April 6, 2001

 HETA 2001-0100

Mr. Bob Clark 

Vice President

Seven Crown Resorts

322 Lakeshore Road

Boulder City, Nevada 89005

Dear Mr. Clark:

On December 8, 2000, the National Institute for Occupational Safety and Health (NIOSH)

received a request from management officials of Seven Crown Resorts to evaluate carbon

monoxide (CO) concentrations associated with the operation of houseboats on Lake Mead. On

January 24 - 25, 2001, NIOSH investigators conducted a site visit at Lake Mead to investigate

CO concentrations on houseboats located at Echo Bay Marina, Nevada. This letter describes our

evaluation methods, findings, and conclusions.

Background

Previous investigations were performed by NIOSH industrial hygienists and representatives from

several agencies in September 2000 and October 2000 in response to CO related poisonings and

deaths on houseboats at Lake Powell, Arizona. These investigations characterized the

circumstances of boat related CO poisonings through review of emergency medical service

(EMS) transport records, and measured hazardous CO concentrations on houseboats.1, 2 Incident

reports provided by the National Park Service revealed 9 known boat-related CO poisoning

deaths on Lake Powell since 1994. Some of these incidents involved multiple poisonings in

addition to the deaths reported (total of 15 people poisoned in the 8 incidents involving

fatalities). Information regarding the fatalities is addressed in a previous report.1

 An additional

evaluation conducted in October 2000 at Lake Cumberland, Kentucky also revealed hazardous

CO concentrations around the swim platform on houseboats with gasoline powered

generators/motors.3

 

Some of the severely hazardous situations identified during the September and October 2000

evaluations at Lake Powell and Lake Cumberland included:

! The open space under the swim platform could be lethal under certain circumstances

(i.e., generator/motor exhaust discharging into this area) on some houseboats. 
Page 2 - Mr. Bob Clark

! Some CO concentrations above and around the swim platform were at or above the

immediately dangerous to life and health (IDLH) level (greater than 1,200 parts of

CO per million parts of air [ppm]). 

! At Lake Powell, measurements of personal CO exposure during boat maintenance

activities indicated that employees may be exposed to hazardous concentrations

of CO. (Personal monitoring on workers at Lake Cumberland was not conducted) 

Please refer to Attachments 1 and 2 for discussions of health effects of CO exposure and relevant

evaluation criteria. 

 

Methods and Materials

During our investigation at Lake Mead, CO was measured in the area on the back of houseboats

when only the generator was in operation, and when the generator and boat engines were

operating simultaneously. 

The environment near the generator exhaust discharge was characterized using a KAL Equip

Model 5000 Four Gas Emissions Analyzer (KAL Equip, Cleveland, Ohio). This analyzer

measures CO, carbon dioxide (CO2), hydrocarbons, and oxygen (O2). Carbon monoxide and O2

measurements are expressed as percentages. (One percent of contaminant is equivalent to

10,000 ppm.) 

Carbon monoxide concentrations were measured on the back of the houseboats using ToxiUltra

Atmospheric Monitors (Biometrics, Inc., Middletown, Connecticut) with CO sensors. All

ToxiUltra CO monitors were calibrated before and after each use according to the

manufacturer’s recommendations. These monitors are direct-reading instruments with data

logging capabilities. The instruments were operated in the passive diffusion mode, with a 30

second sampling interval. The instruments have a nominal range from 0 ppm to 500 ppm with

the highest accurate instantaneous reading of 1000 ppm. Figure 1 illustrates a typical houseboat

(seen during previous CO evaluations) and where ToxiUltra CO monitors were placed. Some of

the locations varied on different houseboats depending on the swim deck and swim platform

designs. Echo Bay Marina houseboats were pontoon houseboats and did not have slides located

on the back deck. 

Carbon monoxide measurements were also made with detector tubes (Drager CO, CH 29901–

range 0.3% [3,000 ppm] to 7% [70,000 ppm], and Drager CO, CH 25601-range 100 - 700 ppm)

in the areas near the exhaust and around the swim deck. The detector tubes are used by drawing

air through the tube with a bellows–type pump. The resulting length of the stain in the tube

(produced by a chemical reaction with the sorbent) is proportional to the concentration of the air

contaminant.
Page 3 - Mr. Bob Clark

“Grab” samples were collected using Mine Safety and Health Administration (MSHA)

50–milliliters (mL) glass evacuated containers. These samples were collected by snapping open

the top of the evacuated glass container and allowing the air to enter. The containers were sealed

with wax–impregnated MSHA caps. The samples were then sent by overnight delivery to the

MSHA laboratory in Pittsburgh, Pennsylvania where they were analyzed for CO using a HP6890

gas chromatograph equipped with dual columns (molecular sieve and porapak) and thermal

conductivity detectors. 

