NIOSH HEALTH HAZARD EVALUATION REPORT 

HETA #2000-0400-2956 

HETA #2002-0325-2956 

Glen Canyon National Recreation Area 

Arizona and Utah 

January 2005 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health
ii 

PREFACE

The Hazard Evaluation and Technical Assistance Branch (HETAB) of the National Institute for 

Occupational Safety and Health (NIOSH) conducts field investigations of possible health hazards in the 

workplace. These investigations are conducted under the authority of Section 20(a)(6) of the Occupational 

Safety and Health (OSHA) Act of 1970, 29 U.S.C. 669(a)(6) which authorizes the Secretary of Health and 

Human Services, following a written request from any employers or authorized representative of 

employees, to determine whether any substance normally found in the place of employment has 

potentially toxic effects in such concentrations as used or found. 

HETAB also provides, upon request, technical and consultative assistance to federal, state, and local 

agencies; labor; industry; and other groups or individuals to control occupational health hazards and to 

prevent related trauma and disease. Mention of company names or products does not constitute 

endorsement by NIOSH. 

ACKNOWLEDGMENTS AND AVAILABILITY OF REPORT

This report was prepared by Jane McCammon, MS, CIH, NIOSH Denver Field Office, HETAB, Division 

of Surveillance, Hazard Evaluation, and Field Studies. Field assistance was provided by Ron Hall, Rob 

McCleery, and Eric Esswein (NIOSH). Additional field assistance was provided by representatives of the 

US Department of Interior, National Park Service, US Coast Guard, and individual boat owners. 

Analytical support was provided by Ardith Grote, Division of Applied Research and Technology 

(DART). Desktop publishing was performed by Lisa Maestas. Ellen Galloway provided editorial 

assistance. 

Copies of this report have been sent to employee and management representatives at Glen Canyon 

National Recreation Area, the US Department of the Interior, the US Coast Guard Office of Boating 

Safety, and the OSHA Regional Office. This report is not copyrighted and may be freely reproduced. The 

report may be viewed and printed from the following internet address: 

www.cdc.gov/niosh/hhe/hhesearch.html. Single copies of this report will be available for a period of three 

years from the date of this report. To expedite your request, include a self-addressed mailing label along 

with your written request to: 

NIOSH Publications Office 

4676 Columbia Parkway 

Cincinnati, Ohio 45226 

800-356-4674 

After this time, copies may be purchased from the National Technical Information Service (NTIS) at 5825 

Port Royal Road, Springfield, Virginia 22161. Information regarding the NTIS stock number may be 

obtained from the NIOSH Publications Office at the Cincinnati address. 

For the purpose of informing affected employees, copies of this report 

shall be posted by the employer in a prominent place accessible to the 

employees for a period of 30 calendar days.
Highlights of the NIOSH Health Hazard Evaluation

Identification of Boat-Related Carbon Monoxide (CO) Poisonings and Related Risk 

Factors in Glen Canyon National Recreation Area (GCNRA), Arizona/Utah

What NIOSH Did

Worked with Department of Interior and National 

Park Service representatives in searching law 

enforcement, emergency medical services, and

hospital records to identify diagnosed boat-related

CO poisonings on Lake Powell within GCNRA. 

Led investigations to measure CO on and near 

houseboats and other types of recreational boats. 

 

iii 

What NIOSH Found

Between 1990 and 2004, 176 acute boat-related 

CO poisonings occurred on Lake Powell within

GCNRA, 14 of which resulted in death. 

 Many of these poisonings were related to: 

CO from generators and/or propulsion engines 

contained within the airspace formed by an 

extended rear houseboat deck 

Water-level exhaust of generators on

houseboats or cabin cruisers 

Features on pleasurecraft that encourage 

occupancy in proximity to CO sources 

Failure of CO detectors inside living quarters 

of houseboats 

CO concentrations measured in the airspace under 

the extended rear deck of houseboats were as high 

as 30,000 ppm. 

Operation of propulsion engines alone resulted in

CO concentrations as high as 88,200 ppm in this 

airspace. 

CO concentrations measured near water-level

generator exhaust reached as high as 41,600 ppm

at the exhaust terminus, and were consistently

greater than 1,200 ppm as far away as 5 feet from 

the terminus. 

CO measured on other recreational watercraft 

indicated that CO 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

poisoning incidents occurring inside houseboat

cabins. 

What National Park Service Managers Can Do

Ensure that Safety Officers use visitor and 

employee injury and exposure data to develop

effective prevention programs to reduce the

number and severity of boat-related CO

poisonings. 

What Other Agencies and Boat Manufacturers 

Can Do

Continue to support effective engineering changes 

to control CO at the source. 

Develop educational programs and warning labels 

aimed at preventing poisonings on boats. 

What To Do For More Information:

We encourage you to read the full report. If you would 

like a copy, either ask your health and safety 

representative to make you a copy or call 

1-513-841-4252 and ask for

 HETA Report #2000-0400-2956 and 2002-0325-2956
 Highlights of the HHE Report 

Health Hazard Evaluation Report 2000-0400-2956 & 

 2002-0325-2956 

Glen Canyon National Recreation Area (GCNRA), 

Utah and Arizona 

January 2005 

Jane McCammon, MS, CIH 

Ronald Hall, MS, CIH 

SUMMARY

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 oxygendeficient 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. 

Keywords: SIC 9229 (Public Order and Safety). Carbon monoxide, CO, boat, houseboat, CO poisoning, 

COHb, exhaust, teak surfing, CO detectors, EMS, Emergency Medical Services

iv 
Table of Contents 

Preface..........................................................................................................................................................ii

Acknowledgments and Availability of Report..........................................................................................ii

Summary.....................................................................................................................................................iv

Introduction.................................................................................................................................................1

Background .................................................................................................................................................3

Methods........................................................................................................................................................4

Health Effects ..............................................................................................................................................7

Evaluation Criteria .....................................................................................................................................8

Carbon Monoxide Occupational Exposure Criteria............................................................................8

Confined Space Entry Criteria ..........................................................................................................9

Results ........................................................................................................................................................10

Medical/Epidemiologic Results............................................................................................................10

Boat-Related Carbon Monoxide Poisoning Case-Finding.............................................................10

Drowning Case-Finding....................................................................................................................11

Industrial Hygiene Results ...................................................................................................................12

Conclusions/...............................................................................................................................................15

Discussion ..................................................................................................................................................15

Recommendations.....................................................................................................................................17

References..................................................................................................................................................22

Tables .........................................................................................................................................................25

Table 1. Confined Space Classification ..............................................................................................25

Table 2. Checklist of Considerations for Entry, Working In and Exiting Confined Spaces.........26

Table 3. Number of Boat-Related CO Poisonings by Year – Glen Canyon National Recreation 

Area* ......................................................................................................................................................27

Figures........................................................................................................................................................28
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 1 

INTRODUCTION

In August 2000, after the death of two young 

brothers swimming near their family houseboat, the 

US Department of Interior (DOI) requested 

assistance from the National Institute for 

Occupational Safety and Health (NIOSH) to 

determine the potential exposures to carbon 

monoxide (CO) from generators on houseboats on 

Lake Powell, within Glen Canyon National 

Recreational Area (GCNRA). DOI expressed 

interest in evaluating the exposure to employees 

who work on or around houseboats while the 

generators operated, and also to the public who 

operate the boats. In their request, DOI stated: 

“The National Park Service [NPS] is very 

concerned about this issue considering 

the two recent fatalities where kids 

swimming around the boat were 

overcome. The exhaust ports for the 

generators are located on the stern of the 

boats and the exhaust accumulates in this 

area on days with little air movement. It 

also collects under the diving platform on 

the stern and creates a hazard to 

swimmers. If possible, we would like 

you to work with boat manufacturers, the 

concessionaire, and NPS staff to develop 

solutions to the CO problem in order to 

protect our employees and the public.” 

DOI attached three letters to the request: two were 

from NPS to the Commandant of the US Coast 

Guard (dated 1994 and 1999). The third was a 

letter of response from the Coast Guard (1999). In 

the first letter, NPS expressed concern about CO 

exposure hazards related to a houseboat design and 

asked for help in effecting a design change to 

relocate onboard generator exhaust ports. The 

letter referred to a recent death on such a boat and 

two prior non-fatal incidents. The design of these 

boats is shown in Figures 1–3. 

The second letter referred to two deaths in 1998 

that occurred within 12 days of each other, and 10 

CO-related deaths and injuries investigated by NPS 

occurring on boats designed as discussed above. 

NPS again recommended redesigning these types 

of boats by relocating the generator exhaust 

terminus and increasing air exchange in the stern 

cavity. 

The third attachment, the letter of response from 

the Coast Guard, stated that regulations affecting 

the routing of exhaust lines or the installation of 

swim platforms did not exist. The letter referred 

NPS to the American Boat and Yacht Council’s 

(ABYC) voluntary standards related to the exit 

location of exhaust piping. The Coast Guard letter 

also referred to positioning of the swim platform 

relative to exhaust openings and platform design as 

recent ABYC technical committee topics. 

Subsequent to NIOSH receipt of the request for 

assistance, DOI asked the NPS to provide listings 

of fatalities within the GCNRA and NPS 

emergency medical services (EMS) responses for 

CO poisonings. DOI also asked NPS to gather 

investigative records related to the recent fatalities 

and all others for which CO exposure was a 

contributing factor. 

NIOSH and DOI investigators traveled to GCNRA 

on September 18, 2000, to join an investigative 

team assembled by GCNRA NPS. Following an 

administrative meeting, NIOSH and DOI directed 

environmental investigations on three houseboats 

designed similarly to those on which fatal and nonfatal CO poisonings had occurred. Concern arising 

from the very high CO concentrations measured on 

and around these boats combined with the deaths of 

the victims led NIOSH investigators and DOI to 

ask participants to reconvene at Park headquarters 

on September 21, 2000. The group was briefed 

about the need for immediate action in a number of 

areas, including notifying boat manufacturers again 

about the extent of the problem under investigation 

at Lake Powell and notifying the owners of the 

boats on which the environmental investigations 

had been conducted. 

The first interim report of results, dated September 

28, 2000, provided preliminary information about 

investigative record review; environmental 

investigation of exposures on and near the boats, 

recommendations related to the immediate severe 

concerns, and plans for the future direction of the 

interagency investigation. 
Page 2 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

Because of the alarming nature of the hazard 

revealed by the initial investigative results, NIOSH 

investigators and other participants took the 

following additional steps to warn others of the 

identified hazards. These included: 

On October 3, 2000, the interim report was 

sent to 65 houseboat manufacturers. The 

cover letter warned the manufacturers of the 

hazard related to swimming near or standing 

on the rear swim platform of houseboats, 

identified CO concentrations measured in 

these areas as a significant threat to public 

health, and asked for response related to 

design changes the manufacturers may have 

made specifically related to CO exposures. Of 

the 65 manufacturers, four responded, 

detailing changes or original design features 

on their boats related to this issue. 

On December 12, 2000, NIOSH investigators, 

DOI, and the Medical Director for Prehospital 

Medical Care at GCNRA forwarded the 

interim report to 12 national boating safety 

organizations. The cover letter warned the 

organizations of the hazard and requested their 

assistance in a public awareness campaign by 

informing their membership of the GCNRA 

findings. 

