SEARSMONT, Maine — The Maine State Fire Marshal's Office says the fire and explosion at the Robbins Lumber mill in Searsmont, Maine, is being considered accidental.

Officials say the fire remains under investigation, but a preliminary report was released on Tuesday.

FMO Investigators and ATF Special Agents worked throughout the Memorial Day weekend at the scene of the May 15 Robbins Lumber fire and explosion in Searsmont. During that time, personnel paused to honor Morrill Firefighter Andrew Cross and remember military members who made the ultimate sacrifice in service to their communities.

The Office of State Fire Marshal and the Bureau of Alcohol, Tobacco, Firearms and Explosives National Response Team began demobilization operations on Monday following completion of the initial scene examination. While the on-scene phase of the investigation concluded, the investigation itself remains active and ongoing. Over the weekend, crane operations were completed to lift and move the silo structure, allowing investigators access to areas critical to the scene examination and the evidence recovery effort.

Based on the information obtained to date, the cause of the fire is considered accidental. Investigators believe the fire originated in the area of the unloader mechanism at the base of the silo. Before fire suppression operations could fully contain the smoldering fire, a rapid ignition of suspended particulate material resulted in an explosion within the silo. Investigators determined during the explosion that the silo lifted from its concrete base, releasing large amounts of sawdust and additional particulate material. The silo then toppled over, at which point the surrounding area became rapidly engulfed in fire. The fire rapidly spread to adjacent buildings and structures within the mill complex, contributing to the extensive damage to multiple buildings.

In the coming months, investigators will return to the facility to conduct a more detailed examination of the unloader systems, which may include additional testing in coordination with insurance representatives and additional technical experts to further identify a cause. Investigators also determined the facility’s fire suppression system, which was located near the top of the silo, did not activate because temperatures at that elevation did not reach the activation threshold after the fire originated at the base of the silo.

The investigation is expected to remain open while follow-up analysis, testing, reports, and coordination continue. Freedom of Access Act (FOAA) requests related to the investigation will be directed to the ATF. The Office of State Fire Marshal will be coordinating with the National Institute for Occupational Safety and Health (NIOSH) regarding firefighter safety and has initiated the line-of-duty death review processes.