Penetrating Gases ~ Methane and Radon
Methane † methane is produced by deposited organic material
decaying in the ground. It often occurs with carbon dioxide and
traces of other gases to form a cocktail known as landfill gas. It
has become an acute problem in recent years, as planning
restrictions on green-field' sites have forced development of derelict and reclaimedbrown-field' land.
The gas would normally escape to the atmosphere, but under a
building it pressurizes until percolating through cracks, cavities and
junctions with services. Being odourless, it is not easily detected
until contacting a naked flame, then the result is devastating!
Radon ~ a naturally occurring colour/odourless gas produced by
radioactive decay of radium. It originates in uranium deposits
of granite subsoils as far apart as the south-west and north of
England and the Grampian region of Scotland. Concentrations of
radon are considerably increased if the building is constructed
of granite masonry. The combination of radon gas and the tiny
radioactive particles known as radon daughters are inhaled. In
some people with several years' exposure, research indicates a high
correlation with cancer related illness and death.
Protection of buildings and the occupants from subterranean gases
can be achieved by passive or active measures incorporated within
the structure.
Passive protection consists of a complete airtight seal
integrated within the ground floor and walls. A standard
LDPE damp proof membrane of 03 mm thickness should be
adequate if carefully sealed at joints, but thicknesses up to
1 mm are preferred, combined with foil and/or wire
reinforcement.
Active protection requires installation of a permanently
running extract fan connected to a gas sump below the
ground floor. It is an integral part of the building services
system and will incur operating and maintenance costs
throughout the building's life.
(See next page for construction details)
Gas Resistant Membranes