The inquest into the death of Sean McGrotty, who died in the Buncrana pier tragedy last year, has heard that he had a blood alcohol level of 159mg.
Pathologist Dr Catriona Dillon said that the current blood alcohol level is 50mg.
Mr McGrotty's level was within the toxic range which may indicate a level of intoxication, she said.
But on cross examination Dr Dillon said she could not say what level of impairment he had due to that amount of alcohol because each person is different.
Earlier, the man who called emergency services when he saw the car in the water told the inquests into the deaths of the five people who lost their lives that the Audi Q7 sank around 12 minutes after he dialled 999.
Mr McGrotty, 49, his two sons Mark, 12 and Evan, eight, his partner’s mother, Ruth Daniels, 59, and her daughter, Jodie-Lee Tracey, who was 14, died when their car slid off the slipway and into Lough Swilly on Sunday 20 March 2016.
Mr McGrotty's daughter, four-month-old Rioghnach-Ann, was the sole survivor of the tragedy.
Her mother, Louise James, has said her daughter was her only reason to go on living.
Ms James told the inquest that she went to Liverpool on 18 March for a hen party, and last saw her family at 4pm that day.
She said she tried to contact them at 7.25pm on the Sunday as she was about to board a plane back to Belfast.
Ms James added that she knew something was wrong when she could not make contact.
Eyewitness Francis Crawford told the inquest that that by the time the RNLI lifesavers reached the scene the Derry family's car had disappeared into Lough Swilly.
He said: "The car was floating, bobbing in the water, 10 to 15 yards from the slipway, and slowly floating, bobbing off to the right of the slipway.
"I could still hear people and the child screaming from the car, all the time the car must have been taking on water.
"I was hoping that the emergency services would arrive and the car would not go down.
"I could hear sirens, the nose of the car dipped ... and the car sank to the bottom."
Mr Crawford had called the coast guard for help after Mr McGrotty urged him to seek emergency assistance.
He said said it took 12 minutes for the RNLI to arrive.
There was no suggestion the speed of the response was inappropriate.
Green algae had covered the slipway.
The first witness to the inquest in Buncrana added: "It was treacherous to walk on, slippery as ice."
Mr Crawford said that he parked about half way down the slipway and saw a black people carrier about three to four yards off the slipway in the water and almost parallel to it with the driver's side facing it.
Mr Crawford said he rolled down his window and shouted at the driver "are you okay?".
The driver shouted back to him to call the coast guard.
Mr Crawford got out of his car and said the man kept shouting at him in a panicked voice to call the coast guard.
He said he dialled 999 and was put through to Malin Head and told them of the seriousness of the situation - that there was a family in the car and a tragedy was about to happen.
Mr Crawford said he could hear children crying. Another car then arrived on the slipway and a man and woman got out.
The man was Davitt Walsh and Mr Crawford asked him if he could swim.
He said Mr Walsh stripped to his boxer shorts and swam out to the car before returning with a baby.
He said Mr Walsh told him he thought there were four people in the car, two adults and two children.
Mr Walsh said "take the baby, take the baby" and Mr Crawford thought it was the woman who had arrived with Mr Walsh who took the baby.
Mr Walsh told the inquest that when he realised the situation he swam straight to the car and as he arrived Mr McGrotty smashed a window and handed the baby out to him.
He said Mr McGrotty then sat out of the vehicle on the window ledge, his head and shoulders were out and his hands on the roof - but his legs were still inside.
He said at that stage water that had been seeping in turned into a surge.
Mr Walsh said: "It was like a wave rushing in ... it gushed in.
"I saw a young boy inside the car trying to clamber out past the driver.
"I reached in and grabbed the wee boy, I tried to pull the wee boy out but he seemed to get stuck on something.
"When the driver sat on the window ledge I remember the car tilted and the water then started to gush into the car.
"Just as I was trying to pull the wee boy out of the car the water rushed in and I had to let go.
"The father climbed back into the car, looked back at me and said 'save my baby'.
"The water gushed in and the car went under the water.
"I had to let go because I was struggling as hard as I could to avoid getting sucked into the water."
When he made it back to the slipway and handed the baby to his girlfriend, he collapsed with exhaustion and had to be helped from the slippery surface.
It was freezing cold and he suffered cuts to his feet, which he was treated for in hospital.
Mr Crawford said that local people would know not to go down onto the slipway but a stranger would not.
He said that it had happened about ten times before, but always with single people in the cars who were able to get out.
Mr Crawford's wife, Kay, told the inquest that when she and her husband arrived at the slipway the water was up to the wheel level on the Audi.
She said the tide was going out and she could see the car was being pulled out by the current.
Mrs Crawford said that the driver's window was fully down, she could not make out anyone else in the jeep but she could hear children screaming from inside it.
Garda Sergeant Mark Traynor said gardaí were on the scene within four or five minutes of the call but by that stage there was no sign of the car.
He said gardaí were at the back gate of the station when they received the call.
He added that the RNLI responded within a similar time as its members were returning from an exercise.
Coroner Denis McCauley said: "It is a really short time."
The inquest has heard that since the tragedy, Donegal County Council has closed the gate at the slipway and installed new lifebuoys there.
Engineer John McLaughlin said that consultants employed by the council have also recommended six new signs at the slipway.
However, at this point he said there are no plans for a sign warning of a slippery surface but the council would take into account any views or recommendations coming out of this inquest.
He also said it is intended that the gate will be reopened but again they are awaiting the outcome of the inquest.
Mr McLaughlin said the pier was built in 2001 and the main purpose was to facilitate the Lough Swilly ferry.
It is the only slipway with gates in the county and they were installed to deal with issues relating to people disembarking from the ferry.
He said there is no way of preventing algae from growing on a slipway and people would expect it there, the risks are self-evident, he said, there are waves either side of you and you would have to make a very decided journey to head down the ramp.
Mr McLaughlin said that the council was appalled with what happened at Buncrana - it was one of the worst tragedies ever to affect the county and their hearts absolutely go out to those affected.