Evaluation of Heat 

Stress at a Glass Bottle 

Manufacturer

Chad H. Dowell, MS, CIH

Loren C. Tapp, MD, MS

Health Hazard Evaluation Report

HETA 2003-0311-3052

Owens-Illinois

Lapel, Indiana

November 2007

DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention 

Workplace

Safety and Health

 National Institute for Occupational 

Safety and Health
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 2003-0311-3052 Page i

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

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

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

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

Assessment.........................................................................3

Results and Discussion .......................................................4

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

Recommendations...............................................................7

References ........................................................................10

Contents

Appendix A

Appendix B

Appendix C

NIOSH-Recommended Heat-Stress Alert and Heat-Stress 

Exposure Limits ................................................................20

Acknowledgements and Availability of Report...................21

Occupational Exposure Limits & Health Effects ................11

Estimating Metabolic Heat Production Rates by Task 

Analysis .............................................................................17

Use of Personal Monitoring Methods to Reduce HeatRelated Illness...................................................................19

Appendix 

Acknowledgment
Page ii Health Hazard Evaluation Report 2003-0311-3052

ACGIH® American Conference of Governmental Industrial Hygienists

BPM beats per minute

BUN blood urea nitrogen

CBT core body temperature

CFR Code of Federal Regulations

ECF extracellular fluid

ICF intracellular fluid

ISO International Standards Organization

kcal/hour kilocalories per hour

kcal/min kilocalories per minute

lbs pounds

mEq/L milliequivalents per liter

mosm/L milliosmoles per liter 

NIOSH National Institute for Occupational Safety and Health

NOAA National Oceanic and Atmospheric Administration

OEL occupational exposure limit

OSHA Occupational Safety and Health Administration

PEL permissible exposure limit

RAL recommended action limit

REL recommended exposure limit

SRreq required sweat rate

STEL short term exposure limit

TLV® threshold limit value

TWA time-weighted average

WBGT wet bulb globe temperature

WEEL workplace environmental exposure limits 

Abbreviat
Health Hazard Evaluation Report 2003-0311-3052 Page iii

The National Institute for 

Occupational Safety and 

Health (NIOSH) received 

a confidential employee 

request for a health hazard 

evaluation (HHE) at OwensIllinois in Lapel, Indiana. A 

group of employees submitted 

the HHE request because 

of a concern with the hot 

working conditions in the 

forming department. NIOSH 

investigators conducted an 

HHE in September 2006.

Highlights of 

NIOSH 

Hazard Eval

What NIOSH Did

● We talked with management and union officials about the hot 

working conditions.

● We measured employees’ exposure to the heat in the forming 

department.

● We interviewed forming department employees about their 

work environment.

● We reviewed injury and illness records.

What NIOSH Found

● Employees were not exposed to excessive heat at the time of the 

NIOSH evaluation.

● There is a chance for greater heat exposure during the hotter 

summer months.

● Some employees had heat-related symptoms on hot summer 

days before the NIOSH evaluation.

● Some employees said they were not trained on hot working 

environment hazards.

● No formal heat stress management program was in place.

What Managers Can Do

● Set up a preventive maintenance schedule for the man coolers 

and swamp coolers.

● Let employees take unscheduled breaks if they feel weak, 

nauseated, excessively tired, confused, and/or irritable due to 

the heat.

● Develop a continuing education program about the hot 

working environment.

● Develop a heat-related illness surveillance program.

● Check heat exposures.

● Start a heat alert program.

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.

● Work with a buddy, and watch for signs and symptoms of 

excessive heat exposure in one another.
Page iv Health Hazard Evaluation Report 2003-0311-3052

In August 2003, NIOSH received a confidential employee request 

for an HHE at Owens-Illinois in Lapel, Indiana. The requestors 

were concerned about heat-related illnesses among employees 

exposed to the hot conditions in the forming department. In 

response to this request, NIOSH investigators visited the facility 

in September 2006. We conducted an opening conference with 

management and union representatives, a walk-through survey of 

the forming department, confidential medical interviews, a review 

of the Logs of Work-Related Injuries and Illnesses (OSHA’s Form 

300), and heat stress measurements in the forming department.

