By Greg Argos

PHILADELPHIA (CBS) — Crews returned on Tuesday to the site of a devastating fire in Old City as they prepare to tear the building down.

Workers are back on the scene at 237 Chestnut Street trying to stabilize the building before they can demolish it. They’re doing this to allow investigators inside and to figure out how the fire started before the scheduled demolition next week.

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The massive fire essentially gutted an entire Old City apartment building and seriously damaged at least three other adjacent buildings.

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A spokesperson from the Philadelphia Bureau of Alcohol, Tobacco, Firearms and Explosives says workers are removing the roof and the air conditioning units from 237 Chestnut Street.

The structure is simply too weak to support the weight. They’re also securing the neighboring building at 239 Chestnut Street. That is where investigators believe the blaze started.

That apartment building is a total loss and part of its roof is only being supported by a few rows of bricks.

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It’s so dangerous right now that certified fire investigators with the ATF have not actually stepped foot inside, rather they’ve been lowered in buckets by overhead cranes to assess the damage and look for evidence.

The four-alarm fire began in the early-morning hours of Feb. 18. More than 40 people escaped as flames ripped through the block. Some pets died, but no one else was injured.

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With the nor’easters over the past few weeks, there have been delays in stabilizing the building, but the ATF says they hope to get their investigators inside this week.

Demolition, which will be overseen by the city’s Department of Licenses and Inspections, will take place next week.

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This means there are some traffic issues in Old City as 3rd Street between Walnut and Market Streets are closed, as is Chestnut Street between 4th and 2nd Streets.