The fire on the S.S. Grandcamp produced a dense, brilliantly-colored smoke that could be seen all over town. Fires around the docks were a fairly common occurrence in Texas City; it was not unusual for residents to travel down to the docks to watch the fires and the firemen working, which may explain why there were so many bystanders present – and subsequently so many casualties – at explosion of the S.S. Grandcamp.

The ammonium nitrate onboard the Grandcamp detonated at 9:12 AM, rupturing the ship and sending the cargo of peanuts, tobacco, twine, bunker oil and the remaining bags of ammonium nitrate 2,000 to 3,000 feet into the air. Fireballs streaked across the sky and could be seen for miles across Galveston Bay as molten ship fragments erupted out of the pier. The blast caused a fifteen-foot tidal wave that crashed onto the dock and flooded the surrounding area. Windows were shattered in Houston, 40 miles to the north, and people in Louisiana felt the shock 250 miles away. Most of the buildings closest to the blast were flattened, and there were many more that had doors and roofs blown off. The Monsanto plant, only three hundred feet away, was destroyed by the blast.