Police in Sapporo, northern Japan, say the manager of a real estate office where an explosion took place had emptied a large number of spray cans without being aware of the danger of doing so.
The blast on Sunday in Toyohira Ward completely destroyed a building that housed the office, and injured 42 people.
Investigative sources say the manager and staff at the office told police they'd emptied about 120 deodorizer spray cans at their office to dispose of them.
NHK has learned from the sources and the spray manufacturer that the product has almost no gaseous odor when sprayed.
The maker says that although such products contain flammable dimethyl ether, they're also made with sap from over ten types of trees including pine and Japanese cypress, and smell like wood.
The manager reportedly told the real estate office that he didn't realize he was handling flammable gas.