A construction site proved deadly to two workmen Monday. Two men died and five were sent to the hospital after being overcome by hydrogen sulfide gas. Hydrogen sulfide is a gas not usually found in dangerous concentrations except in industrial settings. It has a strong, bad smell, too, but the workers were used to it — they’d been on this job almost a year, replacing miles of sewer pipe on Des Moines’ industrial east side. They may not have noticed a higher-than usual concentration of the gas in the trench they were digging Monday, but when several workers for the Missouri-based construction company collapsed, the Capital City’s HAZMAT team responded. In addition to the workers who were pronounced dead at the scene and those taken to local hospitals, three Des Moines fire-rescue workers were treated for exhaustion in the 95-degree heat.