TM

NIOSH HEALTH HAZARD EVALUATION REPORT 

HETA #2002-0014-2958 

U.S. Department of Transportation 

St. Lawrence Seaway Development Corporation 

Massena, New York 

March 2005 

DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention 

National Institute for Occupational Safety and Health

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

This Health Hazard Evaluation (HHE) report and any recommendations made herein are for the specific facility evaluated and may not be universally

applicable. Any recommendations made are not to be considered as final statements of NIOSH policy or of any agency or individual involved.

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports

Additional HHE reports are available at http://www.cdc.gov/niosh/hhe/reports
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 Jeffrey Nemhauser, MD, and Lynda Ewers, PhD, CIH, of HETAB, Division 

of Surveillance, Hazard Evaluations and Field Studies (DSHEFS). Field assistance was provided by Brian 

Curwin, Bradley King, Ann Krake, and Ashok Nimgade. Analytical support was provided by Ardith A. 

Grote and Daniel Lewis of NIOSH and DataChem Laboratories. Desktop publishing was performed by 

Ellen Blythe and Robin Smith. Editorial assistance was provided by Ellen Galloway. 

Copies of this report have been sent to employee and management representatives at the St. Lawrence 

Seaway Development Corporation (SLSDC) 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 3 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.
iii 

Highlights of the Health Hazard Evaluation

Highlights of the NIOSH Health Hazard Evaluation

Evaluation of Airborne Exposures and Health Effects Among 

Lock Maintenance Workers

In October 2001 the National Institute for Occupational Safety and Health (NIOSH) received a joint 

labor/management request for a health hazard evaluation (HHE) at the Eisenhower and Snell Locks on the St. 

Lawrence Seaway, Massena, New York. The request described “flu-like symptoms” and “general ill health” among 

workers exposed to stagnant water and decaying marine life during the annual winter inspection, cleaning, and 

repairs of the locks. 

What NIOSH Did

 We looked at maintenance and repair activities in 

the Snell and Eisenhower Locks. 

 We took air samples for endotoxins, hydrogen 

sulfide (H2S), carbon monoxide (CO), and volatile 

organic compounds (VOCs). All of these were 

possible causes of some of the respiratory symptoms 

in the lock workers. 

 We interviewed 27 lock maintenance workers 

and asked them about their health. We also looked at 

medical records of some workers. 

What NIOSH Found

 Lock maintenance workers are potentially 

exposed to endotoxins, H2S, and VOCs. However, 

short-term respiratory illness due to these exposures 

is unlikely. Concentrations of CO were low. 

 NIOSH considers the locks to be confined spaces 

when maintenance work is done. 

 Most of the 27 workers described a respiratory 

illness, including bronchitis, pneumonia, or an 

aggravation of their asthma. However, since so few 

workers participated, we 

cannot draw conclusions whether there is a 

relationship between winter work activities and the 

risk of developing short-term respiratory illnesses. 

What St. Lawrence Seaway Development Corporation 

Managers Can Do 

 Continue to check for H2S during lock 

maintenance, especially where there are barriers to the 

free flow of air and during concrete chipping activities. 

 Increase general ventilation in the locks to further 

reduce H2S concentrations. 

 Winter work employees should receive medical 

clearance before returning to work following a 

hospitalization, a severe respiratory illness, or while 

taking prescription medications. 

 Develop a confined space entry plan following 

NIOSH recommendations.

What the St. Lawrence Seaway Development 

Corporation Employees Can Do 

 Tell your supervisor if you have been ill or have 

had a medical procedure before you return to 

maintenance or repair work in the locks. 

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 #2002-0014-2958
ii 

Health Hazard Evaluation Report 2002-0014-2958 

U.S. Department of Transportation 

St. Lawrence Seaway Development Corporation 

Massena, New York 

March 2005 

Jeffrey B. Nemhauser, MD 

Lynda Ewers, PhD, CIH

SUMMARY

In October 2001, the National Institute for Occupational Safety and Health (NIOSH) received a joint 

labor/management request to conduct a health hazard evaluation (HHE) at the Dwight D. Eisenhower and 

Bertrand H. Snell Locks on the St. Lawrence Seaway, near Massena, New York. The request described 

“flu-like symptoms” and “general ill health” as concerns among workers exposed to stagnant water and 

decaying marine life during the annual winter inspection, cleaning, and repairs of the locks. Another 

impetus for the request was the collapse of one worker at the bottom of a lock during the previous winter. 

During site visits in 2002 and 2003, NIOSH investigators collected personal breathing zone (PBZ) and 

area air samples for endotoxins, hydrogen sulfide (H2S), carbon monoxide (CO), crystalline silica, and 

volatile organic compounds (VOCs). Endotoxin concentrations above relative limit values were measured 

on two workers. However, because these employees (both painters) left the worksite while wearing the 

monitoring equipment during part of their work shift, the exposures cannot be said to be work related. 

Peak PBZ H2S concentrations up to 87 parts per million (ppm) were measured while workers used 

pneumatic drills and jack hammers to remove deteriorating concrete from lock walls; the NIOSH 

recommended ceiling value is 10 ppm. Concentrations of CO, crystalline silica, and VOCs were below 

applicable NIOSH and OSHA occupational exposure limits. NIOSH investigators also concluded that the 

locks are confined spaces. 

NIOSH investigators identified 71 employees as having regular or intermittent exposure to the locks 

during winter work; 27 were interviewed or had information in their medical records that could be 

abstracted to identify disease trends or patterns. Most of the 27 workers reported a history of respiratory 

illness including bronchitis, pneumonia, or an aggravation of their asthma while working on the locks. 

Although several workers provided a history of seeing their health care provider for a winter illness, only 

two provided a history of having been hospitalized. Given the small percentage of workers who 

participated in this study, we cannot draw conclusions about the relationship between winter work 

activities and the risk of developing acute respiratory illnesses. 

NIOSH investigators conclude that some employees conducting winter work at the 

Dwight D. Eisenhower and Bertrand H. Snell Locks on the St. Lawrence Seaway are 

exposed to endotoxins, H2S, and VOCs. Acute respiratory illness due to H2S or VOC 

exposures at the levels measured during the NIOSH evaluation is unlikely. 

Recommendations are provided to consider the locks as confined spaces and to increase 

the ventilation inside the locks while winter work activities are conducted. 

Keywords: SIC 4432 (Freight Transportation on the Great Lakes-St. Lawrence Seaway), seaway locks, 

construction, confined space, maintenance, endotoxins, hydrogen sulfide, carbon monoxide, crystalline 

silica
Table of Contents 

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

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

Highlights of the Health Hazard Evaluation ...........................................................................................iii

Summary......................................................................................................................................................ii

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

Background .................................................................................................................................................1

St. Lawrence Seaway ..............................................................................................................................1

Lock Inspection and Repair...................................................................................................................2

Confined Space Entry.............................................................................................................................3

Worker-Reported Health Effects ..........................................................................................................3

Methods........................................................................................................................................................3

Industrial Hygiene ..................................................................................................................................3

Endotoxins ...........................................................................................................................................3

Hydrogen Sulfide and Carbon Monoxide.........................................................................................4

Crystalline Silica .................................................................................................................................4

Volatile Organic Compounds.............................................................................................................4

Medical.....................................................................................................................................................5

Employee Interviews...........................................................................................................................5

Medical Record Review......................................................................................................................5

Evaluation Criteria .....................................................................................................................................5

Endotoxins ...............................................................................................................................................6

Hydrogen Sulfide ....................................................................................................................................6

Carbon Monoxide ...................................................................................................................................7

Crystalline Silica .....................................................................................................................................7

Volatile Organic Compounds.................................................................................................................8

Confined Space Entry.............................................................................................................................8

Results ..........................................................................................................................................................8

Industrial Hygiene ..................................................................................................................................8

Endotoxins ...........................................................................................................................................8

Area Samples.......................................................................................................................................9
Hydrogen Sulfide ................................................................................................................................9

Carbon Monoxide ...............................................................................................................................9

Silica .....................................................................................................................................................9

Volatile Organic Compounds.............................................................................................................9

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

Medical.....................................................................................................................................................9

Confidential Interviews and Medical Record Review ...................................................................10

Discussion/ Conclusions............................................................................................................................10

Recommendations.....................................................................................................................................12

References..................................................................................................................................................13

Appendix A..................................................................................................................................................6
Health Hazard Evaluation Report No. 2002-0014-2958 Page 1 

INTRODUCTION

On October 5, 2001, the National Institute for 

Occupational Safety and Health (NIOSH) 

received a joint labor/management request to 

conduct a health hazard evaluation (HHE) at the 

Dwight D. Eisenhower and Bertrand H. Snell 

Locks on the St. Lawrence Seaway, near 

Massena, New York. The request described “flulike symptoms” and “general ill health” as 

concerns among workers exposed to stagnant 

water and decaying marine life during the annual 

winter inspection, cleaning, and repair of these 

locks. During initial discussions with the 

requestors, NIOSH investigators learned that 

employees had experienced these adverse health 

effects for years prior to the submission of this 

HHE request. Subsequent discussions revealed 

that the main impetus for submitting this HHE 

request was the collapse of one worker at the 

bottom of a lock while participating in the 

previous year’s winter maintenance. 

