The purpose of the alert, aimed at builders and developers, managing agents, landlords, is to raise awareness of a potential poisoning risk.

The risk arises from a particular arrangement of flues for gas boilers. Such boilers, most commonly found in multi-storey flats and apartments built since 2000, may have a flue that runs through the ceiling void. HSE has become aware that some flues may not have been installed properly, or may have fallen into disrepair.

If the flue is not in good condition, this could affect the performance of the boiler, which if not working efficiently, may produce high levels of carbon monoxide (CO). This may then enter the ceiling void through any breaks in the flue (e.g. if joints are not sealed properly) and into the living space below, placing occupants at risk of CO poisoning.

When commissioning, servicing or maintaining boilers, gas installers need to be able to visually check the flue system. Where a flue runs through a ceiling or similar void, a means of access should be provided at strategic locations. A number of properties built recently have not been provided with such means of access so it is not possible to tell if the flue was correctly installed or has subsequently deteriorated.

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, and to agree appropriate action. Relevant Government departments have also been alerted.

The safety alert gives advice on potential warning signs; what owners or tenants should do if they think they may be at risk; relevant legal requirements; key actions for property developers and sources of further information. The alert can be found on HSE's website at: http://www.hse.gov.uk/gas/domestic/alert021008.htm