Evaluation of Heat 

and Carbon Monoxide 

Exposures to Border 

Protection Officers at 

Ports of Entry 

Chad Dowell, MS, CIH 

Judith Eisenberg, MD, MS 

Health Hazard Evaluation Report

HETA 2005-0215-3099

Department of Homeland Security 

U.S. Customs and Border Protection

El Paso, Texas

December 2009

Department of Health and Human Services

Centers for Disease Control and Prevention

Workplace

Safety and Health

 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/
The employer shall post a copy of this report 

for a period of 30 calendar days at or near 

the workplace(s) of affected employees. The 

employer shall take steps to insure that the 

posted determinations are not altered, defaced, 

or covered by other material during such 

period. [37 FR 23640, November 7, 1972, as 

amended at 45 FR 2653, January 14, 1980].
Health Hazard Evaluation Report 2005-0215-3099 Page i

Appendix A

Report Abbreviations.......................................................................i

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

Summary .............................................................................v

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

Assessment.........................................................................2

Results.................................................................................3

Discussion ...........................................................................7

Conclusions.........................................................................7

Recommendations...............................................................8

References ........................................................................11

Contents

Acknowledgments and Availability of Report.....................27

Methods.............................................................................12

Occupational Exposure Limits & Health Effects ................14

Acknowledgment

Appendix B
Page ii Health Hazard Evaluation Report 2005-0215-3099

ACGIH® American Conference of Governmental Industrial Hygienists

BEI® Biological exposure limit

bpm Beats per minute

BUN Blood urea nitrogen

CBP Customs and Border Protection

CBT Core body temperature

CFR Code of Federal Regulations

CO Carbon monoxide

COHb Carboxyhemoglobin

HHE Health hazard evaluation

IDLH Immediately dangerous to life and health

kcal/hour Kilocalories per hour

mEq/L Milliequivalents per liter

mg/dL Milligrams per deciliter

mosm/L Millimoles per liter

NIOSH National Institute for Occupational Safety and Health

OEL Occupational exposure limit

OSHA Occupational Safety and Health Administration

PBZ Personal breathing zone

PEL Permissible exposure limit

ppm Parts per million

RAL Recommended action limit

REL Recommended exposure limit

STEL Short term exposure limit

TLV® Threshold limit value

TWA Time-weighted average

WBGT Wet bulb globe temperature

WEEL Workplace environmental exposure level

Abbreviat
Health Hazard Evaluation Report 2005-0215-3099 Page iii

Highlights of 

NIOSH 

Hazard Eval

The National Institute for 

Occupational Safety and 

Health (NIOSH) received a 

union request for a health 

hazard evaluation at the 

Customs and Border 

Protection (CBP) ports of 

entry in El Paso, Texas. 

The request concerned 

CBP officers’ work in 

hot environments and 

potential exposure to 

carbon monoxide from 

vehicle exhaust.

What NIOSH Did

● We made a site visit in August and September 2005.

● We talked with management and union officials about the 

working conditions in outdoor vehicle inspection areas.

● We measured officers’ exposure to heat and humidity in 

outdoor vehicle inspection areas.

● We measured officers’ exposure to carbon monoxide in 

outdoor vehicle inspection areas.

● We talked to officers about their work environment, work 

practices, and work-related concerns.

What NIOSH Found

● Officers were not exposed to excessive heat at the time of this 

evaluation; however, heat exposure can be greater during the 

summer.

● No formal heat stress management program was in place.

● Officers did not report symptoms related to heat exposure.

● Officers’ carbon monoxide exposures were over the peak 

limit but not the full-shift exposure limit.

● None of the officers exceeded the recommended limit for 

carboxyhemoglobin, an indicator of carbon monoxide 

exposure.

What Managers Can Do

● Start a formal heat stress management program.

● Allow officers to take unscheduled breaks away from the 

hot environment if needed. Signs of excess heat exposure 

include weakness, nausea, confusion, excessive tiredness, or 

irritability.

● Develop a hazard communication program. The program 

should address working in hot environments and working 

around vehicle exhaust.

● Continue to rotate officers between primary and secondary 

vehicle inspection areas.

● Monitor officers’ exposure to carbon monoxide.

● Require that vehicles be turned off during inspection of the 

undercarriage.
Page iv Health Hazard Evaluation Report 2005-0215-3099

Highlights of 

NIOSH 

Hazard Eval

(continued

What Employees Can Do

● Tell your supervisor if you feel weak, nauseated, excessively 

fatigued, confused, and/or irritable due to the heat.

● Drink plenty of fluids.

● Require drivers to turn off their vehicle when inspecting the 

undercarriage.

● Do not place your head near the vehicle’s exhaust while the 

vehicle is running.
Health Hazard Evaluation Report 2005-0215-3099 Page v

Summ

Heat stress and strain 

measurements collected 

during this evaluation 

showed that CBP officers 

in the outdoor vehicle 

inspection areas were not 

exposed to heat stress 

over the occupational 

recommendations. 

Officers have the 

potential for high peak CO 

exposures. Full shift CO 

exposures and %COHb 

were below occupational 

exposure limits. We 

recommend that CBP 

implement administrative 

controls to minimize the 

potential for heat strain 

and reduce CO exposures.

On April 22, 2005, NIOSH received a union request asking 

NIOSH to evaluate heat stress and CO exposures for CBP officers 

working in the outdoor vehicle inspection areas at the CBP ports 

of entry in El Paso, Texas. The request indicated that some officers 

had experienced heat cramps and heat exhaustion. In response, 

NIOSH investigators monitored heat stress, heat strain, and CO 

in air and exhaled breath on August 29–September 2, 2005, at 

the Bridge of the Americas and Paso del Norte ports of entry in El 

Paso, Texas.

At the time of our evaluation we found that officers working in the 

outdoor vehicle inspection areas were not exposed to heat stress 

that exceeded NIOSH and ACGIH recommendations. None of 

the officers monitored for heat strain showed signs of excessive 

heat stress exposure. However, environmental temperatures 

are often warmer in El Paso than they were on the days of our 

evaluations. Higher temperatures would increase the likelihood 

that occupational heat stress recommendations could be exceeded 

and that employees could be at increased risk of heat strain.

The NIOSH recommended exposure limit ceiling for CO was 

exceeded for some of the officers working in the outdoor vehicle 

inspection areas. This REL was exceeded when the officers 

inspected the vehicle’s undercarriage near the exhaust pipe. None 

of the officers monitored exceeded the full shift TWA occupational 

exposure limits for CO or the limits for COHb.

Investigators recommended creating a formal heat stress 

management program that includes information on heat 

acclimatization and heat stress prevention. Management should 

monitor environmental heat exposure and develop criteria for 

heat alerts. Investigators also recommended turning off vehicles 

in primary inspection lanes, creating a hazard communication 

program for working around vehicle exhaust, continuing to use 

officer rotation schedules, and periodically monitoring officers’ 

CO exposures.

Keywords: NAICS 928110 (National Security), heat stress, heat 

strain, carbon monoxide, vehicle exhaust, vehicle inspection, 

immigration, customs and border protection
This page intentionally left blank.
Health Hazard Evaluation Report 2005-0215-3099 Page 1

Introduct

On April 22, 2005, NIOSH received a request from the American 

Federation of Government Employees for an HHE at the CBP 

ports of entry in El Paso, Texas. The HHE request asked NIOSH 

to evaluate heat stress and CO exposures for CBP officers working 

in the outdoor vehicle inspection areas. The request indicated 

that some CBP officers had experienced heat cramps and heat 

exhaustion. In response, NIOSH investigators monitored heat 

strain, heat stress, CO in air, and COHb on August 29–September 

2, 2005, at the Bridge of the Americas and Paso del Norte ports of 

entry.