On December 28, 2000, NIOSH investigators 

forwarded a second letter to each of the 65 

houseboat manufacturers, enclosing three 

items: 1) a one-page summary of further 

environmental sampling results from boats on 

Lake Powell and Lake Cumberland; 2) a 

publication of preliminary results of the 

review of CO poisoning records at Lake 

Powell1

, and 3) a DOI-prepared summary of 

the overall continuing investigation (dated 

December 7, 2000). 

On June 1, 2001, NIOSH, DOI, and the 

Medical Director for Prehospital Care at 

GCNRA sent individually addressed letters to 

263 boat rental companies warning them of 

the CO hazard on houseboats of this design. 

The letters asked the rental companies to urge 

boat owners at their facilities to retrofit 

generator exhaust to move the exhaust 

terminus out of the airspace beneath the rear 

houseboat deck (noting the February 23, 2001 

Coast Guard houseboat recall that approved 

venting the generator exhaust through the 

vessel’s side as a solution to the design 

problem). Rental companies were also 

advised that regardless of the boat’s design, 

boaters should still be aware of the hazard of 

CO in engine or generator exhaust and avoid 

exposure. Recipients also were provided with 

the DOI website address related to this issue 

for further information and copies of technical 

reports. 

Over the 4-year course of this investigation, there 

were six extensive NIOSH interim investigative 

reports covered under project number HETA 2000-

0400, each with information related to record 

reviews, CO air sampling on various boats, 

investigations of new CO-related fatalities, and 

recommendations related to each issue under 

investigation. On May 8, 2002, the GCNRA Park 

Superintendent requested an extension of NIOSH 

assistance to continue monitoring employee and 

visitor CO-related incidents to ascertain the 

effectiveness of NPS education efforts. This 

request (covered under a new project number – 

HETA 2002-0325) resulted in two additional 

extensive interim reports. Because of the similarity 

of intent and focus of HETA 2000-0400 and 2002-

0325, results of both projects are summarized in 

this final report. 

All interim reports listed below are available at the 

internet website 

http://safetynet.smis.doi.gov/COhouseboats.htm. 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 3 

The initial GCNRA Health Hazard Evaluation 

request led to six additional requests for assistance

related to boats and CO at other lakes.2,3,4,5,6,7

The combined investigations led to extensive 

engineering control evaluations by NIOSH’s 

Division of Applied Research and Technology 

(DART) Environmental and Physical Hazards 

Branch (EPHB). Two of these control technology 

evaluations were conducted in GCNRA. Most of

the EPHB studies were conducted as interagency 

projects through funding provided by the US Coast 

Guard. Although the EPHB work is continuing, a

number of reports have been

finalized.8,9,10,11,12,13,14,15,16

As of this writing, NIOSH has authored or 

coauthored five peer-reviewed journal articles 

related to boat-related CO poisonings and control

technology,1,17,18,19,20 presented related technical

information at over 80 venues, and participated in

extensive national and local print and broadcast

media coverage. Many of these articles,

presentations, media items, and final reports for 

completed NIOSH HETA and EPHB projects and a 

plethora of related materials are available at the 

DOI website at 

http://safetynet.smis.doi.gov/COhouseboats.htm. 

Investigation 

Dates 

Interim

Report Date 

Interim Report 

Subject 

September 19, 

2000 

September 

28, 2000 

Preliminary CO 

air sampling on 

houseboats 

October 10–

13, 2000 

November 

21, 2000 

Further 

investigation of 

CO on GCNRA 

houseboats 

January 23–25, 

2001 

June 4, 

2001 

Review of EMS 

records–Lake

Mead 

June 30, 2004; 

July 1, 2001; 

July 11, 2001

July 31,

2001 

Investigation of 

a “teak surfing” 

fatality at Lake 

Powell 

July 11, 2001 April 1, 

2002 

Fire boat 

investigation 

July 12–19,

2001 

April 23, 

2002 

Boat-related 

occupational 

CO exposures at 

Lake Powell 

August 28–29, 

2002 

December 

3, 2002 

Investigation of 

a fatality near a 

cabin cruiser

October 30–

31, 2002 

March 17, 

2003 

Investigation of 

propulsion

engine exhaust 

clearance from

airspace under 

the stern deck 

of a houseboat 

This report summarizes NIOSH efforts conducted 

at GCNRA from 2000–2004 related to the two

Health Hazard Evaluations (HETA 2000-0400 and

2002-0325) and highlights of the interim results 

already transferred to the NPS. Refer to the interim

reports and related publications for detailed data 

about each field investigation. The amount of data 

related to each investigation in those interim 

reports is too vast to be repeated here. 

BACKGROUND

GCNRA covers a 1,236,800 acre area crossing the 

Arizona-Utah border, and hosts approximately 

3,000,000 international and domestic visitors a 

year. Lake Powell, contained within GCNRA, was 

formed in 1963 with the construction of the Glen

Canyon Dam on the Colorado River in Page, 

Arizona. The second largest man-made lake in the 

United States, it covers approximately 13% of the 

total land area of the GCNRA. The lake is 187

miles long, and has nearly 2,000 miles of shore line

comprised of 96 major side canyons with huge

sheer cliffs of sandstone rock formations rising 

straight up from the water. The surface of the lake

is approximately 3,700 feet above sea level, and the 

deepest part of the lake is more than 500 feet. 

Houseboaters are drawn to this lake due to the

canyons that afford privacy, protection from wind, 

and striking scenic beauty. NPS estimates that

there are between 2,000 and 3,000 houseboats on 

Lake Powell, and that this probably represents two

thirds of the boat traffic on the lake. Many of the

privately-owned houseboats moored on Lake

Powell are shared ownership partnerships between

numerous families or individuals. 
Page 4 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

As the agency with proprietary legal jurisdiction, 

NPS responds to the vast majority of law 

enforcement and emergency service incidents 

occurring within GCNRA. This response is 

coordinated through NPS dispatch. Medical 

direction for NPS EMS services has been provided 

primarily by one physician since 1983, through 

Banner Good Samaritan Regional Medical Center 

in Phoenix, Arizona. NPS holds sole jurisdiction 

for EMS response on the lake. 

The lake is difficult to access, with paved roads 

leading to only four locations along its length. 

Although 90% of the lake is in Utah, the only 

hospital near the lake is in Page, AZ. That hospital 

operates a satellite clinic in Bullfrog, Utah, staffed 

by physician assistants. Emergency medical 

transport is conducted by NPS by boat or airplane, 

or by the contracted flight service also dispatched 

through NPS. The isolation of the lake and the 

dearth of nearby medical facilities results in few 

“self-transports” (people transported by private 

vehicle to the hospital). Thus, most medical 

emergencies occurring on the lake are managed by 

NPS. 

Patients requiring more extensive care than can be 

provided at Page Hospital or the Bullfrog Clinic are 

flown to hospitals more than 400 miles away 

(primarily located in Salt Lake City UT, Phoenix 

AZ, or Grand Junction CO). 

The isolation of the lake, and the central authority 

for law enforcement and medical activities, 

contributed to recognizing that CO poisonings were 

occurring on or near a variety of boats on Lake 

Powell beginning in the early 1990s. However, in 

1994 with the first documented CO-related 

drowning, a particular houseboat design drew 

concern. A child exposed to CO drowned while 

swimming near a houseboat with a design similar 

to the one on which the double fatality occurred in 

2000. Both vessels had an onboard generator used 

to supply electricity for appliances, and the 

generator exhaust terminus was under the extended 

rear deck of the boat. NPS stated in its letter to the 

Coast Guard that the area under the aft deck is 

inviting for children to explore because it 

resembles a small cave. The child who died in 

1994 was exposed to generator exhaust for 

approximately 3 minutes before drowning. (A 

second juvenile was also swimming in the area, but 

was able to get out of the water before losing 

consciousness.) 

Between 1994 and the beginning of this 

investigation in September 2002, a total of nine 

deaths were documented as CO-related on or near 

boats on Lake Powell. Of these nine deaths, seven 

occurred on houseboats of similar design. NPS 

made two attempts to gain assistance in dealing 

with this problem, but none became available until 

the deaths in August 2000. 

METHODS

Medical/Epidemiologic Methods 

During the course of these two NIOSH health 

hazard evaluations, boat-related CO poisonings 

occurring within GCNRA were identified to 

determine the number and distribution of cases, and 

risk factors related to the poisoning. All drownings 

that occurred in the GCNRA were also identified to 

allow assessment of the total number of drownings 

and the proportion of drownings related to 

recreational boating and carbon monoxide. 

Boat-related carbon monoxide 

poisoning case-finding 

An analysis of preliminary data abstracted from 

GCNRA EMS response records was published in 

December 2000. At that time, 111 boat-related CO 

poisonings occurring between 1990 and 2000 had 

been identified at GCNRA. Identification of such 

poisonings has continued since that publication as 

described below. 

Retrospective CO Poisoning Case-Finding

Review of three listings initially provided to the 

investigative team was the starting point for 

identifying boat-related CO poisonings. These lists 

contained information related to dispatch events 

from 1991 (when such records were first 

computerized) through the death of the two 

brothers in August 2000, and had been created 

through queries of the GCNRA NPS law 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 5 

enforcement dispatch database. The dispatch 

database contains information about the date, time, 

and location of the dispatch; officer responding; the 

type of incident (EMS versus a traffic violation, for 

example); and a brief narrative field for details 

about the call for assistance. About 5%–10% of 

the EMS dispatch entries contain no information in 

the narrative field. NPS staff involved with the CO 

poisoning issue at GCNRA had also collected EMS 

run sheets from 1990, and these records were also 

included in this study. 

List 1 identified deaths occurring within GCNRA. 

List 2 identified EMS dispatches for which CO 

poisoning was recorded as the cause for the 

response. List 3 identified GCRNA EMS 

dispatches for which symptoms recorded in the 

dispatch database were consistent with CO 

poisoning (but CO poisoning was not directly 

recorded). Investigative records related to the 

medical events identified in the lists were requested 

for review. Investigative records varied from very 

complex (usually for events involving a fatality) to 

very simple, but consistently contained EMS run 

sheets and some level of description of the event. 

Review of these records allowed differentiation 

between an unrelated medical event (such as a 

broken arm) and an event medically assessed as a 

boat-related CO poisoning. If the patient was 

transported to Page Hospital, the related hospital 

record was also requested. 

A database was developed to allow organization, 

abstraction, and analysis of records. The database 

included approximately 90 variables related to the 

victim, extent of available records, circumstances 

of poisoning, the boat, medical findings, and a 

lengthy narrative field describing the incident. 

As this study moved forward, the NPS provided a 

listing of all dispatch events for 2001. A review of 

that listing indicated that a request for all EMS 

dispatch entries for 1991–2000 was warranted to 

ensure that all CO poisoning cases had been 

identified through the computer query. The 

narrative field for each EMS entry was reviewed, 

and further investigative records were requested. 

An additional source of information, known as the 

“death book,” was also reviewed to identify fatal 

CO poisonings. The death book, begun in 1959, 

contains information about fatal incidents 

occurring within GCNRA, including a oneparagraph description of the circumstances of each 

death. Investigative records related to these 

fatalities were requested and reviewed. Boatrelated CO poisonings identified through these 

additional reviews were abstracted into the 

database. 

In addition, Page Hospital carboxyhemoglobin 

(COHb) analysis records were requested to ensure 

that CO poisoned patients transported to the 

hospital by other emergency responders or private 

individuals were identified. Page Hospital began 

conducting in-house COHb analyses in 1997, with 

cumulative records of all results hand-recorded by 

a staff member in the Respiratory Therapy 

department. Hospital records related to treatment 

of patients identified through this listing were 

requested to determine if the poisoning occurred on 

a boat within GCNRA, and data were abstracted as 

appropriate. 

