The deterioration of a chemical substance included in explosives may have triggered the massive blast at a gunpowder factory in the town of Taketoyo, Aichi Prefecture, earlier this week, experts said Friday.
Hideyo Osada, professor emeritus at Kyushu Institute of Technology, told reporters it is possible the deterioration of cellulose nitrate, a key component of explosives, may have caused the disaster.
If heat, which is generated in the process of the substance's deterioration, accumulates in the substance's container, it can cause an explosion, he explained.
He also said groups of experts from the National Police Agency's National Research Institute of Police Science's Explosion Investigation Section and Aichi Prefectural Police should look into the structure of the containers holding the explosives and how much and for how long the explosives were stored.
The NPA's experts joined the investigation Thursday.
The head of the factory has said the gunpowder would not have been able to ignite by itself. Only fire, temperatures of at least 200 degrees or a heavy impact could have triggered the blast, he said.
The investigation has so far revealed that there were no employees at the storage unit of the factory run by NOF Corp., a Tokyo-based chemical company, at the time of the explosion, which injured 72 local residents.
According to town officials, Tuesday's explosion damaged 780 houses and buildings in Taketoyo and the neighboring cities of Tokoname and Handa, of which 12 were totally destroyed.
The residents of the damaged houses have expressed concerns about whether the company will pay them sufficient compensation.