One of the workers, identified as Lee, 24, was pronounced dead at 3:43 p.m., while the other two, surnamed Joo and Kim, ages 26 and 54 respectively, remained unconscious.

The equipment is designed to put out fires by emitting carbon dioxide, which lowers the level of oxygen in a room and deprives the fire of the oxygen it needs to continue burning. Samsung believes a carbon dioxide leak occurred while the workers were inspecting the equipment.

The three employees involved are affiliated with Chang Sung Corp., a Samsung contractor. They were found unconscious next to the carbon dioxide-emitting equipment, according to the company.

An investigation is currently underway to determine the exact cause of the accident, Samsung said.

Expressing regret, Samsung said it will cooperate faithfully with the investigation.

A similar incident occurred in 2014, when a worker died of carbon dioxide poisoning at the company’s Suwon plant, according to previous media reports.

By Sohn Ji-young (jys@heraldcorp.com)