El Paso has three ports of entry from Mexico: Bridge of the 

Americas, Paso del Norte, and Ysleta. All three ports of entry 

operate 24 hours a day with CBP officers inspecting incoming 

vehicles and pedestrian traffic. Bridge of the Americas is the largest 

of the three ports of entry with 14 primary vehicle inspection lanes 

staffed by approximately 28 CBP officers per 8-hour shift. The Paso 

del Norte port of entry has 9 primary vehicle inspection lanes, and 

Ysleta has 12 lanes, although typically only 6 of the 12 lanes are 

open for vehicular inspection due to limited demand. Each port 

of entry has a secondary vehicle inspection area. Both the primary 

and secondary vehicle inspection areas at all three ports of entry 

are covered with a canopy roof.

All vehicular traffic enters the ports of entry through one of the 

primary inspection lanes. During the primary inspection, the 

driver’s credentials are checked, and the vehicle is inspected. 

CBP officers often use a hand-held mirror and mallet to check 

the undercarriage of the vehicle, a practice requiring them to 

bend down near the exhaust pipe. Although the CBP officer can 

require the driver to turn off the vehicle during the inspection, 

many CBP officers do not require this because the driver may be 

unable to restart the vehicle, thus blocking the lane. If a more 

thorough inspection is necessary, cars are directed to the secondary 

inspection area and turned off.

The inspection booths at the three ports of entry are similar in size 

and configuration and are provided outdoor air from overhead 

ducts. This air can be heated but not cooled. Directly outside 

the inspection booth, overhead air showers blow outdoor air 

downward in the area where CBP officers perform most of their 

duties. Each primary inspection lane has one CBP officer, while 

the secondary inspection area has multiple CBP officers. The CBP 

officers’ job responsibilities require them to work mostly outside 

the inspection booths except when they are recording and entering 
Page 2 Health Hazard Evaluation Report 2005-0215-3099

Introducti

(continued

Assessment

information into a computer. The inspection booths have sliding 

glass doors that face the inspection lane, but these are frequently 

left open to facilitate access between the inside of the inspection 

booth and the vehicles. The secondary inspection area is covered 

by a canopy. CBP officers rotate between the primary inspection 

lanes and the secondary inspection area throughout their work 

shift with a 30-minute lunch break. All shifts are 8 hours long, but 

employees have options for voluntary overtime.

Beneath the secondary inspection canopy area, fans mounted on 

the canopy roof provide dilution ventilation. The CBP officers 

control these fans. None of the ports of entry is equipped with 

local exhaust ventilation systems for controlling automobile 

exhaust in the primary or secondary inspection areas.

Heat stress, heat strain, and CO exposures were assessed at the 

Bridge of the Americas and Paso del Norte, the two busiest El 

Paso ports of entry. These two ports of entry perform similar 

vehicular inspection operations with only minor differences in 

the neighboring buildings and the number of inspection lanes. 

The Ysleta port of entry was not evaluated because of the limited 

number of cars passing through. This decision was made in 

consultation with the union and CBP management.

To evaluate heat stress conditions, eight WBGT measurements 

were collected in the primary and secondary inspection lanes 

and inside the primary inspection booths and head house. For 

the heat strain evaluation, 24 participants volunteered to be 

monitored for physiological responses to the conditions of the 

work environment. Twenty-three CBP officers were monitored 

over one shift and one CBP officer over two shifts, for a total of 25 

individual measurements. CBT, heart rate, preshift and postshift 

weight, and blood chemistries were measured for each participant. 

Blood chemistries monitored included serum sodium, potassium, 

chloride, BUN, and glucose. Hemoglobin and hematocrit were 

also measured. Thirty-three participants, including 24 CBP officers 

involved in the heat strain monitoring and 9 additional CBP 

officers, volunteered to be monitored for CO exposure. All 33 

participants wore PBZ CO monitors, and 28 had their preshift and 

postshift COHb levels evaluated by exhaled breath measurements. 

A detailed discussion of the methods used for this evaluation 

is available in Appendix A, and a detailed discussion of the 

applicable occupational exposure limits is available in Appendix B.
Health Hazard Evaluation Report 2005-0215-3099 Page 3

Heat Stress 

Individual WBGT measurements are reported in Tables 1 and 2. 

The highest WBGT reading between Bridge of the Americas and 

Paso del Norte was 82.9°F, with dry bulb temperatures averaging 

between 82.5°F and 85.1°F. In the head house (the CBP officers’ 

break room) the highest WBGT reading was 71.4°F, with a dry 

bulb temperature of 78.1°F. At the time of this evaluation the dry 

bulb (ambient) temperatures were cooler than usual for that time 

of year [NOAA 2000]. These cooler ambient temperatures likely 

lessened the heat stress hazard in the inspection areas during the 

week of our evaluation.

Results

Table 1. Heat stress measurements, Bridge of the Americas, August 30–31, 2005

Monitoring Location Sample Time Temperature (oF)

WBGT (range) Dry Bulb (range)

Inside inspection booth of lane 5 0903–1600 72.4oF (66.4oF–77.8oF) 83.6oF (74.7oF–93.1oF)

Secondary inspection area* 0900–1601 71.2oF (65.1oF–81.8oF) 85.1oF (73.7oF–96.5oF)

Head house† 0914–1208‡ 59.5oF (53.9oF–71.4oF) 64.5oF (58.1oF–78.1oF)

Outside booth of lane 5* 0902–1600 71.8oF (65.7oF–77.6oF) 84.9oF (74.8oF–96.4oF)

* Outdoor measurement

† Indoor WBGT value, representative of where some CBP officers take their breaks.

‡ Monitor turned off by a CBP officer overnight.

Table 2. Heat stress measurements, Paso del Norte, September 1–2, 2005

Monitoring Location Sample Time Temperature (oF)

WBGT (range) Dry Bulb (range)

Inside inspection booth of lane 5 0854–1555 70.1oF (65.1oF–78.2oF) 77.0oF (71.6oF–89.5oF)

Secondary inspection area* 0841–1559 70.9oF (64.2oF–82.9oF) 82.5 oF (69.6oF–98.2oF)

Head house† 0851–1601 68.2oF (66.0oF–70.9oF) 76.7oF (74.0oF–81.4oF)

Outside booth of lane 5* 0846–0402 71.2oF (64.1oF–77.6oF) 82.7oF (69.4oF–95.4oF)

* Outdoor measurement

† Indoor WBGT value, representative of where some CBP officers take their breaks
Page 4 Health Hazard Evaluation Report 2005-0215-3099

Results (continued) The metabolic rates for the CBP officers working in the primary

and secondary inspection areas were estimated between 120 and 

156 kcal/hour. Because the CBP officers wore a uniform (long 

sleeve shirt and pants), no clothing-adjustment factors were added 

to the WBGT measurements. The metabolic rates and the WBGT 

data listed in Table 1 and 2 were compared to the NIOSH and 

ACGIH heat stress recommendations. Neither the NIOSH nor the 

ACGIH heat stress recommendations were exceeded for any of the 

CBP officers.

Heat Strain

A total of 24 participants completed a short heat stress 

questionnaire. The median age of the participating CBP officers 

was 37 years. The median duration of employment at the two 

El Paso ports of entry was 3 years, with range of 3 months to 15 

years. None of the officers gave positive responses for the question 

regarding “any problems with heat exposure in the past year.”

Individual heat strain measurements are reported in Table 3. 