Maintenance work on the locks occurs each year 

from December until late March or early April. 

During this time, the Seaway is closed to 

nautical traffic. From January 16–17, 2002, 

NIOSH industrial hygienists and medical 

officers visited the Snell Lock and conducted 

voluntary health surveys with available 

employees. NIOSH investigators returned to the 

Snell Lock on February 25–28, 2002, to carry 

out an industrial hygiene survey, during which 

time they collected personal breathing zone 

(PBZ) and general area air samples over one 8-

hour shift. NIOSH investigators screened for the 

presence of (and worker exposure to) airborne 

endotoxins and volatile organic compounds 

(VOCs), compounds that could cause the 

reported “flu-like symptoms” or “general ill 

health.” Endotoxins, substances released from a 

type of bacteria, are expected to be present in 

environments containing rotting organic matter; 

VOCs are released from oil-fueled furnaces or 

from the by-products of various maintenance 

activities such as welding and painting. Both are 

known to cause adverse respiratory effects in 

humans. 

One year later (February 3–6, 2003) NIOSH 

investigators returned to Massena to conduct an 

industrial hygiene evaluation at the Eisenhower 

Lock. Area and PBZ endotoxin samples were 

collected. Investigators measured “real time” 

levels of hydrogen sulfide (H2S) and carbon 

monoxide (CO); exposure to sufficiently high 

levels of either of these gases can result in a 

worker’s collapse. In response to a 

supplementary management request, NIOSH 

investigators measured exposure to crystalline 

silica among workers using pneumatic drills and 

jack hammers to remove deteriorating concrete 

from lock walls. NIOSH investigators also 

collected area and PBZ air samples for VOCs. 

BACKGROUND

St. Lawrence Seaway 

Eight locks exist between Lake Ontario (to the 

west) and the Gulf of St. Lawrence (to the east), 

where the St. Lawrence River flows into the 

Atlantic Ocean. Six of these eight locks are 

owned and operated by the Canadian 

government. Two locks, the Dwight D. 

Eisenhower and the Bertrand H. Snell, are 

owned, operated, and maintained by the St. 

Lawrence Seaway Development Corporation 

(SLSDC), which is subject to the policy 

direction and supervision of the United States 

Department of Transportation (DOT). These two 

locks are the focus of this investigation. 

Each of the U.S. owned locks measures 

approximately 900 feet (ft) in length (L), 50 ft in 

width (W), and 110 ft in depth (D). Water levels 

within the lock are regulated by two sets of 

valves. Refilling a lock after the normal 

operation of lowering a vessel requires 20 

million gallons of water and takes approximately 

9 minutes to complete. Water turbulence 

associated with this rate of flow is reduced by 

channeling the water through 12 ft (D) by 14 ft 

(W) culverts that run alongside the locks. Water 

enters the main chamber of the lock through 

ports spaced intermittently along common walls 

shared by the culverts and the lock. 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 2 

Lock Inspection and Repair 

During most of the year, SLSDC employees 

operate the locks. From mid- to late December 

until the end of March, when the Seaway is 

closed to traffic, about 70 – 80 of the SLSDC 

workers inspect, clean, and repair the locks, 

generally working a single 8-hour shift (0730 – 

1600), 5 days a week. Workers are permitted 

two 15-minute breaks per shift plus a 5-minute 

wash period before each break. They leave the 

job site to take showers at 1530. Although a 

second shift may be added to complete specific 

time-dependent tasks, work was confined to the 

first shift only during the NIOSH site visits. 

SLSDC management schedules extensive repair 

projects to occur in only one lock in any given 

year. Any worker may be called upon to perform 

a variety of tasks and most workers can rotate 

jobs as necessary. Skilled trades represented on 

the job site include millwrights (who maintain 

and troubleshoot machinery), carpenters, 

electricians, pipe-fitters, and painters. 

In preparation for winter work, the locks are first 

dewatered and then partially enclosed with 

plastic sheeting and plywood barriers and 

covered with corrugated sheet metal. Two 1.5 

million British Thermal Unit (BTU) furnaces 

fueled by #8 fuel oil provide heat for the general 

lock area; furnace stacks extend through the 

sheet metal roofs covering the locks. Propane 

heaters provide supplemental heat in some of the 

more remote areas of the locks. Direct-reading 

CO monitors are installed throughout the work 

environment. 

A major task of winter work involves dislodging 

zebra mussels (Dreissena polymorpha) from all 

structures within the lock that are under water 

during the open season. Zebra mussels, an 

opportunistic species of freshwater bivalve 

mollusk native to Eastern Europe, are believed 

to have been introduced into the Great Lakes in 

the mid- to late 1980s. Shortly thereafter, they 

were found at Snell Lock on the St. Lawrence 

Seaway,1

 within locks in the greater Niagara 

region including Black Rock Lock in Buffalo, 

New York,2

 and in the upper Mississippi River 

at Lock and Dam 6 in Trempealeau, Wisconsin.3

By the winter of 1990 – 1991, Snell Lock was 

reported to be infested by zebra mussels.1

 By 

1992, nearly all underwater structures within 

Black Rock Lock, including those made of 

concrete, steel, granite, oak, and polyvinyl 

chloride pipe were infested by the same species. 

Layers of mussels as much as 4 inches thick 

were recorded at Black Rock Lock.2

 In 1993, 

following dewatering and during completion of 

routine maintenance, personnel at Black Rock 

Lock noticed that areas not cleaned by the sweep 

of the gates had a 3- to 4-inch coating of live and 

dead mussels; behind the lock gates, zebra 

mussel debris measured 10 to 12 inches deep. 

By the winter of 1991 – 1992, numbers of zebra 

mussels at Snell Lock had reportedly decreased 

while at Eisenhower Lock, located 

approximately 3 miles upstream from Snell 

Lock, the numbers had increased significantly.1

As was the case at Black Rock Lock, zebra 

mussels found at Eisenhower Lock covered the 

walls, floor, sills, miter gates, and cables. 

Workers most commonly found colonies of 

mussels on damaged concrete, but intact 

concrete, wood, and painted metal surfaces were 

also infested with mussels either in clusters of 

50 – 150, or singly.1

 Despite the large numbers 

of zebra mussels present within the locks on the 

St. Lawrence Seaway, workers reportedly found 

no interference with the proper operation of 

gates, with water flow or pressure, or with 

water-level sensing equipment.1

 

While the population explosion of zebra mussels 

has caused extensive “biofouling” of the waterintensive industries throughout the Great Lakes 

region, during the second NIOSH site visit 

investigators observed noticeably fewer 

mollusks within the locks. According to 

management, indigenous fish had learned to eat 

zebra mollusks and this predation had apparently 

greatly reduced the numbers of mussels. 

Workers usually clean the locks and the lock 

gates with brushes or scraping tools without 

using any chemical cleaning agents. In addition 

to zebra mussel removal, lock maintenance 

involves repairing metal and concrete structures 

within the locks. Structural repair to the metal 

components of the locks involves cutting, 

burning, and welding (both Metal Inert Gas 

[MIG] welding and Tungsten Inert Gas [TIG] 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 3 

welding). Incomplete clearing of zebra mussels 

can result in their incineration during burning 

and welding. 

