an appropriate provision is made to detect and give warning of the release of carbon monoxide only where it applies to solid fuel appliances, i.e. wood burning stoves and open fires.

Furthermore, it has been acknowledged since long before requirement J3 (or J2A as it was previously known) or the Secretary of State’s view, that carbon monoxide poisoning can occur from appliances which do not burn solid fuels.  In addition to all of this, the guidance also recommends that, whilst not required, carbon monoxide alarms can still reduce the risk of poisoning from other types of appliance.

Taking the above into consideration, the question should be asked as to why there is not a requirement for carbon monoxide alarms to be installed when any fixed combustion appliance is installed, and why the contradictory guidance is not re-worded to avoid misunderstanding or misinterpretation.  Whilst it must be acknowledged that the government is now reviewing the legislation to determine whether it is still fit the purpose, there is reasonable argument to say that this review is akin to closing the barn door after the horse has bolted and that the guidance relating to whether a carbon monoxide alarm is required or not never really was fit for purpose.  It is impossible to say what the impact of not including a blanket requirement or consistent guidance is, but it is reasonable to suggest that the potential for carbon monoxide poisoning incidents has been increased because the 2010 Edition of the regulations was remiss in its guidance.

By contrast, the regulations in both Scotland and Northern Ireland require carbon monoxide alarms to be installed when new or replacement combustion appliances are fitted, which applies to any fuel burning appliance.

Provisions 2.34-2.36 provide further guidance on the installation and positioning of carbon monoxide alarms.  The guidance states that alarms should comply with BS EN 50291:2002, be provided in the room where the appliance is located and be powered by a battery designed to operate for the working life of the alarm.  Alternatively, the alarm can be mains-powered, provided the alarm is a BS EN 50291 Type A carbon monoxide alarm with fixed wiring and a sensor failure warning device.  Plug-in carbon monoxide alarms are not enough to satisfy the guidance, likely due to the ease at which they can be unplugged and rendered useless.  A further reason for this may be that, in new dwellings, sockets serving habitable rooms throughout a dwelling should be positioned between 450-1200mm above floor level (Approved Document M, Vol. 1) which would result in any plug-in type alarm being positioned in the lower half of the room.  This contradicts the guidance within provision 2.36 which states that a carbon monoxide alarm should be located on the ceiling, at least 300mm from a wall or, if located on a wall, as high up as possible (above any doors and windows) but not within 150mm of the ceiling.

This raises an additional question because there is a common misconception regarding the weight of carbon monoxide.  Is the ceiling, or high up on the wall, the best location for a carbon monoxide alarm?  In several conversations the Author has had with associates, there has been a consensus that carbon monoxide is heavier than air.

In truth, carbon monoxide is ever so slightly, and negligibly, lighter than dry air.  If we use the composition of dry air; Nitrogen (78.1%), Oxygen (20.9%), Argon (0.9%) and Carbon Dioxide (0.03%), as well as trace amounts of other gases, and we calculate the molar masses against these percentages, we can work out that the molar mass of dry air is 28.90 g/mol (grams per mole).  The molar mass of carbon monoxide is 28.01 g/mol.  That is a difference of only 3%.

Taking the above into consideration, it is apparent that whilst the gas may eventually rise, the weight difference is so negligible that any rise will be far slower than a much lighter gas such as Methane (which has a molar mass of 16.04 g/mol).  Furthermore, considering molecular diffusion and air movement within the room, the gas will likely spread evenly until it is of equal concentration throughout.

The Center for Hyperbaric Medicine at Virginia Mason Medical Centre in Seattle conducted an experiment in 2012 to determine whether the placement of carbon monoxide detectors should be influenced by carbon monoxide’s weight relative to air.  In the experiment, the weight of carbon monoxide was calculated to be slightly lighter than air, and an eight-foot-tall airtight Plexiglas chamber constructed with carbon monoxide monitors placed within at the top, middle and bottom.

Carbon monoxide test gas was infused into the chamber at three different heights in different trials, with the carbon monoxide levels measured over time.

The test demonstrated that carbon monoxide did not layer on the floor, float at the mid-level of the chamber or rise to the top but rather, in each case, the levels equalised throughout the chamber.  It was conceded that the carbon monoxide took longer to equalise when infused at the top of the chamber, but levels always became identical with time.

