Methane deaths? Was it the cause?

In the routine performance of their jobs, three men consecutively descended into an open drainage pit to recover a fallen grate lid. Each man, in turn, was immediately overcome and died within minutes of his descent. Initial analysis of the pit's air indicated a methane level of 15%. Therefore, it was initially assumed that death was attributable to methane poisoning. Postmortem analysis of the victims' tissues, however, yielded methane levels in only faint trace quantities (0-100 mcg/100 g range). Analysis of air samples taken at various pit levels revealed that as one descended, there was a decrease in oxygen levels, from 20% at the top to 3% at the bottom. CO2 levels, however, increased from the top of the pit, and reached a level of 22% at the 6-ft. depth of the pit. The accepted lethal level is only 10%. The cause originally attributed to these deaths was shown to be in error. This paper demonstrates the importance of proper investigation of the "scene of occurrence" in order to properly certify the cause of death.