Missouri man was killed when a 12-foot deep trench he was working in as part of a sewer project collapsed, burying him in earth past his legs. OSHA is investigating the accident.
Once the victim is buried past his legs, the chances of death increase greatly because the pressure from the earth puts pressure on the diaphragm, resulting in suffocation.
The article that was the basis of this story has an excellent discussion about the necessary safety precautions that have to be taken in excavation work and about who is responsible for those. In this case, responsibility for assessng the quality of the soil and what precautions were needed fell to the project engineers.