Forensic analysis of a methane gas explosion in a block of apartments

•Explosion in a residential building.•Inspection and analysis of the damaged building.•Taking samples and gas analysis.•Flow of methane gas from coal through the natural ground.•Analysis of the formation of the explosive atmosphere and ignition.

The present work contributes the results of forensic analysis after a methane gas explosion in a block of apartments located in Asturias main coal basin (N Spain).Explosion origin and causes were exhaustively researched. Gas nature and origin were studied, and several hypotheses on explosive atmosphere formation were considered, while little likely or unlikely hypotheses were discarded. Possible ignition sources were also determined and located.The obtained data and completed analyses allow us to determine fire causes and development. Explosion was due to methane gas emissions in areas of natural ground under basements of blocks. Only the degree of deflagration was reached, which prevented personal damage, and limited material damage.