Finally, the Arizona Department of Health Services 

analyzed hospital discharge data for 1995–1999 to 

identify boat-related CO poisoning cases admitted 

for treatment at any Arizona nonfederal hospital, 

including Page Hospital, using the ICD-9-CM 

nature of injury diagnosis code for CO poisoning 

(N986) and external cause codes E830 – E838. 

Prospective CO Poisoning Case-Finding

Under the terms of the contract between GCNRA 

and the Banner Health System, all EMS “run 

sheets” (records documenting EMS procedures in a 

given medical response) are forwarded to the 

GCNRA EMS Medical Director for review. 

Beginning in 2001, all GCNRA CO-related 

medical events were identified through this 

mechanism, as well as through direct 

communication between NIOSH investigators, 

DOI, and NPS GCNRA staff members. 

Investigative reports related to CO-related EMS 

events were provided to NIOSH as they were 

completed and data from these records were 

abstracted. Self-transports were identified for 

2001–2004 through annual requests for COHb 

analysis records from Page Hospital. 
Page 6 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

Drowning Case-Finding 

To assess the proportion of all drownings and 

reportable boat-related drownings for which CO 

poisoning was a contributing or primary cause of 

death, drownings that occurred within GCNRA 

from 1994–2004 were identified. The 1994 

starting point was chosen because that was the year 

for which the first CO-related drowning was 

identified. 

Three sources were used to identify possible 

drownings, including: List 1 (described 

above, and covering 1991–2000); the death 

book (described above, and covering all 

years); and updated queries of dispatch log 

records for EMS and Search and Rescue 

response activity related to fatal events 

occurring from 1994–2004. 

Investigative records related to identified 

drownings were requested. The investigative 

records ranged in scope, but most contained a 

lengthy narrative of events, documented 

timelines backed by dispatch information, 

Medical Examiner (ME) records or verbatim 

accounts of ME findings, EMS run sheets 

(when applicable), information about the 

location of the incident, records related to 

body search and recovery, and chain of 

custody information related to transport of the 

body. 

For those incidents where official cause of death 

was not documented in the NPS record, either the 

Utah or Arizona State Health Departments were 

contacted for verification that drowning was listed 

in cause of death information on the death 

certificate. 

Data from these drowning records were 

abstracted into a database grouped under the 

following categories: extent of records 

available; cause of death; chronological 

information about the incident (onset time, 

time of body recovery, where within the park 

the drowning occurred, etc.); victim 

demographics and activity of the victim when 

the drowning occurred; medical information 

(COHb concentrations, blood alcohol 

concentration, etc.); information about the 

boat; and a lengthy narrative field for 

describing the incident. 

Case Definition 

Boat-Related CO Poisoning

All identified boat-related CO poisonings were 

medically assessed as such by EMS responders, 

hospital emergency department staff, or medical 

examiners. Medical assessments of patients with 

adequate documentation of the following were 

accepted as cases: either death or sudden onset of 

signs and symptoms consistent with CO poisoning 

(i.e., loss of consciousness, seizures, headache, 

nausea, confusion, weakness, and/or altered state of 

consciousness) that improved upon removal from 

exposure or autopsies; and adequate documentation 

of exposure to CO. 

Two types of exposure documentation were 

accepted: 

1) a laboratory-confirmed elevated 

carboxyhemoglobin level (>2% in either children 

or nonsmoking adults or >9% in smoking adults or 

adults for whom smoking status was unknown); 

2) details in the record documenting that the person 

was either near the emissions of an operating 

source of CO (i.e., a generator or a propulsion 

engine) when symptom onset occurred, or that the 

person was with a group of similarly symptomatic 

people on a boat with an operating source of CO. 

COHb concentrations measured 3 or more halflives after cessation of exposure were considered 

irrelevant. 

Drownings

A drowning case was defined as a person who 

unintentionally drowned within the boundaries of 

GCNRA as documented by circumstances of death 

detailed in GCNRA records and by designation of 

drowning as primary or contributing cause of death 

in Medical Examiner reports or on the death 

certificate. Drownings were classified as COrelated based on the incident’s circumstances and a 

COHb concentration indicating that CO exposure 

was a contributing factor in the incident (again 

>2% in either children or nonsmoking adults or 

>9% in smoking adults or adults for whom 

smoking status was unknown). 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 7 

Identified drowning cases were classified as: 1) 

unrelated to boating activities (i.e., drownings 

associated with cliff jumping, swimming from 

shore, or other activities where no boat was 

involved); 2) related to boating activities, but not 

meeting Coast Guard Boating Accident Report 

Database (BARD) Reporting Criteria and 

Guidelines for Recreational Vessel Accidents (and 

thus not reportable); and 3) drownings reportable 

to the Coast Guard BARD. 

Industrial Hygiene Methods 

Overall, NIOSH investigators assisted DOI and 

NPS at GCNRA by leading seven extensive field 

investigations in which CO concentrations on and 

around boats on Lake Powell were measured. DOI 

and NPS industrial hygienists also participated in 

four of the seven surveys. Included in these seven 

surveys are NIOSH-led supplemental field 

investigations of three of the five CO-related 

fatalities that occurred at GCNRA from 2001–

2004. 

Industrial hygiene methods used in these seven 

surveys are detailed in previous interim reports, 

and thus will not be repeated in detail here. 

Overall, measurements were made using a number 

of direct reading instruments equipped to measure 

CO in differing ranges of concentrations. Low 

range direct-reading instruments were useful in 

characterizing CO concentrations at or below 1,000 

ppm. High-range direct-reading instruments were 

capable of measuring CO in percentages, with 1% 

being equivalent to 10,000 ppm. The 

measurements that used direct-reading analytical 

instruments were confirmed by direct-reading highrange detector tubes, and by collecting air samples 

in evacuated glass containers that were then 

shipped to Mine Safety and Health Administration 

for analysis. 

HEALTH EFFECTS 

Carbon Monoxide 

CO is a colorless, odorless, tasteless gas produced 

by incomplete burning of carbon-containing 

materials such as gasoline or propane fuel. The 

initial symptoms of CO poisoning may include 

headache, dizziness, drowsiness, or nausea. 

Symptoms may advance to vomiting, loss of 

consciousness, and collapse if prolonged or high 

exposures are encountered. If the exposure level is 

high, loss of consciousness may occur without 

other symptoms. Coma or death may occur if high 

exposures continue.21, , , , , 22 23 24 25 26 The display of 

symptoms varies widely from individual to 

individual, and may occur sooner in susceptible 

individuals such as young or aged people, people 

with preexisting lung or heart disease, or those 

living at high altitudes. 

Exposure to CO limits the blood’s ability to carry 

oxygen to tissues by binding with the hemoglobin 

to form COHb. Once exposed, the body 

compensates for the reduced bloodborne oxygen by 

increasing cardiac output, thereby increasing 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 

increased cardiac output. 

Blood has an estimated 210–250 times greater 

affinity for CO than oxygen, so the presence of CO 

in the blood can interfere with oxygen uptake and 

delivery to the body. Once absorbed into the 

bloodstream, the half-time of CO disappearance 

from blood (referred to as the “half-life”) varies 

widely by individual and circumstance (i.e., 

removal from exposure, initial COHb 

concentration, partial pressure of oxygen after 

exposure, etc.). Under normal recovery conditions 

breathing ambient air, the half-life can be expected 

to range from 2 to 6.5 hours. This means that if the 

initial COHb level was 10%, it could be expected 

to drop to 5% in 2 or more hours, and then 2.5% in 

another 2 or more hours. If the exposed person is 

treated with oxygen, as happens in emergency 

treatment, the half-life time 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 to 

approximately 20 minutes. 

Carboxyhemoglogin measurements are typically 

made when a patient arrives at the hospital or a 

body arrives at the morgue. The time elapsing 

between CO exposure and COHb analysis may 

explain the poor clinical correlation between 
Page 8 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

symptoms of carbon monoxide poisoning and 

COHb level. This complicates any discussion of 

“normal” COHb concentrations and COHb 

concentrations associated with symptoms. 

Carboxyhemoglobin concentrations among 

unexposed non-smokers are typically between 1%–

2%, and between 3%–8% for smokers.27 

Exposures resulting in COHb concentrations less 

than 10% usually cause no appreciable symptoms; 

exposures resulting in COHb greater than 50% are 

often fatal. However, COHb levels as low as 1%–

10% have been associated with severe symptoms 

(including prolonged loss of consciousness), and 

COHb levels as high as 47% resulted in no 

associated loss of consciousness.28 Thus, elevated 

COHb concentration can only be used to confirm 

exposure, not to confirm poisoning severity. 

EVALUATION CRITERIA

Carbon Monoxide Occupational 

Exposure Criteria 

As a guide to the evaluation of the hazards posed 

by workplace exposures, NIOSH field staff employ 

environmental evaluation criteria for assessing a 

number of chemical and physical agents. These 

criteria are intended to suggest levels of exposure 

to which most workers may be exposed up to 10 

hours per day, 40 hours per week for a working 

lifetime without experiencing adverse health 

effects. It is, however, important to note that not 

all workers will be protected from adverse health 

effects even though their exposures are maintained 

below these levels. A small percentage may 

experience adverse health effects because of 

individual susceptibility, a pre-existing medical 

condition, and/or hypersensitivity (allergy). In 

addition, some hazardous substances may act in 

combination with other workplace exposures, the 

general environment, or with medications or 

personal habits of the worker to produce health 

effects even if the occupational exposures are 

controlled at the level set by the criterion. These 

combined effects are often not considered in the 

evaluation criteria. Also, some substances are 

absorbed by direct contact with the skin and 

mucous membranes, which potentially increases 

the overall exposure. Finally, evaluation criteria 

may change over the years as new information on 

the toxic effects of an agent become available. 

The primary sources of environmental evaluation 

criteria for the workplace are: (1) NIOSH 

Recommended Exposure Limits (RELs)29, (2) the 

American Conference of Governmental Industrial 

Hygienists (ACGIH®) Threshold Limit Values 

(TLVs®)30, and (3) the U.S. Department of Labor, 

Occupational Safety and Health Administration 

(OSHA) Permissible Exposure Limits (PELs).31 

Employers are encouraged to follow the OSHA 

limits, the NIOSH RELs, the ACGIH TLVs, or 

whichever is the more protective criterion. 

OSHA requires an employer to furnish employees 

a place of employment that is free from recognized 

hazards that are causing or are likely to cause death 

or serious physical harm.32 Thus, employers 

should understand that not all hazardous chemicals 

have specific OSHA exposure limits such as PELs 

and short-term exposure limits (STELs). An 

employer is still required by OSHA to protect 

employees from hazards, even in the absence of a 

specific OSHA PEL. 

A time-weighted average (TWA) exposure refers to 

the average airborne concentration of a substance 

during a normal 8- to 10-hour workday. Some 

substances have recommended STEL or ceiling 

values which are intended to supplement the TWA 

where there are recognized toxic effects from 

higher exposures over the short-term. 

Occupational criteria for CO exposure apply to 

employees who may be at risk for CO poisoning. 

