A coroner's inquest into two GTA fires got underway Tuesday, beginning with a fire that killed three teenagers in Whitby nearly four years ago.

The first exhibit heard Tuesday was the 911 call the victims placed as the fire tore through the home. The teens were trapped on the second floor.

Family members of the victims left the courtroom before the replay of the call, in which the teens can be heard screaming for help. Those who remained in the courtroom were reduced to tears.

Whitby fire victim's mother

Jeannette Adams, mother of Holly Harrison, who died in the Whitby fire nearly four years ago, said she hopes the coroner's inquest helps prevent similar tragedies. (CBC)

Police and firefighters were called to a house at 917 Dundas Street West in Whitby in the early morning hours of April 29, 2012. Benjamin Twiddy, 19, rented an apartment in the home. Two friends — Hollie Towie, 17, and Holly Harrison, 18 — were visiting at the time.

The fire was deemed an accident, but a coroner's inquest is probing safety in the home, which had been divided into multiple units, including how many working smoke alarms were inside. The inquest will also look at the timing of firefighters' response to the blaze.

The first witness was an officer with the Durham Regional Police Service who was one of the first emergency responders to arrive at the scene.

Const. Andrew Chmelowsky said he and his partner arrived at the home before firefighters, which was very uncommon.

"Rarely do I beat the fire department to a call," said Chmelowsky, who said he felt that the response from the fire department was slow even though a fire hall was just a few hundred metres away.

According to Chmelowsky, two young firefighters arrived at the scene and seemed ready to make their way into the home, but were held back by a supervisor.

"My thinking is, 'get moving, let's go, there's people in there,'" he said.

Once firefighters got into the house, Chmelowsky said, he watched as one came out and tried to get one of the teens onto a stretcher. Instead, the firefighter dropped him on his head, he said.

'You lose a lot of sleep'

First responders found the entire incident traumatic, Chmelowsky said, and had a tough time dealing with their experience that night.

"You lose a lot of sleep over it," he said. "It affected a lot of people at the scene. They were not good."

Jeannette Adams, Holly Harrison's mother, said Tuesday that her daughter left behind many grieving friends and family.

"She had a purpose, she had a goal to achieve," Adams said. "She loves kids, and she loves animals."

She said she hopes that another tragedy like the one that took her daughter's life can be prevented.

"What they're trying to do is have things in place going forward to help save other families so they don't have to endure this," Adams said. "And I think that's a wonderful thing."

The inquest into the two fires will hear from a total of 53 witnesses and is expected to last for eight weeks.