At the time of this NIOSH evaluation we found that workers 

in the forming department were not exposed to heat stress in 

excess of the NIOSH and ACGIH screening criteria. However, 

environmental temperatures may be warmer than those on the days 

of our evaluation, making it more likely that NIOSH and ACGIH 

heat stress screening criteria would be exceeded and that employees 

would be at increased risk for heat stress.

Interviews with forming department employees and a review of the 

Logs of Work-Related Injuries and Illnesses (OSHA’s Form 300) 

found that some workers reported that they had developed heat 

strain symptoms during their shifts on hot summer days.

This report includes recommendations to help identify potential 

heat stress and strain risks and how to limit heat-related illnesses 

in hot end workers. These recommendations include creating 

a formal heat stress management program regarding heat 

acclimatization, continuing education for heat stress prevention, 

heat-related illness surveillance, environmental heat exposure 

monitoring, criteria for heat alerts, and preventive maintenance of 

man coolers and swamp coolers.

Environmental temperature 

measurements and work 

load assessments during 

this evaluation showed that 

workers in the forming 

department were not exposed 

to heat stress in excess of the 

occupational screening criteria. 

However, some employees 

reported developing heat 

strain symptoms during their 

shifts on hot summer days. 

We recommend the company 

create a formal heat stress 

management program.

Summ

Keywords: NAICS 327213 (Beverage containers, glass, 

manufacturing), heat stress, heat strain, hot work environment, glass, 

glass bottles
Health Hazard Evaluation Report 2003-0311-3052 Page 1

Introduct

In August 2003, NIOSH received a confidential employee request 

to perform an HHE at Owens-Illinois in Lapel, Indiana. The 

request concerned heat-related illnesses among employees exposed 

to the hot working environment in the hot end of the plant, which 

includes the forming department. Based on discussions with the 

employee requestors, the initial visit to Owens-Illinois was delayed 

until September 2006, following the completion of another 

unrelated HHE at this facility.

On September 12, 2006, we held an opening conference with 

Owens-Illinois management; the Glass, Molders, Pottery, Plastics 

and Allied Workers International Union, Local 207; and 

international union representatives. The meeting included an 

overview of the NIOSH HHE program, a review of the issues that 

prompted the HHE request, and a discussion of the scope of this 

evaluation. After the meeting, a walk-through survey of the forming 

department was conducted. On September 13, 2006, confidential 

medical interviews were conducted with all forming department 

employees present on the first and second shifts, and heat stress 

measurements were taken in the forming department.

Process Description

Owens-Illinois manufactures glass containers for the beer, spirit, 

juice, and tea industries at the Lapel, Indiana, facility. This plant 

is approximately 100 years old, and employs approximately 200 

production, packing, and shipping workers. Approximately 30 

employees work in the forming department. Operations are 

continuous, with four crews (A, B, C, and D) working 8-hour shifts 

that rotate weekly, and a Z crew that works an 8-hour shift Monday 

through Friday. 

In the hot end of the glass-making process, raw materials (cullet 

[recycled glass], sand, soda ash, and limestone) are melted together 

in a gas furnace at temperatures of 2,300°F to 2,800°F. The molten 

glass is cut into uniform gobs and sent to one of four individual 

section forming machines that force the molten gobs into a mold. 

The glass containers are then conditioned in an annealing lehr. 

The glass containers are then inspected and packaged for shipment 

to the customer. About 500 bottles are manufactured per minute 

on each of the four lines.
Page 2 Health Hazard Evaluation Report 2003-0311-3052

Introduction (contin

Owens-Illinois uses various controls in the hot end of the plant 

during the hot summer months to reduce the risk of heat-related 

illness. These controls include fans which supply cooler air from 

the basement of the facility (man coolers), evaporative cooling 

fans (swamp coolers), sports drinks, two 25-minute worker rest 

breaks (plus additional breaks during the summer months at the 

discretion of management), and a review of heat safety during 

safety meetings or through posters. At the time of our evaluation 

no formalized programs were in place to determine when the 

controls should be implemented, nor was a formalized heat 

acclimatization program in place.
Health Hazard Evaluation Report 2003-0311-3052 Page 3

Assessment

We evaluated the heat stress conditions in the forming department 

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 around each of the four bottle forming 

machines, in the break room, and outside, and were allowed 

to equilibrate for a minimum of 15 minutes before being read. 

