“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…”

Expert: Carbon monoxide from arson filled clinic in one minute | The Asahi Shimbun: Breaking News, Japan News and Analysis