All except two CBP officers were considered acclimatized to 

their work environment; two CBP officers reported they had 

just returned from a 4-day absence. The average CBT ranged 

from 98.71°F to 100.2°F, below the 101.3°F for medically fit, 

heat-acclimatized employees. The ACGIH recommendation for 

unacclimatized employees of 100.4°F was not exceeded for either 

of the two unacclimatized CBP officers. None of the CBP officers 

developed signs of heat strain when compared to the ACGIH 

recommendation for acclimatized employees.

Participants’ heart rates did not exceed the ACGIH 

recommendation of 180 bpm minus the employee’s age. Due to 

instrument error, no heart rate measurements were collected on 

September 2, 2005.

Body weight changes over the participants’ shift ranged from a 1% 

loss to a 2% gain, with an average of a 0.2% gain. None of the CBP 

officers tested had a body weight change of more than the ACGIH 

recommendation of a 1.5% loss.
Health Hazard Evaluation Report 2005-0215-3099 Page 5

Results (continued

Table 3. Individual physiological measurements

Date Sampling Period Average CBT

(oF)

Average Heart 

Rate (bpm)

Body Weight 

Change (%)

Bridge of the Americas

August 30, 2005 0823–1333* 98.71 74 0.0

0833–1351* 99.29 50 −0.2

0836–1339 † 77 −0.3

0850–1403 99.03 96 −1

0841–1535 99.41 88 0.8

August 31, 2005 0722–1505 99.21 ‡ 2

0757–1547 99.00 84 1

0803–1544 99.44 73 0.0

0720–1333 100.2 70 2

0852–1516 99.54 96 0.0

0816–1340 99.91 83 0.5

0929–1519 99.72 91 0.0

Paso del Norte

September 1, 2005 0729–1333 99.94 99 0.9

0813–1328 99.72 97 0.2

0817–1607 99.68 60 −0.9

0719–1446 99.36 † −0.8

0829–1539 99.72 84 1

0719–1446 99.36 74 −0.4

0854–1547 † 84 0.6

0918–1349 98.75 † 0.9

September 2, 2005 0715–1534 99.50 † −0.3

0736–1332 99.28 † 0.0

0840–1526 99.25 † −0.7

0900–1328 99.63 † −0.3

0908–1528 99.51 † −0.7

* Unacclimatized CBP officer

†

 No data collected

‡

 No data reported due to instrument error
Page 6 Health Hazard Evaluation Report 2005-0215-3099

Results (continued) Most serum electrolytes, including serum sodium, potassium,

chloride, BUN, and glucose, were within normal limits for both 

preshift and postshift testing. The reference range for serum 

sodium is 135–145 mEq/L. A corrected serum sodium was 

calculated for those participants with elevated serum glucose levels 

because high serum glucose (> 100 mg/dL) can cause falsely low 

measurements of serum sodium. Once the corrected sodium was 

calculated for those participants, all participants had preshift 

and postshift serum sodium levels within the reference range. 

The serum osmolality reference range is 275–290 mosm/L; the 

formula used for its calculation incorporates the values of serum 

sodium, BUN, and glucose. Aside from those participants who had 

elevated serum glucose levels, all other preshift and postshift serum 

osmolalities fell within the reference range.

No participants had a past medical history of diabetes, nor did 

any of the participants with elevated glucose readings report 

symptoms consistent with hyperglycemia such as polyuria (frequent 

urination), polydipsia (excessive thirst), headache, abdominal pain 

or blurred vision.

Carbon Monoxide 

Full shift CO exposures ranged up to 22 ppm, with an average 

concentration of 8 ppm; none exceeded the OSHA PEL of 50 

ppm, the NIOSH REL of 35 ppm, or the ACGIH TLV of 25 

ppm. Peak CO exposures greater than 999 ppm (the maximum 

limit of the CO monitor) were measured on 14 participants; 

these concentrations exceeded the NIOSH recommended ceiling 

limit of 200 ppm. CBP officers reported noticing their monitors 

responding to these peak CO concentrations when they were 

inspecting near a vehicle’s exhaust pipe.

When analyzing results for COHb, different reference ranges are 

used for nonsmokers and smokers because smokers generally have 

higher baseline COHb levels. For all the nonsmoker employees we 

measured in this evaluation, the average preshift COHb level was 

0.86%, and the average postshift level was 0.88%, an increase of 

2.3%. For all smokers, the average preshift COHb level was 3.0%, 

and the average postshift level was 2.7%, representing a decrease 

of 8.8%. None of the nonsmoking participants exceeded the 

ACGIH BEI for CO of 3.5% COHb at the end of shift. All of the 

participants were within or below the World Health Organization’s 

reference ranges for COHb of 1%–2% for nonsmokers and 

3%–8% for smokers.
Health Hazard Evaluation Report 2005-0215-3099 Page 7

At the time of our evaluation, CBP had no formal program in 

place for ensuring that the CBP officers were protected from 

heat stress and CO exposure. A few administrative controls were 

in place, though not intended for health reasons. For example, 

a work schedule required the CBP officers to rotate from the 

primary inspection lanes to the secondary inspection areas every 

30 minutes. This rotation policy, however, was implemented for 

security reasons to prevent any CBP officer from being able to tell 

anyone where they would be working at any specific time. CBP 

officers in the primary inspection lanes were also given the option 

of requiring specific drivers to turn off the vehicle during the 

inspection if it was in a state of poor repair or using a poor quality 

fuel. However, many of the CBP officers reported that they did not 

ask drivers to turn off their vehicles because the drivers may not 

have been able to restart them.

One medication taken by some participants that could potentially 

affect heat stress responses was Toprol XL, an extended release 

form of a beta blocker. One participant reported being treated for 

hypertension but could not recall the type of medication. Beta 

blockers are medications that directly depress heart rate and are 

commonly used in patients with cardiovascular atherosclerotic 

disease and hypertension. 

Those individuals with mild elevations of serum glucose (between 

100–200 mg/dL) were advised to follow up with their personal 

physicians within a week to have their blood sugar retested. Two 

participants with serum glucose levels over 200 mg/dL were given 

copies of their results and encouraged to make an appointment 

with their personal physicians.

CBP officers working in the primary and secondary vehicle 

inspection areas were not exposed to heat stress and strain that 

exceeded the occupational recommendations during the NIOSH 

evaluation. However, ambient temperatures may be warmer at 

other times during the summer, raising the potential for heat stress 

and strain [NOAA 2000].

The NIOSH recommended ceiling limit for CO was exceeded for 

some of the CBP officers. These CBP officers’ peak CO exposures 

lasted less than a minute and were associated with inspection 

Discussi

Conclusion
Page 8 Health Hazard Evaluation Report 2005-0215-3099

Conclusion

(continued) activities near a vehicle exhaust pipe. However, no CBP officer

monitored for CO exceeded a full shift OEL, and none of the 

participants exceeded the ACGIH BEI for %COHb.

The following recommendations help identify potential heat 

stress and strain risks and help limit heat-related illnesses in CBP 

officers.

1. Develop a heat-acclimatization program to decrease the risk 

of heat-related disorders. Such a program involves exposing 

CBP officers to hot work environments for progressively 

longer periods. NIOSH recommends that CBP officers who 

have had previous experience in jobs where heat levels are 

high enough to produce heat stress (CBT and heart rate 

increase, but do not exceed recommended levels) should 

work in the environment 50% of the shift on day one, 60% 

on day two, 80% on day three and 100% on day four. New 

CBP officers who will be similarly exposed should start with 

20% on day one, with a 20% increase in exposure each 

additional day [NIOSH 1986]. The duration of exposure 

required for full acclimatization is highly variable between 

individuals, and some CBP officers may be able to work 

a full shift before this process is completed. The body’s 

acclimatization will continue to improve each day in that 

hot environment for up to 3 weeks.