Results

Grand Sierra Pontoon Houseboat #112

During the afternoon of January 24, 2001, CO samples were collected on a Grand Sierra pontoon

houseboat with the specifications listed below. During this evaluation, the gasoline generator

operated alone for approximately 25 minutes. Subsequently, the gasoline motors and generator

were operated together for approximately 16 minutes. The test was conducted just prior to a

storm moving through the area; therefore, the test was conducted under windy conditions. 

Engines: One outboard marine corporation (OMC) 70 HP Johnson motor, and 

one Evinrude 70 HP engine

Generator: 8.5 Kw Westerbeke, 4 cylinder, 1.0 liter gasoline generator

Exhaust Configuration: Generator exhaust discharged out to the side of the

houseboat. 

Wind speed above deck: air speed readings ranged between 560 - 1580 feet per

minute

Area around exhaust and off back of houseboat

Figure 2 shows a portion of the back deck of the Grand Sierra pontoon houseboat, and illustrates

the generator exhaust discharging out the side. Figure 3 shows a close-up view of the exhaust

discharge, and warning label above the discharge. 

One evacuated glass container sample was collected in the area near the generator exhaust

discharge. This sample indicated a CO concentration of 463 ppm. The emissions analyzer

sampling probe was placed near the generator exhaust discharge of the houseboat. A total of 17

readings were obtained (over a 19 minute period) when only the generator was in operation. The

recorded CO concentration ranged from 0.01% (100 ppm) to 0.22 % (2,200 ppm) with an

average of 0.08 % (800 ppm) while the generator was in operation. A total of 12 CO

concentration readings were obtained near the generator exhaust discharge when the generator

and engines were both in operation. These CO concentrations ranged from 0.0 % (0 ppm) to

0.18% (1800 ppm) with an average of 0.05 % (500 ppm).
Page 4 - Mr. Bob Clark

A detector tube sample collected in the area around the generator exhaust indicated CO

concentration greater than 700 ppm while the generator was in operation.

Area Above Swim Deck on Back of Boat 

The prevailing wind direction was moving from the front of the houseboat toward the back of the

of the houseboat. Therefore, the wind was moving away from the back deck under windy

conditions (a storm was moving into the area during the evaluation). Table 1 lists the CO

monitor results obtained on the back of the Grand Sierra pontoon houseboat, with the generator

and motors operating. 

Table 1. Sample locations and CO results on the Grand Sierra houseboat.

Location CO average (ppm) CO peak (ppm)

Only Gasoline Generator Running (ran for approximately 25 minutes without motors operating)

Right side of swim platform (when on boat and facing

the water) at floor level

118 306

Left side of swim platform (when on boat and facing the

water) at floor level

6 23

On gate going to swim platform on back deck 0.6 2

On the right side of the rear portion of the back deck (at

floor level)

0.8 12

On stairs going up to top deck (at breathing zone height) 10 34

On the top deck of boat 0.9 2

 On patio door on back deck No CO Detected

Gasoline Generator and Gasoline Powered Outboard Motors Running 

(ran together for approximately 16 minutes)

Right side of swim platform (when on boat and facing

the water) at floor level

147 333

Left side of swim platform (when on boat and facing the

water) at floor level

123 260

On gate going to swim platform on back deck 1.3 5

On the right side of the rear portion of the back deck (at

floor level)

1.3 3
Page 5 - Mr. Bob Clark

Gasoline Generator and Gasoline Powered Outboard Motors Running 

(ran together for approximately 16 minutes)

On stairs going up to top deck (at breathing zone height) 14 24

On the top deck of boat 1.2 3

 On patio door on back deck 0.14 2

Crown Ship Pontoon Houseoat

During the morning on January 25, 2001, CO samples were collected on a Crown Ship pontoon

houseboat with the specifications listed below. During this evaluation, the gasoline generator

operated alone for approximately 33 minutes. Subsequently, the gasoline motors and generator

were operated together for approximately 25 minutes.

Engines: Two Outboard Johnson Motors (one 70 HP and one 60 HP)

Generator: 8.5 Kw Westerbeke, 1 liter gasoline generator

Exhaust Configuration: Generator exhaust out side of the boat.

