Wilson, N.C. — A Wilson plant was dark and quiet Sunday as investigators tried to piece together what caused an accident that killed two workers Saturday.

Kidde Aerospace and Defense Company decided to keep the plant closed until Monday as investigators with the state Department of Labor began to interview everyone who was there when contractors Ethan Jones and Milton Johnson collapsed of suspected carbon monoxide poisoning early Saturday afternoon.

What happened in the minutes before the toxic fumes overcame Jones and Johnson was under scrutiny. Tests showed that carbon monoxide levels of more than 500 parts per million were found in the area where they were cutting concrete before they became ill. That level is 50 times more than what emergency officials consider safe.

Investigators said they are looking into early reports from Wilson emergency workers that the two contractors employed by Wheeler Electric Company may have sealed off a room and possibly turned on a gas-powered saw before their collapse.

Wheeler Electric owner Davis Wheeler said Saturday that the two men were installing electrical wiring beneath a concrete floor as part of a larger expansion project at the Wilson plant.

Investigators also said they plan to look into employee training for Wheeler Electric employees who were working inside the Kidde plant. If irregularities or a violation of work safety rules are discovered, the Department of Labor may issue citations.

Officials with Wheeler Electrical Company were unavailable for comment on Sunday.