2. Develop inservice education programs to ensure that all 

CBP officers potentially exposed to hot environments 

stay current on heat stress and heat stress prevention 

information. CBP officers working in the outside inspection 

area should have inservice education at least yearly. An 

effective heat stress training program should include at least 

the following components:

● knowledge of the hazards of heat stress

● recognition of predisposing factors, danger signs, and 

symptoms

● awareness of signs and symptoms of heat-related illness 

and first-aid procedures for treatment

● CBP officer responsibilities in avoiding heat stress 

and informing their healthcare providers of their 

occupational exposures

Recommendatio
Health Hazard Evaluation Report 2005-0215-3099 Page 9

Recommendatio

(continued) ● medical conditions that may increase the risk of heatrelated illnesse

● information that certain prescription medications can 

interfere with the body’s compensation mechanisms for 

heat stress and dehydration

● dangers in using drugs of any type (over-the-counter, 

prescription, or illicit) with stimulant properties, in hot 

and physically demanding work environments, as these 

substances increase the demand on the heart

● education of employees that alcoholic beverages will 

worsen dehydration in hot environments and should 

not be used for rehydration purposes

● preventive measures that can be taken to reduce heat 

stress

● encouraging CBP officers to take their breaks in a cool 

location such as the break room

3. Monitor environmental heat exposures during the hottest 

parts of the summer using a WBGT monitor at, or as close 

as possible to, the area where the CBP officers are exposed. 

CBP officers’ break areas and other work areas may differ 

in temperature and should also be measured; results should 

be used to calculate hourly TWA WBGTs. Make at least 

hourly WBGT measurements during the hottest part of 

each shift, during the hottest parts of the year, and when 

heat waves occur or are predicted to occur. If two sequential 

measurements exceed the applicable recommendations 

(NIOSH RAL or REL, or ACGIH TLV), then work 

conditions should be modified until two more sequential 

WBGT measurements are within these exposure limits. On 

these days, administrative controls such as increasing the 

number of breaks and CBP officers in the inspection area, 

use of cooling methods, and additional awareness training 

can be implemented to help reduce the risk of heat-related 

illness.

4. Establish criteria for the declaration of a heat alert. 

For example, a heat alert may be declared if the area 

weather forecast for the next day predicts a maximum air 

temperature of 95°F or higher, or 90°F if this temperature 

is 9°F above the maximum reached in any of the preceding 

3 days. Procedures to follow during the state of heat alert 

include:
Page 10 Health Hazard Evaluation Report 2005-0215-3099

Recommendatio

(continued) ● increasing the number of CBP officers in each team to

reduce each employee’s metabolic rate

● increasing rest allowances

● reminding CBP officers to drink small amounts of water 

frequently to prevent dehydration and maintain body 

weight, and to weigh themselves before and after the 

shift

● checking CBP officers’ oral temperature and pulse 

during their most severe heat-exposure period

● exercising additional caution on the first day of a shift 

change to make sure CBP officers are not overexposed 

to heat, because they may have lost some of their 

acclimatization over the weekend and during days off

● restricting overtime work

5. Develop a heat-related illness surveillance program that 

includes establishing and maintaining accurate records 

of any heat-related disorder events and noting the 

environmental and work conditions at the time of disorder. 

Such events may include repeated accidents, episodes of 

heat-related disorders, or frequent health-related absences. 

Job-specific clustering of specific events or illnesses should 

be followed up by environmental and personal monitoring 

and medical evaluations.

6. Ensure that CBP officers stay hydrated and do not lose 

more than 1.5% body weight during their shift. Always 

provide cool (50°F–60°F) water or any cool liquid (except 

alcoholic beverages) and encourage CBP officers to drink 

small amounts frequently (e.g., one cup every 20 minutes). 

Drinking from individual containers improves water 

intake over the use of drinking fountains. Although some 

commercial drinks contain salt, this is not a necessary 

requirement because most people add enough salt to their 

diets to accommodate working in this environment.

7. Allow CBP officers to take unscheduled breaks if they report 

feeling weak, nauseated, excessively fatigued, confused, and/

or irritable on days with high temperatures. Any individual 

experiencing loss of consciousness should be immediately 

transferred to the nearest emergency department for 

treatment of possible heat stroke, the most severe form of 

heat stress. These heat strain symptoms, and any other signs 
Health Hazard Evaluation Report 2005-0215-3099 Page 11

Recommendatio

(continued

Referenc

of heat overexposure, should be reported by CBP officers to 

their supervisor for investigation and follow-up.

The following recommendations can help reduce CO exposures 

and related illnesses in CBP officers.

1. Require all drivers entering the primary inspection area to 

turn off their vehicle when the CBP officer is inspecting 

the undercarriage. Turning off the vehicle will reduce peak 

exposures caused by the vehicle’s exhaust. CBP officers 

indicated that vehicles are often left running because a large 

number fail to restart if they are shut off. If this remains a 

concern, CBP should evaluate having a tow truck on site to 

clear the stalled vehicle(s) from the inspection lane.

2. Develop a hazard communication program using the OSHA 

hazard communication standard as a program guideline. 

Sample programs can be found on the OSHA website at 

www.osha.gov/SLTC/hazardcommunications/index.html.

3. Continue CBP officer rotation even if it is not required 

for security reasons. The rotation acts as an administrative 

control by lowering the average CO exposure over a work 

shift.

4. Monitor CBP officers’ CO exposure when changes in 

the workplace are made and compare these results with 

applicable OELs. Changes in ambient conditions, vehicle 

traffic, work practices, and a variety of other variables could 

greatly affect these results.

NOAA [2000]. Climatography of the United States report No. 

20: El Paso Intl AP, TX. Asheville, NC: U.S. Department of 

Commerce, National Oceanic and Atmospheric Administration, 

National Environmental Satellite, Data, and Information Service.

NIOSH [1986]. Criteria for a recommended standard: 

occupational exposure to hot environments, rev. Cincinnati, OH: 

U.S. Department of Health and Human Services, Centers for 

Disease Control, National Institute for Occupational Safety and 

Health, DHHS (NIOSH) Publication No. 86-113.
Page 12 Health Hazard Evaluation Report 2005-0215-3099

Heat Stress 

We evaluated the heat stress conditions in the outside vehicle inspection areas by collecting WBGT 

measurements using four QUESTemp°36 instruments (Quest Technologies, Inc., Oconomowoc, 

Wisconsin). These monitors measure temperatures of 23°F–212°F and are accurate to within ± 0.9°F. In 

addition to temperature, the monitors measure relative humidity of 0%–100% and are accurate to within 

± 5%. The WBGT index accounts for air velocity, temperature, humidity, and radiant heat and is a useful 

index of the environmental contribution to heat stress. WBGT is a function of dry bulb temperature (a 

standard measure of air temperature taken with a thermometer), natural wet bulb temperature (simulates 

the effects of evaporative cooling), and black globe temperature (estimates radiant [infrared] heat load). 

The WBGT monitors were placed throughout the primary and secondary vehicle inspection areas and in 

the head house. The monitors were set up to data log continuously. WBGT measurements were collected 

to document the heat stress conditions during the time that heat strain monitoring was conducted. 

Appendix B contains a discussion of occupational exposure limits and the health effects of working in hot 

environments.

Heat Strain 

We assessed CBP officers’ heat strain by collecting CBT measurements using the CorTempTM Wireless 

Core Body Temperature Monitoring System (HQ, Inc., Palmetto, Florida). The CorTemp Temperature 

Sensor is swallowed and provides continuous monitoring of CBT to within ± 0.2°F. The sensor, intended 

for one-time use only, is passed through the gastrointestinal tract and exits the body in an average time of 

72 hours. The sensor transmits the temperature to the CT2000 data logger. The participants’ CBTs were 

recorded at 1-minute intervals.