Repairing the concrete walls of the lock and 

culverts often requires use of pneumatic drills 

and jack hammers to remove spalling and 

deteriorating concrete, a task performed by 

“chippers.” Once crumbling concrete is 

removed, plywood forms are installed, and 

ready-mix cement is used to fill the repairs. The 

Eisenhower Lock, made of locally acquired 

natural Portland cement, is structurally less 

sound and requires more frequent and extensive 

concrete repair than the Snell Lock, which is 

made of manufactured Portland cement. 

SLSDC management had already identified 

worker exposure to crystalline silica from 

concrete as a potential health problem. In 

response, they initiated employee training and 

the use of personal protective equipment (PPE) 

to minimize silica exposures. The PPE used by 

employees during winter work includes powered 

air purifying respirators (PAPRs) with high 

efficiency filters, elastomeric half-mask 

respirators, or welding hoods, depending on the 

nature of the work being done. Other protective 

equipment used by SLSDC employees includes 

eyewear, gloves, coveralls, and galoshes. 

Confined Space Entry 

In addition to the potential hazards identified by 

management and labor representatives in their 

HHE request, NIOSH investigators identified 

both the Snell and Eisenhower Locks as 

confined spaces. At first, the locks did not 

appear to meet the definition of a typical 

confined space. For example, when dewatered, 

most working areas are very large and 

employees engage in their normal activities 

unhindered and unencumbered. Nevertheless, 

entry into and egress from the locks is via 

temporary scaffolding descending over 100 feet, 

and even the largest areas are not designed for 

continuous human occupancy, thus satisfying 

two important NIOSH criteria in the definition 

of a confined space.4

Worker-Reported Health Effects 

According to the HHE requestors, workers begin 

to experience “flu-like symptoms” and “general 

ill health” approximately 1 month after the onset 

of winter work, a pattern that has been observed 

over many years. The requestors stated that 

worker health typically worsens during the 

season and then gradually improves following 

the reopening of the Seaway. Although the 

requestors reported to NIOSH investigators that 

employees had been diagnosed with 

occupational asthma, the percentage of workers 

affected was not known since employees are 

seen by their private physicians. Management 

and employee representatives both suggested to 

NIOSH investigators that exposure to rotting 

and decaying marine life at the bottom of the 

locks following drainage is a possible cause of 

worker symptoms. Because zebra mussels are so 

numerous, and the odor from their decay so 

noticeable, much attention has been focused on 

them by management and employees as an 

explanation for the workers’ illness. 

METHODS

Industrial Hygiene 

Endotoxins 

Samples were collected on tared 5.0 micrometer 

(μm) pore size, 37 millimeter (mm) polyvinyl 

chloride filters using a calibrated flow rate of 2 

liters per minute (L/min). The filters were 

subsequently analyzed for endotoxin content using 

the Kinetic-QCL Limulus Amebocyte Lysate 

(LAL) assay kit (BioWhittaker, Walkerville, 

Maryland) according to the manufacturer’s 

recommended procedures. For these analyses, 10 

endotoxin units (EU) are equivalent to 1 nanogram 

of endotoxin. 

In 2002, NIOSH investigators measured levels of 

exposure to endotoxins among SLSDC employees 

in the Snell Lock by collecting seven full-shift PBZ 

air samples from five welders and two painters. 

Ten area air samples were obtained and, for 

comparison, five background air samples were also 

collected. 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 4 

In 2003, NIOSH investigators collected full-shift 

PBZ air samples from two painters, three chippers, 

one pipe-fitter, and two fender pit maintenance 

workers in the Eisenhower Lock. Three area air 

samples were collected. For comparison, four 

background air samples were obtained and 

analyzed. 

Hydrogen Sulfide and Carbon 

Monoxide 

The Toxi Ultra single sensor gas detector 

(Biosystems Inc.) provides real time monitoring 

for the presence of H2S and CO in the 

environment. As with most direct reading 

instruments, however, the possibility exists for 

compounds in the environment to interfere with 

the Toxi Ultra’s electrochemical sensors, 

resulting in erroneously high or low readings. 

Two gases reported by the instrument 

manufacturer to have such an effect on H2S 

measurements are nitrogen dioxide and chlorine, 

both of which can reduce the H2Ssignal by about 

20%.5

 CO concentration signals may be 

increased by the presence of H2S, sulfur dioxide, 

nitrous oxide, chlorine gas, hydrogen gas, 

hydrogen cyanide, and hydrogen chloride. 

In 2003 at the Eisenhower Lock, NIOSH 

investigators collected PBZ samples for H2S 

from three chippers, one painter (sampled on 2 

days), and a fender pit maintenance worker. Two 

area air samples for H2S were also collected. 

Samples for CO were collected from two 

painters and a pipe-fitter, in addition to one area 

sample. 

Crystalline Silica 

Samples of crystalline silica were collected on 

37-mm polyvinyl chloride filters using a 10-mm 

nylon cyclone pump calibrated at 1.7 L/min flow 

rate. Sample analysis was performed using x-ray 

diffraction with a Siemens Model D5000 

Diffractometer. Samples were analyzed using 

the NIOSH Manual of Analytical Methods 

(NMAM) Method 7500 with modifications.6

Analytical method modifications were as 

follows: 1) filters were dissolved in 

tetrahydrofuran rather than by furnace ashing, 

and 2) standards and samples were run 

concurrently and an external calibration curve 

was prepared using peak heights rather than the 

suggested normalization procedure. 

Crystalline silica PBZ air samples were 

collected in 2003 from three workers who used 

pneumatic drills and jack hammers to remove 

deteriorating concrete from the Eisenhower 

Lock walls. In addition, two area samples for 

crystalline silica were collected within the area 

where chipping took place. 

Volatile Organic Compounds 

For qualitative VOC sample collection, NIOSH 

investigators routinely use stainless steel thermal 

desorption (TD) tubes that contain three beds of 

sorbent material (designated as “type I” tubes in 

this report). For this HHE, however, a second 

type of thermal desorption tube (“type II” tube) 

was also used to collect VOC samples. Type II 

tubes more accurately measure reactive 

compounds such as sulfur compounds and 

possibly amines, both of which are expected to 

be produced by decomposing mollusks. 

Each TD tube was attached to a sampling train 

and pump calibrated at a flow rate of 50 

milliliters per minute (mL/min). Type I tubes 

were stainless steel with three compartments 

containing CarbopackTM Y, CarbopackTM B and 

CarboxenTM 1003 sorbents. Type II tubes were 

SulfinertTM-coated stainless steel tubes, which 

contain only two beds of sorbent material, a 

front bed of TenaxTM TA sorbent, and a back 

bed of SpherocarbTM. All TD tube samples were 

desorbed in a Perkin-Elmer® ATD 400 system at 

300 degrees Celsius ( ̊C). The thermal unit was 

interfaced directly to an HP5890A gas 

chromatograph with a HP5970 mass selective 

detector. A 30 meter DB-1 fused silica capillary 

column was used for analyses. 

During general area air sampling conducted in 

2002 at the Snell Lock, NIOSH investigators 

collected qualitative side-by-side VOC samples 

using both of the above-described TD tubes. 

Samples were then analyzed to identify the 

major VOC species present in the lock. In 2003, 

quantitative sampling for VOCs within the 

Eisenhower Lock was performed using charcoal 

tubes to measure the major VOC species 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 5 

identified by the qualitative TD screening 

conducted the previous year. Samples collected 

from three painters and one pipe-fitter were 

analyzed for toluene, methyl isobutyl ketone 

(MIBK), propylene glycol monomethyl ether 

acetate (PGMEA), and xylenes. All samples 

were analyzed using NIOSH Methods 1501, 

1550, and the OSHA Chemical Information 

Manual modified by using gas chromatography 

with a capillary column and oven conditions and 

carrier gas flow rates varied to achieve 

separation of compounds.6

 

Medical 

Employee Interviews 

During the first site visit to Massena, two 

NIOSH medical officers conducted confidential 

employee interviews with available workers who 

volunteered to participate in this survey. 

Interview questions included the employee’s 

age, the number of years the employee had 

worked at the lock doing winter work, and the 

symptoms, if any, the employee experienced 

during the winter. 

