Abstract: On April 2, 2007, Employee #1 was assigned to connect pool heaters to a gas line located in the pool pump room at the Sky Las Vegas condominium construction site. Part of that job task required him to purge the gas line of air, dirt and debris until gas came through the line. A water heater had also been installed in the room and had to be purged prior to the lighting of the water heater. Employee #1 opened the gas cock, valve, to the water heater gas line and purged it for a few seconds but no smell of gas was noted. He then purged the gas line that would be connected to the pool heaters for a few seconds but only dirt and debris came out and no smell of gas was noted. The gas line was purged twice more but Employee #1 could not smell the gas as well as Employee #2 who had entered the room. Employee #1 left the room and returned several minutes later at which time an explosion occurred inside the pool pump room. The explosion also affected nearby facilities including the two bathrooms and stairwell. Access was not restricted to the pool pump room and adjacent areas to only the employee involved in the purging process. Ignition sources were not prohibited inside the pool pump room and outside adjacent areas. Artificial illumination was not restricted to listed safety type flashlights and safety lamps. Electric switches were operated. Employees, working with natural gas were not instructed in the safe handling and use of this material. Employee #1 and #2 were hospitalized and treated for burn. Employees #3, #4 and #5 received cuts but were not hospitalized.