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HSE warns of CO risk posed by boiler flue ceiling voids

Builders, gas installers, property developers and building owners are being warned about the risk of carbon monoxide poisoning from gas boilers with flues in voids.
The HSE is concerned about properties where a boiler's flue runs through a ceiling void (the space between the ceiling and floor of the room above) or other concealed route where there is no means for the flue to be visually checked (to establish whether it has been installed correctly or is still in good condition), when the boiler is serviced.

A spokesman for the Health and Safety Executive said “Just because the flue may run through a ceiling void doesn’t mean that you’re at risk. It’s when the flue was not properly installed or has been damaged that there may be a problem”.

If a flue is not in good condition, it could affect the boiler's performance, which may start to produce high levels of carbon monoxide gas. The gas could enter the ceiling void/enclosure through breaks in the flue (e.g. where joints are not sealed properly or where the flue material has degraded over time),

The type of installation causing concern is most common in multi-storey flats and apartments built since 2000 and some modern terraced homes could also be affected.

HSE is working with property developers, the gas industry and construction trade associations to try and establish how many properties may have been developed with flues in ceiling voids but without means of access for inspection. Relevant government departments have also been alerted.

For gas installers, guidance on flues in ceiling voids is available in the CORGI Technical Bulletin, “Room-sealed fanned draught systems concealed within voids (TB200)”. It mentions the need to install access to the flue at strategic locations to allow for visual inspection.

As well as covering the initial installation of flues in ceiling voids, TB200 gives advice on maintenance and inspection of existing installations where there is no access to the ceiling space or enclosure. It directs gas installers to assess the risk, and details factors they should consider (e.g. such as stains in the ceiling/enclosure area which could indicate leakage from the flue).

A safety alert was issued by the HSE after it learned that flues in some properties might be defective during its ongoing investigation into a CO fatality at a new development of apartments. The development was only three or four months old. The flue from the boiler in the property ran through a ceiling void and it is believed that CO escaped through defects in the flue and entered the apartment.

The HSE safety alert said “It is clear that the need to install means of access to flues in ceiling voids/enclosures was neglected in some properties constructed after TB200 was published. Increasingly, it appears that awareness of the requirements of TB200 and the need for inspection points amongst installers and developers is not as widespread in the industry as HSE would have expected”.

Gas installers or builders/property developers undertaking work in premises should get industry guidance outlined in CORGI’s Technical Bulletin TB200. Copies can be obtained from CORGI’s website at or by phoning 0800 915 0485.
3 October 2008


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