This Alert warns that using gasoline powered engines and tools indoors is not safe. Four instances of carbon-monoxide (630080) (CO) poisoning are cited. The first involved a farm owner who died of CO poisoning after using an 11 horsepower, gasoline powered pressure washer to clean his barn. The second involved a municipal employee at an indoor water treatment facility who lost consciousness while trying to exit a room in which he had been using an 8 horsepower, gasoline powered pump. The third instance involved five workers who had been using two 8 horsepower, gasoline powered pressure washers in a poorly ventilated underground parking garage. The fourth case involved a plumber using a gasoline powered concrete saw in a basement with open doors and windows and a cooling fan. Precautions are given concerning where the use of such equipment must be avoided, learning to recognize the symptoms and signs of CO overexposure, placing the pump and power unit of high pressure washers outdoors, considering substitute tools, and using personal CO monitors. A workplace survey should be performed to identify all potential sources of CO exposure and workers must be educated as to the hazards. Recommendations are also provided for tool manufacturers and tool rental agencies.