We also assessed heat strain by collecting heart rate measurements using the Mini-Mitter Mini-Logger® 

Series 2000 (Mini-Mitter Company, Inc., Bend, Oregon) with a Polar® chest band heart rate monitor. The 

Polar chest band heart rate monitor counts up to 250 bpm and is accurate to within ± 1 bpm. Heart rate 

was monitored at 1-minute intervals.

We measured participants’ preshift and postshift body weights to determine their degree of dehydration. 

Participants were weighed in uniform clothing near the beginning and end of the work shift using a selfcalibrating electronic digital scale Model 812 (Measurement Specialties, Inc., Fairfield, New Jersey).

Following informed consent, preshift and postshift blood chemistry levels and hematology quantities were 

measured using the i-STAT® handheld analyzer, with i-STAT 8+ cartridges. Blood chemistries included 

serum sodium, potassium, chloride, BUN, and glucose. Hemoglobin and hematocrit (number of red 

blood cells per volume of blood) were also measured. Dehydration results in an increase in serum sodium, 

BUN, and hematocrit, whereas hyperhydration results in their decrease. Whole blood (65–95 microliters) 

was placed in the well of the cartridge prior to inserting the cartridge into the analyzer. Serum osmolality, 

dissolved particle concentration in the blood, is measured in mosm/L and was calculated from the blood 

Appendix A: Metho
Health Hazard Evaluation Report 2005-0215-3099 Page 13

Appendix A: Method  (continu

chemistries using the following formula [Wallach 2000].

A corrected serum sodium must be calculated for persons with elevated glucose levels because high serum 

glucose (> 100 mg/dL) can cause measurements of serum sodium to be falsely low. The formula for the 

corrected serum sodium is:

All participants completed a short heat stress questionnaire at the postshift assessment. This questionnaire 

included questions on medical history, possible heat stress symptoms, and factors that would affect 

acclimatization.

Carbon Monoxide 

We assessed participants’ CO exposure by collecting PBZ air measurements using Toxi Ultra single gas 

detectors (Biosystems, Middletown, Connecticut). These detectors data log the CO levels in real time at 

1-minute intervals. The full shift TWA exposure and peak exposures were calculated. The detectors use 

an electrochemical cell to detect CO levels and were calibrated daily on site prior to use. The detectors 

are capable of measuring CO levels of 0–1,000 ppm; the generally accepted accuracy of electrochemical 

sensors is ± 5% or ± 2 ppm, whichever is greater. Potential interfering compounds found in vehicular 

exhaust include sulfur dioxide, nitrogen dioxide, nitric oxide, and hydrogen.

We also conducted biological monitoring to assess employees’ CO exposure over the course of their shift. 

We used the MicroCO Meter (Micro Medical Limited, Rochester, Kent, United Kingdom) to measure CO 

in exhaled breath. The MicroCO Meter then calculates a corresponding %COHb that can be compared 

with the ACGIH BEI for COHb. The %COHb is used as a biological indicator of CO exposure. Before 

and after the shift we asked employees to inhale, then exhale completely, and then inhale deeply and hold 

their breath for 20 seconds. At the end of 20 seconds the employee exhaled through a one-way valve on 

the MicroCO Meter over an electrochemical sensor. By looking at the difference between preshift and 

postshift %COHb levels, we were able to determine the change over the shift, irrespective of employee 

smoking status.

Reference

Wallach J [2000]. Core blood analytes: alterations by diseases. In: Wallach J, ed. Interpretation of 

diagnostic tests, 7th ed. Philadelphia, PA: Lippincott, Williams and Wilkins, pp. 68–69.
Page 14 Health Hazard Evaluation Report 2005-0215-3099

In evaluating the hazards posed by workplace exposures, NIOSH investigators use both mandatory (legally 

enforceable) and recommended OELs for chemical, physical, and biological agents as a guide for making 

recommendations. OELs have been developed by Federal agencies and safety and health organizations to 

prevent the occurrence of adverse health effects from workplace exposures. Generally, OELs suggest levels 

of exposure to which most employees may be exposed up to 10 hours per day, 40 hours per week for a 

working lifetime without experiencing adverse health effects. However, not all employees will be protected 

from adverse health effects even if their exposures are maintained below these levels. A small percentage 

may experience adverse health effects because of individual susceptibility, a preexisting medical condition, 

and/or a 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 

employee to produce health effects even if the occupational exposures are controlled at the level set by 

the exposure limit. Also, some substances can be absorbed by direct contact with the skin and mucous 

membranes in addition to being inhaled, which contributes to the individual’s overall exposure.

Most OELs are expressed as a TWA exposure. A TWA refers to the average exposure during a normal 8- 

to 10-hour workday. Some chemical substances and physical agents have recommended STEL or ceiling 

values where health effects are caused by exposures over a short period. Unless otherwise noted, the STEL 

is a 15-minute TWA exposure that should not be exceeded at any time during a workday, and the ceiling 

limit is an exposure that should not be exceeded at any time.

In the United States, OELs have been established by Federal agencies, professional organizations, state 

and local governments, and other entities. Some OELs are legally enforceable limits, while others are 

recommendations. The U.S. Department of Labor OSHA PELs (29 CFR 1910 [general industry]; 29 

CFR 1926 [construction industry]; and 29 CFR 1917 [maritime industry]) are legal limits enforceable in 

workplaces covered under the Occupational Safety and Health Act. NIOSH RELs are recommendations 

based on a critical review of the scientific and technical information available on a given hazard and the 

adequacy of methods to identify and control the hazard. NIOSH RELs can be found in the NIOSH Pocket 

Guide to Chemical Hazards [NIOSH 2005]. NIOSH also recommends different types of risk management 

practices (e.g., engineering controls, safe work practices, employee education/training, personal protective 

equipment, and exposure and medical monitoring) to minimize the risk of exposure and adverse health 

effects from these hazards. Other OELs that are commonly used and cited in the United States include 

the TLVs recommended by ACGIH, a professional organization, and the WEELs recommended by the 

American Industrial Hygiene Association, another professional organization. The TLVs and WEELs are 

developed by committee members of these associations from a review of the published, peer-reviewed 

literature. They are not consensus standards. ACGIH TLVs are considered voluntary exposure guidelines 

for use by industrial hygienists and others trained in this discipline “to assist in the control of health 

hazards” [ACGIH 2008a]. WEELs have been established for some chemicals “when no other legal or 

authoritative limits exist” [AIHA 2008].

Outside the United States, OELs have been established by various agencies and organizations and include 

both legal and recommended limits. Since 2006, the Berufsgenossenschaftliches Institut für Arbeitsschutz 

(German Institute for Occupational Safety and Health) has maintained a database of international OELs 

Appendix B: Occupational Exposure Limits & He
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Appendix B: Occupational Exposure Limits & Heacts       

from European Union member states, Canada (Québec), Japan, Switzerland, and the United States at 

www.dguv.de/bgia/en/gestis/limit_values/index.jsp. The database contains international limits for over 

1250 hazardous substances and is updated annually.

Employers should understand that not all hazardous chemicals have specific OSHA PELs, and for some 

agents the legally enforceable and recommended limits may not reflect current health-based information. 

However, an employer is still required by OSHA to protect its employees from hazards even in the absence 

of a specific OSHA PEL. OSHA requires an employer to furnish employees a place of employment free 

from recognized hazards that cause 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))]. Thus, NIOSH investigators encourage 

employers to make use of other OELs when making risk assessment and risk management decisions to 

best protect the health of their employees. NIOSH investigators also encourage the use of the traditional 

hierarchy of controls approach to eliminate or minimize identified workplace hazards. This includes, in 

order of preference, the use of: (1) substitution or elimination of the hazardous agent, (2) engineering 

controls (e.g., local exhaust ventilation, process enclosure, dilution ventilation), (3) administrative controls 

(e.g., limiting time of exposure, employee training, work practice changes, medical surveillance), and (4) 

personal protective equipment (e.g., respiratory protection, gloves, eye protection, hearing protection). 

