The facts:
According to police, the warehouse in Tianjin’s port was designed to house dangerous and toxic chemicals, and was storing mainly ammonium nitrate, potassium nitrate and calcium carbide at the time of the blasts.
The official Xinhua news agency has said several containers in the warehouse had caught fire before the blasts.
Lei Jinde, the deputy propaganda department head of China’s fire department, a part of the Ministry of Public Security, said that the first group of fire fighters on the scene had used water.
Calcium carbide reacts with water to create acetylene, a highly explosive gas. The explosion could have been caused by fire fighters spraying the calcium carbide with water. The fire fighters did not know if the calcium carbide had already exploded or where it was located in the warehouse.
David Leggett, a chemical safety expert based in California, told Reuters the acetylene explosion could have detonated the ammonium nitrate. The two blasts were about 30 seconds apart, the second much larger than the first. “In my mind, the presence of ammonium nitrate makes it easier to explain the level of devastation,” he said.
Xinhua identified the owner of the warehouse as Tianjin Dongjiang Port Ruihai International Logistics. The Tianjin Maritime Safety Administration said the company violated packaging standards during a safety inspection two years ago. Of 4,325 containers that were checked, five failed the inspection because packaging was sub-standard, according to a report posted on the administration’s website in January 2014.