The Halifax Explosion: Canada's Worst Disaster

‘A sound for God to make, not man.’

The thunderclap that accompanied the explosion echoed up and down the length of the harbour channel. It boomed across the city of Halifax and neighbouring Dartmouth, and it was audible much farther away.

The crew of the American cruiser the USS Tacoma heard the boom eighty kilometres out to sea. The warship’s lookout had just sighted on the horizon the Devil’s Island lighthouse, nineteen kilometres southeast of the entrance to Halifax harbour. “At 9:05 heard heavy explosion in general direction of Halifax, observed great clouds of smoke high in air,” the officer on watch recorded in the ship’s logbook.

The same rumble that drew the attention of the Tacoma’s crew was audible as far away as Cape Breton Island, two hundred and seventy-five kilometres to the northeast. In Truro, ninety-five kilometres north of Halifax, the blast’s concussive shock broke some windows and shook a clock off the wall in the railway dispatcher’s office. As one observer said, the rumble of the Halifax explosion was “a sound for God to make, not man.”

The great Halifax harbour explosion of 1917 unleashed the energy equivalent of three kilotonnes of TNT. When detonated, one tonne of TNT releases about a billion calories of heat energy. Kilo being the Greek word for “a thousand,” it follows that the calories of heat released in the explosion of one kilotonne of TNT is a thousand times a billion. A trillion calories.

The destructive power of a shock wave as intense as the one the Halifax harbour explosion generated is terrifying. On a bright, sunlit day, it is invisible, yet it can send human bodies and objects as big as a house flying like dry leaves in a gale. It can crush a person’s internal organs, rupture eyeballs, and shatter eardrums. It can snap trees, lampposts, and telephone poles. It can level buildings that are close to ground zero, while those farther away that remain upright still see their doors blown off their hinges, roofs destroyed, and windows shattered; glass shards from broken windows fly like tiny arrows that maim, blind, and kill as they sever heads and limbs.

The pressure generated by the chemical reaction in the Mont-Blanc’s cargo hold amounted to thousands of “earth atmospheres” — the 14.70 pounds per square inch (psi) air pressure that is normal at sea level. (By comparison, the pressure at the wreck site of the Titanic, four kilometres deep, is about 6,500 psi.) At the same time, the air temperature flared to about 5,000 degrees Celsius, which is almost as hot as the surface of the sun, and hot enough to vaporize the Mont-Blanc.

Just as a stone dropping into the still waters of a pond creates rings of disturbance, the destructive shock wave of the explosion surged outward for more than a kilometre in all directions and launched skyward molten remnants of the ship’s hull and its cargo. Some bits of this shrapnel were as large as a refrigerator; others were the size of marbles. All were lethal, ripping into human flesh, slamming into wooden buildings, or perforating metal ships.

A piece of the Mont-Blanc’s five-hundred-kilogram anchor soared through the air for four kilometres before it crashed through a roof. The ship’s 90-mm aft deck gun ended up near a small lake on the Dartmouth side of the harbour, five kilometres from ground zero. A large chunk of metal from one of the Mont-Blanc’s boilers smashed into the Royal Naval College of Canada, coming to rest in a lecture hall, where it flattened the master’s dais and several student desks. Fortunately, the room was empty at the time.

The heat of the explosion that obliterated the Mont-Blanc superheated the water around and under the ship, gasifying the sea to the harbour floor, six metres beneath. As water rushed in to fill the vacuum, it threw up a tsunami. The massive wall of water nine metres high raced across the harbour to Dartmouth. It also roared up and down the harbour channel and far out into the Atlantic. In the confined space of the harbour, the impact was murderous. The tsunami battered ships, swamped boats, and tossed vessels of all sizes up onto the shore. It dragged people to their deaths when it washed over piers and sped waist-deep along streets on both sides of the harbour. “[The tsunami] boiled over the shore and climbed the [Fort Needham] hill as far as the third cross-street [Albert Street], carrying with it the wreckage of small boats, fragments of fish, and somewhere, lost in the thousands of tons of hissing brine, the bodies of men,” [wrote Hugh MacLennan in Barometer Rising].

Even then, the murderous wave was yet wreaking havoc. On its retreat, the water snatched up still more debris along with the bodies of explosion victims, some alive, others dead. And with them it carried off personal property, vegetation, animals, and the remains of crumpled homes and workplaces. There was still more misery to come.

In the wake of the tsunami’s retreat, a towering cloud of noxious gases … drifted over Halifax. “For ten minutes after the explosion a ‹black rain” was observed to fall from the sky. This was an oily soot, the unconsumed carbon of the explosives. It blackened clothing almost like liquid tar,” recalled Archibald MacMechan, the Dalhousie English professor who would become the “official historian” of the explosion. “It blackened the faces and bodies of all it fell on. … It penetrated clothing to the skin and coated the ruins of the houses, until the snow and rain storms washed it away.”