The Health and Safety Executive is investigating the death of a miner at a Warwickshire pit.
Trevor Steeples, 46, was stretchered out of Daw Mill - Britain's biggest pit - after collapsing underground on Monday evening. He was later pronounced dead.
It is thought to be the first death in a UK Coal mine since 2002.
A spokesman for the firm which runs the deep mine near Nuneaton, said the investigation was focusing on a build-up of methane gas in the area where Mr Steeples was working just before the incident.
The compound supervisor, from West Bridgford, Nottinghamshire, was part of a small team preparing for the recovery of equipment when the incident occurred.
The spokesman said investigations by the Mines Inspectorate, UK Coal and mining officials were continuing into the circumstances surrounding his death and said colleagues had chosen not to work yesterday as a mark of respect for the "experienced and well-respected" employee.
Mr Steeples, who lived with his partner Nicola and 13-year-old son Andrew, worked previously at several mines including Gedling and Ollerton, in Nottinghamshire, and Asfordby in Leicestershire.
He transferred to Daw Mill, which employs 500 and produces three million tonnes of coal a year, in 1997.