Abstract: At approximately 1:00 p.m. on September 24, 2002, an employee of Oasis Landscaping and Tree Experts, Inc., used a gasoline-powered Honda GX340 power washer to clean off the walls and floor in the basement of a residence under construction. He worked unsupervised. At approximately 3:17 p.m., the site superintendent found him lying unconscious on the basement floor. The superintendent brought the employee out of the basement so that the fresh air would revive him. Emergency Medical Services was called and the Howard County Fire and Rescue Service arrived at approximately 3:22 p.m. and administered emergency aid. The employee was transported by Trooper 8 helicopter to the Shock Trauma Center in downtown Baltimore, where he was treated for carbon monoxide poisoning. His carboxyhemoglobin was 33.7 percent. Carbon monoxide levels measured at the site by the EMS team and fire department upon their arrival registered 44 parts per million (ppm) at the doorway leading into the basement and 1,500 ppm at the center of the basement floor. The employee apparently brought the power washer into the basement because the water hose was only 25-ft long and did not reach into the basement from its current location. The employee later stated that it was common practice to bring the power washer into the basement and to use it there.