The Grandcamp was a recently re-activated 437-foot-long (133 m) Liberty ship. Originally christened the SS Benjamin R. Curtis in Los Angeles in 1942, the ship served in the Pacific theatre and was mothballed in Philadelphia after World War II. In a Cold War gesture, the ship was assigned to the French Line to assist in the rebuilding of Europe. Along with ammonium nitrate—a very common cargo on the high seas—it was carrying small arms ammunition, machinery, and on the deck bales of sisal twine. The SS High Flyer was another ship in the harbor, about 600 feet (200 m) away from the SS Grandcamp. The High Flyer contained an additional 961 tons of ammonium nitrate and 3,600,000 pounds (1,800 tons) of sulfur. The ammonium nitrate in the two ships and in the adjacent warehouse was fertilizer on its way to farmers in Europe. The Grandcamp had arrived from Houston, Texas, where the port authority did not permit loading of ammonium nitrate.
It was manufactured in a patented explosives process, mixed with clay, petrolatum, rosin and paraffin to avoid moisture caking. It was also packaged in paper sacks, then transported and stored at temperatures that increased its chemical activity. Longshoremen reported the bags were warm to the touch prior to loading.
Around 08:10, smoke was spotted in the cargo hold of the Grandcamp. Attempts at control failed as a red glow returned after each effort.
Shortly before 9:00 AM, the Captain ordered his men to steam the hold, a firefighting method where steam is piped in to put out fires in the hope of preserving the cargo. Meanwhile, the fire had attracted a crowd of spectators along the shoreline, who believed they were a safe distance away. Spectators noted that the water around the ship was already boiling from the heat, an indication of runaway chemical reactions. The cargo hold and deck began to bulge as the forces increased inside.
At 09:12, the ammonium nitrate reached an explosive threshold and the vessel then detonated, causing great destruction and damage throughout the port. The tremendous blast sent a 15-foot (4.5 m) wave that was detectable over nearly 100 miles (160 km) of the Texas shoreline. The blast leveled nearly 1,000 buildings on land. The Grandcamp explosion destroyed the Monsanto Chemical Company plant and resulted in ignition of refineries and chemical tanks on the waterfront. Falling bales of burning twine added to the damage while the Grandcamp's anchor was hurled across the city. Sightseeing airplanes flying nearby had their wings sheared off , forcing them out of the sky. Ten miles away, people in Galveston were forced to their knees; windows were shattered in Houston, Texas, 40 miles (60 km) away. People felt the shock 250 miles (400 km) away in Louisiana. The explosion blew almost 6,350 tons of the ship's steel into the air, some at supersonic speed. Official casualty estimates came to a total of 567, but many victims were burned to ashes or literally blown to bits, and the official total is believed to be an underestimate. The entire volunteer fire department of Texas City was killed in the initial explosion, and with the fires raging, first responders from other areas were initially unable to reach the site of the disaster.
The first explosion ignited ammonium nitrate cargo in the High Flyer. The crews spent hours attempting to cut the High Flyer free from its anchor and other obstacles, but without success. After smoke had been pouring out of its hold for over five hours, and about fifteen hours after the explosions aboard the Grandcamp, the High Flyer blew up demolishing the nearby SS Wilson B. Keene, killing at least two more people and increasing the damage to the port and other ships with more shrapnel and fire.
 Scale of the disasterOne of Grandcamp's anchors in Texas City Memorial Park
The Texas City Disaster is generally considered the worst industrial accident in American history. Witnesses compared the scene to the fairly recent images of the 1943 Air Raid on Bari and the much larger devastation at Nagasaki. The official death toll was 581. Of the dead, 405 were identified and 63 have never been identified. These 63 were placed in a memorial cemetery in the north part of Texas City near Moses Lake. A remaining 113 people were classified as missing, for no identifiable parts were ever found. This figure includes firefighters who were aboard Grandcamp when it exploded. There is some speculation that there may have been hundreds more killed but uncounted, including visiting seamen, non-census laborers and their families, and an untold number of travelers. However, there were some survivors as close as 70 feet (21 m) from the dock. The victims' bodies quickly filled the local morgue, and several bodies were laid out in the local high school's gymnasium for identification by loved ones.
Over 5,000 people were injured, with 1,784 admitted to twenty-one area hospitals. More than 500 homes were destroyed and hundreds damaged, leaving 2,000 homeless. The seaport was destroyed and many businesses were flattened or burned. Over 1,100 vehicles were damaged and 362 freight cars were obliterated—the property damage was estimated at $100 million.
A 2 ton anchor of Grandcamp was hurled 1.62 miles (2.61 km) and found in a 10-foot (3 m) crater. It now rests in a memorial park. The other main 5 ton anchor was hurled 1/2 mile (800 m) to the entrance of the Texas City Dike, and rests on a Texas shaped memorial at the entrance. Burning wreckage ignited everything within miles, including dozens of oil storage tanks and chemical tanks. The nearby city of Galveston, Texas, was covered with an oily fog which left deposits over every exposed outdoor surface.
 Firefighting casualtiesFirefighters Memorial
Some of the deaths and damage in Texas City were due to the destruction and subsequent burning of several chemical plants (including Monsanto and Union Carbide), oil storage, and other facilities near the explosions. Twenty-seven of the twenty-eight members of Texas City's volunteer fire department and three members of the Texas City Heights Volunteer Fire Department were killed after an attempt to extinguish the fire on the first ship in what was one of the worst 20th century firefighter tragedies. More firefighters died at one time than had ever died in any previous fire in the nation. One firefighter, Fred Dowdy, who had not responded to the initial call, coordinated other firefighters arriving from communities up to 60 miles (100 km) away. Eventually two hundred firefighters arrived, from as far away as Los Angeles. Fires resulting from the cataclysmic events were still burning a week after the disaster, and the process of body recovery took nearly a month. All four fire engines of Texas City were twisted and burned hulks.
A positive result of the Texas City disaster was widespread disaster response planning to help organize plant, local, and regional responses to emergencies.