Abstract: Employee #1 entered a new manhole approximately 21 ft in depth and was overcome, lost consciousness, and was unresponsive. Employee #2 entered the manhole in an attempt to rescue Employee #1 and was also overcome and lost consciousness. Two additional co-workers attempting to rescue Employee's #1 and #2 but became dizzy, disoriented and experienced shortness of breath. These employees were able to exit the manhole. The manhole had been installed approximately two weeks earlier and was placed over an existing and active sewer line which had not yet been tapped. Employee #1 was pronounced dead at the scene and Employee #2 was hospitalized.