Water poured into Gleision mine after explosion, court hears
28 March 2014 Last updated at 20:38 GMT
A blast at the Gleision colliery near Pontardawe caused 650,000 gallons of water to pour through a section of the mine where four miners were killed, Swansea Crown Court has heard.
The detonation of explosives at the pit opened a path for water to flow in from old mine workings.
Pit manager Malcolm Fyfield denies manslaughter through gross negligence, while the operators, MNS Mining, deny corporate manslaughter.
Cemlyn Davies reports for BBC Wales Today.