Here's what the Halifax Explosion might look like in other Canadian cities

If you haven't been to Halifax, it's hard to picture just how big the explosion was.

The largest human-caused explosion prior to the atomic bomb, the 1917 catastrophe levelled two square kilometres of the city. As soon as it happened, all buildings within 800 metres were destroyed.

The blast killed some 2,000 people, injuring about 9,000 more. Many more would likely die if it happened today.

To put the Halifax Explosion in perspective on its 100th anniversary, CBC Radio has plotted out what the explosion might look like if it were to happen today in other Canadian cities with waterfronts — Toronto, Montreal, Vancouver, Charlottetown, St. John's and Kingston, Ont.

Toronto

• Destroyed: Jack Layton Ferry Terminal
• Damaged: Union Station, CBC Broadcasting Centre, CN Tower, Rogers Centre, Hockey Hall of Fame

The blast is replicated by looking at the amount of explosives from the 1917 explosion and converting them into an equivalent amount of TNT. Historians estimate the ships' lethal mix of gun cotton, TNT and picric acid totalled 2,989 tonnes of TNT.

Alex Wellerstein, a professor at New Jersey's Stevens Institute of Technology, studies nuclear explosions and has mapped them out using his famed Nukemap tool. Though the Halifax explosion was not nuclear, he said it was used as a benchmark when the atomic bomb was being developed to guess what would happen in Hiroshima and Nagasaki.

"It's not apocalyptic," he said of the Halifax explosion's size. "[But] it would be terrible."

Montreal

• Damaged: Notre-Dame Basilica, Parc Jean-Drapeau, Jacques Cartier Bridge, majority of Old Montreal

A common way to measure explosions is through pounds per square inch (PSI), depicted in the legend on each of these city maps. It was most commonly used during the Cold War but some researchers and historians still use it today.

The higher the PSI, the worse the damage.

"Twenty pounds per square inch is pretty close to where the bomb is going to be. You don't want to be there," said Wellerstein.

Vancouver

• Destroyed: Waterfront SeaBus Terminal, Canada Place
• Damaged: Gastown Steam Clock, BC Place, Vancouver Art Gallery, CBC Vancouver, Rogers Arena

All the variables means it would be pretty hard to figure out how many people would die in these imagined blasts. Perhaps the most important variable is where a person is during the blast. Wellerstein said people can withstand lower PSI amounts.

"It might knock you over, but it's not going to bust you up."

But the same amount of PSI could cause a building to collapse, potentially killing people inside.

"Your body is OK at taking pressure, but your house is not."

Charlottetown

• Destroyed: Confederation Landing park
• Damaged: Prince Edward Island Convention Centre, Confederation Centre of the Arts, Charlottetown City Hall, Queen Charlotte Armoury

These are merely estimates of what might happen if a same-sized explosion were to happen in one of these cities. Thankfully, explosions like this don't happen very often.

It's Jack Rozdilsky's job to think through what happens if they did. He's a professor at York University, specializing in disaster and emergency management.

He said it's best to compare these types of blasts to nuclear ones, but cautioned there's no way to know precisely what would happen.

Depending on the blast, Rozdilsky said the damage could extend well beyond the markers on these maps. Alternately, the blast damage could be lessened by certain buildings that are in the way.

St. John's

• Damaged: The Rooms, George Street, Commissariat House, Mile One Centre, majority of The Battery

Rozdilsky said the safety standards are higher now than they were in 1917. He's doubtful any ship would be carrying the dangerous cocktail of explosives that caused the blast in Halifax.

That said, there's always a small possibility.

"I would not go as far as to say that it wouldn't happen again," he said. An on-land equivalent would be mass chemical explosions, like the 2015 blast in the Chinese port of Tianjin.

"It has a low probability but a high impact."

Kingston

• Destroyed: Kingston ferry terminal
• Damaged: K-Rock Centre, Fort Frontenac, City Hall, Hotel Dieu Hospital, parts of Queen's University