Air speed off back deck: air speed readings ranged between 10-39 feet per

minute

Area around exhaust off back of houseboat

An evacuated glass container sample was collected in the area near the generator exhaust

discharge at the back of the houseboat when the generator was in operation (motors were not

operating). The sample was collected upstream of the wind movement near the exhaust and

indicated a CO concentration of 5 ppm. 

The emissions analyzer sampling probe was placed near the generator exhaust discharge. A total

of 14 readings were obtained (over a 19 minute period) when only the generator was in

operation. The recorded CO concentration ranged from 0.01% (100 ppm) to 0.47 % (4,700 ppm)

with an average of 0.22 % (2,200 ppm). A total of 17 CO concentration readings were obtained

near the generator exhaust discharge when the generator and engines were both in operation. 

These CO concentrations ranged from 0.00 % (0 ppm) to 0.31 % (3,100 ppm) with an average of

0.11 % (1,100 ppm). During brief periods, when the generator was in operation and CO

concentrations were high, the emissions analyzer would also indicate that the area directly

around the exhaust discharge was oxygen deficient (< 19.5 % O2 ).

Area Above Swim Deck on Back of Boat 

The prevailing wind direction was toward the front left corner of the rear deck (when on back of

boat and facing the water) and flowing across the back deck to the back right corner. The 
Page 6 - Mr. Bob Clark

generator exhaust was discharging out the right side of the houseboat (See Figure 4). Figure 5

shows a close-up view of the exhaust discharge. Table 2 lists the CO monitor results.

Table 2. Sample locations and CO results on the Crown Ship Pontoon Houseboat.

Location CO average (ppm) CO peak (ppm)

Only Generator Running (ran for approximately 33 minutes without motors operating)

Left side on rear portion of back deck on rail 23 73

Left side of the back deck (at floor level) 50 158

Right side of back deck (on generator box) 65 198

Center of back deck (on left portion of generator box) 43 140

Right side on rear portion of back deck 40 150

On the top deck of boat 5 29

 Inside the boat (patio door open) 14 56

Under front of boat between the pontoons 120 286

Generator and Motors Running (ran together for approximately 25 minutes)

Left side on rear portion of back deck on rail 24 56

Left side of the back deck (at floor level) 102 254

Right side of back deck (on generator box) 67 178

Center of back deck (on left portion of generator box) 68 323

Right side on rear portion of back deck 31 96

On the top deck of boat 6 18

 Inside the boat (patio door open) 8 21

Under front of boat between the pontoons 23 115

Summit Ship Pontoon Houseboat

During the mid-morning on January 25, 2001, CO samples were collected on a Summit Ship

pontoon houseboat with the specifications listed below. This houseboat was equipped with a

gasoline generator and motors. The generator was operated for approximately 29 minutes. 

Subsequently, the motors and generator were operated simultaneously for approximately 21

minutes. 
Page 7 - Mr. Bob Clark

Engines: Two 60 HP outboard Evinrude engines

Generator: 8.5 Kw Westerbeke, 1.0 liter - 4 cylinder gasoline generator

Exhaust Configuration: Generator exhausted out the side of the boat.

Air speed on left side of back deck: air speed readings ranged between 294 -

540 feet per minute on the back deck

Air speed on center of back deck: air speed readings ranged between 0 - 13 feet

per minute

Area around exhaust off back of houseboat and beneath swim deck

Two evacuated glass container samples collected up-wind of the generator exhaust discharge did

not detect CO. The exhaust discharge was located on the side of the boat in an area that could

not be easily accessed. Therefore, an evacuated container sample could not be collected close

the generator exhaust discharge. Detector tube samples could be collected near the exhaust

discharge. Two detector tubes collected close to the generator exhaust indicated CO

concentrations of approximately 3,000 ppm. An evacuated container sample was collected off

the back of the boat when the generator and engines were operating simultaneously. This sample

indicated a CO concentration of 253 ppm. See Figure 6 for exhaust discharge and back of

Summit Ship pontoon houseboat.

The emissions analyzer sampling probe was placed in the area directly near the generator

exhaust discharge. A total of 10 readings were obtained when the generator was in operation,

exclusively. The recorded CO concentration (obtained directly near the exhaust discharge)

ranged from 0.14 % (1,400 ppm) to 0.42 % (4,200 ppm) with an average of 0.33 % (3,300 ppm). 

