TIJUANA (Border Report) — The four people who died when a natural gas storage tank exploded were killed by flying debris and shrapnel according to the Tijuana Fire Department.

It says the victims, all women, were working in an office about 150 meters away from where the tank blew and caught fire.

Three others were also injured by the flying metal.

The blast happened Tuesday afternoon at a natural gas storage facility on Tijuana’s east side.

Investigators say the explosion took place when a valve malfunctioned on a large cylinder-shaped storage tank that is used to fill smaller tanks that are sold and rented throughout the city of Tijuana, where most residents can’t get gas delivered to their homes via gas lines.

According to the Tijuana Fire Department, the explosion also created a gas leak that led to the evacuation of the immediate area for several hours.

Tijuana’s Fire Department says more details related to the blast will be released once it finishes its investigation.