Wastewater treatment plant operator that receives trucked waste here . Those trucks usually are pressurized to create a vacuum when emptying a portapotty , and uses gravity to discharge and should be equipped with a pressure release valve for this reason . Sewage begins to break down in anaerobic conditions and produce a mixture of methane , carbon dioxide and small amounts of hydrogen sulfide and other trace gases . Portapotties are also equipped with enzymes and microbes that begin to digest the waste to mask smell , and work even faster in warmer conditions . So a combination of this being a possibly outdated trucka place with crappy regulations , warm weather , and the enzymes working over time producing gas as cellular respiration led to it over pressurizing the tank .