 Not included in the official fatalities number were deaths that were recorded as pneumonia . Workers alleged that this diagnosis was a cover for death from carbon monoxide poisoning , brought on by the use of gasoline @-@ fueled vehicles in the diversion tunnels , and a classification used by Six Companies to avoid paying compensation claims . The site 's diversion tunnels frequently reached 140 ° F ( 60 ° C ) , enveloped in thick plumes of vehicle exhaust gases . A total of 42 workers were recorded as having died from pneumonia ; none were listed as having died from carbon monoxide poisoning . No deaths of non @-@ workers from pneumonia were recorded in Boulder City during the construction period . 
