The CFB Wainwright fire has turned a routine training afternoon in Alberta into one of the worst peacetime tragedies the Canadian military has seen on home soil. Four soldiers are dead, and on Tuesday the defence minister said thirty-three of the injured are still in hospital.

Here is what we know so far, and what investigators still have to answer.

What happened on Saturday

The blaze broke out at about four in the afternoon local time on Saturday, October seventeenth, at the base southeast of Edmonton. According to Global News, Maj.-Gen. Wade Rutland, who commands the First Canadian Division, said eighty-four members of the Third Battalion, Princess Patricia's Canadian Light Infantry, were training with live munitions. Most were throwing hand grenades on a range, while ten were rehearsing an attack on simulated enemies ahead of possible deployments overseas, including Latvia.

Training leaders knew about a grass fire roughly a kilometre away but did not treat it as a threat. Then the wind changed. Rutland said it is not normal for a fire to move a kilometre in thirty to sixty seconds, and that the commander on the ground described seeing no fire and then flames right on top of the troops.

Environment Canada had already issued a high-wind warning, with gusts of up to one hundred kilometres an hour in parts of the province. CBC News reported that experts called conditions at the time extreme, with a powerful cold front bringing a sharp temperature drop and strengthening, shifting winds.

The people we lost

The Canadian Armed Forces named the four dead as Sgt. Morgan Wong of Edmonton, Pte. Shaun Farrell of Prince Albert, Saskatchewan, Pte. Aidan Goulding of North Vancouver, and Pte. Hayden Lykkemark of Langley, British Columbia. According to Vision Times, Goulding was twenty-three, Lykkemark was nineteen and Wong was twenty-six.

Wong's family said he was always there for anyone who needed him. Prime Minister Mark Carney told the House of Commons the chamber was meeting united in grief, and described Farrell and Lykkemark as best friends who were rarely apart. Conservative Leader Pierre Poilievre, whose riding includes the area, said he remembered meeting Goulding at a Canada Day event on the base.

Flags are flying at half-mast on federal buildings, flowers have been left at the gates, and a vigil is planned for the Wainwright community.

The wounded and the response

Thirty-nine people were hurt, and Alberta Premier Danielle Smith said nineteen were in critical condition on Sunday. Hospitals declared a Code Orange, the alert used for mass-casualty events, and thirty emergency units, including twenty-two ground ambulances and eight aircraft, were sent in. Patients went to hospitals in Edmonton, Calgary and Red Deer.

On Tuesday, according to CBC News, Defence Minister David McGuinty said thirty-three of the thirty-nine injured members remain in hospital. Smith has warned that people with severe burns face weeks and months of intensive care.

The questions investigators have to answer

Officials say there is no sign of terrorism or outside interference, and Rutland said the cause is still under investigation. Global News reported that military sources believe a munition from the live exercise may have sparked the grass fire, but that has not been confirmed. Rutland also said the fire did not start inside the training area.

Three probes are underway: a criminal investigation by military police and the RCMP, a fire marshal review, and a Canadian Armed Forces Board of Inquiry. Carney said about fifty investigators are on the ground. The military's top commander has promised the findings will be made public, though investigators warn it could take weeks to learn how the fire started.

The big question is why live-fire training carried on once a nearby fire was known. CBC News has obtained the base's range standing orders, a one hundred and thirty-nine page document with a section on handling fires on site, which is likely to be a focus of the review.

Why this one hits different

For a lot of young Canadians, the military can feel distant. This was nineteen-year-olds and early-twenties soldiers doing exactly what they signed up for, preparing to deploy, and being caught by a wildfire-style blaze that moved faster than anyone could react. Carney called it one of the worst tragedies for the Armed Forces on Canadian soil in peacetime.

It also lands as extreme weather becomes a bigger factor in everything from base safety to emergency staffing. For more on how that is reshaping Canada, see our Canada coverage. We will keep tracking the investigation as answers come in.