The occupational exposure limits noted below 

should not be used for interpreting general 

population exposures because occupational 

standards are intended for healthy worker 

populations. The effects of CO are more 

pronounced in a shorter time if the person is 

physically active, very young, very old, or has 

preexisting health conditions such as lung or heart 

disease. Persons at extremes of age and persons 

with underlying health conditions may have 

marked symptoms and may suffer serious 

complications at lower levels of COHb.33 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 9 

The NIOSH REL for CO is 35 ppm for full shift 

TWA exposure, with a ceiling limit of 200 ppm 

that should never be exceeded. The NIOSH REL 

of 35 ppm is designed to protect workers from 

health effects associated with COHb levels in 

excess of 5%. NIOSH has established the 

immediately dangerous to life and health (IDLH) 

value for CO as 1,200 ppm. An IDLH value is 

defined as a concentration at which an immediate 

or delayed threat to life exists or at which an 

individual's ability to escape unaided from a space 

would be compromised. 

The ACGIH recommends an 8-hour TWA TLV of 

25 ppm based upon limiting shifts in COHb levels 

to less than 3.5% to minimize adverse 

neurobehavioral changes such as headache, 

dizziness, etc., and to maintain cardiovascular 

exercise capacity. ACGIH also recommends that 

exposures never exceed five times the TLV (i.e., 

125 ppm). ACGIH recommends a Biological 

Exposure Index (BEI) for end of shift exhaled 

breath analysis in nonsmoking workers exposed to 

CO of 3.5% COHb (or 20 ppm). The BEI 

generally indicates a concentration below which 

nearly all workers should not experience adverse 

health effects. 

The OSHA PEL for CO is 50 ppm for an 8-hour 

TWA exposure.31 

Carbon Monoxide Exposure Criteria 

Relevant to the General Public 

The EPA has promulgated a National Ambient Air 

Quality Standard (NAAQS) for CO. This standard 

requires that ambient air contain no more than 

9 ppm CO for an 8-hour TWA, and 35 ppm for a 1-

hour average.34 The NAAQS for CO was 

established to protect “the most sensitive members 

of the general population” by maintaining increases 

in COHb to less than 2.1%. 

The World Health Organization has recommended 

guideline values and periods of TWA exposures 

related to CO exposure in the general population.

WHO guidelines are intended to ensure that COHb 

levels do not exceed 2.5% when a normal subject 

engages in light or moderate exercise. Those 

guidelines are: 100 mg/m3

 (87 ppm) for 

15 minutes, 60 mg/m3

 (52 ppm) for 30 minutes, 

30 mg/m3

 (26 ppm) for 1 hour, and 10 mg/m3

(9 ppm) for 8 hours. 

Confined Space Entry Criteria 

The airspace under the rear deck of houseboats of 

the design related to the CO-poisoning and 

drowning deaths at GCNRA meets the definition of 

a confined space, therefore confined space entry 

procedures must be followed if the airspace must 

be entered. 

OSHA regulation 29 CFR 1910.146 defines a 

confined space as a space that meets three criteria: 

(1) is large enough and configured so that an 

employee can bodily enter and perform any 

assigned work; (2) is a space that has limited or 

restricted means for entry or exit (for example, 

tanks, vessels, storage bins, vaults, and pits with 

limited means of entry); and (3) is a space not 

designed for continuous employee occupancy. The 

standard then defines a permit–required confined 

space as a space that meets one or more of the 

following additional criteria: (1) a space that 

contains or has a potential to contain a hazardous 

atmosphere; (2) a space that contains a material 

that has the potential for engulfing (surrounding 

and capturing a person by a liquid or finely divided 

solid substance that can be aspirated and cause 

death or that can exert enough pressure to cause 

death by strangulation, constriction, or crushing) 

the person entering the space; (3) a space whose 

internal configuration is designed in a way that the 

person entering the space could be trapped or 

asphyxiated by inwardly converging walls or by a 

floor that slopes downward and tapers to a smaller 

cross section; or (4) a space that contains any other 

recognized serious safety or health hazard.35 

NIOSH defines a confined space as “an area which 

by design has limited openings for entry and exit, 

unfavorable natural ventilation which could contain 

(or produce) dangerous air contaminates, and 

which is not intended for continuous employee 

occupancy.36 The NIOSH criteria for working in 

confined spaces further classify confined spaces 

based upon the atmospheric characteristics such as 

oxygen level, flammability, and toxicity. As 

shown in the confined space classification in Table 

1, if any of the hazards present a situation 

immediately dangerous to life or health, the 
Page 10 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

confined space is designated Class A. A Class B 

confined space has the potential for causing injury 

and/or illness, but is not an IDLH atmosphere. A 

Class C confined space is one in which the hazard 

potential would not require any special 

modification of the work procedure. 

The checklist in Table 2 lists the confined space 

program elements that are recommended (or must 

be considered by a qualified person, as defined by 

the criteria) before entering and during work within 

confined spaces based on the established hazard 

classification. 

 

RESULTS

Medical/Epidemiologic Results 

Boat-Related Carbon Monoxide 

Poisoning Case-Finding 

Records related to 327 patients treated at GCNRA 

and/or in Page Hospital from 1990–2004 were 

reviewed. Of these, 176 were CO poisonings on 

boats, and 14 of the poisonings resulted in death. 

Fifty-nine of the 162 surviving cases lost 

consciousness as a result of their exposure. Six of 

the surviving cases were noted as having seizures 

at some point during exposure. The numbers of 

fatal and non-fatal cases by year and boat type are 

listed in Table 3. 

Figures 5–8 show the following information: Boatrelated CO poisonings by month of the year; by age 

of victim; by source of CO exposure; by location of 

the victim when exposed. 

COHb concentration was available for all fatal 

cases, and for 78 of the 162 surviving cases. 

COHb concentrations for fatal cases ranged from 

1.9% (after 7 hours of oxygen by intubation) to 

59%; COHb for surviving cases ranged from 2.2% 

(after 4 hours of oxygen therapy) to 38.5% (50 

minutes after exposure ended). COHb 

concentrations were measured at the treating 

hospital (primarily Page Hospital) by blood 

analysis and/or by estimation based upon expired 

breath CO measurement. In 2003, NPS also began 

analyzing expired breath CO in the field, allowing 

more efficient triage and identification of CO 

poisoning cases. 

Glasgow Coma Scale (GCS) determination was 

available for 115 of the surviving cases, and ranged 

from 3 to 15. (GCS is a medical rating system that 

was developed to quantify observations of 

unconsciousness by applying a numeric scale to 

arousability and eye opening, whether spontaneous 

or as response to verbal or pain stimulus, with 15 

being the highest score possible.) 

Cause of death for the 14 fatalities listed on the 

medical examiner or autopsy report was either 

drowning secondary to CO intoxication (11), CO 

intoxication (2), or drowning with no secondary 

cause listed (1). 

Seven of the people poisoned were employees 

(either concessionaire or NPS employees), and five 

of these employees were engaged in work tasks at 

the time of poisoning. Four of the 5 poisoned 

employees lost consciousness as a result of their 

exposure, indicating the severity of their exposure. 

One of these poisonings occurred in September 

2001, when a concessionaire maintenance 

employee lost consciousness while tightening bolts 

on or under the swim platform of a houseboat. 

This boat was tied to another houseboat 

(Houseboat #2) on which the generator was 

operating. Houseboat #2's generator exhaust 

terminated on the side of the boat directed toward 

the houseboat where the employee was working. 

He was exposed in this position for approximately 

2 minutes. His COHb concentration, after 26 

minutes of oxygen therapy, was over 30%. This 

poisoning reinforced the need to reassess employee 

training and education at the Park, as well 

reinforcing the hazard presented by rafting boats 

with side-exhausting generators. (“Rafting” is the 

practice of lashing boats together, side-by-side.) 

Houseboat poisonings: 

Fourteen people (five children and nine adults) 

were known to have been poisoned as a result of 

CO exposure within the airspace beneath the 

outdoor rear deck of houseboats of the design 

shown in Figures 1–3. Seven of the 14 died and 

two survivors lost consciousness. 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 11 

Additionally, six people (two children, four adults) 

were poisoned near the rear deck boats of this 

design, but the poisoning was either an 

unwitnessed fatality (thus unknown if they entered 

the space) or the record of the incident did not 

document entry into the space. Two of these six 

people died as a result of their exposure. 

The estimated duration of exposure for the 14 

people known to have entered the airspace ranged 

from 1 minute to several hours as follows: nine 

were exposed less than 10 minutes; two were 

exposed between 10 and 20 minutes; two were 

exposed for 30 minutes or more; there was no 

estimated exposure duration for one case. 

 

Nine of the 14 people who entered the airspace 

were adults accessing the outdrive of houseboats to 

conduct maintenance activities or free propellers 

from entanglements, and three of these adults died 

as a result of their exposure. Three children died 

after entering this airspace while playing. 

Overall, 80 people survived poisonings inside 

houseboats in 15 incidents. COHb concentrations 

were available for 37 of these people, and ranged 

from 2.2% to 47.8%. Fifty of the 80 people were 

poisoned in boats that were documented to have 

CO detectors in the living quarters. However, in 

only one incident (four people poisoned) did the 

alarm sound alerting the occupants to their 

exposure. Twenty were poisoned in three separate 

instances involving disarmed or “broken” 

detectors. Twenty-two people were poisoned in 

four instances involving functional detectors that 

failed to sound during the poisoning incident. Ten 

people were poisoned in a houseboat that was not 

equipped with CO detectors. Twenty people were 

poisoned in houseboats in which the record failed 

to document absence or presence of detectors. 

Other recreational boats

Six people, all 21 years of age or younger, were 

poisoned as a result of occupancy of the waterlevel swim platform of a recreational boat other 

than a houseboat (referred to as a ski boat in the 

record). One of the six died, and three of the 

survivors lost consciousness. Four people 

(including one that died) were poisoned during an 

activity referred to as “teak surfing” or “platform 

dragging”, shown in Figure 4. Two others lost 

consciousness while sitting on the platform of a 

stationary ski boat, either pausing while accessing 

the boat or playing with a shower device that uses 

warm water from the operating boat engine. COHb 

concentrations, available for three of the six, were 

as follows: 18% after 50 minutes of oxygen 

therapy; 32% after 37 minutes of oxygen therapy; 

56% on autopsy. 

Four people, aged 14 to 28, survived poisoning 

while occupying the cushioned rear bench seat on 

the transom of a recreational boat referred to in the 

record as a “ski boat.” In all incidents, the boat 

was moving slowly through the water. Three of 

these people lost consciousness as a result of their 

exposure. COHb concentrations were available for 

all 4, and were as follows: 25% and 31% measured 

before oxygen therapy; 31% after 48 minutes of 

oxygen therapy; and 35% after 10 minutes of 

oxygen therapy. 

Ten people were poisoned in three incidents inside 

the cabin of boats described as cabin cruisers. 

None of these records included information about 

the presence or functionality of CO detectors in the 

living quarters of these boats. 

Drowning Case-Finding 

Seventy-two people died of unintentional 

drowning within GCNRA from 1994–2004. 

Nearly half (46%) of the drownings in 

GCNRA (33/72) occurred with no boat 

involved (i.e., hikers washed away in a flash 

flood, cliff jumpers, people swimming from 

shore). Twelve (17%) of 72 people who 

drowned at GCNRA were first poisoned by 

CO from marine generators or propulsion 

engines of houseboats or other recreational 

boats. 

Thirteen (18%) of the 72 identified drownings 

were related to boating activities but in 

circumstances that did not meet BARD 

reporting criteria (i.e., wandering on land or in 

the water near their moored boat; swimming 

from shore to retrieve a boat that was drifting 

or being blown from shore). Twenty-five 

(35%) of the 72 identified drownings met 
Page 12 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

Coast Guard BARD reporting requirements 

for boating accidents, and 12 (48%) of the 25 

were first poisoned by CO. 

