The condition of father-of-four Michael Healy, 48, from Tierclea, Tarbert, is unchanged since his admission to Cork University Hospital five days ago.
A colleague Pat McCroghan, 38, died from injuries sustained in the fire at the switch-gear room in the electricity generating station.
A third person, Derek Thornton, 43, from Corbally, Limerick, is also being treated at the burns unit in Cork University Hospital.
Mr Thornton remains in a stable condition.
Inspectors from the Limerick office of the Health and Safety Authority are investigating the cause of the fatal
Safety specialists from the ESB are also conducting their own inquiries.
But the company emphasised that there was also full co-operation with the Health and Safety Authority.
Both teams of investigators indicated they are not prepared to make any initial public disclosures about the likely cause of last Thursday’s lunchtime accident.
A spokesperson for the HSA said: “The investigation is at a preliminary stage but it is not our policy to discuss the findings at any stage of an investigation.
“It’s not the type of investigation that is likely to be concluded within a short timeframe,” he said.
Electricity generating is unaffected with two 60MW unit plants, in separate buildings to the damaged switch-gear room, producing supplies for the ESB’s national grid.
An ESB spokesperson said upwards of 160 workers are continuing shift operations at the site.
“The accident site remains sealed off and presents no danger or risk to the workers at the station.
Safety remains a priority,” said the ESB spokesman.