An explosion in Sapporo that injured 42 people over the weekend occurred after two employees of a real estate office located at the site emptied about 100 deodorizer spray cans at once, sources close to the matter said Tuesday.

Apaman Co., which operates the real estate office, said in a statement that the employees reported having turned on a water heater afterward. The blast damaged buildings as far as 100 meters away.

Investigators believe gas built up inside the office, the doors and windows of which were closed at the time.