Industrial Hygiene Results 

Complete data from the seven NIOSH field 

investigations involving air sampling for CO are 

contained in the interim reports listed in the 

introduction, and found at the DOI website. Major 

findings of each investigation are listed 

chronologically below by the date of investigation. 

September 19, 2000 (sample date); 

September 28, 2001 (report date) 

This initial air sampling investigation related to 

houseboats with extended rear decks and gaspowered generators with exhaust terminus exiting 

the boat transom under the deck (shown in pictures 

and diagram in Figures 1–3). The generators 

supply the boat with electrical power to operate onboard appliances (i.e., air-conditioner, refrigerator, 

lights, charging batteries, etc. 

GCNRA NPS and concessionaire staff had 

measured CO concentrations on three houseboats 

of this design on August 25, 2000. They measured 

CO concentrations of 1,393 ppm, 1,451 ppm, and 

greater than 2,000 ppm (the maximum 

concentration their instruments could measure) at 

water level below the swim deck of the three boats, 

each measurement taken approximately 10 minutes 

after generator activation. CO measurements 

collected on the swim platforms were 800 ppm, 

100 ppm, and 1156 ppm. During the first test, two 

of the people conducting the test began to 

experience headache, mild nausea, and weakness. 

NIOSH sampling on September 19, 2000 

documented three severely hazardous situations 

requiring immediate attention. The environment in 

the open space under the swim platform of 

houseboats with an extended rear deck can be 

lethal under certain circumstances and should not 

be entered by anyone for any reason as 

demonstrated by measurements as high as 30,000 

ppm in that space, and a concurrent oxygen 

deficiency of 12% in the space. The environment 

above and around the swim platform may be 

hazardous as was demonstrated when immediately 

dangerous to life and health (IDLH for CO is 

defined as greater than 1,200 ppm) concentrations 

of CO were measured on the rear deck of a 

houseboat during startup of one of the two engines. 

Employees may be exposed to hazardous 

concentrations of CO during boat maintenance 

activities as evidenced by the short-term, near the 

IDLH concentrations measured on one 

maintenance employee. 

 

October 10–13, 2000 (sample dates); 

November 21, 2000 (report date) 

This investigation confirmed the issues of concern 

regarding CO on houseboats expressed in the first 

report, again documenting that when generators are 

in operation, the area beneath the rear deck and 

around the back of the swim platform (near water 

level) contains extremely hazardous CO 

concentrations. These hazardous conditions also 

exist when the engines are in operation on the 

boats. CO concentrations measured with three 

separate methods (i.e., real time instruments, 

evacuated containers, and detector tubes) indicated 

concentrations well above the NIOSH established 

IDLH value of 1,200 ppm. Individuals swimming 

or working in the area under the swim platform, or 

around the area directly behind the swim platform 

(near the water level), with the generator or motors 

in operation could experience CO poisoning or 

death within a short period of time. 

The area on the swim deck of the houseboats was 

also documented as an area of concern. During 

this second NIOSH evaluation, CO concentrations 

in this area reached 1000 ppm (the upper limit for 

the CO monitors used in this evaluation). 

Investigators stated that when generator or motors 

were in operation, the area around the back deck of 

the houseboats could be hazardous under certain 

environmental conditions (i.e., lack of air 

movement), as substantiated by the CO poisonings 

and deaths reported in this area of the boat. CO 

measurements obtained on the top deck of the boats 

did not indicate a CO hazard during this evaluation. 

Personal sampling results indicated that some 

workers were exposed to CO concentrations that 

exceed the NIOSH ceiling limit of 200 ppm. One 

Park Service maintenance worker received a peak 

CO concentration of 780 ppm. 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 13 

June 30, 2004, July 1, and July 11, 2001 

(sample dates); July 31, 2001 (report date) 

This letter reported NIOSH evaluation methods, 

findings, and conclusions related to the death of an 

18-year-old boy. In summary, this person 

succumbed to exposure to extremely high 

concentrations of CO within 5 minutes of 

beginning an activity that the family referred to as 

“teak surfing.” This activity, shown in Figure 4, is 

made possible by specific design features of ski 

boats with an extended water-level teakwood swim 

platform and recessed propeller. The boy’s 

measured COHb was reported by the coroner as 

56%. At the time of this report, NIOSH was aware 

of four other similar fatal poisonings nationwide, 

and at least two non-fatal CO poisonings resulting 

in loss of consciousness also associated with 

similar activities and boats. 

CO concentrations as high as 23,800 ppm were 

measured in the unobstructed airspace above the 

swim platform where the teak surfer’s face and 

upper body would be during the activity. Engine 

maintenance conducted between the first and 

second day of air sampling did not reduce CO 

concentrations enough to have prevented this 

death. When the airflow above the platform was 

obstructed by a form simulating the shape of the 

upper torso of a person with extended arms, CO 

concentrations above the platform were 

consistently between 10,000 and 26,700 ppm after 

engine maintenance was conducted (this testing 

was not conducted prior to engine maintenance and 

thus comparison is not possible). 

July 11 ,2001 (sample date); April 1, 2002 

(report date) 

On this day, NIOSH monitored CO concentrations 

on the fire boat recently purchased by the GCNRA. 

The fire boat (an Almar 30’ X 11’) is used by NPS 

employees for fire suppression and other rescue 

operations. The CO sampling was conducted based 

upon employee concerns about the location of the 

boat’s gasoline-powered generator and related 

possible CO exposure hazards. The generator, 

which powered lights and other equipment during 

rescue/fire operations, was located in the staging 

area for these operations. The generator also 

served as a passenger seat. The exhaust terminus 

on the generator was directed toward the port deck 

side of the generator. 

Maximum CO concentrations at the generator 

exhaust ranged from 22,000 to 28,000 ppm when 

the generator operated with no load. When the 

microwave was operating, the range was 30,000 to 

32,700 ppm, indicating that area concentrations 

could be expected to be significantly higher when 

the generator was under full load as would be the 

case during a rescue operation. In summary, very 

high CO concentrations were reached within 

minutes of activating the generator. The location 

and configuration of the exhaust resulted in rapid 

dispersal of CO throughout the areas of the boat 

that would be occupied during a rescue/fire 

operation. NIOSH investigators recommended that 

GCNRA NPS immediately suspend use of the 

generator until it, or its exhaust terminus, could be 

relocated. GCNRA removed the generator from 

the boat. 

 

July 12–19, 2001 (sample dates); April 23, 2002 

(report date) 

In this investigation, NIOSH monitored employee 

exposure to CO at various locations within 

GCNRA. NIOSH had previously measured 

GCNRA employee CO exposures on three separate 

occasions and had also provided assistance in 

analyzing NPS EMS response records from 1990–

2001. In the previous exposure assessments, 

NIOSH characterized hazardous exposure zones 

near and under the rear deck and swim platforms of 

houseboats; measured employee CO exposures 

approaching the IDLH concentration (1,200 ppm) 

during boat maintenance activities; and collected 

personal sampling results indicating that some 

workers were exposed to CO concentrations in 

excess of the NIOSH ceiling limit of 200 ppm. 

The outcome of the employee exposure monitoring 

conducted in July 2001 is summarized below. 

•Toll booth operator exposures at the North and 

South Entrance Stations and the Antelope Point 

Entrance station were consistently very low, with 

exposure concentrations averaged over the 

sampling period ranging from 0 to 2 ppm, and no 

peak exposure greater than 48 ppm at any time 

during the 6 days of sampling these employees. 
Page 14 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

•Boat/vehicle maintenance worker exposures 

measured during 3 days of sampling were also 

consistently very low, with average CO exposures 

during the sampling period ranging from 0 to 2 

ppm, and peak exposures of 65 and 72 ppm. 

Unfortunately, we were not able to sample as many 

workers in this group as we had hoped, due to low 

participation by the concessionaire, and loss of one 

day’s data (discussed more fully in the report). 

•Exposures of maintenance employees working at 

pump-out stations and collecting garbage (Lone 

Rock, State Line, Bullfrog) averaged over the 

sampling period ranged from 1 to 9 ppm. Peak 

exposures of these employees ranged from 13 to 

685 ppm. 

•Maintenance employees conducting constructionrelated activities (operating a backhoe, installing 

water lines, working with a chainsaw) had average 

exposures ranging from 0 to 17 ppm. Peak 

exposures for this group ranged from 3 to 504 ppm. 

•Exposures of park rangers on boats conducting 

water quality patrol or other enforcement duties 

were monitored extensively. Exposures averaged 

over the sampling period measured during 5 days 

of workshifts for several employees in this group 

ranged from 0 to 16 ppm. Peak exposures during 

these same sampling periods ranged from 40 to 875 

ppm. 

•Exposures of park rangers working on boat launch 

ramps were measured during three workshifts. 

Exposures averaged over the sampling period 

ranged from 0 to 3 ppm. Peak exposures ranged 

from 42 to 364 ppm. 

•The employee with the highest exposure measured 

during this survey was a fuel dock worker on the 

North lake who was exposed to 28 ppm averaged 

over an 8-hour work shift, with peak exposures 

greater than the reliable sampling range of our 

instruments, approximately 1,000 ppm. 

August 28– 29, 2002 (sample dates); December 

3, 2002 (report date) 

In this investigation, NIOSH assisted industrial 

hygienists from the DOI and the Washington DC 

NPS office in the investigation of a fatal and a nonfatal CO poisoning occurring behind a cabin 

cruiser on August 17, 2002. The interagency 

investigation was supplemental to the GCNRA 

NPS investigation, and provided exposure 

information relevant to the poisoning of two 9-

year-old girls on that date. 

Because it was very windy on the first day of 

sampling (in contrast to the reportedly calm day of 

the poisoning), sampling was repeated the 

following calm morning. Data from both days are 

discussed in the full report, but only the second 

day’s sampling is discussed here, as it was more 

indicative of what was happening on the day the 

girls were poisoned. 

On the relatively still morning of August 29, 2002, 

NIOSH/DOI/NPS investigators found the 

following: 

• CO concentrations ranging from 37 to 41,600 

ppm were measured within 2–6 inches of the boat’s 

generator exhaust terminus. Among these samples, 

those with 13,400 ppm and higher CO were 

accompanied by oxygen-deficient environments 

(measured as low as 12.29% oxygen). 

• CO concentrations were consistently in excess of 

the maximum measurable value for the continuous 

CO monitors (>1,200 ppm) on the swim platform 

and in-line with the exhaust flow approximately 

one and two feet from the exhaust terminus. The 

CO concentration at these distances and locations 

was consistently in excess of the NIOSH IDLH 

concentration, indicating that the actual 

concentration was between 1,200 ppm and the 

maximum value measured at the exhaust terminus 

(41,600 ppm). 

• CO concentrations in line with the exhaust flow 

approximately 5 feet from the terminus were often 

in excess of the capacity of the monitors (>1,200 

ppm), as were CO concentrations at an angle to the 

exhaust flow 1 and 2 feet from the terminus. 

October 30–31, 2002 (sample dates); March 17, 

2003 (report date) 

In this investigation, NIOSH assisted industrial 

hygienists from DOI, the Washington DC NPS 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 15 

office, and the US Coast Guard in gathering data 

related to a fatal poisoning that occurred in 

GCNRA on September 28, 2002. This death 

occurred when a man entered the airspace beneath 

the extended rear deck of a houseboat to free 

anchor ropes fouling the propellers. The boat’s 

generator was not involved in this poisoning, as it 

exhausted out the side of the boat’s hull, outside 

the airspace beneath the rear deck. He was 

exposed to propulsion engine exhaust only, and the 

propulsion engines were not operating at the time 

he entered the airspace. 

