In a landfill mixture of gases, consisting principally of methane and carbon dioxide, may be produced by microbial degradation of organic waste under anaerobic conditions. Methane is explosive at concentrations between 5 and 15% by volume. Other gases, for instance hydrogensulphide, mercury and ethane, may be emitted at low concentrations, but usually do not represent a health hazard following normal atmospheric dilution. Indoor climate may be affected, though, in cases of accumulation in closed spaces. A case is presented where two persons died following an explosion caused by lighting a cigarette in their house which was surrounded on three sides by a landfill. The explosion occurred after heavy precipitation on a day with low atmospheric pressure. Methane measurements showed values consistent with risk of explosion.