I normally do not share construction accidents, as I am not a construction safety professional. I would not even attempt to play one on TV! However, this case is an excellent example for the general industry and those who work with hazardous chemicals. One of the reasons why my HAZCOM training is 2+ hours is I teach workers how to read an SDS. Far too many have no idea what Vapor/Gas Density is and how it can affect them. This fatal OSHA case is a perfect example of how this lack of knowledge impacts workers.
NIOSH definition:
Vapor density refers to the relative weight of a gas or vapor compared to air, with air having an arbitrary value of 1; a vapor density less than 1 indicates a lighter-than-air vapor, while a value greater than 1 indicates a heavier-than-air vapor.