Medical Record Review 

In addition to conducting confidential employee 

interviews, the principal NIOSH medical officer 

also obtained written consent from employees to 

request medical records from their individual 

health care providers. The NIOSH medical 

officer specifically requested records relating to 

the diagnosis, treatment, and follow-up of 

respiratory diseases (including bronchitis, 

pneumonia, and asthma) or any “flu-like 

illnesses” acquired by the employee in January, 

February, or March. Any records of these 

illnesses, regardless of the year of diagnosis, 

were requested. 

EVALUATION CRITERIA

As a guide to the evaluation of the hazards posed 

by workplace exposures, NIOSH field staff use 

environmental evaluation criteria to assess 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, 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, and thus potentially 

increase 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),7

 (2) the American Conference of 

Governmental Industrial Hygienists’ (ACGIH®) 

Threshold Limit Values (TLVs®),8

 and (3) the 

U.S. Department of Labor, Occupational Safety 

and Health Administration (OSHA) Permissible 

Exposure Limits (PELs).9

 Employers are 

encouraged to follow the NIOSH RELs, the 

ACGIH TLVs, the OSHA limits, 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 

[Occupational Safety and Health Act of 1970, 

Public Law 91–596, sec. 5(a)(1)]. Employers 

should understand that not all hazardous 

chemicals have specific OSHA exposure limits 

such as PELs and short-term exposure limits 

(STELs). However, an employer is still required 

by OSHA to protect their employees from 

hazards, even in the absence of a specific OSHA 

PEL. 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 6 

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. 

Endotoxins 

Gram negative bacteria (GNB), the source of 

endotoxins, are found everywhere in the 

environment. Endotoxins, lipopolysaccharide 

compounds found within the outer cell wall of 

GNB, are released from the cell wall when the 

bacteria die.10,11 In experimental studies, human 

volunteers inhaling high concentrations of 

endotoxins experienced airway and alveolar 

inflammation as well as chest tightness, fever, and 

malaise, and had acute reductions in lung function, 

as measured by the forced expiratory volume in 1 

second (FEV1).12,13 Airborne endotoxin exposures 

between 45 – 400 endotoxin units per cubic meter 

of air (EU/m3

) are associated with acute airflow 

obstruction, mucous membrane irritation, chest 

tightness, cough, shortness of breath, fever, and 

wheezing.11,14,15,16 Chronic health effects associated 

with airborne endotoxin exposure include chronic 

bronchitis, bronchial hyper-reactivity, chronic 

airway obstruction, hypersensitivity pneumonitis, 

and emphysema. Permanent decreases in 

pulmonary function, along with respiratory 

symptoms, have been reported in several crosssectional epidemiological studies.

Although endotoxins have come to be accepted as a 

cause of adverse human health effects, no doseresponse relationship has yet been established due 

to problems with analytical methods. Until the 

problems are resolved, comparison of samples 

collected at different times or analyzed by different 

laboratories is not considered valid. For these 

reasons, ACGIH has proposed using relative limit 

values (RLVs), rather than the more usual TLVs as 

evaluation criteria for concentrations of 

endotoxins in the environment. 

To measure RLVs, air samples must be 

collected from the area of interest and from an 

area representative of background levels of 

endotoxins in the local environment. These 

samples are then analyzed at the same time. The 

RLV is expressed as a comparison (or ratio) 

between the endotoxin level measured in the 

area of interest and the background endotoxin 

level. ACGIH has proposed that if the level of 

endotoxin exposure within the area of interest 

exceeds the level of endotoxin measured in the 

background by a factor of 10 (and if there are 

health effects consistent with endotoxin 

exposure) then the RLV action level has been 

exceeded. When exposures exceed the RLV 

action level, actions to remediate endotoxins are 

recommended. It is important to note that the 

nature of the relationship between the RLV and 

adverse human health effects has not been 

elucidated at the time of writing this report.

Hydrogen Sulfide 

Hydrogen sulfide (H2S), also called swamp gas 

or sewer gas, is highly flammable and a 

dangerous fire hazard. It is the leading cause of 

sudden death in the workplace.17,18 A naturally 

occurring gas released by volcanoes and hot 

springs, H2S is also formed by bacteria, fungi, 

and other microorganisms that live on decaying 

organic matter.19 Entering confined spaces 

where decaying organic matter is abundant (e.g., 

a dewatered lock) without proper monitoring 

equipment or respiratory protection is potentially 

dangerous. 

People are generally exposed to H2S through the 

air that they breathe, and it may also be absorbed 

through the skin; oral exposures are not an 

important route of intoxication.17,19 H2S is 

colorless and has the odor of rotten eggs. 

Because of its characteristic odor, people are 

usually able to smell this gas at low 

concentrations in the air ranging from 0.0005 to 

0.3 parts per million (ppm).19 In urban areas, the 

concentration of H2S derived from natural 

sources that can be measured in the air is 

generally less than 1 part per billion (ppb; one 

one-thousandth of a ppm).19 In communities 

situated near natural or industrial sources of 

hydrogen sulfide, however, air levels of 90 ppb 

or greater have been measured.19 Although H2S 

can be detected by its smell at 90 ppb, at this 

concentration it is still several orders of 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 7 

magnitude below the level reported to cause 

adverse health effects. 

At concentrations of 100 – 150 ppm (and above) 

H2S rapidly damages the nasal cells responsible 

for the sense of smell and people lose their 

ability to smell the characteristic odor of this 

toxic gas.8,19 Moreover, it is at these higher 

concentrations that H2S becomes a recognized 

human health hazard. And, since damage to the 

cells of the nose occurs very quickly, the 

inability to detect the odor of H2S at high 

concentrations makes exposure to this gas 

dangerous. Human data indicate that the organs 

most sensitive to the effects of H2S at higher 

levels of exposure are the nervous system, the 

respiratory tract, and the eyes.8,17,18,19

Acute exposures to H2S concentrations of 

greater than 500 ppm (lasting for less than 1 

hour) cause unconsciousness followed by 

apparent recovery.19 H2S causes serious acute 

damage to the human respiratory tract, 

especially at very high concentrations of 

exposure. At lower concentrations, H2S acts as 

an irritant to the respiratory tract. Low level 

exposures may be responsible for nasal 

irritation, sore throat, cough, shortness of breath, 

and increased visits to the hospital emergency 

room due to breathing problems (including 

asthma).19 People with asthma may be more 

sensitive than others to the effects of H2S; in 

studies of non-asthmatic workers exposed to 

H2S, scientists found no changes in their lung 

function.19 

Like the lungs and the brain, the eyes are also 

sensitive to the effects of H2S exposure.8,17,19

Conjunctivitis and keratitis (eye irritation and 

inflammation) have been reported to occur at air 

concentrations of H2S ranging from 5 to 30 

ppm.8,18 A 1-hour exposure to concentrations of 

H2S ranging between 50 and 100 ppm may 

produce worsening eye irritation with pain, 

tearing (lacrimation), and increasing sensitivity 

to light (photophobia).8,18 

Chronic headaches, fatigue, dizziness, 

irritability, and loss of libido are all examples of 

health effects reportedly due to long-term, lowlevel H2S exposure.8

 However, adequate studies 

have not been conducted to identify whether 

exposures to H2S at concentrations less than 20 

ppm may cause the reported adverse health 

effects.8,18 Health effects attributed to long-term, 

low-level exposures could result instead from 

unmeasured peak high-level exposures in 

healthy persons.8 

OSHA has established a legal airborne PEL 

ceiling value for H2S of 20 ppm and a 10-minute 

maximum peak of 50 ppm.9

 The NIOSH REL is 

a ceiling value of 10 ppm, which should not be 

exceeded at any time.18 The ACGIH TLV-TWA 

of 10 ppm and the TLV-STEL of 15 ppm are 

recommended for occupational exposure to 

hydrogen sulfide.8 

Carbon Monoxide 

CO is a colorless, odorless, tasteless gas 

produced by incomplete burning of carboncontaining materials such as gasoline. It 

combines with hemoglobin in red blood cells to 

form carboxyhemoglobin (COHb), which 

prevents the transport of oxygen throughout the 

body. Symptoms of CO poisoning begin with 

headache, dizziness, drowsiness and nausea, and 

may progress to loss of consciousness and 

eventually death.20 The NIOSH REL for CO is 

35 ppm for an 8-hour TWA. NIOSH also 

recommends a 200 ppm ceiling which should 

not be exceeded and an immediately dangerous 

to life and health value (IDLH) of 1200 ppm.20

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

exposure.9

 The ACGIH recommends a TLV of 

25 ppm 8-hour TWA.8

Crystalline Silica 

Exposure to crystalline silica (quartz, 

cristobalite, and other forms) has been 

associated with silicosis, a fibrotic lung disease 

caused by the deposition of fine particles of 

crystalline silica within the lungs. Symptoms 

usually develop insidiously with cough, 

shortness of breath, chest pain, weakness, 

wheezing, and non-specific chest illnesses. 

