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.

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