“On page four he recalled the several unpleasant incidents when coffins in the vaults of the new London cemeteries had exploded, and undertakers were sent for in order to re-solder the lead coffins to contain the corruption. Scientists and medical men of the day were puzzled about the exact composition of the gases produced by a decomposing body, and experiments with lighted candles were carried out when a lead coffin did in fact leak.” 

James Curl, The Victorian Celebration of Death