Silicosis usually occurs after years of exposure 

but may appear in a shorter period of time if 

exposure concentrations are very high.21 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 8 

The NIOSH REL for respirable crystalline silica 

is 50 micrograms per cubic meter of air (μg/m3

) 

as a TWA for up to 10 hours per day during a 

40-hour work week.21 The REL is intended to 

prevent silicosis although some evidence 

indicates that crystalline silica is also a potential 

occupational carcinogen.22,23,24 

The ACGIH TLVs for respirable quartz and 

cristobalite are 100 and 50 μg/m3

, as 8-hour 

TWAs, respectively.8

 The OSHA PEL (8-hour 

TWA) for crystalline silica (as respirable quartz) 

varies based on the percentage of silica.9

Volatile Organic Compounds 

VOCs describe a large class of chemicals which 

are organic (i.e., contain carbon) and have a 

sufficiently high vapor pressure to allow some of 

the compound to exist in a gaseous state at room 

temperature. Many of the paints used by SLSDC 

winter work employees are formulated with 

VOCs, including toluene, MIBK, PGMEA, and 

xylene. Routes of exposure to solvents include 

inhalation of the vapors (lungs), direct contact 

with the liquid (skin), and ingestion or 

swallowing (gastrointestinal tract). Because 

many organic solvents have relatively high 

vapor pressures and readily evaporate, inhalation 

of vapors is considered the primary route of 

exposure. Exposure to solvents may result in 

eye, nose, and throat irritation, central nervous 

system depression, headache, and nausea. Some 

solvents are also described in the medical 

literature to adversely affect the liver, the 

kidneys, and other organs.25,26

Table 1 presents the current recommendations 

and standards for the quantified VOCs. 

Evaluation criteria are not established for 

PGMEA in the United States.

Confined Space Entry 

According to NIOSH, confined spaces meet the 

following criteria: 1) they have limited openings 

for entry and exit; 2) they have unfavorable 

natural ventilation which could contain or 

produce dangerous air contaminants; and 3) they 

are neither designed nor intended for continuous 

employee occupancy. Confined spaces include 

(but are not limited to) storage tanks, 

compartments of ships, process vessels, pits, 

silos, vats, degreasers, reaction vessels, boilers, 

ventilation and exhaust ducts, sewers, tunnels, 

underground utility vaults, and pipelines. Within 

the larger category of confined space entry, 

NIOSH has further established three specific 

classes of confined space hazards. Designated A, 

B, and C, each confined space class is defined in 

the NIOSH Criteria for a Recommended 

Standard.

4

A “Class A” designation indicates a confined 

space atmosphere that is immediately dangerous 

to life and health. NIOSH defines “Class B” as a 

confined space in which the atmosphere is 

dangerous, but not immediately life-threatening. 

The toxicity of a “Class B” confined space is 

defined as greater than the contamination level 

referenced in 29 CFR Part 1910 subpart Z, but 

less than the IDLH. A “Class C” designation 

indicates a confined space that is a potential 

hazard with a toxicity of less than the 

contamination level referenced in subpart Z. The 

OSHA definition of a permit required confined 

space (PRCS) does not include those spaces that 

fall under the NIOSH Class C confined space 

category. Thus, OSHA does not mandate any 

special procedures upon entry of a Class C 

confined space. 

RESULTS

Industrial Hygiene 

Endotoxins 

Personal Breathing Zone Samples 

Snell Lock: 2002 

PBZ samples for endotoxin were collected from 

five welders and two painters (Table 2). 

Endotoxin concentrations for the welders ranged 

from less than detectable to 5.0 EU/m3

. The 

endotoxin concentrations measured for the two 

painters were 120 and 130 EU/m3

, respectively. 

However, these painters reported that they had 

left the worksite by driving to an off-site paint 

store while wearing the NIOSH sampling 

equipment. 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 9 

Eisenhower Lock: 2003 

NIOSH industrial hygienists repeated endotoxin 

sampling in 2003. Concentrations ranged from 

1.2 – 8.9 EU/m3

 for workers involved with 

painting, chipping concrete, pipe-fitting, and 

fender pit maintenance (Table 2). By using a 

measured background level of 0.82 EU/m3

, any 

PBZ greater than 8.2 EU/m3

 resulted in a 

calculated RLV of greater than 10. Therefore, 

the exposure of the person performing 

maintenance in the fender pit area was higher 

than the ACGIH-recommended RLV. 

Area Samples 

Thirteen area samples for endotoxin 

concentrations were collected from various 

locations within each of the locks over the 2 

years of sampling (Table 3). Nine samples 

collected from outside the locks were considered 

representative of background levels of 

endotoxins. The in-lock results ranged from 0.1 

– 20 EU/m3

. The highest value, collected from 

the upstream fender recess, exceeded the RLV. 

Hydrogen Sulfide 

NIOSH investigators sampled for H2S at the 

Eisenhower Lock on February 4–5, 2003. 

Concrete chipping took place between 10:00 

a.m. and 12:00 p.m. During this time period, a 

general area air sample collected near the 

concrete chipping measured a maximum H2S 

peak of 19 ppm. Sensors placed on each of the 

three workers using pneumatic drills and jack 

hammers to remove deteriorating concrete 

recorded maximum peak values of 18 ppm, 87 

ppm, and 68 ppm, respectively. Also during this 

time period, the sensors recorded a broader 

series of peaks, several of which exceeded the 

NIOSH ceiling of 10 ppm and the OSHA ceiling 

of 20 ppm. One PBZ sample on a painter who 

was not working in or around the chipping area 

also had an H2S exposure that exceeded the 

NIOSH ceiling value. The results of real time 

H2S sampling are presented in Table 4. 

Carbon Monoxide 

The 2003 results of CO sampling are presented 

in Table 5. All measured CO concentrations 

were within the NIOSH and ACGIH 

recommendations, and the OSHA PEL. 

Silica 

All 5 PBZ air samples for respirable cristobalite 

were below the minimum detectable 

concentration (MDC) of 0.050 μg/m3

. Four of 

five samples for respirable crystalline quartz 

were below the MDC of 0.024 μg/m3

, and the 

one remaining sample had a trace amount 

(between 0.024 and 0.071 μg/m3.) MDCs were 

calculated using a sample volume of 422 liters 

(the minimum volume of the air samples). 

Volatile Organic Compounds 

No sulfur or amine compounds were detected in 

any TD tube samples. Based on the TD results, 

the following VOCs were quantified using 

charcoal tubes: toluene, MIBK, PGMEA, and 

xylene. With the exception of PGMEA (for 

which neither a REL nor an OSHA PEL has 

been established), these results were below their 

respective NIOSH RELs (Table 6). 

Confined Space Entry 

The Snell and Eisenhower Locks meet the 

criteria used by NIOSH to define a “Class C” 

confined space. NIOSH investigators contacted 

the area director of OSHA in Syracuse, New 

York, to determine how their inspectors have 

categorized the locks in the past. In a letter dated 

December 3, 2002, the area director responded 

that neither the general lock spaces nor the 

cross-under for the locks (the stairwells and 

tunnel beneath the locks) are considered 

confined spaces. PRCSs within the Snell and 

Eisenhower Locks, according to OSHA, include 

the piston holes and inside the lock gates. 

