On 19 January 2007, a trainer died while preparing a "confined space mock-up".  The man, an Occupational and Environmental Safety Engineer, was found half inside a cardboard box with tubes connected to a supply of nitrogen.  There was also a gas monitor connected to the box.  The man was working alone.  It was estimated that he died 8 hours before being found by police following a report from his wife that he had not returned from work.

See: http://phoenix.swarthmore.edu/2007-03-22/news/17058