Detecting Methane: It is well known that the presence of methane gas can be highly hazardous to human health. However, the fact that methane is a colourless, odourless gas means that there is no simple indicator of its presence until such a time as explosive limits are reached and an incident occurs. For this reason, it is vital that sources of methane are identified prior to any work on a (construction) site commencing, and that measures are put in place to prevent a dangerous build-up of gas within buildings.

Detecting Carbon Dioxide: Is also a colourless, odourless gas, which, although non-flammable, is both toxic and an asphyxiant because it displaces oxygen. As carbon dioxide is denser than air, it will collect in low points and depressions, which can be an extreme hazard during foundation construction and earth movements on development sites or in finished buildings and structures.

64 Council houses In Gorebridge, West Lothian. Local health professionals first noted a cluster of health complaints which eventually lead to Midlothian Council calling in consulting and structural engineers (Fairhurst) to carry out an investigation, which resulted in a 195 page report . Fairhurst demonstrated the migration of CO₂ from former coal mine workings and as can be seen in Figure 1 below, the pathways are dependent upon the localised geology, in this case predominantly sandstone, clay and sand.