Medical 

Prior to the initial site visit to Massena, SLSDC 

management provided NIOSH investigators with 

the names of 50 employees likely to be working 

in the locks during winter work. Subsequently, 

NIOSH investigators received an employee 

roster (dated October 30, 2001) listing 149 fulltime, permanent employees of the SLSDC. This 

roster included the names of office and 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 10 

administrative staff and employees actively 

engaged in winter work. 

Following completion of both site surveys, 

representatives from SLSDC helped classify the 

149 employees that appeared on the roster as 

working either “regularly,” “intermittently,” 

“seldom,” or “never” in the locks when winter 

work activities take place. Regular exposure was 

defined as working in the locks on a daily basis; 

intermittent exposure was defined as working in 

the locks at least once per week but not on an 

everyday basis. Employees classified as being 

seldom or never exposed to the lock 

environment were identified as working in the 

locks once per month or less. Seventy-one of 

149 (48%) employees were identified by 

SLSDC representatives as having either regular 

or intermittent exposure to the locks during 

winter work. Of these 71 employees, 37 were 

among the 50 names originally provided to 

NIOSH in advance of the initial site visit. 

Confidential Interviews and 

Medical Record Review 

Of the 71 employees identified as having either 

regular or intermittent exposure to the lock 

environment during winter work, NIOSH 

investigators conducted confidential interviews 

with 22 who volunteered to be interviewed. 

Thirteen of the 71 employees identified as 

having regular or intermittent exposure provided 

medical records for review and participated in 

interviews, while nine were interviewed but did 

not provide medical records. 

Twenty-six employees (of the 71 identified as 

having regular or intermittent exposure to the 

lock environment during winter work) provided 

medical records for review. This encompasses 

the 13 employees identified above. The other 13 

employees who provided medical records were 

either unavailable to be interviewed or declined 

to be interviewed. 

By combining data collected from confidential 

interviews and the medical record review, a total 

of 27 employees identified as having regular or 

intermittent exposure to the lock environment 

during winter work over the past several years 

had information that could be abstracted. 

Twenty of 27 employees had a history of some 

respiratory illness occurring in the past several 

years during the winter months of January, 

February, or March, while working at SLSDC. 

Specifically, 14/27 provided a history of ever 

having had an occurrence of bronchitis, 8/27 

ever had a case of pneumonia, and 3/27 provided 

a history of ever having had an aggravation of 

their asthma during the winter months of 

January, February, or March in their time of 

employment over the past several years; some 

employees had more than one illness. One 

employee provided a history of occupational 

asthma most likely due to a chemical exposure 

in the remote past unrelated to winter work; he 

noted a worsening of his symptoms when 

entering fender pit areas. 

Eighteen of 27 provided a history of having been 

seen by their health care provider for an illness 

during the months of January, February, or 

March during their time of employment over the 

past several years; two provided a history of 

having been hospitalized with a respiratory 

illness during these months. Six of 27 reported a 

history of tobacco use. 

 

DISCUSSION/

CONCLUSIONS

Large numbers of zebra mussels within the 

locks on the St. Lawrence Seaway present at 

least two potential hazards for SLSDC 

employees actively engaged in performing 

winter work: 1) the possibility of exposure to 

toxins known to accumulate within the soft 

tissues of the mussels; and 2) exposure to the 

significant odor that results as these animals 

decay when the lock is dewatered. Zebra 

mussels filter water for food and oxygen and 

several studies have shown that high levels of 

metals such as cadmium, mercury, lead, and 

copper, and organic contaminants such as 

polychlorinated biphenyls (PCBs), pesticides, 

and petroleum hydrocarbons may become 

concentrated in their soft tissues.27,28 

Subsequent studies (reported by the U.S. Army 

Engineer Waterways Experiment Station) 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 11 

indicate that the shells of the zebra mussels act 

to dilute the overall concentration of 

contaminants within their soft tissues.28 As the 

size of an individual mussel increases so does its 

overall shell mass. Thus, because contaminants 

are only associated with the soft tissues of these 

animals (rather than with their shells) 

contaminant concentrations decrease as the size 

of the shells increase. Additional research has 

identified that the concentrations of 

contaminants in whole zebra mussels (soft tissue 

and shells combined) are relatively low. When 

compared with the U.S. Environmental 

Protection Agency’s (EPA) sediment guidelines, 

zebra mussel waste is considered “nonpolluted.”28 Zebra mussels have, therefore, been 

determined to be non-hazardous.28

The second concern (as mentioned above) for 

SLSDC employees coming into regular contact 

with large numbers of dead and decaying zebra 

mussels is exposure to the foul odor.27,29

Although thick layers of mussels are known to 

survive even in dewatered locks,2

 most zebra 

mussels will not survive out of water or in the 

extreme cold temperatures of the locks on the St. 

Lawrence Seaway. Since both the Snell and 

Eisenhower Locks are covered in the winter, it 

has been suggested that the resulting odor from 

dead zebra mussels cannot readily vent to the 

atmosphere and may be “particularly 

noticeable.”1

Methane, organic sulfur compounds, and H2S 

are three gases likely to be responsible for the 

odor associated with decaying zebra mussels.27,29

These byproducts result from the bacterial 

decomposition of the zebra mussels under 

anaerobic conditions.30 Methane and H2S are 

toxic to humans; methane may displace oxygen 

from the environment and H2S poisons the body 

by interfering with the proper use of oxygen by 

the body. In a confined space (such as a covered 

lock chamber) in the absence of adequate 

ventilation, the risk of toxicity to workers may 

be greater than in an open area. NIOSH 

investigators conducting this HHE conclude that 

the general lock area meets the definition of a 

NIOSH “Class C” confined space. 

Using direct-reading instruments, NIOSH 

industrial hygienists measured elevated 

concentrations of H2S, suggesting that exposure 

to elevated concentrations of this gas occurs 

episodically in areas near concrete chipping 

activities. Maximum instantaneous peaks for the 

three chippers exceeded both the NIOSH and 

OSHA ceiling values. In addition, one painter 

also had a maximum peak H2S exposure that 

was higher than the NIOSH ceiling value. 

Since other gases in the environment are known 

to interfere with direct-reading real time 

monitors, we recommend confirming the 

presence of H2S by conducting additional 

sampling. The NIOSH Manual of Analytical 

Methods Number 6013 is one such confirmatory 

method.6

 It is important to note that the results 

of this test are purely confirmatory; they may be 

used only to exclude or confirm other gases as 

potential sources of interference with real time 

monitoring equipment. The results obtained 

from confirmatory testing (measured as a timeweighted average) cannot be used to establish 

whether or not H2S exceeds the ceiling value 

recommended by the NIOSH criterion. 

During the first NIOSH site visit (2002), 

sampling identified high concentrations of 

endotoxins in two painters. NIOSH 

investigators, however, are unable to fully 

account for the activities or location of these two 

employees during the interval while they were 

away from the locks. Thus, we cannot conclude 

that exposures within the lock environment were 

responsible for the elevated endotoxin sample 

concentrations. With the exception of these two 

very high readings, exposures to endotoxins 

among most SLSDC employees engaged in 

winter work were below the RLV recommended 

by ACGIH. Moreover, directed monitoring of 

painters for endotoxins during the second 

NIOSH site visit (2003) did not reveal similarly 

high concentrations. Ultimately, since only the 

samples collected from the two painters who left 

the worksite showed exposure to high 

concentrations of endotoxins, it is not possible to 

determine the significance of these findings. 

Area samples for endotoxins were slightly 

elevated in the upstream fender recess area of 

the Snell Lock. 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 12 

Of the samples collected to measure 

concentrations of CO, crystalline silica, or 

VOCs, none exceeded any listed NIOSH or 

OSHA criteria. NIOSH industrial hygienists did 

find PGMEA at higher concentrations than the 

other VOCs in one PBZ sample collected from a 

single painter but this particular organic 

compound does not have established exposure 

criteria and the health effects at this 

concentration, if any, are not known. 

Approximately one-third of employees 

identified as having regular or intermittent 

exposure to the lock environment during winter 

work were interviewed or provided medical 

record information. Of those employees who 

participated in the NIOSH survey, most 

provided a history of some type of respiratory 

illness occurring in the past several years during 

the winter months of January, February, or 

March, while working at SLSDC. Respiratory 

illnesses are commonly occurring conditions 

among the population, especially in the winter. 