Control banding, a qualitative risk assessment and risk management tool, is a complementary approach 

to protecting employee health that focuses resources on exposure controls by describing how a risk needs 

to be managed. Additional information on control banding is available at www.cdc.gov/niosh/topics/

ctrlbanding/. This approach can be applied in situations where OELs have not been established or can be 

used to supplement the OELs, when available.

Heat Stress 

NIOSH defines heat stress exposure as the sum of the heat generated in the body (metabolic heat) plus 

the heat gained from the environment (environmental heat) minus the heat lost from the body to the 

environment, primarily through evaporation. Many bodily responses to heat stress are desirable and 

beneficial because they help regulate internal temperature and, in situations of appropriate repeated 

exposure, help the body adapt (acclimatize) to the work environment. However, at some stage of heat 

stress, the body’s compensatory measures cannot maintain internal body temperature at the level required 

for normal functioning. As a result, the risk of heat-induced illnesses, disorders, and accidents substantially 

increases. Increases in unsafe behavior, behavior that may lead to accidents, are also seen as the level of 

physical work of the job increases [NIOSH 1986].

Many heat stress guidelines have been developed to protect people against heat-related illnesses. The 

objective of any heat stress index is to prevent a person’s CBT from rising excessively. The World Health 

Organization concluded that, “it is inadvisable for CBT to exceed 100.4°F or for oral temperature to 

exceed 99.5°F in prolonged daily exposure to heavy work and/or heat” [WHO 1969]. According to 

NIOSH, a CBT of 102.2°F should be considered reason to terminate exposure even when CBT is being 

monitored. This does not mean that an employee with a CBT exceeding those levels will necessarily 
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Appendix B: Occupational Exposure Limits & Hea          

experience adverse health effects; however, the number of unsafe acts increases as does the risk of 

developing heat stress illnesses [NIOSH 1986]. A CBT increase of only 1.8°F above normal encroaches on 

the brain’s ability to function [ACGIH 2008a].

NIOSH recommends controlling total heat exposure so that unprotected healthy employees who 

are medically and physically fit for their required level of activity are wearing, at most, long-sleeved 

work shirts and trousers or equivalent, and are not exposed to metabolic and environmental heat 

combinations exceeding the applicable NIOSH recommendations. Most healthy employees who work in 

hot environments and are exposed to combinations of environmental and metabolic heat less than the 

NIOSH RALs for nonacclimatized employees, or the NIOSH RELs for acclimatized employees, should 

be able to tolerate total heat stress without substantially increasing their risk of incurring acute adverse 

health effects. Also, no employee should be exposed to combinations of metabolic and environmental heat 

exceeding the applicable ceiling limits shown in Figures 1 or 2 without being provided with and properly 

using appropriate and adequate heat-protective clothing and equipment [NIOSH 1986].

 

Figure 1. Recommended heat-stress alert Figure 2. Recommended heat-stress limits

limits (unacclimatized employees). (acclimatized employees).

ACGIH guidelines require the use of a decision-making process that provides step-by-step situationdependent instructions that factor in clothing insulation values and physiological evaluation of heat strain 

[ACGIH 2008b]. ACGIH WBGT screening recommendations factor in the ability of the body to cool 

itself (clothing insulation value, humidity, and wind) and, like the NIOSH recommendations, can be 

used to develop work/rest regimens for employees. The ACGIH WBGT-based heat exposure assessment 

was developed for a traditional work uniform of long-sleeved shirt and pants, and represents conditions 

under which it is believed that nearly all adequately hydrated, unmedicated, healthy employees may be 
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Appendix B: Occupational Exposure Limits & Heacts       

repeatedly exposed without adverse health effects. Clothing insulation values and the appropriate WBGT 

adjustments, as well as descriptors of the other decision-making process components can be found in 

ACGIH’s Documentation of the Threshold Limit Values for Chemical Substances and Physical Agents and Biological 

Exposure Indices [ACGIH 2008b]. The ACGIH TLV for heat stress provides a framework for the control 

of heat-related illnesses only. Although accidents and injuries can increase with increasing levels of heat 

stress, the TLVs are not directed toward controlling these [ACGIH 2008a].

NIOSH and ACGIH recommendations can only be used when WBGT data for the immediate work 

area are available and must not be used when employees wear encapsulating suits or garments that are 

impermeable or highly resistant to water vapor or air movement. Further assumptions regarding work 

demands include an 8-hour work day, 5-day work week, two 15-minute breaks, and a 30-minute lunch 

break, with rest area temperatures the same as, or less than, those in work areas, and at least some air 

movement. It must be stressed that because NIOSH and ACGIH guidelines do not establish a fine line 

between safe and dangerous levels, professional judgment must be used in administering a heat stress 

management program to ensure adequate protection. The OSHA technical manual’s section on heat stress 

refers back to the ACGIH document for guidelines to evaluate employee heat stress and how to investigate 

the workplace [OSHA 1999].

Heat Strain

The body’s response to heat stress is called heat strain [NIOSH 1986; ACGIH 2008b]. Operations 

involving high air temperatures, radiant heat sources, high humidity, direct physical contact with hot 

objects, and strenuous physical activities have a high potential for inducing heat strain in employees. Heat 

strain is highly individual and cannot be predicted based upon environmental heat stress measurements. 

Physiological monitoring for heat strain becomes necessary when impermeable clothing is worn, when 

heat stress recommendations are exceeded, or when data from a detailed analysis (such as the International 

Standards Organization required sweat rate) shows excess heat stress [ACGIH 2008b].

One indicator of physiological strain, sustained peak heart rate, is considered by ACGIH to be the best 

sign of acute, high-level exposure to heat stress. Sustained peak heart rate, defined by ACGIH as 180 bpm 

minus an individual’s age, is a leading indicator that thermal regulatory control may not be adequate 

and that increases in CBTs have, or will soon, occur. Sustained peak heart rate represents an equivalent 

cardiovascular demand of about 75% of maximum aerobic capacity. During an 8-hour workshift, although 

sustained peak demands may not occur, excessive demand may still be placed on the cardiovascular system. 

These ‘chronic’ demands can be measured by calculating the average heart rate over the shift [ACGIH 

2008b]. A study of Marine Corps recruits revealed that decreases in physical job performance were 

observed when the average heart rate exceeded 115 bpm over the entire shift. This level is equivalent to 

working at roughly 35% of maximum aerobic capacity, a level sustainable for 8 hours [Minard 1961].

According to ACGIH, an individual’s heat stress exposure should be discontinued when any of the 

following excessive heat strain indicators occur:
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Appendix B: Occupational Exposure Limits & Hea          

● Sustained (over several minutes) heart rate is in excess of 180 bpm minus the individual’s age in 

years, (180 bpm – age) for those with normal cardiac performance

● CBT is greater than 100.4°F for unselected, unacclimatized personnel and greater than 101.3°F for 

medically fit, heat-acclimatized personnel

● Recovery heart rate at 1 minute after a peak work effort exceeds 110 bpm

● Symptoms of sudden and severe fatigue, nausea, dizziness, or lightheadedness

An individual may be at greater risk of heat strain if:

● Profuse sweating is sustained over several hours

● Weight loss over a shift is greater than 1.5% of body weight

● 24-hour urinary sodium excretion is less than 55 millimoles

Health Effects of Exposure to Hot Environments 

Heat disorders and health effects of individuals exposed to hot working environments include (in 

increasing order of severity) skin disorders (heat rash, hives, etc.), heat syncope (fainting), heat cramps, 

heat exhaustion, and heat stroke. Heat syncope results from blood flow being directed to the skin for 

cooling, resulting in decreased supply to the brain, and most often strikes employees who stand in place 

for extended periods in hot environments. Heat cramps, caused by sodium depletion due to sweating, 

typically occur in the muscles employed in strenuous work. Heat cramps and syncope often accompany 

heat exhaustion, or weakness, fatigue, confusion, nausea, and other symptoms. The dehydration, sodium 

loss, and elevated CBT (above 100.4°F) are usually due to performing strenuous work in hot conditions 

with inadequate water and electrolyte intake. Heat exhaustion may lead to heat stroke if the patient is not 

quickly cooled and rehydrated.

