A deadly explosion and fire at a Pennsylvania nursing home last month occurred hours after staff reported a smell of natural gas and local utility company workers identified a leak, according to a preliminary report released on Jan. 28.

The report released by the National Transportation Safety Board provided details in the hours leading up to the explosion at the Bristol Health & Rehab Center on Dec. 23 in Bristol Township, a suburb of Philadelphia. The blast, which authorities described as catastrophic, killed three people and injured 20 others, according to the report.

PECO, the local energy company, previously confirmed that its crews were responding to reports of a gas odor at the nursing home before the explosion rocked the facility. But at the time, the company said it could not determine whether its equipment or natural gas was involved in the incident.

Shortly after 11 a.m. local time on Dec. 23, the NTSB report states that the facility's maintenance director reported to PECO that there was a natural gas odor in the basement boiler room and a first-floor hallway. Other staff members also reported smelling gas in the basement, first floor, and second floor of the building.

Nearly an hour after the odor was detected, an energy technician arrived at the facility and identified a leak on a meter set valve in the basement boiler room, according to the report. The technician requested repair assistance, and a meter services technician arrived at the facility at around 1:20 p.m. local time.