Two men lost their lives, and another was hospitalized after inhaling toxic fumes from a coal brazier left burning overnight in their office in Delhi’s Mundka area, police reported on Sunday.

The trio had used a coal angithi to keep warm in a room locked from the inside, falling asleep as carbon monoxide fumes built up to lethal levels, a police officer explained.

The incident was discovered when Pawan, a co-worker from Haryana, contacted the authorities.

Police identified the victims as Rajesh (44) from Ladpur village in Delhi, and Rajender Singh (44) from Araji Jadaupur in Uttar Pradesh. Their colleague, Mukesh Pandey (26) from Ravidass Nagar in Uttar Pradesh, was found unconscious and rushed to Mangolpuri Hospital, where he is receiving treatment.

Preliminary findings point to suffocation from carbon monoxide as the cause of death, aggravated by poor ventilation in the room, according to officials.

The bodies have been sent for autopsy, and an investigation is ongoing, police added.