Two cases of colonic gas explosion during surgery are reported. The treatment of the lesions required a partial colectomy in one case and a total colectomy in the other case. The different factors involved in such accidents are discussed. Three factors are necessary to trigger off an explosion of intestinal gases: the presence of combustible gases (hydrogen, methane), the presence of combustive gases (oxygen, nitrous oxide) and an initiating heat source (endoscopic or surgical electrocautery). The mannitol used for bowel cleansing undergoes partial colonic bacterial fermentation increasing the intraluminal concentration of hydrogen. During anaesthesia the oxygen-nitrous oxide mixture increases the intestinal concentration of these two major combustive gases. Electrocautery provides the spark triggering the explosion. The use of mannitol for colonic preparation should be questioned; the use of electrocautery to open the colon is advised against.