The purpose of this interagency investigation was 

to provide data about clearance of propulsion 

engine exhaust CO from the airspace beneath the 

extended stern deck of boats associated with deaths 

at GCNRA. A previous NIOSH report provided 

data related to CO accumulation from propulsion 

engine and generator exhaust in this space, and 

documented that it took approximately 8 minutes 

for the CO concentration to decay to 0 ppm 

following deactivation of both engines. 15

In the October investigation, NIOSH conducted air 

sampling on two houseboats with extended stern 

decks, a lower swim platform the width of the boat, 

and propulsion engines exhausting into the airspace 

under the deck. For each sampling cycle, the boat 

propulsion engines were operated until a relatively 

stable concentration of CO accumulated in the 

airspace under the stern deck. The engines were 

then deactivated, with CO measurement continuing 

until the concentration decayed to 2 ppm or lower. 

The boat used on the first day of sampling (Boat 1) 

had side louvers (2 feet by 16 feet) for venting the 

under deck airspace and two access ports (8 feet by 

19 feet) above the swim platform parallel to the 

transom of the boat. Wind speed was 0–2 miles per 

hour (mph), with gusts to 5 mph. Five cycles of 

sampling were conducted using different 

configurations of open and blocked louvers/ports. 

During these five sampling periods, the CO 

concentration in the airspace beneath the stern deck 

decayed to 2 ppm or less after a period of 10 to 30 

minutes. Maximum peak concentrations in the 

airspace ranged from 15,100 to 62,500 ppm during 

the sampling periods. 

During this day of sampling, the boat’s CO 

detector located inside the rear sleeping quarters 

sounded on more than one occasion. NIOSH air 

sampling equipment housed in this room (which 

was used as an equipment staging area) indicated 

only sporadic low (less than 10 ppm) CO 

concentrations, indicating that there was no cause 

for it to sound. 

The boat used on the second day of sampling (Boat 

2) was the one under which the recent fatality 

occurred. This extended stern deck was completely 

enclosed, with no openings other than 2-inch holes 

for the mounting bracket for personal water craft. 

Wind speed ranged from 4–12 mph, with gusts to 

14 mph. Five cycles of sampling were conducted, 

with no changes in the airspace configuration. The 

CO concentration beneath the stern deck of Boat 2 

decayed to 2 ppm or less after a period of 10–20 

minutes during five sampling periods. Maximum 

peak concentrations in the airspace ranged from 

27,800 to 88,200 ppm. 

Because the detector on the previous boat had 

sounded on several occasions for no reason, the 

detector on Boat 2 was tested for performance. 

The alarm sounded when the test button was 

pressed, indicating that the detector was powered 

and capable of sounding. Three 2-liter mylar 

sampling bags were filled with air collected from 

the airspace beneath the swim platform. The 

concentration of CO in the bags (as indicated by 

high range detector tube measurement) was in 

excess of 40,000 ppm. The contents of the bags 

were released near the sensor of the detector in the 

rear bedroom of the houseboat. The detector never 

sounded, neither when the exhaust was released, 

nor in the 2 hours that passed before the boat was 

vacated. 

CONCLUSIONS/ 

DISCUSSION

The body of work represented in this report relates 

to a number of boat-related issues, each addressed 

through epidemiologic and environmental 

investigations. Conclusions below are grouped 

according to primary issues researched and 
Page 16 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

addressed over the period of HETA 2000-0400 and 

2002-0325. 

Acute, fatal boat-related CO poisonings occurring 

outside the cabins of boats are not unique to 

GCNRA. The 176 CO-related deaths and nonfatal 

poisonings (near misses) identified at GCNRA 

differ little from the 395 fatal and non-fatal 

poisonings identified on other U.S. bodies of 

water.37 

Without doubt, the cavity below the swim platform 

of houseboats with an extended rear deck presents 

a severe, sometimes fatal hazard that must be 

immediately addressed through design changes and 

public education. In all, we know of 21 people 

nationwide who have been poisoned by entering 

this airspace (14 on Lake Powell and 7 on other 

bodies of water), 13 of whom died (7 on Lake 

Powell, 6 on other bodies of water). This hazard is 

present during the operation of on-board generators 

housed in the engine compartment and exhausting 

into the cavity, as well during the operation of 

propulsion engines. Exhaust lingers in this 

airspace for an extended period following 

deactivation of either type of engine. 

Initial recommendations contained in interim 

reports for this project were that the airspace 

beneath the extended rear deck of houseboats 

should never be entered for any reason. 

Unfortunately, the current design of this type of 

houseboat necessitates entry into the airspace to 

access the propulsion engine outdrives (to conduct 

maintenance and repair) or propellers that often get 

fouled by anchor ropes. CO concentrations 

measured in the airspace of these types of boats, 

and related fatalities associated with this airspace, 

confirmed the need: 1) for manufacturers to 

immediately address the placement of the generator 

exhaust terminus (get it out of that space and up to 

an location that is not accessible by swimmers or 

boat occupants); 2) for manufacturers to develop 

safe entry procedures for boaters until this space 

can be redesigned; and 3) to educate boaters about 

exercising extreme caution when entering this 

airspace. 

 

Changing the generator exhaust terminus location 

from the transom to the side of the boat (as was 

required by the US Coast Guard as part of their 

recall in 2001) improved the situation, but did not 

eliminate CO poisonings. The two reasons for this 

are that fatal and nonfatal poisonings related to 

water-level generator exhaust outside the confined 

airspace have also been identified (see the GCNRA 

incident involving the death of a young girl outside 

a cabin cruiser in 2002) and fatal and nonfatal 

poisonings related to propulsion engine exhaust in 

the airspace have also been identified (see the 

GCNRA death of a 42-year-old man entering the 

airspace in 2002). Data collected at GCNRA 

demonstrated that even a relatively small generator 

(5 kilowatts) produces enough CO to result in rapid 

and fatal poisoning out in the open as far away as 5 

to 10 feet from the terminus when the weather is 

relatively calm. 

Another equally emergent issue arose during the 

course of the GCNRA investigations – deaths and 

severe poisonings related to ski boat and cabin 

cruiser features that attract occupancy at the rear of 

the boat. Most prominently covered in news media 

and subsequent legislative measures in 

Pennsylvania, California, and Nevada was 

occupancy of the water-level swim platforms of ski 

boats during an activity called “teak surfing” or 

“platform dragging,” or during other activities 

while the boat moves slowly in the water, or is 

stationary. The six poisonings identified at 

GCNRA related to occupancy of the swim platform 

of recreational speed boats were strikingly similar 

to 43 severe (17 resulting in death and 19 others 

resulting in loss of consciousness) poisonings 

occurring on swim platforms of recreational speed 

boats identified randomly in other states 

(http://safetynet.smis.doi.gov/COhouseboats.htm). 

Four GCNRA poisonings were related to 

occupancy of padded bench seats (also referred to 

as “sunning decks” or “tanning decks”) on the 

transom of ski boats. This feature also encourages 

occupancy of an area rich in CO when the boat 

engine is operating. These poisonings occurred in 

2001 and 2004, and reinforce concern about 

poisonings on ski boats that occur outside of any 

enclosure. A similar poisoning occurred on Lake 

Minnetonka, Minnesota in July 2000, when a 15-

year-old girl survived CO poisoning while she was 

lying on the rear padded sunning deck of a ski boat. 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 17 

Boat occupants were waiting for a fireworks 

display, with the engine operating to power the onboard music system. Other occupants thought the 

girl was sleeping until they tried unsuccessfully to 

awaken her. She had stopped breathing. Her 

COHb concentration (measured at an unspecified 

time after her removal from exposure) was 30%. 

In addition, during the course of this work, a 

feature described as a shower that operates using 

warm water from the operating propulsion engine 

arose as a serious concern. This device draws 

heated water from the propulsion engine, meaning 

that the engine has to be operating for the device to 

work. In the GCNRA incident, a 4-year-old girl 

was poisoned. She had been playing with a shower 

hose that was fed hot water by the engine. While 

sitting on the swim platform she clenched her arms, 

started crying, and her eyes rolled to the top of her 

head. She appeared to stop breathing. She 

survived. However, in a 1995 incident occurring in 

Flaming Gorge, Utah, three boys were hospitalized 

and another died in connection with the use of a 

similar device. In the Flaming Gorge incident, the 

boat had been completely covered because of rain. 

When the boat was occupied, a panel was unzipped 

and a door to the rear of the boat was opened to 

allow access to the ski platform. All four boys were 

discovered unconscious; the COHb of the boy who 

died was 46.6%. 

Finally, the failure of on-board CO detectors in the 

living quarters of houseboats on Lake Powell raises 

concern about the impact of such devices in CO 

poisoning prevention. Improving the effectiveness 

of these devices is complex, as there were four 

types of problems identified, each indicating a 

different corrective strategy. (Identified problems 

included: failure to alarm; alarming when they 

shouldn’t; disarmed or dysfunctional detector; 

absence of detectors.) Failure of functional 

detectors to warn occupants of high CO 

concentrations and the sounding of alarms for no 

discernable cause are related to detector sensor 

technology. A likely explanation of disabling of 

detectors by boaters is that the detectors are 

sounding frequently and the boater either cannot 

identify a cause for the alarm (also a detector 

technology issue) or cannot resolve the issue that is 

causing CO to enter the cabin (an issue related to 

boat design, technology, and boater education). 

Data gathered at GCNRA point to the need for 

improved national data collection to identify the 

scope of the problem of boat-related CO 

poisonings. Better data collection hinges on both 

improved case identification and improved case 

reporting. 

RECOMMENDATIONS

The following recommendations, listed by subject 

category, are a consolidation of those found in all 

the interim reports, and are still relevant, despite 

the Coast Guard recall and all prevention efforts 

conducted to-date. 

Engineering Controls 

1. GCNRA should investigate engineering controls 

to reduce exposures of boat maintenance 

mechanics. If repairs are conducted outside and at 

the boat dock (where electric power is easily 

available), using a high volume fan or other airmoving device may help to prevent short-term 

IDLH exposures as measured during at least one 

investigation. 

2. Employers (NPS and concessionaire) of 

boat/vehicle engine maintenance staff should 

conduct further CO monitoring on these employees 

to characterize their extent of exposure and 

determine if engineering controls are warranted and 

feasible to control exposures. 

3. Manufacturers should examine options for 

modifying houseboat design to prevent the buildup 

of hazardous CO concentrations from any engine 

exhausting into the airspace under the deck. Design 

changes could include modification of the structure 

of the stern deck and/or sufficient pressurization of 

the airspace to reduce CO concentrations to safe 

concentrations within 1 minute of engine 

deactivation. 

4. GCNRA, NPS, and DOI should continue to 

encourage research into effective technologies to 

control CO exposure through emission control 

devices on generators and propulsion engines. 
Page 18 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

5. Manufacturers should change boat design 

features that encourage passengers to occupy 

environments rich in CO. Examples of such 

changes might include: removal of the swim 

platform, thus removing the opportunity to teak 

surf; changing the direction/location of the exhaust; 

working with engine manufacturers to add or 

develop emission control devices for marine 

engines. 

6. The location of generators and the configuration 

of generator exhaust should be taken into 

consideration for any future NPS equipment 

purchases. This recommendation is based on 

sampling conducted on the newly purchased 

GCNRA Fire Boat on which the auxiliary power 

generator was located in the staging area for 

emergency responders. The generator exhaust 

terminus should be located in an area that is neither 

accessible nor occupied. 

