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Investigation of Carbon Monoxide Exposure at the



The Mohave County Health Department requested that the Arizona Department of HealthServices (ADHS) investigate the extent that recreational boaters in Lake Havasu City,Arizona, are exposed to carbon monoxide from a variety of watercraft. The request came asa result of several drownings where elevated levels of carbon monoxide were found in thebodies at autopsy. To determine whether people recreating in the area were exposed tocarbon monoxide, ADHS used exhaled carbon monoxide as a measure of the amount ofcarboxyhemoglobin (COHb) in the blood of recreational boaters. ADHS asked the Agencyfor Toxic Substances and Disease Registry's ADHS Cooperative Agreement Program tointerpret the data and to determine whether a public health hazard exists at Lake Havasuwhen large numbers of watercraft are present on the water.


Carbon monoxide is an odorless, colorless gas that results from incomplete combustion ofcarbon compounds. Until recently, carbon monoxide poisonings were thought to occur onlyin enclosed, poorly ventilated areas. However, open-air cases of carbon monoxidepoisoning are being reported that include exposures from exhaust from various kinds ofwatercraft such as houseboats, cabin cruisers, and ski boats. Unlike automobiles, boatengines do not have mechanisms to reduce carbon monoxide emissions.

Large numbers of boaters use the channel of water beneath the London Bridge for recreationon weekends during the summer. There are hundreds of watercraft in the channel water atRotary Beach on holiday weekends. The density of watercraft and the large numbers ofpeople using the channel creates the opportunity for individuals to be exposed to excessivecarbon monoxide emissions. Indeed, the Havasu Regional Medical Center EmergencyDepartment has seen a number of patients in the last several years that have been diagnosedwith carbon monoxide poisoning while recreating in or near the channel of water beneath theLondon Bridge in Lake Havasu City.

This health consultation documents ADHS's evaluation of the extent of carbon monoxideexposure in recreational boaters in the Rotary Beach area near the London Bridge in LakeHavasu City, Arizona, during the Memorial Day Holiday in 2003 (5/24/03 - 5/25/03). TheRotary Beach area is a very popular location for recreation, including boating, swimming,sunbathing, shopping, and other activities.

The objective of this evaluation is to determine whether a public health hazard from carbon monoxide exposure exists in an area heavily used by recreational boaters.


ADHS examined the concentration of carbon monoxide in the exhaled air of volunteers thatwere recreating in the Rotary Beach area near the London Bridge in Lake Havasu City duringthe Memorial Day Holiday in 2003 (5/24/03 - 5/25/03). Exhaled carbon monoxide was usedas a measure of the amount of carboxyhemoglobin (COHb) in the participant's blood.

Volunteers provided samples by blowing exhaled air into a single-use mouthpiece. Eachmouthpiece was discarded after each use. A Scott/Bacharach Instrument Carbon monoxideSniffer with a Breath Analysis Module was used to analyze the exhaled air samples. Themodule includes an internal mechanism to ensure that ethanol does not interfere with theanalytical results.

An ADHS investigator administered a short questionnaire while the sample was beinganalyzed in the field. Voluntary participants were asked whether or not they are a smoker,what kinds of recreation activities they had been doing, and how many hours they had beenrecreating in the area. The investigator did not collect personal identifiers. A total of 62individuals participated in the study.

The investigator recorded the time of day, the general weather conditions, and theconcentration of carbon monoxide in the exhaled air of the participant. Exhaled carbonmonoxide levels were converted to percent COHb using a standardized conversion chart. The results were input into Microsoft Access® for analysis.


The results of the analysis suggest that significant carbon monoxide exposure occurredamong participants during the investigation. The percent COHb among non-smokingparticipants increased from an average of 1% between 10 am and 2 pm to 11% between 6 pmand 8 pm (Figure 1). Similarly, among smokers, the average percent COHb increased from 3% between 12 pm and 2 pm to 13% between 6 pm and 8 pm (Figure 2).

The average percent COHb was greater in all participants that had been recreating outdoorsin the areas for longer periods of time. The average percent COHb among non-smokingparticipants ranged from 1.4 % for those recreating outdoors for 1 hour, to more than 5 %for those recreating outdoors for 5 hours or more (Figure 3). Similarly, the average percentCOHb among smokers increased from 3% after 1 hour of recreation to 7% for thoserecreating outdoors for 5 hours or more (Figure 4).


Average % COHb in Nonsmokers by Time of Day - Rotary Beach

Average % COHb in Smokers and Nonsmokers by Time of Day

Average % COHb in Nonsmokers by Number of Hours at Rotary Brach

Average % COHb by Number of Hours on Rotary Brach


The initial symptoms of carbon monoxide poisoning may include headache, dizziness,drowsiness, or nausea. Symptoms may advance to vomiting, loss of consciousness, andcollapse from prolonged or high exposure. Coma or death may occur if high exposurescontinue.(1-6) The symptoms vary widely from individual to individual, and may occursooner in sensitive persons such as young or aged people, people with preexisting lung orheart disease, or those living at high altitudes. Table 1 displays the symptoms associated with exposure to carbon monoxide.

