Dave Griffiths was a miner who worked at the Llanfairfach Colliery. He and Bert Pritchard were on duty when Dai Evans went down to try and find out what had killed Ted Hughes. When Evans called on the phone for help, Bert, accompanied by Jo Grant from UNIT, went down to assist him, whilst Dave operated the lift. When he tried to bring them back up, he discovered the controls wouldn't respond. He didn't know Hinks had sabotaged the mechanism.
They were able to repair the damage. He and the Doctor went down into the mine to find the trio. They found the dead Evans and the ailing Bert, but no sign of Jo. After Bert told them Jo had gone on ahead, the Doctor went to find her, telling Dave to get Bert topside quickly. After Bert was taken away in an ambulance, a remorseful Dave blamed himself for Evans' death and Bert's predicament, however Clifford Jones reassured him it wasn't his fault.