While heat exhaustion victims continue to sweat as their bodies struggle to stay cool, heat stroke victims 

cease to sweat as their bodies fail to maintain an appropriate core temperature. Heat stroke occurs when 

hard work, hot environment, and dehydration overload the body’s cooling capacity. Heat stroke is a lifethreatening emergency requiring immediate medical attention. Signs and symptoms include irritability, 

confusion, nausea, convulsions or unconsciousness, hot dry skin, and a CBT above 106°F. Death can 

result from damage to the brain, heart, liver, or kidneys [Cohen 1990].

Prolonged increases in CBT and chronic exposures to high levels of heat stress are associated with 

disorders such as temporary infertility (male and female), elevated heart rate, sleep disturbance, fatigue, 

and irritability. During the first trimester of pregnancy, a sustained CBT greater than 102.2°F may 

endanger the fetus [ACGIH 2008a]. In addition, one or more occurrences of heat-induced illness in a 

person predisposes him/her to subsequent injuries and can result in temporary or permanent loss of that 

person’s ability to tolerate heat stress [NIOSH 1986; OSHA 1999].
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Appendix B: Occupational Exposure Limits & Heacts       

The level of heat stress at which health effects occur is highly individual and depends upon the heat 

tolerance capabilities of each individual. Age, weight, degree of physical fitness, degree of acclimatization, 

metabolism, alcohol or illicit drugs, over-the-counter and prescribed medications, and a variety of medical 

conditions, such as hypertension and diabetes, all affect a person’s sensitivity to heat. At greatest risk are 

unacclimatized employees, people performing physically strenuous work, those with previous heat illnesses, 

the elderly, people with cardiovascular or circulatory disorders (diabetes, atherosclerotic vascular disease), 

those taking medications that impair the body’s cooling mechanisms, people who use alcohol or who used 

it recently, people in poor physical condition, and those recovering from illness. Prescribed medications 

such as beta blockers and calcium-channel blockers, which are used to treat hypertension, limit maximal 

cardiac output and alter normal vascular distribution of blood flow in response to heat exposure. 

Diuretics, such as alcohol, can limit cardiac output and affect heat tolerance and sweating; antihistamines, 

phenothiazines, and cyclic antidepressants can impair sweating.

Acclimatization 

When employees are first exposed to a hot environment, they show signs of distress and discomfort, 

experience increased CBTs and heart rates, and may have headaches and/or nausea. Repeated exposure 

results in marked adaptation to the hot environment known as acclimatization. Acclimatization is 

the process that allows the body to begin sweating sooner and more efficiently, reduces electrolyte 

concentrations in the sweat, and allows the circulation to stabilize so that the employee can withstand 

greater amounts of heat stress while experiencing reduced heat strain signs and symptoms.

Acclimatization begins with consecutive exposures to working conditions for 2 hours at a time, with a 

requisite rise in metabolic rate. This will cause the body to reach 33% of optimum acclimatization by the 

fourth day of exposure. Cardiovascular function will stabilize, and surface and internal body temperatures 

will be lower by day 8 when the body has reached 44% of optimum acclimatization. A decrease in sweat 

and urine electrolyte concentrations is seen at 65% of optimum (day 10); 93% of optimum is reached by 

day 18, and 99% by day 21 [ACGIH 2008b].

The loss of acclimatization begins when the activity under those heat stress conditions is discontinued, 

and a noticeable loss occurs after 4 days. This loss is usually rapidly made up so that by Tuesday, employees 

who were off on the weekend are as well acclimatized as they were on the preceding Friday. Chronic 

illness, an acute episode of mild illness (e.g., gastroenteritis), the use or misuse of pharmacologic agents, 

a sleep deficit, a suboptimal nutritional state, or a disturbed water and electrolyte balance may reduce the 

employee’s capacity to acclimatize [ACGIH 2008b].

Dehydration and Hyponatremia

When working in hot environments it is often difficult to completely replace lost fluids as the day’s work 

proceeds. High sweat rates with excessive loss of body fluids may result in dehydration and electrolyte 
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Appendix B: Occupational Exposure Limits & Hea          

imbalances [Bates et al. 1996]. Some studies have shown that even small deficits adversely affect 

performance [Sawka et al. 1993]. Dehydration also negates the advantage granted by high levels of aerobic 

fitness and heat acclimatization [Ekblom et al. 1970].

Several studies have shown that dehydration increases CBT during exercise in temperate and hot environments; 

a deficit of only 1% of body weight increases CBT during exercise. As the magnitude of the water deficit 

increases, an accompanying elevation in CBT occurs when exercising in the heat. The magnitude of this 

elevation ranges from 0.2°F–0.4°F for every 1% body weight loss [Sawka et al. 1979]. A 2% loss of body weight 

is generally accepted as the threshold for thirst stimulation [Szlyk et al. 1989]. A 3% decrease in body weight 

causes an increase in heart rate, depressed sweating sensitivity, and a substantial decrease in physical work 

capacity [Candas et al. 1986].Some investigators have reported that a 4%–6% water deficit has been associated 

with anorexia, impatience, and headache, while a 6%–10% deficit is associated with vertigo, shortness of 

breath, cyanosis, and spasticity. With a 12% water deficit, an individual will be unable to swallow and will need 

assistance with rehydration. Body weight loss of 1.5% or less indicates mild dehydration, whereas a loss of 

greater than 1.5% indicates a greater risk of heat stress.

Because water is the most abundant constituent in the body, comprising approximately 60% of the body 

weight in men and 50% in women, maintaining enough water improves the body’s overall function. Total 

body water is distributed in two major compartments: 55%–75% is intracellular fluid and 25%–45% is 

extracellular fluid [Singer and Brenner 1998]. The solute, or dissolved particle concentration of a fluid, 

is known as its osmolality, expressed as mosm/L. The major extracellular fluid component is sodium; 

therefore, extracellular fluid volume reflects total body sodium content.

Normal plasma osmolality ranges from 275–290 mosm/L and is kept within a narrow range by 

mechanisms capable of sensing a 1%–2% change in plasma concentration. Most people have an 

obligate water loss consisting of urine, stool, and evaporation from the skin and respiratory tract. In 

order to maintain a steady state, water intake must equal water excretion. Disorders of water regulation 

result in hyponatremia or hypernatremia. Changes in urine and plasma osmolality are better suited 

for diagnosing hydration status than changes in hematocrit, serum protein, and BUN, which are more 

dependent on factors other than hydration [Wallach 2000; ACGIH 2008a]. The primary stimulus for 

water ingestion is thirst, which can be triggered by the following physiological mechanisms: an increase in 

osmolality, a decrease in extracellular fluid volume, or a decrease in blood pressure. Osmoreceptors in the 

hypothalamus are stimulated by a rise in serum concentration. The average osmotic threshold for thirst is 

approximately 295 milliosmoles per kilogram and varies among individuals. Under normal circumstances, 

daily water intake exceeds physiological requirements [Rolls 1993].