Medical 

1. To improve boat-related CO poisoning case 

identification, the following are needed: 

●Training for EMS providers to help them 

recognize CO as a possible contributor and 

to give them guidance in collecting needed 

information about CO sources; 

●Information materials for the medical 

community (EMS, Emergency Department, 

and Coroners/Medical Examiners) that stress 

the need for immediate COHb 

measurements anytime a drowning occurs 

near a boat or boat passengers experience 

symptoms consistent with CO poisoning; 

2. Emergency medical services on bodies of water 

with large concentrations of boaters should 

consider using expired CO monitors when 

responding to medical emergencies. This 

equipment allows improved case identification as 

well as improved case management. The 

practicality and cost-effectiveness of using this 

equipment has been demonstrated during the past 

two years in GCNRA. Symptoms of CO poisoning 

are similar to those of dehydration, excessive 

alcohol consumption, and many other illnesses. 

The use of expired CO monitors allows medics to 

clearly assess CO poisonings and assists them in 

convincing patients to accept appropriate medical 

care.

Record Keeping / Reporting CO Poisonings 

1. Awareness among EMS personnel is critical to 

accurate diagnosis and treatment of CO poisonings, 

as is developing related records for EMS personnel 

to use to thoroughly document CO poisoning. NPS 

should encourage the use of a standard data 

collection form when boat occupants requesting 

assistance present with or report symptoms 

consistent with CO poisoning (headache, nausea, 

dizziness, loss of consciousness, convulsions, etc.). 

An example of this type of form for use by EMS or 

other park rangers investigating the incident can be 

found on the Internet at: 

http://safetynet.smis.doi.gov/COhouseboats.htm. 

2. EMS personnel should ensure that the 

information collected above is transferred to the 

receiving medical facility to aid the treating 

physician in treatment and diagnosis decisions. In 

addition, this information should be shared with 

coroners/medical examiners who receive the bodies 

of drowning victims (particularly if the drowning 

was unwitnessed or nontraumatic in nature) or 

people who died of natural causes. The goal of this 

recommendation is to encourage the collection of 

blood and/or breath samples for COHb analysis at 

the hospital emergency department or other 

medical facility receiving the patient. 

3. NPS EMS Medical Directors’ tasks should 

include monitoring trends reflected in data from 

EMS records on a periodic basis. Frequency of this 

review of data should be based upon such things as 

size of the park, number of incidents, and available 

resources.

4. NPS and other agencies responsible for 

responding to emergencies on bodies of water 

should work with the appropriate US Coast Guard, 

national NPS, and DOI staff to develop a 

systematic method of reporting and tracking severe 

medical events. 

5. GCNRA should ensure that all boating 

accidents (including CO-related boating accidents) 

are reported through appropriate State Reporting 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 19 

Authority to the U. S. Coast Guard Boating 

Accident Report Database. 

Regulatory / Guidelines / Procedural 

1. When houseboats with a confined airspace 

beneath the extended rear deck are on the water, 

the area under the swim deck meets NIOSH and 

OSHA criteria for a permit-required confined 

space. Therefore, permit-required confined space 

procedures must be followed before any workers 

enter this airspace. 

2. The similar hazard for boat occupants is no less 

important. Boat manufacturers should develop 

similar safe entry procedure guidelines for boaters 

that many also have to enter this space. Boaters 

should be cautioned that entry into this airspace has 

resulted in at least 13 deaths, and several more 

severe poisonings as well. Boaters should contact 

the boat manufacturer for guidance about safe entry 

procedures. 

3. Employees should avoid rafting boats (lashing 

two or more boats together side-by-side) as much 

as possible. If boats must be rafted (as is the case 

for EMS responses, etc.), employees should 

deactivate all engines including auxiliary engines, 

such as generators. Employees should avoid 

occupying the rear of the boat until engines are 

deactivated and exhaust has dissipated. 

4. Legislators should consider rules prohibiting 

occupancy of swim platforms and transommounted padded seats when the propulsion engines 

are operating. NPS should similarly prohibit such 

activities on bodies of water under their 

jurisdiction. 

5. Manufacturers should immediately place 

warning labels on all boats with design features 

that encourage or allow occupancy of areas that are 

rich in CO. These labels should warn of the 

hazardous circumstances and specifically tell 

passengers to stay away from the rear of the boat 

when the engines are operating. Information about 

the hazard of indoor and outdoor CO poisonings on 

boats should also be prominently placed in owner’s 

manuals. 

6. GCNRAA should assess additional active 

strategies that could be implemented to prevent CO 

poisonings at Lake Powell. Examples of possible 

GCNRA active strategies were discussed during an 

interagency meeting at a June 19, 2002 interagency 

meeting. Additionally, GCNRA should consider 

dedicating more resources to CO poisoning 

prevention efforts within the Park by filling vacant 

positions such as that of the safety officer. If filled, 

that position could coordinate visitor safety issues 

within the Park, including CO poisoning. 

7. Portable shower devices that operate using hot 

water from an operating propulsion engine should 

be evaluated for potential recall. 

CO Detectors in Boat Living Quarters 

1. The U.S. Coast Guard should extend laboratory 

testing of marine-rated CO detectors (conducted 

under Contract Number DTCG39-00-D-R0009, 

Task Order 01-F-00016, August 17, 2004) to 

include comprehensive field testing of detector 

efficiency and effectiveness. 

2. Even though alarms may sound in the absence 

of high CO levels, boat owners and operators 

should never disable CO detectors and should 

always heed the warning alarm when it sounds. 

3. Boat owners should report detector failures to 

the manufacturer. 

4. Boat owners should comply with owner’s 

manual instructions to ensure that they understand 

the proper functioning of the onboard CO detector. 

5. Boat owners should routinely check alarm 

function. 

6. Boat rental companies should check the proper 

function of CO detectors before each new rental. 

7. Boating accident investigators should gather 

detailed information about CO detector failure, 

including reasons for detectors being disabled. 

This information should be communicated to the 

appropriate state boating accident reporting 

authority. Detectors that fail to alarm during a 

poisoning incident should be tested. 

 
Page 20 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

Training / Sharing Information 

1. Training about the severity of CO hazards in 

boating should be reviewed and continued for Park 

Service personnel, especially EMS providers, so 

that symptoms experienced by employees or other 

boat operators might be more easily associated 

with exposures. This training should include both 

environmental data and information about the 

number and circumstances of CO poisonings on the 

lake. 

2. Awareness campaigns to inform boaters of boatrelated CO hazards on NPS and other lakes should 

be continued and enhanced. Training about the 

specific boat-related CO hazards provided for boat 

renters should be enhanced to include specific 

information about the circumstances and number of 

poisonings and deaths. The training (including 

videotaped training) should include anecdotal 

information about deaths and near misses, and 

should specifically warn against entering air spaces 

under the boat (such as the cavity below the swim 

platform) that may contain a lethal atmosphere. 

3. Boat manufacturers should enhance their 

existing warning and/or educational materials for 

consumers to include guidelines for safe entry into 

the airspace beneath the stern deck. 

4. NPS should work with receiving medical 

facilities and medical examiners/coroners to 

increase awareness of CO exposure and poisonings 

on boats. The goal of this recommendation is to 

encourage improved identification of CO-related 

fatalities through regular measurement of COHb 

when victims die of unwitnessed non-traumatic 

drownings. 

5. NPS and their concessionaires should educate 

all boat users about CO hazards (both symptoms of 

poisoning, and what circumstances lead to 

poisoning). Examples of educational materials 

developed for this purpose can be found on the 

Internet at 

http://safetynet.smis.doi.gov/COhouseboats.htm. 

NPS should ensure that this training and 

information is provided for all boat owners and 

users, regardless of the type of boat ownership or 

management. 

6. Employees on boat patrol duties should be made 

aware of CO hazards and be careful to stay away 

from boat engine and generator exhaust as much as 

possible. 

7. Maintenance employees should never work 

anywhere on or near the rear deck of houseboats 

when the generator or propulsion engines are 

operating. Employees should never place 

themselves in close proximity to the exhaust 

terminus of a generator. 

8. Manufacturers of houseboats must continue to 

be informed of the environmental data that has 

been collected, and the related design concerns. 

This relates most critically to the issue of sideexhausting generators. NIOSH sampling and 

deaths occurring near houseboats and cabin 

cruisers with water-level generator exhaust 

configuration, regardless of direction, has 

repeatedly demonstrated a CO poisoning hazard. 

This hazard is enhanced when boats are rafted 

(aligned boats moored to each other), as is very 

often the case with houseboat use. NIOSH control 

technology studies have demonstrated that 

rerouting generator exhaust through a properly 

designed “stack” terminating well above the upper 

deck effectively reduces CO concentrations in 

potentially occupied areas around houseboats 

9. Boat manufacturers should continue to be 

informed that the presence of design features that 

encourage occupancy at the rear of the boat (i.e., 

extended easy-to-access swim platforms in 

combination with a recessed propeller, padded 

transom-mounted “sunning decks”, and showers 

that operate using hot water from the engine) are in 

an environment that is very hazardous when the 

engines operate. 

10. Boat users should be made aware of the very 

real hazard of fatal outdoor CO poisonings 

associated with boats in general and specifically 

with this and other activities that involve 

occupancy of the swim platform when the boat 

engine is operating. Manufacturers and other 

appropriate agencies should develop educational 

materials and effective dissemination strategies to 

“get the word out.” 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 21 

11. GCNRA should reassess educational materials 

distributed as part of their public awareness 

program to include a broader spectrum of boatrelated CO hazards. Due to the transient nature of 

the visitors the public awareness program should 

be continuous. The following items should be 

included in the awareness campaign at GCNRA. 

●Post additional permanent CO warning signs 

at locations boat users frequent, such as 

pumpouts, fuel docks, ramps, and other 

locations that presently don’t have a sign. 

●Personalize the notices on past fatalities and 

poisonings so that boaters will be able to 

relate more closely with the hazard. 

●Continue distributing materials on CO safety 

(brochures and park guide/newspaper) at 

entrance stations. 

●Continue printing CO articles in the 

spring/summer park guide/newspaper. 

●Include CO Alert insert or news releases 

about CO poisonings with slip/mooring 

monthly billing statements. 

●Ensure that all concessionaires include CO 

safety issues in boat operator orientation 

materials (video, written, and verbal 

orientation) as a condition of their permit. 

●Print items such as “special attention” tent 

cards/wall notices that personalize the CO 

issue on past fatalities and near misses. 

●Encourage dissemination of CO information 

during GCNRA employee contacts with boat 

operators (ramp contacts, boat patrols, 

maintenance activities, etc.) 

●Repeat Public Service Announcements in 

local media (radio, newspaper) during boating 

season. 

12. NPS should ensure that similar educational 

programs are available for dissemination at other 

appropriate parks (those with bodies of water that 

allow powered boats). 

13. GCNRA/NPS should work with the U.S. Coast 

Guard to determine the best method to ensure that 

boat manufacturers, boat distributors, sales staff 

members, and consumers are made aware of the 

hazards of CO from generator and propulsion 

engine exhaust and options for hazard reduction. 

Hazard communication materials for these groups 

should include detailed information, including the 

possibility of fatal poisoning even if exposure 

occurs outside of any enclosure or obstruction of 

engine emissions. 