A total of 15 readings were obtained when the generator and motors were in operation. The

recorded CO concentration (obtained directly near the exhaust discharge) ranged from 0.19 %

(1,900 ppm) to 0.71 % (7,100 ppm) with an average of 0.41 % (4,100 ppm). During brief

periods, when the CO concentrations were high, the emissions analyzer would also indicate that

the area directly around the exhaust discharge was oxygen deficient (< 19.5 % O2 ). 

Area Above Swim Deck on Back of Boat 

The wind velocity ranged between 294 - 540 fpm on the left side back deck of the houseboat (the

side the generator exhaust is located on). The prevailing wind direction was from the front of the

boat toward the back of the boat and flowing away from the back deck. Table 3 list the CO

monitor results.
Page 8 - Mr. Bob Clark

Table 3. CO results on the Summit Ship Pontoon Houseboat.

Location CO average (ppm) CO peak (ppm)

Only Generator Running (ran for approximately 29 minutes without motors operating)

On patio door 3 13

Left side of the back deck (on generator box) 17 166

Right side of back deck on gate (near stairs that lead

down to water)

3.5 16

Center of back deck 11 45

Right side on rear portion of back deck (on rail) 0.9 3

On the top deck of boat 1 2

 Inside the boat (patio door open) 1.8 2

Under front of boat between the pontoons 1 4

Generator and Motors Running (ran together for approximately 21 minutes)

On patio door 5 48

Left side of the back deck (on generator box) 12 61

Right side of back deck on gate (near stairs that lead

down to water)

10 22

Center of back deck 46 106

Right side on rear portion of back deck (on rail) 0.7 1

On the top deck of boat 0.9 1

 Inside the boat (patio door open) 1.8 2

Under front of boat between the pontoons 0.3 1

Grand Sierra Pontoon Houseboat #112

During the early afternoon of January 25, 2001, CO samples were collected again on the Grand

Sierra pontoon houseboat with the specifications listed below. The test on this houseboat were

repeated because of the environmental conditions (a storm was moving into the area) under

which the first test was conducted. During this evaluation, the gasoline generator operated alone

for approximately 32 minutes. Subsequently, the gasoline motors and generator were operated

together for approximately 23 minutes. 
Page 9 - Mr. Bob Clark

Engines: One outboard marine corporation (OMC) 70 HP Johnson motor, and 

one Evinrude 70 HP engine

Generator: 8.5 Kw Westerbeke, 4 cylinder, 1.0 liter gasoline generator

Exhaust Configuration: Generator exhaust discharged out to the side of the

houseboat. 

Wind speed above deck: air speed readings ranged between 390 - 660 feet per

minute

Area around exhaust and off back of houseboat

Figure 2 shows a portion of the back deck of the Grand Sierra pontoon houseboat, and illustrates

the generator exhaust discharging out the side. Figure 3 shows a close-up view of the exhaust

discharge, and warning label above the discharge, on the Grand Sierra Houseboat. 

One evacuated glass container sample was collected in the area near the generator exhaust

discharge. This sample indicated a CO concentration of 224 ppm. Two additional evacuated

container samples were collected while the generator and motors were in operation. One of

these samples was collected above the stairs (the stairs are located on the opposite side of the

back deck from the generator exhaust) that lead down to the water. This sample indicated a CO

concentration of 17 ppm. The other evacuated container sample was collected off the back of the

swim platform (on the right side when on the back of the boat and facing the water). This

sample indicated a CO concentration of 147 ppm. 

The emissions analyzer sampling probe was placed in the area directly near the generator

exhaust discharge of the houseboat. A total of 15 readings were obtained (over a 20 minute

period) when only the generator was in operation. The recorded CO concentration ranged from

0.02% (200 ppm) to 0.21 % (2,100 ppm) with an average of 0.08 % (800 ppm). A total of 13 CO

concentration readings were obtained near the generator exhaust discharge when the generator

and engines were both in operation. These CO concentrations ranged from 0.02 % (200 ppm) to

0.52% (5,200 ppm) with an average of 0.14 % (1,400 ppm). 

A detector tube sample collected in the area directly near the generator exhaust indicated CO

concentration of 4,000 ppm while the generator was in operation, exclusively. 

Area Above Swim Deck on Back of Boat 

The prevailing wind direction was moving from the front of the houseboat toward the back of the

of the houseboat. Therefore, the wind was moving away from the back deck. Table 4 lists the

CO monitor results obtained on the back of the Grand Sierra pontoon houseboat, with the

generator and motors operating. 
Page 10 - Mr. Bob Clark

Table 4. Sample locations and CO results on the Grand Sierra houseboat.