The results of the test concluded that carbon monoxide infused anywhere within the chamber would diffuse until it was of equal concentration throughout.  Additionally, it was concluded that mixing would be even faster in a home environment than a laboratory environment, due to draughts caused by motion or temperature.  Therefore, it would be reasonable to place a carbon monoxide alarm at any height within a room.


Taking all the above into consideration, despite the requirements stating that carbon monoxide alarms are only required where solid fuel appliances are installed within dwellings, it is considered that carbon monoxide alarms are an extremely cost-effective solution to reducing the risk of carbon monoxide poisoning from any fixed combustible appliance.

The regulations have also acknowledged that alarms can reduce the risk of carbon monoxide poisoning from other appliances.

Therefore it is considered that, although not a requirement, carbon monoxide alarms should be fitted wherever combustible appliances are installed and those alarms are tested regularly.  It should be acknowledged that carbon monoxide alarms are not a substitute for maintaining and regularly servicing combustible appliances.

Furthermore, evidence demonstrates that it is reasonable to place a carbon monoxide alarm at any height within the room, and not just the ceiling or high on the wall.  Therefore, whilst an alarm at any height should be effective, it is considered that a carbon monoxide alarm would operate at its most efficient when around 1500mm (5-feet) above floor level.  Statistically, this is approximately the mean height of a standing person and a sitting person (including wheelchair users) and would therefore provide the earliest possible warning of carbon monoxide for occupants within the room.  Early detection is pivotal due to the severity of symptoms associated with carbon monoxide poisoning.

Whilst it is demonstrated and acknowledged that carbon monoxide would diffuse fully until it was of equal concentration throughout a room, very high levels of carbon monoxide can cause the rapid onset of symptoms.

Finally, the regulations state that an alarm should be located between 1 metre and 3 metres horizontally from the appliance.  Whilst this element of the guidance has not been examined specifically, it is reasonable to say that room users will likely occupy this space and therefore this guidance seems practical.

For further reading, more information on carbon monoxide poisoning can be found on the NHS website.


Department of Environment, Transport and the Regions. The Building Regulations 1991. 1992 Edition. Approved Document J: Heat producing appliances, London: NBS, part of RIBA Enterprises Ltd.

Office of the Deputy Prime Minister. The Building Regulations 2000. 2002 Edition. Approved Document J: Combustion appliances and fuel storage systems, Norwich: NBS, The Stationary Office.

HM Government. The Building Regulations 2000. 2010 Edition. Approved Document J: Combustion appliances and fuel storage systems, Newcastle Upon Tyne: NBS, part of RIBA Enterprises Ltd.

HM Government. The Building Regulations 2010. 2010 Edition incorporating further 2010 amendments. Approved Document J: Combustion appliances and fuel storage systems, Newcastle Upon Tyne: NBS, part of RIBA Enterprises Ltd.

HM Government. The Building Regulations 2010. 2015 Edition. Approved Document M: Access to and use of building – Volume 1: Dwellings, Newcastle Upon Tyne: NBS, part of RIBA Enterprises Ltd.

Billingham, M.J. Barnshaw, S.P. Bridge, K.T. Crooks, A., (2017). The Building Regulations Explained and Illustrated. Fourteenth Edition. John Wiley & Sons Ltd.

Hampton, N.B. Courtney, T.G. Holm, J.R., (2011). Should the Placement of Carbon Monoxide (CO) Detectors be Influenced by CO’s Weight Relative to Air? Center for Hyperbaric Medicine, Virginia Mason Medical Center, Seattle, Washington.

Socratic. 2016. What is the molecular weight of air? [ONLINE] Available at: [Access 5 November 2018].

Ministry of Housing, Communities & Local Government. 2018. Carbon monoxide alarm requirements review: terms of reference. [ONLINE] Available at: [Accessed 8 November 2018].

Policy Connect. 2018. Government Responds to APPCOG CO Alarm Recommendations. [ONLINE] Available at: [Accessed 8 November 2018].

NHS. 2016. Carbon Monoxide Poisoning. [ONLINE] Available at: [Accessed 8 November 2018].

PubChem Open Chemistry Database. 2004. Carbon Monoxide. [ONLINE] Available at: [Accessed 8 November 2018].

Department of Health and Social Care. 2011. Carbon monoxide poisoning sends 4,000 people to A&E each year. [ONLINE] Available at: [Accessed 11 November 2018].

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