Photo/Illutration A police officer stands guard on Dec. 24 in front of the building that was set on fire a week ago in Osaka’s Kita Ward. (Takuya Tanabe)

OSAKA--Carbon monoxide from a fire set inside a clinic in a multitenant building here spread so quickly that escape was nearly impossible, according to a computer simulation conducted by a fire safety expert.

“One minute was enough for the gas to fill the insides of all the rooms,” said Tokiyoshi Yamada, a former specially appointed professor of fire safety engineering at the University of Tokyo.

Carbon monoxide (CO) poisoning was the cause of death for the 25 people who were killed in the arson attack, Osaka prefectural police said.

Yamada used a 3-D replication of the clinic and its rooms in the simulation. Windows and doorways were located only at the reception and waiting areas.

He simulated gasoline being set on fire near the elevator at the clinic, which produced CO and smoke that reached and stagnated near the ceiling.

But 20 seconds later, the entire waiting room was filled with CO, and a minute later the gas had reached the examination room at the rear of the clinic, the simulation showed.

By that time, the CO level reached around 500 parts per million (ppm), which causes strong headaches or vomiting if inhaled for a certain time.

“Based on the findings so far, the spread of the fire is estimated to have increased the CO level to a few thousand ppm, which is a fatal amount for humans, a few minutes later,” Yamada said.

“The black smoke would have blocked light from coming inside while victims who collapsed on the floor kept inhaling the smoke, leading to their deaths,” he said.

Firefighters have advised people to cover their mouths and noses with handkerchiefs and get closer to the floor to limit the damage from CO during fires.

“But in this arson case, the suspect reportedly set fires on the doorways and used his body to prevent people from escaping,” Yamada said. “The victims were trapped inside closed rooms where the black smoke was circulating round and round.

“They must have lost consciousness after two to three minutes,” he said.

The design of such buildings has been called into question before, particularly after a fire killed dozens of people at a multitenant building in Tokyo’s Kabukicho district in 2001.

“It is desirable that two-direction evacuation routes are secured,” Yamada said. “If not, people should check the building structure and flee from such dangerous places by themselves at times of emergency.”

(This article was written by Hajimu Takeda and Takefumi Horinouchi.)

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