Location CO average (ppm) CO peak (ppm)

Only Gasoline Generator Running (ran for approximately 32 minutes without motors operating)

Right side of swim platform (when on boat and facing

the water) at floor level

95 363

On the left side of the rear portion of the back deck (on

rail)

0.2 1

On the right side of the rear portion of the back deck (on

rail)

3 3

On stairs going up to top deck (at breathing zone height) 5 19

On the top deck of boat 0.5 11

On patio door on back deck 0.7 2

Inside boat (back door open) 0.8 1

In front of boat between the pontoons 0.15 2

Gasoline Generator and Gasoline Powered Outboard Motors Running 

(ran together for approximately 23 minutes)

Right side of swim platform (when on boat and facing

the water) at floor level

130 212

On the left side of the rear portion of the back deck (on

rail)

0.02 1

On the right side of the rear portion of the back deck (on

rail)

3 3

On stairs going up to top deck (at breathing zone height) 5 27

On the top deck of boat 0.13 3

On patio door on back deck 1.3 3

Inside boat (back door open) 0.9 1

In front of boat between the pontoons No CO Detected
Page 11 - Mr. Bob Clark

Discussion and Recommendations

The Seven Crown Resorts houseboats evaluated at Echo Bay Marina were designed as pontoon

boats with the generator exhaust discharging out to the side. The back of the houseboats did not

have slides, and the stairs leading down to the water were located on the opposite side of the boat

away from the generator exhaust. Warning CO labels were located on the back of the boat and

directly above the generator exhaust discharge (see Figures 3, 5, and 6). These design features

help deter individuals from spending time directly near the generator exhaust discharge area. 

During our evaluation at Echo Bay Marina the prevailing wind was moving the exhaust gases

away from the back of the houseboats and not toward the back decks. Therefore, no extremely

high CO concentrations (CO concentrations above the NIOSH IDLH value of 1,200 ppm4) were

measured on the back of the houseboats. IDLH environments were measured with detector

tubes and the emissions analyzer directly near the generator exhaust discharge. Therefore, the

possibility of high CO concentrations may exist under environmental conditions that would carry

the exhaust gases toward the back of the houseboat. A previous study has documented that the

area around the back deck of houseboats can be hazardous under certain environmental

conditions (i.e., lack of air movement) when the generator or motors are in operation.1

Individuals swimming or working in the area directly near the generator exhaust (with the

gasoline generator in operation) could be exposed to extremely high CO concentrations resulting

in CO poisoning or death within a short period of time. 

This evaluation was performed in January which is not in the prime operating season for

houseboats. Activities at the dock were slow, due to the low number of houseboat rentals. 

Therefore, personal sampling was not conducted. However, general recommendations are

provided to help control potential worker CO exposures. In addition, recommendations are

provided to reduce the potential for CO exposure around the generator exhaust and back deck on

houseboats. 

1) Public education efforts must immediately inform and warn all individuals (including boat

owners, renters, and dock workers) potentially exposed to these CO hazards. Public education

programs should continue until engineering control solutions that eliminate the problem are in

place. The pontoon boats evaluated during this study have a space between the pontoons in

which individuals may enter and swim. Individuals should be instructed that this is not a safe

practice and under certain environmental conditions (with the generator in operation) CO

concentrations could potentially be elevated in this area. This practice should be prohibited. 

An effort is being made to inform manufacturers of houseboats about the environmental data that

has been collected, and the related design concerns. On September 1, 2000, the National Park

Service (NPS) sent each of these manufacturers a letter informing them of the numerous deaths

that may be attributed to CO poisoning from houseboat generator and/or engine exhaust. In

these letters, the Park Service specifically pointed out that most of the deaths occurred when the

victim was either on the back deck or in the water near or under the swim platform. In addition

to this effort, the initial NIOSH letter describing the first evaluation of CO on houseboats at Lake
Page 12 - Mr. Bob Clark

