When NIOSH investigators started their probe of an explosion at a Searsmont lumberyard that claimed the lives of two firefighters, a common mistake quickly emerged.

 "Over the past 40 years, NIOSH investigated several incidents where firefighters directing water into an oxygen-limiting silo unintentionally caused explosions," authors wrote in a report released Thursday.

Morrill Firefighter Andrew Cross, 27, was found amid debris and pronounced dead at the scene while Searsmont Assistant Fire Chief Wayne Woodbury, 76, and a mill worker died a month later of their injuries.

Other firefighters and employees also were hurt.

NIOSH investigators determined:

• Firefighters around the silo heard a “whoosh” noise as smoke began to quickly emanate from the air material separator on the top of the silo.
•  The silo launched into the air followed by a large plume of fire at the bottom as it rose.  
• The explosion threw surrounding facility employees, firefighters, and EMS providers away in a blast of pressure and fire.
• The burning contents of the silo covered the area and those thrown by the blast.  

Investigators determined through interviews that firefighters were unaware that Cross was missing until a state fire marshal conducted a full personnel accountability report two hours after the explosion.

Authors recommend that incident commanders use:
• Tactical worksheets 
• Command boards 
• Company responding boards 
• Electronic bar-coding systems 
• Accountability passports or keys  

Among the factors listed in the report include silo fire tactics, lack of incident command, lack of pre-planning for lumber yard fires that would have identified associated dangers.

"Facility employees and firefighters were unaware that the silo was oxygen-limiting or that its contents were a combustible dust hazard," investigators concluded.