Table 1. Health Effects from Overexposure to Carbon Monoxide

Table 1.

Health Effects from Overexposure to Carbon Monoxide
% COHb Symptom
< 5%None
5-10%Slight headache, decreased exercise tolerance
10-20%Mild dyspnea on exertion, headache
20-30%Throbbing headache, mild nausea, some impaired judgment
30-40%Severe headache, nausea and vomiting, impaired judgment
40-50% Confusion and syncope
50-60%Syncope, coma, seizures
60-70%Coma, seizures, cardiorespiratory depression, death
>70%Failing hemodynamic status, death

Exposure to carbon monoxide limits the ability of the blood to carry oxygen to the tissuesby binding with the hemoglobin to form carboxyhemoglobin. Once exposed, the bodycompensates for the reduced blood borne oxygen by increasing cardiac output, therebyincreasing blood flow to specific oxygen-demanding organs such as the brain and heart. This ability may be limited by preexisting heart or lung diseases that inhibit increasedcardiac output.

Blood has an estimated 210-250 times greater affinity for carbon monoxide than oxygen.Carbon monoxide in the blood interferes with oxygen uptake and delivery to the body. Once absorbed into the bloodstream, the half-life ranges from 2 to 6.5 hours.(7) If oxygenis administered to the exposed person, as happens in emergency treatment, the half-lifetime is decreased again by as much as 75% (or to as low as approximately 40 minutes). Delivery of oxygen under pressure (hyperbaric treatment) reduces the half-life toapproximately 20 minutes.

The average percent COHb among non-smoking participants was low (1% COHb)between 10 am and 2 pm and among those non-smokers that had spent less than 2 hoursrecreating outdoors. These participants were below symptom thresholds. However, theaverage percent COHb among non-smoking participants increased to 11% between 6 pmand 8 pm, suggesting that these persons may have had a headache or decreased exercisetolerance as a result of their exposure to environmental carbon monoxide.

Smoking participants showed a similar increase in COHb over time. However, smokingcigarettes and other tobacco products increases COHb, and the increase in COHb levelsin these participants is likely due to both environmental exposures and active smoking oftobacco products. These persons likely experience chronic mild symptoms of carbonmonoxide exposure, including headache or decreased exercise tolerance as a result oftheir active smoking. Other factors that may influence COHb levels among the volunteersinclude occupation, living in proximity to factories or highways, and other factors thatmight bring the volunteers into contact with carbon monoxide.

The maximum COHb level observed for non-smokers was 23% COHb, and themaximum for smokers was 26%. These participants were likely experiencing moresignificant symptoms of carbon monoxide exposure, including more severe headache,nausea, and impaired judgment. These data suggest that while the average COHbconcentrations found were still in the mild carbon monoxide poisoning range, someindividuals may have significantly more exposure, resulting in the potential for moreserious consequences such as drowning. A 31-year-old drowning victim during theweekend of this investigation had a 47% COHb concentration at the time of autopsy,suggesting that his death was at least partially due to carbon monoxide exposure.

Alcohol consumption was common among the participants. Alcohol consumption is welldocumented to cause similar symptoms as carbon monoxide including headache,impaired judgment, nausea and vomiting. The combination of alcohol consumption andcarbon monoxide exposure likely creates a more significant health hazard. In addition,the recreational activities conducted during the investigation were predominately in ornear water, creating a drowning hazard for those with impaired judgment or more severesymptoms of carbon monoxide exposure or alcohol consumption. Additional hazards inthe environment include those associated with moving propellers and other movingwatercraft.

The levels of carbon monoxide in outdoor air during the investigation were not availabledue to a lack of adequate sampling equipment, and the investigation could not determinewhether the source of carbon monoxide exposure among non-smokers was primarily dueto ambient carbon monoxide or exposure close to tailpipe sources.


ATSDR and ADHS recognize that the unique vulnerabilities of infants and children demandspecial emphasis in communities faced with contaminants in air. The developing bodysystems of children can sustain permanent damage if toxic exposures occur during criticalgrowth stages. Children that are participating in recreational activities at times when carbon monoxide levels are high are at risk of carbon monoxide poisoning, which could result in death.


The results of the analysis suggest that people were exposed to carbon monoxide when largenumbers of watercraft were present in the London Bridge area of Lake Havasu becausecarbon monoxide poisoning occurred among participants during the investigation. Thecumulative carbon monoxide exposure increased as the day progressed. The COHb levelsobserved late in the day posed a public health hazard.

