Balanced flues in concealed voids

In October 2008 the Health and Safety Executive issued a safety alert. The alert raised awareness of the potential dangers from certain types of flues serving gas central heating appliances. The alert is mainly concerned with the provision of an inaccessible extended flue contained within a void such as a ceiling void.
Corgi Technical Bulletin 200 (TB 200), 2007 clarifies what is needed to meet the requirements of the Gas Safety (Installation and Use) Regulations.
Guidance is also provided in Paragraph 1.47 and Diagram 14 of Approved Document J.
Both documents should be referred to but in essence the following.
The flue refers to a balance flue which enables the supply of combustion air and a flue gas exhaust. The flue can be either formed in plastic or metal. The flue type must be approved by the appliance manufacturer.
The CORGI registered gas installer is responsible the flue is installed correctly and will need to test and commission the installation.
The flue within the void should be as straight as possible, with a minimum number of joints and take priority over other services such as plumbing and ventilation ducts.
The flue should be continuous, have correctly assembled joints, adequately supported and in the case of a condensing boiler have a uniform gradient back to the boiler.
The void will need to be accessible with the provision of sufficient access panels for the purposes of inspection and repair. The access panels should not detrimentally affect the fire resistant or sound properties of the ceiling/floor structure.
Further guidance on Approved Document J will soon be available on the Oculus web site.