When routine gas‐monitoring operations were carried out at Breeze Hill School, Oldham, more than 20% methane (by volume) was recorded beneath the floor of the sports block. Following consultations with interested parties the school was evacuated. The results of subsequent investigations suggested that biodegradable material beneath and adjacent to the school was the source of the gas. The geometry of the landfilled material and the site geology were such that there was a potential for migration of the resulting landfill gas. Methane is a flammable gas. An explosive risk exists whenever a methane/air mixture is present comprising 5–15% methane (by volume). Higher concentrations are no less hazardous since dilution of the concentrated gas in air will result in flammable or explosive mixtures. This paper details the nature of the investigations and the gas control measures carried out at Breeze Hill School.