What NIOSH Found in the Robbins Lumber Explosion

Firefighters battling a May 15 blaze at the Robbins Lumber mill in Searsmont, Maine, used water inside a silo without knowing the structure was an oxygen-limiting model in which water or foam can trigger an explosion, according to a new report from the National Institute for Occupational Safety and Health.

The report says the silo, about 95 miles northeast of Portland, blasted upward after crews injected water into the burning chamber. The application of water likely forced air into the silo headspace, stirred up dust and created a combustible mixture, NIOSH concluded. The blast killed Robbins Lumber co-owner Alden Robbins, assistant fire chief Wayne Woodbury and firefighter Andrew Cross, and injured at least 13 people.

Investigators note that both the silo manufacturer and fire safety organizations publish guidance warning against spraying water or foam into oxygen-limiting silos, because doing so can pressurize the sealed structure with combustible gases and create an explosive concentration. The report recommends that fire departments train on silo types and never direct water or foam into oxygen-limiting chambers.

The fire drew 299 firefighters from 46 departments across four counties. The Maine State Fire Marshal's Office has called the fire and explosion accidental, while local officials say a final investigation is still ongoing.

Advertisement

Why the Silo Fire Turned Explosive — and the Safety Gaps It Exposed

Why the silo turned explosive

Oxygen-limiting silos are sealed structures designed to limit oxygen inside, which can allow combustible gases to build during a fire. The NIOSH report explains that injecting water or foam forces air into the silo, stirs up settled dust and can create a suspended dust concentration that ignites explosively. That sequence turned a contained silo fire into a blast that lifted the structure from its concrete base and spread sawdust and flame.

The training gap the report exposes

NIOSH's finding that firefighters didn't know the silo type points to a gap in pre-incident knowledge rather than a single department's failure. The response involved dozens of mostly rural departments; a volunteer or small-town crew may not routinely encounter industrial silo construction. The report's recommendation for additional training on silo hazards signals that the problem is systemic enough to require broader changes in fire service education.

What comes next for Robbins Lumber and investigators

The company has said it is working with industry experts to rebuild and aims to "exceed" current safety standards. A final investigation by local officials remains open, and state fire investigators have ruled the fire and explosion accidental. The statements from Searsmont officials caution against rushing to judgment, but the NIOSH report already provides a concrete operational lesson for any fire department near wood products, grain or similar storage facilities.

For Fire Departments and Industrial Operators: What the NIOSH Report Changes

The NIOSH recommendations give fire departments and industrial operators specific steps they can take before another silo fire occurs:

  • Identify whether any silos in a fire response area are oxygen-limiting and obtain the manufacturer's firefighting guidance before an incident.
  • Update pre-incident plans for lumber, grain and wood-products sites to explicitly prohibit water or foam into oxygen-limiting silo chambers.
  • Ensure industrial operators share silo type and emergency procedures with responding departments during the initial 911 notification.
  • Add oxygen-limiting silo hazards to firefighter training, especially for mutual-aid departments that may respond to industrial farms or mills.