Our review of medical records and interviews 

(combined with an examination of exposure data 

collected during the two NIOSH site visits) did 

not identify characteristics among SLSDC 

employees that would lead us to believe that the 

reported respiratory conditions were unusual in 

this working population over time. 

As noted previously in this report, human 

volunteers who inhaled high concentrations of 

endotoxins experienced chest tightness, fever, 

and inflammation of the lungs. These health 

effects are seen when people are exposed to 

airborne endotoxin concentrations between 45 – 

400 EU/m3

. In our survey, however, only two 

workers had endotoxin concentrations in this range, 

and both had left the worksite; drawing conclusions 

regarding these two workers cannot be done 

adequately. Personal breathing zone concentrations 

obtained for other employees (as well as area air 

monitoring results) were not sufficiently high to 

suggest that endotoxins represent a source of 

recurrent winter illnesses among exposed 

employees. 

H2S represents another potential source for 

recurrent respiratory illness among SLSDC winter 

work employees. Some personal breathing zone 

and area air monitoring results were at levels found 

in other studies to cause eye and upper airway 

irritation in exposed individuals. Employees 

interviewed as part of this NIOSH survey did not 

describe having these symptoms. 

Based on our findings, NIOSH investigators do 

not believe that workplace exposures account for 

the “flu-like symptoms” and “general ill health” 

reported by SLSDC employees. However, this 

conclusion is based upon the airborne exposures 

measured on the days of our evaluation and on 

the medical survey, which was limited by the 

small numbers of workers who participated in 

the interviews or who provided medical records 

for review. 

RECOMMENDATIONS

1. Perform real-time monitoring for H2S in all 

areas within the locks, especially areas with 

barriers to the free flow of air and during 

concrete chipping activities. 

2. Increase general area ventilation to further 

reduce H2S concentrations (some of which 

exceeded the NIOSH ceiling of 10 ppm). 

3. Begin a confined space entry plan following 

the guidelines detailed in Appendix A (the 

confined space entry procedures used by NIOSH 

investigators during the second year of this 

survey). At a minimum, NIOSH recommends 

the following before allowing workers to enter 

into a “Class C” confined space: (1) a permit 

system; (2) initial atmospheric testing for 

hazardous gases/vapors or lack of oxygen; (3) 

training; (4) labeling and posting; (5) entrance, 

communication, rescue, and work procedures; 

(6) provision of safety belts; and (7) rescue 

equipment.4

4. Continue to spray water on concrete surfaces 

while chipping to minimize the generation of 

airborne silica dust. 

5. Start a medical surveillance program. We 

recommend consulting with a physician to 

conduct annual surveillance for acute respiratory 

illnesses among SLSDC winter work employees. 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 13 

This physician should have experience in 

evaluating individuals with workplace exposures 

and should have a good understanding of 

conducting epidemiological studies. Comparison 

of rates of illness from year to year among those 

having regular exposure to the lock environment 

will help identify job assignments or work 

locations (if any) within the locks that may 

result in exposures most likely to cause 

respiratory illnesses. Annual surveillance may 

also serve as an effective means of minimizing 

concerns among employees about the likelihood 

of developing respiratory illnesses as a 

consequence of participating in winter work. 

6. Provide all SLSDC winter work employees 

with medical clearance prior to returning to 

work following a hospitalization or medical 

procedure, a severe respiratory illness, or while 

taking medication(s) prescribed by a health care 

provider. Each of these conditions may 

compromise an individual’s ability to safely use 

personal protective equipment or to work within 

a confined space. 

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 1. Miller AC, Neilson F, Gunnison K [1993]. 

Susceptibility of navigation locks to zebra 

mussel infestations. Technical Note ZMR-4-03. 

Zebra mussel research program, U.S. Army 

Engineer Waterways Experiment Stations, 

Vicksburg MS. (http://el.erdc.usace.army.

mil/elpubs/pdf/zmr4-03.pdf). Date accessed: 

June 22, 2004. 

 2. Dye G [1994]. Zebra mussel infestation at 

Black Rock lock, Buffalo, New York. Technical 

Note ZMR-1-18. Zebra mussel research 

program, U.S. Army Engineer Waterways 

Experiment Station, Vicksburg MS. 

(http://el.erdc.usace.army.mil/elpubs/pdf/zmr1-

18.pdf). Date accessed: November 27, 2004. 

 3. Yager T [1994]. Zebra mussels at lock and 

dam 6, upper Mississippi River, January 1994. 

Technical Note ZMR-1-23. Zebra mussel 

research program, U.S. Army Engineer 

Waterways Experiment Station, Vicksburg MS. 

(http://el.erdc.usace.army.mil/elpubs/pdf/zmr1-

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 6. NIOSH [1994]. NIOSH manual of 

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(NIOSH) Publication No. 94-113. 

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Health Hazard Evaluation Report No. 2002-0014-2958 Page 1 

Table 1 

Occupational Exposure Limits for Selected Volatile Organic Compounds 

St. Lawrence Seaway, HETA 2002-0014-2958

Toluene 

(ppm) 

MIBK∗

(ppm) 

PGMEA†

(ppm) 

Xylene 

(ppm) 

NIOSH REL 

TWA 100 

ST 150 

IDLH 500 

TWA 50 

ST 75 

IDLH 500 

None 

TWA 100 

ST 150 

IDLH 900 

OSHA PEL 

TWA 200 

C 300 

500 10 min max peak 

TWA 100 None TWA 100 

ACGIH TLV TWA 50 

skin 

TWA 50 

STEL 75 None TWA 100 STEL 150 

*

MIBK = methyl isobutyl ketone 

†

PGMEA = 1-methoxy-2-propylacetate or methoxypropyl acetate 

ppm = parts per million 

REL = Recommended Exposure Limit 

PEL = Permissible Exposure Limit 

TLV = Threshold Limit Value 

TWA = Time-Weighted Average 

ST or STEL = Short Term Exposure Limit – a 15 minute exposure that should not be exceeded at any 

time during a workday 

C = Ceiling concentration that should not be exceeded at any time 

Skin = personal protective clothing is needed 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 2 

Table 2 

Personal Breathing Zone Endotoxin Concentrations 

St. Lawrence Seaway, HETA 2002-0014-2958 

2002 and 2003 

Location Job Title Date Sampling 

Time 

(minutes) 

Air 

Concentration 

(EU/m3) 

Comparison to 

RLV**

Welder 1 2/26/02 410 2.0 Less than 

Welder 2 2/26/02 414 ND* Less than 

Welder 3 2/26/02 432 ND Less than 

Welder 4 2/26/02 430 ND Less than 

Welder 5 2/26/02 318 5.0 Less than 

Painter 1 2/27/02 363 130± Greater than 

Snell Lock 

Painter 2 2/27/02 329 120.± Greater than 

Painter 3 2/4/03 430 1.2 Less than 

Painter 4 2/4/03 349 4.1 Less than 

Painter 4 

(repeat) 2/5/03 393 6.9 Less than 

Chipper1 2/4/03 425 2.0 Less than 

Chipper 2 2/4/03 455 4.3 Less than 

Chipper 3 2/4/03 422 4.2 Less than 

Pipe-fitter 1 2/5/03 393 2.1 Less than 

Fender pit 

maintenance 1 2/5/03 100 8.6 Greater than 

Eisenhower Lock 

Fender pit 

maintenance 2 2/5/03 139 1.9 Less than 

1 The minimum detectable concentration (MDC) was calculated to be 0.60 endotoxin units per cubic 

meter (EU/m3

) using a sample volume of 830 liters. 

*ND = non-detectable, below the MDC. 

**RLV = Relative Limit Value. The average (0.82 EU/m3

) of the background air samples collected 

outside the locks was used to calculate the RLV recommended by the American Conference of 

Governmental Industrial Hygienists (ACGIH). 

±This value exceeds the ACGIH RLV calculated for this worksite (10 times the background level). 

