Houseboat-Associated Carbon Monoxide Poisonings on Lake Powell — Arizona and Utah, 2000

Morbidity and Mortality Weekly Report, Dec 15, 2000

During August 2000 at Lake Powell in the Glen Canyon National Recreation Area on the Arizona-Utah border, two brothers died of carbon monoxide (CO) poisoning as they swam near the stern of a houseboat while the onboard gasoline-powered generator was operating. As a result of these deaths, an investigation was initiated by the U.S. National Park Service (NPS) with assistance from the U.S. Department of the Interior, CDC's National Institute for Occupational Safety and Health, and the U.S. Coast Guard. In addition to investigating the deaths of the two brothers, the multiagency team evaluated visitor and worker boat-related CO exposures at Lake Powell. The study identified nine boat-related fatal CO poisonings since 1994 and approximately 100 nonfatal poisonings since 1990. This report describes the preliminary results of an ongoing investigation of watercraft-related CO poisonings on Lake Powell.

Incident Reports

Incident 1. On August 2, 2000, two families vacationing on a houseboat on Lake Powell started the boat generator to cool the boat interior and operate the television. About 15 minutes later, two brothers (aged 8 and 11 years) swam into the airspace beneath the swim deck enclosed by the swim platform that was near water level (Figure 1) into which the exhaust of the generator was directed. Within an estimated 1-2 minutes, one boy lost consciousness and the other began to convulse before sinking underwater. The brothers' bodies were retrieved the next day. Autopsy results showed that the boys had been overcome by CO and subsequently drowned; autopsy carboxyhemoglobin (COHb) levels were 59% and 52%.

Incident 2. On August 18, 1994, three teenaged boys were swimming off the stern of a houseboat similar in design to that in incident one. The houseboat generator was operating. The boys were climbing up the back of the houseboat and sliding down a rear-mounted slide into the water. After several minutes, one of the boys developed a headache and went inside the boat cabin. While in the water, another boy commented that his legs felt numb and that he was dizzy. He climbed back onto the boat and is believed to have collapsed and fallen back into the water. Approximately 1 hour later, his body was recovered from the bottom of the lake. An autopsy revealed a COHb level of 53.9%.

Incidents 3, 4, and 5. During August 1998, three CO poisonings occurred on Lake Powell within the span of 12 days. All involved entry of the airspace beneath the swim deck for engine maintenance or clearing ropes from propellers, and all boats had designs similar to those in incidents one and two. Two of the incidents resulted in fatal CO poisonings (COHb levels of 55% and 49%); the third incident involved a concessionaire employee who lost consciousness while in the water but who was retrieved and resuscitated.

Review of Medical Records

To further examine risk factors for such incidents, the team reviewed NPS emergency medical service (EMS) transport records for 1990-2000 to characterize the circumstances and number of boat-related CO poisonings. A total of 181 records was selected based on the notation of "CO poisoning" or symptoms consistent with CO poisoning and was reviewed for case classification. Of these, 111 definite cases of boat-related CO poisonings were identified. [*] COHb levels have been obtained for 25 cases.

Nine (8%) of the 111 CO poisonings were fatal, and five deaths occurred after the victim entered the cavity beneath the swim platform of the houseboat during operation of or immediately after deactivation of the generator or boat engines; two additional deaths occurred when the victims were overcome while standing on or swimming near a houseboat swim platform. The remaining two deaths occurred on pleasure crafts. Ages of the persons who died ranged from 8 to 66 years. Of the 111 CO poisonings, 74 (67%) occurred on houseboats and 30 (27%) occurred on pleasure crafts; seven records did not specify a boat type. Of the 74 CO-related poisonings on houseboats, 37 (50%) occurred outdoors, and half of those resulted in loss of conciousness.

Environmental Sampling

Maximum CO concentrations measured in the cavity beneath the stern deck on houseboats on Lake Powell ranged from 6,000-30,000 parts of CO per million parts of air (ppm) while the generators were in operation. Oxygen concentrations as low as 12% also were measured. This oxygen deficient, CO-rich environment in a confined space is lethal within seconds to minutes. In addition, environmental measurements and case reports indicated that CO concentrations on and near the swim platform can reach life-threatening concentrations (measured as high as 7200 ppm). CO tends to accumulate above the water near the platform, and CO concentrations as high as 200 ppm were measured at water level 10 feet away from the platform.

Reported by: RL Baron, MD, National Park Svc Glen Canyon National Recreational Area, and Good Samaritan Regional Medical Center, Phoenix, Arizona. T Radtke, Dept of the Interior, Denver Field Office. Div of Surveillance, Hazard Evaluation, and Field Studies, National Institute for Occupational Safety and Health, CDC.