The explosion killed two men — Glenn Roche and Alan Little — and left 22 others injured in 2012.
On Friday, Chief coroner Lisa Lapointe ruled that an investigation conducted by a forensic engineering firm from Seattle, U.S. should be presented to the coroner's inquest into the incident.
However as the firm was contracted by lawyers for the sawmill owners, their investigation does not have to be shared.
The lawyers for Lakeland have until Monday to decide whether they will waive their privilege and share the investigation.
The company that owned the mill was fined $724,000 by WorkSafeBC last July, but appealed the decision.
No criminal charges were laid after Crown counsel concluded in 2014 that WorkSafeBC's investigation didn't properly gather evidence to determine to what extent management was aware of the risk of an explosion from sawdust accumulation.