Powell was also sent to 58 houseboat manufacturers.1

 This effort should be continued until all

manufacturers are aware of the problem and solutions are formulated to redesign and correct the

exhaust configuration. This should also include the redesigning of side-exhausting boats to help

eliminate CO problems when boats are tied together, or when someone is in the area where the

exhaust gases are expelled from the boat. An investigation was conducted at Lake Powell on a

houseboat with a generator exhaust design that discharged the exhaust gases through a stack well

above the upper deck of the houseboat away from occupied areas. This study indicates that the

exhaust gases can diffuse and dissipate into the atmosphere to relatively safe levels, prior to

reaching occupants on or near the houseboat.5

2) Previous investigations have indicated that boat mechanics can be exposed to high

concentrations of CO.1,2 Therefore, the feasibility and effectiveness of engineering controls

should be investigated to help control CO exposures to boat maintenance mechanics. If repairs

are conducted outside and at the boat dock (where electric power is easily available), the use of a

high volume fan or other air-moving device may be effective in preventing worker short-term

high-level exposures to CO. Research into potential engineering controls needs to be

accomplished to make sure that the workers’ are protected from CO and that any exhaust from

these controls is discharged into a well-ventilated area that is not occupied; therefore,

eliminating the possibility of individuals breathing the exhaust from the control device. 

3) Training about the severity of CO hazards in boating should be developed for marina

personnel, EMS providers, and hospital emergency department staff so that symptoms

experienced by either employees or other boat operators might be more easily associated with

exposures. This training should include both environmental data, as well as information about

the number and circumstances of CO poisonings on the lake. 

4) The U.S. NPS has launched an awareness program to inform boaters on Lake Powell about

boat-related CO hazards. This program included press releases, flyers distributed to boat and

dock-space renters, letters to boat owners, and verbal information included in the boat check-out

training provided for users of concessionaire rental boats. Similar information should be

distributed to boat and dock-space renters at Echo-Bay Marina. Verbal information should be

included in the boat check-out training provided for users of rental boats. Training about the

specific boat-related CO hazards provided to houseboat renters, should include specific

information about the circumstances and number of poisonings and deaths that have been

documented in previous CO evaluations.1

 The training should include anecdotal information

about deaths and near misses, and should specifically target warnings against entering areas near

the gasoline generator exhaust or immediately behind the back deck that may contain a lethal

atmosphere.
Page 13 - Mr. Bob Clark

Thank you for your cooperation with this investigation, and for providing important data related

to this serious issue. Please contact me at (513) 841-4387 if you have any questions regarding

this evaluation. Jane McCammon at (303) 236-6233 is an additional contact who can answer

any questions or concerns you may have regarding CO fatalities and poisoning incident reports

on houseboats. 

Sincerely, 

Ronald M. Hall, M.S. 

Industrial Hygienist 

Industrial Hygiene Section 

Hazard Evaluations and Technical 

 Assistance Branch 

 Division of Surveillance, Hazard 

 Evaluations and Field Studies

cc: Dick Powell, USNPS Safety Director

Lloyd Olson, USNPS

Norm Peterson, Arizona Department of Health

Courtney Casillas, Arizona Public Information Officer

Wayne Ball, Utah Department of Health

Ted Woolley, Utah Parks and Recreation

R.J. Doubt, US Coast Guard

Mike Kaas, USDOI, Office of Managing Risk and Public Safety

William Dickenson, Park Superintendent, Lake Mead National Recreation Area

Burt Byers, Public Affairs Officer, Lake Mead National Recreation Area

Allison Deeb, Safety Manager, Lake Mead National Recreation Area

Phillip Cappel, USCG

Tim Radtke, Industrial Hygienist, Department of Interior

Dr. Robert Baron

Char O’Bergh, NPS Glen Canyon National Recreation Area
Page 14 - Mr. Bob Clark

CO monitor placed

on left of swim

platform

CO monitor placed on

back of slide at breathing

zone height

CO monitor placed on right

 of swim platform

CO monitor placed on Top Deck 

of boat

CO monitor placed on stairs at

breathing zone height

Figure 1. Swim platform and back deck of a houseboat with general CO sample locations.

[This figure indicates the general locations of CO monitors during all houseboat evaluations

and is not a representation of a typical houseboat at Echo Bay Marina]
Page 15 - Mr. Bob Clark

Motors

Generator

Exhaust

Stairs

Figure 2. Back View of the Grand Sierra Pontoon Houseboat.
Page 16 - Mr. Bob Clark

Figure 3. Generator exhaust discharge on the Grand Sierra Pontoon Houseboat.
Page 17 - Mr. Bob Clark

Generator Exhaust Stairs

Emissions Analyzer Probe

Generator Exhaust

CO Warning

Label

Figure 4. Back view of the Crown Ship Pontoon Houseboat. 

