The crew of the French freighter Mont Blanc tried desperately to avert a collision as the Imo, a Norwegian tramp steamer, edged closer. Both ships reversed their engines, but to no avail. The Imo struck the smaller vessel, gouging a wedge in the Mont Blanc and sending a shower of sparks onto its deck. A fire began on the Mont Blanc's deck, and its crew dove into the icy Halifax waters. An ever-growing crowd watched in fascination as the burning ship drifted toward Pier 6. Firefighting boats steered their way to the Mont Blanc, as onshore the city's firefighters raced to the scene.
Nova Scotia is Anglophone Canada, so no one understood why the French-speaking sailors appeared so frantic. Unbeknownst to the people milling on the docks, the Mont Blanc was carrying munitions for the war effort. Its cargo included 200 tons of TNT, 2300 tons of picric acid, 61 tons of gun cotton in the lower hold, and 35 tons of highly flammable Benzyl, stored in barrels on the upper deck. At 9:05 am on December 6, 1917, the flaming benzyl reached the hold and ignited the cargo, setting off the largest man-made non-nuclear explosion of all time.
Approximately 1,600 people died instantly as the Mont Blanc erupted into a pillar of flame, smoke and ash. Fifty miles away windows shattered: the ship's half-ton anchor would later be found in a forested area two miles from the harbor. A tugboat sailing toward the Mont Blanc was blown into the air and thrown aground: Pier 6 disintegrated into a shower of splinters. The Imo's captain was found at his post, his head torn off by a flying shard; all hands above deck were killed in the blast. Many who had been watching the fire from their homes were blinded by flying glass; others were drowned in the tidal wave which for a moment revealed the harbor's bottom, or perished in the fires which burned throughout the city.
As the water receded a rain of heavy black soot, the remains of the Mont Blanc's cargo, fell on the survivors. Bodies and wounded were piled onto any available vehicle and loaded into any buildings which were still standing. Tents were erected to provide shelter for those made homeless by the blast, and a US Hospital ship which had sustained minimal damage, Old Colony, was pressed into service to treat the many injured. Things went from bad to worse when a winter blizzard blanketed the ruins with snow and hindered relief efforts.
As the storm lifted the scope of the disaster became apparent. The city's North End, a residential working-class neighborhood, suffered the brunt of the damage. 750 homes were damaged and another 9,000 required repair. The Protestant Orphanage was levelled, killing 27 children: the city's hospital had lost its roof. 5 square kilometers of Halifax were demolished by the explosion, 21 percent of Halifax's population was either dead or injured and one of the Allies' major ports was rendered inoperable. Aid began pouring in from around the world. Great Britain sent $1 million, with the Lord High Mayor of London contributing $600,000; Australia, Turkey and Jamaica were among the other countries sending aid. The city of Boston was particularly generous, sending medical personnel, supplies, and money to aid the victims of the disaster. (To this day the City of Halifax annually sends Boston its Christmas tree in gratitude).
Inquiries were held, but it was unclear who was to blame for the explosion. The Imo's survivors claimed they had veered toward the Mont Blanc to avoid other oncoming vessels; the Mont Blanc's crew claimed they had difficulties communicating with English-speaking harbor pilots. In the end it was difficult to piece together what had happened because so many of the participants were dead. The effects of the blast would be felt for years to come. In the chaos which followed the disaster, many children lost one or both parents - and many parents lost children, as unauthorized adoptions of unidentified babies and toddlers led to decades of uncertainty and misery for many bereaved parents.
Still, the Halifax which arose from the wreckage was improved in many ways. The Halifax of 1917 had been a grimy industrial town, with poor sanitation and minimal public health regulation. The money spent on relief efforts ensured that post-explosion Halifax would have what one authority called "the finest public program and most complete public health organization in the Dominion." Halifax became a laboratory for various city planners; the "Hydrostone" dwellings erected to replace destroyed rowhouses are still home to the children and grandchildren of those who survived the blast.