The levels of carbon monoxide in outdoor air during the investigation were not availablebecause of a lack of adequate sampling equipment, and the investigators could not determinewhether the source of carbon monoxide exposure among non-smokers was primarily due toambient carbon monoxide or exposure close to tailpipe sources.

The combination of carbon monoxide exposure and alcohol consumption likely creates agreater health hazard. In addition, the recreational activities conducted during theinvestigation were predominately in or near water, creating a drowning hazard for those with impaired judgment or more severe symptoms of carbon monoxide exposure and alcoholconsumption.


  • ADHS should conduct additional biomonitoring studies at this site and at otherrecreational lakes in Arizona over the next 12 months to determine whether a widespreadpublic health hazard exists due to carbon monoxide exposure from motorized watercraft. Additional investigations should include measurements of carbon monoxide in outdoorair in order to better characterize exposures.

  • ADHS should continue to work with the public health officials in Mohave County toincrease awareness about carbon monoxide poisoning among persons that participate inmotorized watercraft activities on busy weekends in the Rotary beach area. Healtheducation materials should include information on how alcohol consumption can resultin similar symptoms of carbon monoxide poisoning and can contribute to the healthhazard.


ADHS is working with Lake Havasu City officials to help the public understand how theycan reduce their exposure to carbon monoxide. The attached carbon monoxide fact sheet isavailable for distribution. Other possible actions will be discussed.

ADHS is conducting other carbon monoxide releases at lakes in Arizona. Equipment is now available to include environmental sampling.


1. NIOSH [1972]. Criteria for a recommended standard: occupational exposure to carbonmonoxide. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, HealthServices and Mental Health Administration, National Institute for Occupational Safety andHealth, DHEW (NIOSH) Publication No. 73-11000.

2. NIOSH [1977]. Occupational diseases: a guide to their recognition. Revised ed. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service,Centers for Disease Control, National Institute for Occupational Safety and Health, DHEW(NIOSH) Publication No. 77-181.

3. NIOSH [1979]. A guide to work-relatedness of disease. Revised ed. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers forDisease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH)Publication No. 79-116.

4. Proctor NH, Hughes JP, Fischman ML [1988]. Chemical hazards of the workplace. Philadelphia, PA: J.B. Lippincott Company.

5. ACGIH [2002]. Documentation of threshold limit values and biological exposure indices. Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

6. NIOSH [1999]. Pocket guide to chemical hazards. Cincinnati, OH: U.S. Department ofHealth and Human Services, Public Health Service, Centers for Disease Control, NationalInstitute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 99-115.

7. World Health Organization. Environmental Health Criteria 213 - Carbon Monoxide(Second Edition). WHO, Geneva, 1999; ISBN 92 4 157213 2 (NLM classification: QV 662). ISSN 0250-863X.


Arizona Department of Health Services
Office of Environmental Health

Will Humble, Principal Investigator
Muhamed Hadzihasanovic
Richard Cox


This health consultation was prepared by the Arizona Department of Health Servicesunder cooperative agreement with the Agency for Toxic Substances and DiseaseRegistry. It is in accordance with approved methodology and procedures existing at thetime the health consultation was initiated.

Gail Godfrey
Technical Project Officer

The Division of Health Assessment and Consultation (DHAC), ATSDR, has reviewedthis health consultation and concurs with its findings.

Roberta Erlwein


Arizona Department of Health Services logo

June 2003

What is carbon monoxide?

Carbon monoxide is a poisonous gas that is produced during combustion and burning ofgasoline and diesel fuel. Carbon monoxide is odorless and colorless, so it is difficult to tell if you are being exposed.

Do boats and other watercraft emit carbon monoxide?

Yes. Boats and other watercraft emit a great deal of carbon monoxide in the exhaustunless they have emission control equipment. Most boats and other watercraft do nothave any emission controls.

Is it dangerous?

Yes, it is deadly. Carbon monoxide interferes with your body's ability to use oxygen.Exposure to low levels can cause health symptoms like headache, dizziness and a loss ofconcentration. Exposure to carbon monoxide can also make you lose consciousness. Losing consciousness around water can be deadly because of the risk of drowning.

Is carbon monoxide a problem around boats and other watercraft?

Yes. Anybody that spends any time at all near the rear end of a boat can be exposed totoo much carbon monoxide. Carbon monoxide poisoning is commonly found in peoplethat have spent time near the back of moving and idling boats. There have beennumerous people that have drowned because of carbon monoxide poisoning from boatexhaust.

How can I avoid carbon monoxide poisoning while boating?

Taking a few simple precautions will prevent carbon monoxide poisoning:

  • Stay away from boat exhaust
  • Keep your boat motor off at all times while you are docked
  • Never allow your boat motor to idle in order to run appliances like radios
  • Avoid crowded areas where lots of boats congregate if some of the boats are idling

Your contact information here

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