Figure 5. Close-up view of the exhaust discharge on the Crown Ship Pontoon Houseboat. 
Page 18 - Mr. Bob Clark

Exhaust Discharge

CO Warning Label

Figure 6. Back deck of Summit Pontoon Houseboat.
Page 19 - Mr. Bob Clark

References

1. McCammon JB, Radtke, T [2000]. Letter of September 28, 2000, from J. McCammon,

National Institute for Occupational Safety and Health, Centers for Disease Control and

Prevention, Public Health Service, U.S. Department of Health and Human Services, and T.

Radtke, US Department of Interior, to Joe Alston, Park Superintendant, Glen Canyon National

Recreation Area, Page, Arizona.

2. Hall, RH, McCammon, JB [2000]. Letter of November 21, 2000, from R. Hall and J.

McCammon, National Institute for Occupational Safety and Health, Centers for Disease Control

and Prevention, Public Health Service, U.S. Department of Health and Human Services, to Joe

Alston, Park Superintendant, Glen Canyon National Recreation Area, Page, Arizona. 

3. Hall, RH,[2000]. Letter of December 18, 2000, from R. Hall, National Institute for

Occupational Safety and Health, Centers for Disease Control and Prevention, Public Health

Service, U.S. Department of Health and Human Services, to Dr. Rice Leach, Commissioner,

Cabinet for Health Services, Commonwealth of Kentucky, Department for Public Health,

Frankfort, Kentucky. 

4. NIOSH [2000]. Immediately dangerous to life and health concentrations. DHHS (NIOSH)

Publication NO. 2000-130, Pocket Guide to Chemical Hazards and other Databases., July.

5. Earnest, GS, Dunn, K, Hall, RH, McCleery, R, McCammon, JB [2001]. An Evaluation of and

Engineering Control to Prevent Carbon Monoxide Poisonings of Individuals on Houseboats. 

Division of Applied Research and Technology, National Institute for Occupational Safety and

Health, Centers for Disease Control and Prevention, Public Health Service, U.S. Department of

Health and Human Services. 
Page 20 - Mr. Bob Clark

Attachment 1

Health Effects of Exposure to Carbon Monoxide

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.(1-6) 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 ability of the blood to carry oxygen to the tissues by binding with the

hemoglobin to form carboxyhemoglobin (COHb). Blood has an estimated 210-250 times greater

affinity for CO than oxygen, thus the presence of CO in the blood can interfere with oxygen

uptake and delivery to the body. Once absorbed into the bloodstream, the half-life of bloodborne

CO at sea level and standard pressure is approximately five hours. This means that an initial

COHb level of 10% could be expected to drop to 5% in five hours, and then 2.5% in another five

hours. If oxygen is administered to the exposed person, as happens in emergency treatment, the

COHb concentration drops more quickly. 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. 

Altitude effects the toxicity of CO. With 50 ppm CO in the air, the COHb level in the blood is

approximately 1% higher at an altitude of 4,000 feet than at sea level. This occurs because the

partial pressure of oxygen (the gas pressure causing the oxygen to pass into the blood) at higher

altitudes is less than the partial pressure of CO. Furthermore, the effects of CO poisoning at

higher altitudes are more pronounced. For example, at an altitude of 14,000 feet, a 3% COHb

level in the blood has the same effect as a 20% COHb at sea level.(7)

References

1. 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. 

2. NIOSH [1977]. Occupational diseases: a guide to their recognition. Revised ed. Cincinnati,

OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for

Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH)

Publication No. 77-181.
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3. NIOSH [1979]. A guide to work-relatedness of disease. Revised ed. Cincinnati, OH: U.S.

Department of Health, Education, and Welfare, Public Health Service, Centers for Disease

Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No.

79-116.

4. Proctor NH, Hughes JP, Fischman ML [1988]. Chemical hazards of the workplace. 

Philadelphia, PA: J.B. Lippincott Company.

5. ACGIH [1996]. Documentation of threshold limit values and biological exposure indices. 

Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

6. NIOSH [1999]. Pocket guide to chemical hazards. Cincinnati, OH: U.S. Department of

Health and Human Services, Public Health Service, Centers for Disease Control, National

Institute for Occupational Safety and Health, DHHS (NIOSH) Publication No. 99-115. 

