AS FIRE officials wade through the "perfect storm" of errors that led to a firefighter's death in a December blaze in West Oak Lane, a ruling has been reached in what caused the inferno.

And it's far from conclusive.

After months of investigation, the Fire Marshal's Office has ruled the cause of the blaze that claimed the life of Lt. Joyce Craig "undetermined."

In a release yesterday, Fire Commissioner Derrick Sawyer said that the ruling comes after conducting "over 40 interviews as well as thoroughly investigating the scene for seven days."

The blaze broke out early Dec. 9 in the basement of a house on Middleton Street near Andrews Avenue. Craig, 37, became trapped in the home while fighting the fire and ultimately died.

She was the first female Philly firefighter to die in the line of duty. The 11-year veteran left behind two children, a teenage son and an infant daughter.

Sawyer said yesterday that the department will reopen its investigation into the fire's cause if new information becomes available.

Veteran firefighters have described that house fire to the Daily News as a "perfect storm" of things that went wrong, including an inexperienced ladder crew taking 18 minutes to respond and Craig being separated from her team, leaving her alone inside the home.

It's unclear when Craig became separated from her lieutenant and partner firefighter. Firefighters didn't notice that Craig was trapped until they got outside and realized she wasn't with them, Sawyer and firefighters union chief Joe Schulle said a few hours afterward.

Craig called for help several times and was found collapsed in the first-floor dining room, suffering from smoke inhalation and burns.

Those close to Craig complain that she was paired with Nyree Bright, a young firefighter who struggled through the Fire Academy. Bright, sources said, is related to a highly placed member of Mayor Nutter's administration.

In an investigative report on the fire obtained by the Daily News, Deputy Fire Chief Richard Davison said Craig's death "identified real training deficiencies within the PFD."

Davison said the department needs "renewed emphasis on training in basic firefighting skills and procedures," especially on how to handle dangerous basement fires, which create a "chimney effect" of upwardly billowing smoke and flame.

Other recommended areas of improvement include how to respond to Mayday calls from firefighters and how to properly ventilate buildings during fires.

Despite the ruling into the fire's cause, the Fire Marshal's Office is continuing its probe into the circumstances surrounding Craig's death.

- Staff writer Dana DiFilippo

contributed to this report.

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