Police raided the offices of a construction firm Tuesday on suspicion the company failed to take appropriate measures to prevent a fire at one of its building sites in suburban Tokyo last month, which caused five deaths and numerous injuries.

Hazama Ando Corp. released a statement saying it will "fully cooperate" with the investigation into the cause of the fire that broke out on the afternoon of July 26 in the city of Tama.

About 320 people had been working on the seven-story structure that has three above-ground levels and four underground.

According to the Metropolitan Police Department, a worker was using a gas torch to cut a steel frame on the third basement level when a spark caused insulation material used in the ceiling of the floor below to catch fire.

The insulation material was a flammable type of urethane, despite the original plans calling for a fire-retardant version, the police said. Workers said the fire broke out despite their putting out sparks with water and laying out sheets to cover the vicinity.

Five people died and another 40 were taken to a hospital, 26 of whom required hospitalization for respiratory tract burns or carbon monoxide poisoning.