In addition to dehydration, there is also the matter of electrolyte depletion as a factor in heat stress, 

Sodium, a vital electrolyte, is excreted as the body sweats in order to utilize evaporative cooling. Two of the 

many functions of sodium in the body are to conduct impulses along neurons and maintain concentration 

gradients in the kidney for proper urine production.
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Appendix B: Occupational Exposure Limits & Heacts       

Most individuals with acute exercise-induced heat disorder are dehydrated with normal to mildly increased 

serum sodium and serum osmolality (hypernatremia). Hyponatremia develops when serum sodium levels 

drop below 135 mEq/L and is a life-threatening condition that has been recognized as a potential health 

consequence of endurance activities conducted in hot environments. Increased water intake prior to 

and during activities in hot environments is highly emphasized to prevent dehydration and heat illness. 

However, drinking too much water can lead to decreased serum sodium concentrations (water toxicity or 

hyponatremia) and has been recognized as an increasing problem among U.S. military recruits [Gardner 

2002].

Hyponatremia may occur with hypo-, hyper-, or normal hydration status [Roetzheim 1991]. Symptomatic 

and potentially life-threating hyponatremia can occur when blood sodium concentrations decrease to 

less than 130 mEq/L and is generally caused by hypervolemia (water overload) secondary to extensive 

overdrinking. Many people with hyponatremia have increased their total body water by about 1 gallon to 

achieve such low serum sodium values [Montain et al. 1999].

Most cases of hyponatremia result from the inability of the kidneys to excrete appropriately diluted urine. 

The most significant clinical signs of hyponatremia involve the central nervous system, where symptoms 

vary from subtle changes in one’s ability to think and decreases in energy levels to severe alterations, such 

as coma or seizure. Symptoms generally parallel the rate of development and degree of hyponatremia 

[Devita 1993].

Fluid Replacement

Palatability of any fluid replacement solution is important to ensure adequate rehydration. Evidence shows 

that adding sweeteners to drinks leads to increased consumption. Glucose-electrolyte solutions have been 

shown to facilitate sodium and water absorption. Also, the glucose in these solutions provides energy for 

muscular activity in endurance events that require vigorous exercise [Rolls 1990]. However, employees 

should be cautioned to avoid drinking large amounts of sugar-laden beverages in hot climates as this causes 

an osmotic diuresis that increases fluid loss through urination. Alcohol intake also increase urinary fluid 

loss and should be avoided. The temperature of the drink also influences consumption of fluids. Ideally, 

fluids should be ingested at temperatures of 50°F–60°F, in small quantities (5–7 ounces), and at frequent 

intervals (every 15–20 minutes).

Average Americans consume adequate, if not excessive, amounts of sodium in their usual diet such that for 

mild dehydration, only water replacement is needed. However, in moderate dehydration or when involved 

in events resulting in prolonged sweating, electrolyte (i.e., sodium) replacement is indicated. Many oral 

electrolyte replacement formulas such as Gatorade® are available. Salt tablets are not recommended as 

they can irritate the stomach, leading to vomiting, which can exacerbate fluid losses and do not address 

water replacement needs. Those with nausea and vomiting from heat stress may require intravenous saline 

administration to replace their water and sodium.
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Appendix B: Occupational Exposure Limits & Hea          

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 any other symptoms. Coma or death may occur if high exposures continue. 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 pre-existing 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 occupying the oxygen 

binding sites on hemoglobin to form COHb. Once absorbed in the bloodstream, the half life (time it takes 

for half of the substance to be removed) of CO disappearance from the blood varies widely by individual 

and circumstance (e.g., removal from exposure, initial COHb concentration, partial pressure of oxygen 

after exposure, etc.). Under normal recovery conditions breathing ambient air, the expected half life is 

approximately 5 hours [Tomaszewski 2002].

The OSHA PEL for CO is 50 ppm for an 8-hour TWA exposure. The NIOSH REL for CO is 35 ppm 

for a 10-hour TWA exposure, with a ceiling of 200 ppm that should not be exceeded [NIOSH 1992]. 

The NIOSH REL is designed to protect employees from health effects associated with COHb levels that 

exceed 5% [NIOSH 1972]. NIOSH has established the IDLH for CO as 1,200 ppm. The IDLH exposure 

conditions pose “a threat of exposure to airborne contaminants when that exposure is likely to cause death 

or immediate or delayed permanent adverse health effects or prevent escape from such an environment” 

[NIOSH 2004].

ACGIH recommends an 8-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 [ACGIH 2008a]. ACGIH also recommends that exposures never 

exceed five times the TLV (thus, never to exceed 125 ppm) [ACGIH 2008b]. ACGIH recommends a BEI 

for end of shift COHb in blood of 3.5% [ACGIH 2008a]. The BEI indicates a concentration below which 

nearly all employees should not experience adverse health effects. The BEI cannot be applied to current 

smokers because they have been shown to have COHb levels between 4% and 10%, and can exceed 15% 

in heavy smokers [ACGIH 2008a; Tomaszewski 2002]. The World Health Organization established the 

reference ranges for COHb between 1%–2% for nonsmokers and 3%–8% for smokers [WHO 1999].

References

ACGIH [2008a]. 2008 TLVs® and BEIs®: threshold limit values for chemical substances and physical 

agents and biological exposure indices. Cincinnati, OH: American Conference of Governmental 

Industrial Hygienists.
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Appendix B: Occupational Exposure Limits & Heacts       

ACGIH [2008b]. Documentation of the threshold limit values and biological exposure indices. 7th ed. 

Cincinnati, OH: American Conference of Governmental Industrial Hygienists; 2002–2008 Suppl.

AIHA [2008]. AIHA 2008 Emergency response planning guidelines (ERPG) & workplace environmental 

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Acknowledgments a

Availability of Re

The Hazard Evaluations 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 Administration (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 employer 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.

The findings and conclusions in this report are those of the 

authors and do not necessarily represent the views of NIOSH. 

Mention of any company or product does not constitute 

endorsement by NIOSH. In addition, citations to websites 

external to NIOSH do not constitute NIOSH endorsement 

of the sponsoring organization or their programs or products. 

Furthermore, NIOSH is not responsible for the content of these 

websites. All Web addresses referenced in this document were 

accessible as of the publication date.

This report was prepared by Chad H. Dowell and Judith Eisenberg 

of HETAB, Division of Surveillance, Hazard Evaluations and Field 

Studies (DSHEFS). Industrial hygiene field assistance was provided 

by Brad King. Medical field assistance was provided by Sang Woo 

Tak. Health communication assistance was provided by Stefanie 

Evans. Editorial assistance was provided by Ellen Galloway. 

Desktop publishing was performed by Robin Smith.

Copies of this report have been sent to employee and management 

representatives at the U.S. Customs and Border Protection, the 

state health department, and the OSHA Regional Office. This 

report is not copyrighted and may be freely reproduced. The report 

may be viewed and printed from www.cdc.gov/niosh/hhe. Copies 

may be purchased from the National Technical Information Service 

(NTIS) at 5825 Port Royal Road, Springfield, Virginia 22161.
Below is a recommended citation for this report:

NIOSH [2009]. Health hazard evaluation report: evaluation of heat and carbon 

monoxide exposures to border protection officers, El Paso, TX. By Dowell C, 

Eisenberg J. Cincinnati, OH: U.S. Department of Health and Human Services, 

Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health, NIOSH HETA No. 2005-0215-3099. 

To receive NIOSH documents or information about 

occupational safety and health topics, contact NIOSH at:

1-800-CDC-INFO (1-800-232-4636)

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