Fire officials are investigating the cause of the 9-alarm fire that resulted in the death of two Boston firefighters on Wednesday.

Investigators were able to get into the 4-story brownstone on Beacon St. on Thursday to begin the process. Officials said they are focusing on the building’s heating system and boiler.

What officials do know is that fierce winds were a factor in the fire’s size. The blaze was originally controlled in the basement before winds blew out the windows, fanning the flames and helping it to spread.

The firefighters union believes the intense flames may have severed the hose of the crew trapped in the basement. They said you can hear the desperation in the heart-wrenching mayday call.

“The wind in the rear that was coming off the Charles and going straight to the building was considerable. Probably more than we’re used to,” said Spokesperson Steve MacDonald of the Boston Fire Department.

The Boston Herald reported the building is owned by an estate that spent money last year to update the fire alarm system and hundreds of thousands of dollars was spent to maintain the building and keep it up to code.

Nothing has been ruled out at this point, although sources said the fire does not appear suspicious. Investigators will continue to look at all possibilities, including the electrical system. Audio also implies that firefighters had trouble getting water.

Officials said the full investigation could take several months, but workers say the building can be saved. The brownstone is being assessed so that a temporary roof could be placed on.

Beacon St. near the scene has been reopened, but police officers will remain on the scene through the weekend.

Lt. Ed Walsh and Firefighter Michael Kennedy died as a result of battling the fire. Eighteen responders in total were transported to area hospitals.

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