7. American Gas Association [1988]. What you should know about carbon monoxide. 

American Gas Association 1985 Operating Section Proceedings. American Gas Association,

Arlington, Virginia. 
Page 22 - Mr. Bob Clark

Attachment 2

Evaluation Criteria

Although NIOSH typically focuses on occupational safety and health issues, the Institute is a

public health agency, and cannot ignore the overlapping exposure concerns in this type of

setting. Lake Mead employees should be in a state of health typical of any industrial worker. 

Thus, occupational criteria for CO exposure are applicable to that group. The general boating

public, however, may range from infant to aged, be in various states of health and susceptibility,

and be functioning at a higher rate of metabolism because of increased physical activity. 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 carboxyhemoglobin.(1) The occupational

exposure limits noted below should not be used for interpreting general population exposures

because they would not provide the same degree of protection they do for the healthy worker

population. 

Occupational Exposure Criteria. As a guide to the evaluation of the hazards posed by

workplace exposures, NIOSH field staff employ environmental evaluation criteria for the

assessment of 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, or a pre-existing medical condition. 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. 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),(2) (2) the American Conference of

Governmental Industrial Hygienists’ (ACGIH®) Threshold Limit Values (TLVs®), (3) (3)

the legal requirements of the U.S. Department of Labor, Occupational Safety and Health

Administration (OSHA) Permissible Exposure Limits (PELs),(4) and (4) the American

Society of Heating, Refrigerating, and Air-ConditioningEngineers (ASHRAE) Standard

for ventilation for acceptable indoor air quality.(5) Employers are encouraged to follow

the more protective criterion listed.
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A TWA exposure refers to the average airborne concentration of a substance during a

normal 8-to-10-hour workday. Some substances have recommended short-term exposure

limits (STEL) or ceiling values which are intended to supplement the TWA where there

are recognized toxic effects from higher exposures over the short-term.

The NIOSH REL for CO is 35 ppm for full shift TWA exposure, with a ceiling limit of

200 ppm which should never be exceeded.(6,7) The NIOSH REL of 35 ppm is designed to

protect workers from health effects associated with COHb levels in excess of 5%.1

NIOSH has established the immediately dangerous to life and health (IDLH) value for

CO as 1,200 ppm.(8) An IDLH value is defined as a concentration at which an immediate

or delayed threat to life exists or that would interfere with an individual's ability to escape

unaided from a space.

The ACGIH recommends an eight-hour TWA TLV of 25 ppm based upon limiting shifts

in COHb levels to less than 3.5%, thus minimizing adverse neurobehavioral changes such

as headache, dizziness, etc, and to maintain cardiovascular exercise capacity.(9) ACGIH

also recommends that exposures never exceed 5 times the TLV (125 ppm). 

The OSHA PEL for CO is 50 ppm for an 8-hour TWA exposure.(10)

Health Criteria Relevant to the General Public. 

The US 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 one-hour average.(11) The NAAQs for CO was established

to protect “the most sensitive members of the general population” by maintaining

increases in carboxyhemoglobin to less than 2.1%. 

References

1. Kales SN [1993] Carbon monoxide intoxication. American Family Physician 48(6):1100-

1104.

2. 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. 

3. ACGIH [2000]. 2000 TLVs® and BEIs®: threshold limit values for chemical substances and

physical agents. Cincinnati, OH: American Conference of Governmental industrial Hygienists.

4. Code of Federal Regulations [1997]. 29 CFR 1910.1000. Washington, DC: U.S.

Government Printing Office, Federal Register.

5. Public Law 91 – 596 Occupational safety and Health Act of 1970, Sec. 5.(a)(1).
Page 24 - Mr. Bob Clark

6. CDC [1988]. NIOSH recommendations for occupational safety and health standards 1988. 

Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers

for Disease Control; National Institute for Occupational Safety and Health. MMWR 37

(supp. S-7).

7. Code of Federal Regulations [1989]. 29 CFR 1910.1000. Washington, DC: U.S.

Government Printing Office, Federal Register.

8. NIOSH [2000]. Immediately dangerous to life and health concentrations. DHHS (NIOSH)

Publication NO. 2000-130, Pocket Guide to Chemical Hazards and other Databases., July.

9. ACGIH [1992]. Threshold limit values and biological exposure indices for 1992-1993. 

Cincinnati, OH: American Conference of Governmental Industrial Hygienists.

10. 29 CFR 1910.1000 Table Z-1: Limits for air contaminants. Code of Federal Regulations,

Department of Labor, Chapter XVII - Occupational Safety and Health Administration. 

11. US Environmental Protection Agency [1991]. Air quality criteria for carbon monoxide. 

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