However, since these employees left the work site while being sampled, we cannot conclude that their 

endotoxin exposures resulted from their work in the lock. 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 3 

Table 3 

Area Endotoxin Concentrations 

St. Lawrence Seaway, HETA 2002-0014-2958

2002 and 2003 

Location Sample Position Date Sample 

Duration 

(minutes) 

Endotoxin 

Concentrations 

(EU/m3)

Comparison to 

RLV** 

Lower part of sill 2/26/02 320 ND* Less than 

Top of stairwell 2/26/02 317 1.0 Less than 

On sill 2/26/02 326 0.1 Less than 

Southside fender 

1 

2/26/02 271 0.7 Less than 

De-watering 

pump 

2/26/02 329 1.0 Less than 

Meter end of 

northgate 

2/26/02 318 ND Less than 

Downstream 

Snell North 

2/27/02 183 1.8 Less than 

Lower level 

upstream 

2/27/02 355 3.2 Less than 

Fender recess 

upstream 

2/27/02 355 20. Greater than 

Snell Lock 

Upper levels 

upstream 

2/27/02 356 1.2 Less than 

Upstream sill 2/4/03 314 2.9 Less than 

Fender recess 

north #1 

2/4/03 299 ND Less than 

Eisenhower 

Lock 

Upstream control 

house (indoors) 

2/4/03 283 ND Less than 

1

The minimum detectable concentration (MDC) was calculated to be 0.60 endotoxin units per cubic meter 

(EU/m3

) using a sample volume of 830 liters. 

* ND = non-detectable, below the MDC. 

**RLV = Relative Limit Value. The average (0.82 EU/m3

) of the background air samples collected 

outside the locks was used to calculate the RLV recommended by the American Conference of 

Governmental Industrial Hygienists (ACGIH). 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 4 

Table 4 

Area and Personal Breathing Zone Air Concentrations of Hydrogen Sulfide (H2S) 

St. Lawrence Seaway, HETA 2002-0014-2958 

2003 

Work Activity or 

Sample Location 

Date TWA*

(ppm)§

STE±

(ppm) 

Maximum Recorded Peak 

(Instantaneous ppm) 

Chipper 1 2/04/03 1 13 18** 

Chipper 2 2/04/03 2 17 87** 

Chipper 3 2/04/03 1 21 68** 

Painter 3 2/04/03 0 1 5 

Painter 3 

(day 2) 2/05/03 0 7 11** 

Fender Pit 

Maintenance Worker 

1 

2/05/03 0 1 2 

Area 

Shed Near Chipping 2/05/03 0 2 3 

Area 

Raft Near Chipping 2/05/03 1 10 19** 

*

TWA = Time-Weighted Average concentration adjusted for 8 hours 

** = Exceeds NIOSH Ceiling of 10 ppm and/or the OSHA Ceiling of 20 ppm 

§

 ppm = parts per million 

±

STE = Short Term Exposure Limit (15 minute exposure) 

Table 5 

Area and Personal Breathing Zone Air Concentrations of Carbon Monoxide 

St. Lawrence Seaway, HETA 2002-0014-2958 

2003

Work Activity or 

Sample Location 

Date TWA*

(ppm)§ 

STE±

(ppm) 

Maximum Recorded Peak 

(Instantaneous ppm) 

Painter 4 2/05/03 0 5 19 

Painter 5 2/05/03 

(p.m. only) 

1 3 8 

Pipe-Fitter 2/05/03 1 3 21 

Area 

Raft Near Chipping 

2/05/03 2 33 58 

*

TWA = Time-Weighted Average exposures for up to a 10-hour workday 

§ ppm = parts per million 

±

STE = Short Term Exposure–a 15 minute exposure 
Health Hazard Evaluation Report No. 2002-0014-2958 Page 5 

Table 6 

TWA*

 Personal Breathing Zone Concentrations of Volatile Organic Hydrocarbons 

St. Lawrence Seaway, HETA 2002-0014-2958 

2003

Location Job Title Date Sampling 

Time 

(minutes)

Toluene

(ppm)§

MIBK 

(ppm) 

PGMEA 

(ppm) 

Xylene 

(ppm) 

Painter 3 2/5/03 336 Trace 0.120 3.12 2.31 

Painter 4 2/5/03 394 0.015 0.017 15.0 0.662 

Painter 5 2/5/03 289 ND** ND ND Traceo 

Eisenhower 

Lock 

Pipe-fitter 2/5/03 393 ND ND 0.033 0.050 

Minimum 

Detectable 

Concentration 

(MDC) 

0.009 0.008 0.010 0.012 

Minimum 

Quantifiable 

Concentration 

(MQC) 

0.032 0.021 0.029 0.036 

* TWA = Time-Weighted Average 

**ND = Non-detectable 

oTrace = Indicates a concentration below the MQC but above the MDC. The MDCs and MQCs 

were based on the minimum sample size of 58.13 L. 

§ ppm = parts per million
Health Hazard Evaluation Report No. 2002-0014-2958 Page 6 

APPENDIX A 

Class C Confined Space Entry SOP for the General Lock Area 

 1. Permit. When each person enters he/she will sign a permit. This permit shall be kept at the job site 

for the duration of the job. If circumstances cause an interruption in the work or a change in the alarm 

conditions for which entry was approved, a new Confined Space Entry Permit must be completed. A 

written copy of St. Lawrence Seaway Development Corporation (SLSDC) rescue procedures shall be at 

the work site for the duration of the job. 

 2. Initial atmospheric testing. Before entering any area, the atmosphere within the space will be tested 

to determine whether dangerous air contamination and/or oxygen deficiency exists. A direct reading gas 

monitor shall be used. Testing shall be performed by the team leader. The parameters to be monitored are 

oxygen deficiency, carbon monoxide, lower explosive limit, and hydrogen sulfide concentration; these 

parameters will be tested for simultaneously. A written record of the pre-entry test results shall be made 

and kept at the work site for the duration of the job. The team leader will certify, in writing, based upon 

the results of the pre-entry testing, that all hazards have been eliminated. Affected employees shall be able 

to review the testing results. If there are no non-atmospheric hazards present and if the pre-entry tests 

show there is no dangerous air contamination and/or oxygen deficiency within the space and there is no 

reason to believe that any is likely to develop, entry into and work within may proceed. 

 3. Continuous testing of the atmosphere in the immediate vicinity of the workers within the space is 

not required in this situation. However, where the Seaway has established monitoring devices, the 

workers will immediately leave the permit space when any of these alarm set points are reached as 

defined. Workers will not return to the area until the team leader has used a direct reading gas detector to 

evaluate the situation and has determined that it is safe to enter. 

 4. Medical surveillance is not required in this situation. However, the surrounding area shall be 

surveyed by the standby person to avoid hazards such as drifting vapors from tanks, piping or sewers. 

 5. Training of personnel will be performed prior to going into the field. 

 6. Labeling and posting will be done. 

 7. Preparations; including isolation/lockout/tagout, purge and ventilate, cleaning processes; are not 

required. 

 8. One standby person will be stationed at the entrance to the locks at all times when any other 

employee is within the lock area. Communications will be established between personnel within the 

confined space and the standby person. 

 9. Safety equipment. Safety helmets, glasses, hand protection, and boots, will be worn. Rubber boots 

and gloves will be provided by the SLSDC. Safety harnesses will be worn by all workers. 

 10. Rescue. An approved hoist and crane must remain available at the site. If at any time there is any 

questionable action or non-movement by the worker inside, a verbal check will be made. If there is no 

response, the worker will be removed immediately. Exception: If the worker is disabled due to falling or 

impact, he/she shall not be removed from the confined space unless there is immediate danger to his/her 

life. Local fire department rescue personnel shall be notified immediately. 

 11. Rescue. Call the fire department services for rescue. Where immediate hazards to injured personnel 

are present, workers at the site shall implement emergency procedures to fit the situation. 
DEPARTMENT OF HEALTH AND HUMAN SERVICES 

Centers for Disease Control and Prevention National Institute for Occupational Safety and Health 4676 Columbia Parkway Cincinnati, OH 45226-1998 OFFICIAL BUSINESS Penalty for private use $300 

Delivering on the Nation's promise: 

Safety and Health at work for all people 

through research and prevention

To receive NIOSH documents or information 

about occupational Safety and Health topics 

contact NIOSH at: 

1-800-35-NIOSH (356-4674) 

Fax: 1-513-533-8573 

E-mail: pubstaft@cdc.gov

or visit the NIOSH web site at: 

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