Further Testing 

1. NPS should ensure that further full-shift CO 

exposure monitoring is conducted for fuel dock 

workers. Sampling results indicated that these 

employees experience exposures over existing 

NIOSH and ACGIH recommended limits, 

including peak exposures greater than 1,000 ppm. 

Significant exposure reduction may be 

accomplished through improved employee training 

and awareness of risk, as well as improved work 

practices such as ensuring that all engines, 

including generators, are deactivated before boats 

are refueled. 
Page 22 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

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Technology/EPHB Report 171-05ee2. 

Unpublished. 

13 Dunn et. al [2001]. An evaluation of an 

engineering control to prevent carbon monoxide 

poisonings of individuals on houseboats. National 

Institute for Occupational Safety and 

Health/Division of Applied Research and 

Technology/EPHB Report 171-28a. Unpublished. 

14 Earnest et. al [2001]. An evaluation of an 

engineering control to prevent carbon monoxide 

poisonings of individuals on houseboats. National 

Institute for Occupational Safety and 

Health/Division of Applied Research and 

Technology/EPHB Report 171-27a. Unpublished. 

15 Dunn et. al [2001]. An evaluation of an 

engineering control to prevent carbon monoxide 

poisonings of individuals on houseboats at 

Sumerset Custom Houseboats, Somerset KY. 
Health Hazard Evaluation Report No. 2000-0400-2956 and 2002-0325-2956 Page 23 

National Institute for Occupational Safety and 

Health/Division of Applied Research and 

Technology/EPHB Report 171-26a. 

16 Earnest et. Al [2001]. An evaluation of an 

engineering control to prevent carbon monoxide 

poisonings of individuals on houseboats. National 

Institute for Occupational Safety and 

Health/Division of Applied Research and 

Technology/EPHB Report 171-25a. Unpublished. 

17 MMWR [2002] Center for Disease Control and 

Prevention Morbidity and Mortality Weekly Report 

(MMWR) Carbon-Monoxide Poisoning Resulting 

from Exposure to Ski-Boat Exhaust --- Georgia, 

June 2002. CDC, Atlanta, GA. 

18 MMWR [2004] Center for Disease Control and 

Prevention Morbidity and Mortality Weekly Report 

(MMWR) Carbon Monoxide Poisonings Resulting 

from Open Air Exposures to Operating Motorboats 

--- Lake Havasu City, Arizona, 2003. CDC, 

Atlanta, GA. 

19 AIHA [2002] American Industrial Hygiene 

Association (AIHA). An Evaluation of an 

Engineering Control to Prevent Carbon Monoxide 

Poisonings of Individuals on and Around 

Houseboats. AIHA, Fairfax, VA 

20 ASSE [2003] American Society of Safety 

Engineers (ASSE) Carbon Monoxide & 

Houseboats An evaluation of a stack exhaust 

system to reduce poisonings associated with 

generator exhaust. ASSE, Des Plaines, IL 

21 ACGIH [2001]. Documentation of threshold 

limit values and biological exposure indices. 7th 

edition. Cincinnati, OH: American Conference of 

Governmental Industrial Hygienists. 

22 NIOSH [1972]. Criteria for a recommended 

standard: occupational exposure to carbon 

monoxide. Cincinnati, OH: U.S. Department of 

Health, Education, and Welfare, Health Services 

and Mental Health Administration, National 

Institute for Occupational Safety and Health, 

DHEW (NIOSH) Publication No. 

73-11000. 

23 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. 

24 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 for Disease Control, 

National Institute for Occupational Safety and 

Health, DHEW (NIOSH) Publication No. 79-116. 

25 Proctor NH, Hughes JP, Fischman ML [1988]. 

Chemical hazards of the workplace. Philadelphia, 

PA: J.B. Lippincott Company. 

26 NIOSH [2004]. Immediately dangerous to life 

and health concentrations. DHHS (NIOSH) 

Publication No. 97-140, Pocket Guide to Chemical 

Hazards and other Databases, Fourth Printing, 

February 2004, with changes and updates. 

27 World Health Organization [1999]. 

Environmental health criteria 213 – carbon 

monoxide (Second Edition). WHO, Geneva. 

ISBN 92 4 157213 2 (NLM classification: QV 662) 

ISSN 0250-863X. 

28 Norkool DM, Kirkpatrick JN [1985]. Treatment 

of acute carbon monoxide poisoning with 

hyperbaric oxygen; a review of 115 cases. Ann 

Emer Med 14: 1168-1171 

29 NIOSH [1992]. Recommendations for 

occupational safety and health: compendium of 

policy documents and statements. Cincinnati, OH: 

U.S. Department of Health and Human Services, 

Public Health Service, Centers for Disease Control 

and Prevention, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication 

No. 92-100. 

30 ACGIH [2004]. 2004 TLVs® and BEIs®: 

threshold limit values for chemical substances and 

physical agents. Cincinnati, OH: American 

Conference of Governmental Industrial Hygienists. 

31 CFR 29 CFR 1910.1000[1997]. Code of 

Federal Regulations. Washington, DC: U.S. 

Government Printing Office, Office of the Federal 

Register. 

32 Occupational Safety and Health Act of 1970, 

Public Law 91-596, sec. 5(a)(1) 

33 Kales SN [1993]. Carbon monoxide 

intoxication. American Family Physician 

48(6):1100-1104. 

34 US Environmental Protection Agency[1991]. 

Air quality criteria for carbon monoxide. 

Publication No. EPA-600/8-90/045F. Washington, 

D.C. 
Page 24 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

35 Code of Federal Regulations [1997]. 29 CFR 

1910.146. Washington, DC: U.S. Government 

Printing Office, Federal Register. 

36 NIOSH [1979]. Criteria for a recommended 

standard: Working in Confined Spaces. 

Cincinnati, OH: U.S. Department of Health, 

Education, and Welfare, Public Health Service, 

Center for Disease Control, National Institute for 

Occupational Safety and Health, DHEW (NIOSH) 

Publication No. 80–106. 

37 http://safetynet.smis.doi.gov/thelistbystate10-

19-04.pdf [2004] Boat-Related CO Poisonings on 

U.S. Waters: National Case Listing. 
Health Hazard Evaluation Report No. 2002-0393-2928 Page 25 

TABLES

Table 1. Confined Space Classification 

Parameters Class A Class B Class C 

Characteristics Immediately dangerous to life 

– rescue procedures require 

the entry of more than one 

individual fully equipped 

with life support equipment – 

maintenance of 

communication requires an 

additional standby person 

stationed within the confined 

space 

Dangerous, but not 

immediately life threatening 

– rescue procedures require 

the entry of no more than 

one individual fully

equipped with life support

equipment – indirect visual 

or auditory communication 

with workers 

Potential hazard – 

requires no modification 

of work procedures – 

standard rescue 

procedures – direct 

communication with 

workers, from outside the

confined space 

Oxygen 16% or less 

*(122 mm Hg) or 

greater than 25% 

*(190 mm HG) 

16.1% to 19.4%

*(122 – 147 mm Hg) 

or 21.5% to 25%

(163 – 190 mm Hg) 

19.5 % – 21.4%

*(148 – 163 mm Hg) 

Flammability 

 Characteristics 

20% or greater of LFL 10% – 19% LFL 10% LFL or less 

Toxicity **IDLH greater than contamination 

level, referenced in 29 CFR 

Part 1910 Sub Part Z – less 

than **IDLH 

less than contamination 

level referenced in 29 

CFR Part 1910 Sub Part 

Z 

* Based upon a total atmospheric pressure of 760 mm Hg (sea level)

** Immediately Dangerous to Life or Health – as referenced in NIOSH Registry of Toxic 

and Chemical Substances, Manufacturing Chemists data sheets, industrial hygiene guides 

or other recognized authorities. 

NIOSH [1979]. Criteria for a recommended standard: working in confined spaces. Cincinnati, OH: 

U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, 

National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. 80–106.
Page 26 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

Table 2. Checklist of Considerations for Entry, Working In and Exiting Confined Spaces 

ITEM CLASS A CLASS B CLASS C 

1. Permit X X X 

2. Atmospheric Testing X X X 

3. Monitoring X Q Q 

4. Medical Surveillance X X Q 

5. Training of Personnel X X X 

6. Labeling and Posting X X X 

7. Preparation 

Isolate/lockout/tag 

Purge and ventilate 

Cleaning Processes 

Requirements for special equipment/tools 

X 

X 

Q 

X 

X 

X 

Q 

X 

Q 

Q 

Q 

Q 

8. Procedures 

Initial plan 

Standby 

Communications/observation 

Rescue 

Work 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

Q 

X 

X 

X 

9. Safety Equipment and Clothing 

Head protection 

Hearing protection 

Hand protection 

Foot protection 

Body protection 

Respiratory protection 

Safety belts 

Life lines, harness 

Q 

Q 

Q 

Q 

Q 

Q 

X 

X 

Q 

Q 

Q 

Q 

Q 

Q 

X 

Q 

Q 

Q 

Q 

Q 

Q 

N/A 

X 

 10. Rescue Equipment X X X 

 11. Recordkeeping/Exposure X X N/A 

X = indicates requirement Q = indicates determination by the qualified person 

NIOSH [1979]. Criteria for a recommended standard: working in confined spaces. Cincinnati, OH: U.S. 

Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute 

for Occupational Safety and Health, DHEW (NIOSH) Publication No. 80–106. 
Table 3. Number of Boat-Related CO Poisonings by Year – Glen Canyon National Recreation Area* 

Year Fatal Poisonings Non-Fatal Poisonings 

Inside the Cabin Outside the Cabin Inside the Cabin Outside the C

Houseboat Motorboat Houseboat Motorboat Houseboat Motorboat Houseboat Mo

1990 0 0 0 0 3 boat type not listed 1 1991 0 0 0 0 0 0 3 1992 0 0 0 0 0 0 2 1993 0 0 0 0 12 0 1 1994 0 0 1 0 1 6 2 1995 0 1 0 1 14 6 3 1996 0 0 1 0 0 0 3 1997 0 0 0 0 0 0 2 

3 

1998 0 0 2 0 9 1 1 boat type not 1999 0 0 1 0 0 0 1 2000 0 0 2 0 0 6 8 2001 0 0 1 1 11 0 2 2002 0 0 1 1 23 0 1 2003 0 0 1 0 0 0 0 2004 0 0 0 0 10 0 0 

80 19 32 

Total 0 1 10 3 3 1

*Source of data – GCNRA law enforcement and emergency medical services records; Page Hospital emergency depa

Health Hazard Evaluation Report No. 2002-0393-2928 Page 27 
Page 28 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

FIGURES

Figure 1. Example of the Houseboat Extended Rear Deck Related to Seven Deaths at Lake Powell 

Figure 2. Airspace Beneath the Houseboat Extended Rear Deck 
Figure 3. Overhead Diagrammatic View Illustrating Generator and Generator Exhaust Terminus

Location on Houseboats of the Design Associated with Seven GCNRA Deaths 

Health Hazard Evaluation Report No. 2002-0393-2928 Page 29 
Page 30 Health Hazard Evaluation Report No. 2000-0400-2956 and2002-0325-2956 

Figure 4. Teak Surfing or Platform Dragging 
Health Hazard Evaluation Report No. 2002-0393-2928 Page 31 
Health Hazard Evaluation Report No. 2002-0393-2928 Page 32 
Health Hazard Evaluation Report No. 2002-0393-2928 Page 33 
Health Hazard E Health Hazard Evaluatio aluation Report No. port No. 2002-0393-2928 Page 34 age 34 
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