Health hazard evaluation report: HETA-2000-0400-2956 & HETA-2002-0325-2956, Glen Canyon National Recreation Area (GCNRA), Utah and Arizona.
After the August 2000 death of two young brothers swimming near their family houseboat, the US Department of Interior (DOI) and the National Park Service (NPS) requested assistance from the National Institute for Occupational Safety and Health (NIOSH) to evaluate potential boat-related exposures to carbon monoxide (CO) on Lake Powell, within Glen Canyon National Recreational Area (GCNRA). DOI and NPS also asked for assistance in identification of boat-related CO poisonings. NIOSH led the identification of 176 boat-related acute CO poisonings occurring on Lake Powell within GCNRA between 1990 and 2004. All poisonings were medically assessed as such by EMS or emergency department personnel. Fourteen poisonings resulted in death due either to drowning or from CO intoxication, and 59 of the 162 people that survived poisonings lost consciousness during their exposure. Factors related to these poisonings included: 1) lethal concentrations of CO from generators and/or propulsion engines contained within the airspace formed by an extended rear houseboat deck; 2) water-level exhaust of generators on houseboats or cabin cruisers creating a direct route of exposure to CO in the exhaust gases; 3) features on pleasurecraft that encourage occupancy in proximity to CO sources (such as water-level swim platforms, padded rear bench seats also referred to as sunning decks, and shower devices using warm water from the operating propulsion engine); 4) CO detectors inside living quarters of houseboats that failed to sound during the poisoning event. During operation of on-board generators (without operation of propulsion engines), concentrations of CO in the airspace under the extended rear deck of houseboats were measured in excess of 30,000 ppm (parts per million); this environment was also determined to be oxygen-deficient (as low as 12% oxygen). Operation of propulsion engines alone resulted in CO concentrations as high as 88,200 ppm in this airspace, with an accompanying oxygen-deficient environment. CO concentrations measured near water-level generator exhaust reached as high as 41,600 ppm at the exhaust terminus, and consistently greater than 1,200 ppm as far away as 5 feet from the terminus. CO measured on other recreational watercraft indicated that exposures as high as 26,700 ppm could be experienced during "teak surfing" on ski boat platforms. On-board CO detectors sounded in only 1 of 15 CO poisoning events occurring inside houseboat cabins (in which a total of 80 people were poisoned). CO in uncontrolled exhaust from boat generators or propulsion engines presents a risk of acute, possibly fatal CO poisoning and CO-related drowning.