Photograph by Michael Bryant, Philadelphia Inquirer/MCT/Zuma Press

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Philadelphia firefighters search through the rubble to find survivors in a collapsed building on Wednesday.

Photograph by Michael Bryant, Philadelphia Inquirer/MCT/Zuma Press

Why Do Building Collapses Like Philadelphia's Happen?

The sudden collapse sent 14 people to the hospital and has reportedly killed six people.

What caused the partial collapse of a four-story building in downtown Philadelphia on Wednesday morning, which sent 14 people to the hospital and reportedly left six people dead, is not yet known.

The accident occurred during a routine demolition of a building that once housed a first-floor sandwich shop and apartments above, which reportedly fell into a neighboring Salvation Army store, trapping people in rubble. (Also see "Bangladesh Building Collapse Due to Shoddy Construction.")

We talked to Dan Jansen, a civil engineer at California Polytechnic State University, about why collapses sometimes happen during building demolitions and what lessons might be learned.

Any idea of why this Philadelphia building collapsed?

This does appear to be an accident. It might have been an error, or a mistake, or someone wasn't following what was going on.

Or maybe they didn't know what was going on internally. Some of these buildings were built a long time ago, and there might not be proper documentation to say what's inside of a wall or what's inside of a column, and people start making assumptions.

I can't say what was going on in this project, but typically when buildings are demolished, you have to go and examine "Okay, when we take out this structure, what's going to happen?"

There's a process of procedures that should be developed for demolishing, just like we'd have one for building a building.

But building collapses like this are usually due to human error?

I would probably say it has to be a human error or misjudgment. There's a lot of judgment that goes into these things. As best as you try to do everything, there's still a little bit of guesswork involved.

It's sort of like cutting down a tree. You apply your best judgment, and you've done it a hundred times before, and then suddenly the tree falls the wrong way.

What will happen next in this case?

OSHA's [the Occupational Safety and Health Administration] going to go and examine what happened. And if there's someone at fault because they weren't following proper procedures, there'll be some serious consequences.

Sometimes these things happen due to lack of experience. OSHA will investigate whether this was an experienced company, and whether they were sloppy or negligent.

Walk us through building demolitions. Is there a formula that engineers follow regarding what structures to take out first? Or is it different for each building?

It's going to be unique for every building... Sometimes they use explosives to implode a building. Those are a lot less certain than other types of building collapses, and in those cases, they really should be vacating people from surrounding areas.

In this case, it looked like they had a crane and were swinging a big ball and knocking walls in. They might have taken out the wrong wall and the building collapsed in the wrong direction.

Do you see any lessons from this accident that could help make future building demolitions safer?

We've got a pretty good record within the United States. It's not that often that we hear about an accident occurring.

And in a way, we don't want to hinder people from demolishing buildings that really need to be taken down because otherwise they're not going to take them down, and they're going to fall down on their own, which is going to be worse.

OSHA is going to look into it, examine it and come out with a report. If there's something fundamental about the way this happened that they think can be applied somewhere else, there will be changes.

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