On the day of the explosion, the 45-year-old Coleman was one of two railway dispatchers working in the Richmond train station. They controlled trains on the mainline into Halifax which ran along the western shore of Bedford Basin from Rockingham Station to the city's passenger terminal at the North Street Station at the corner of Barrington and North Streets. The station was only a few hundred feet from a burning ship.
Sailors sent ashore by a naval officer warned the station staff that the steamship burning after a collision, the Mont-Blanc, was full of explosives. Reportedly upon leaving the ICR telegraph/dispatching office, Coleman returned to the station's telegraph office to send a brief warning message along the rail line as far as Truro to stop trains inbound for Halifax.
Coleman's morse code message was "Stop trains. Munition ship on fire. Making for Pier 6. Goodbye." His warning was heeded and trains stopped all along the line. The closest train to Halifax, the overnight passenger train from Saint John, NB is believed to have halted at Rockingham Station, located on the shore of the basin, approximately 6.4 kilometres (4 miles) from the downtown terminal. After the explosion, Coleman's message, followed by other messages later sent by railway officials who made their way to Rockingham, passed word of the disaster to the rest of Canada. The railway quickly mobilized aid, sending a dozen relief trains with fire and medical help from towns in Nova Scotia and New Brunswick on the day of the disaster followed two days later by help from the United States, notably Boston. Coleman, however, was killed when the fire on the Mont-Blanc ignited its explosive cargo, which devastated the city and crushed and buried the Richmond Station.
Coleman's self-sacrifice was the subject of a Heritage Minute, and he became a prominent character in the CBC miniseries Shattered City: The Halifax Explosion, although there remains some debate among historians about the true nature of his role. The Heritage Minute and other sources also incorrectly describe Coleman as warning others in downtown Halifax and the area surrounding the ICR's North Street Station of the impending explosion. In truth, he worked in the Richmond Station, surrounded by freight yards. Another error is the exaggeration of the number aboard the Saint John train which contained a maximum of 300 people, not 700 as claimed in the Heritage Minute. Coleman's telegraph key, watch, and pen are on display in the Halifax Explosion exhibit at Halifax's Maritime Museum of the Atlantic.
Coleman is interred at Mount Olivet Cemetery in Halifax, at the intersection of Mumford Road with Joseph Howe Drive. He was survived by his wife Frances who lived until 1970. A street is named after him in the Clayton Park neighbourhood of Halifax and in 2007 a section of Albert Street near his old home was renamed Vincent Street in his honour.