WBGT measurements and metabolic rate estimates are compared 

to those listed in the NIOSH REL [NIOSH 1986]. You can find 

a discussion of occupational exposure limits and health effects in 

Appendix A.

We estimated the metabolic rates for the workers using the NIOSH 

table, “Estimating metabolic heat production rates by task analysis” 

(Appendix B) [NIOSH 1986]. This method allows for specificity 

in rate estimation because it breaks the job into categories that 

account for body position and movement, type of work, and basal 

metabolism. The NIOSH values are based upon a standard body 

weight of 154 lbs, so a weight correction factor must be applied 

when workers weigh other than 154 lbs. Individual results vary 

depending on age, sex, fitness level, current health status, and body 

weight. Partly because of observer variability, estimates of metabolic 

rates may vary by ± 10%–15% [NIOSH 1986].

We conducted confidential employee interviews with all employees 

working in the forming department on the first and second shifts. 

Logs of Work-Related Injuries and Illnesses (OSHA’s Form 300) 

were also reviewed from years 2004, 2005, and 2006.
Page 4 Health Hazard Evaluation Report 2003-0311-3052

Individual WBGT measurements are reported in Table 1. The 

highest WBGT reading in the forming department was 87.2°F, 

with a dry bulb temperature of 87.0°F and a globe temperature 

of 115.7°F. The results indicate that most surfaces in the forming 

department were at an elevated temperature and served as radiant 

heat sources. In the hot end break room, where employees 

normally take their breaks, the WBGT reading was 70.3°F, with a 

dry bulb temperature of 75.5°F. During the NIOSH evaluation the 

outdoor WBGT reading was 64.5°F, with a dry bulb temperature 

of 65.5°F, indicating the temperatures were unseasonably cool and 

not an indication of normal summer weather [NOAA 2004]. These 

cooler than normal ambient temperatures may have lessened the 

heat stress hazard in the forming department on the day of our 

evaluation. 

The metabolic heat produced by forming department employees 

was estimated using NIOSH guidelines [NIOSH 1986]. Using this 

method, the average energy expenditure of a standard male worker 

(154 pounds with a body surface of 19.4 square feet) was calculated 

Results and Discuss

Table 1. Heat Stress Measurements in the Forming Department on September 13, 2007 

Individual Section 

Forming Machine 

Time 

(hh:mm)

Indoor

WBGT (°F) 

Wet Bulb 

Temp. (°F) 

Dry Bulb 

Temp. (°F) 

Globe

Temp. (°F) 

Relative 

Humidity (%) 

A1 17:38 85.5 75.5 86.4 109.3 38

A1 17:39 76.4 70.0 74.4 90.3 49

A1 17:39 75.6 68.6 72.8 92.1 60

A1 17:40 72.7 69.0 76.6 81.6 53

A2 17:17 71.7 67.2 77.1 81.7 54

A2 17:15 87.2 75.1 87.0 115.7 38

A2 17:18 81.9 74.6 83.2 99.5 31

A2 17:16 76.3 70.4 83.5 89.4 43

B1 16:47 71.4 67.4 75.8 80.8 56

B1 16:49 80.6 72.6 79.6 99.3 42

B1 16:50 83.2 73.4 82.7 106.7 46

B1 16:51 76.3 70.3 83.2 90.2 46

B2 18:03 68.8 66.2 70.7 74.7 58

B2 18:04 74.5 69.6 80.1 85.6 50

B2 18:02 82.9 73.2 78.3 105.4 44

B2 18:00 85.9 74.2 83.2 113.1 43

Break room 19:21 70.3 68.3 75.5 75.0 74

Outside 19:19 64.5 63.9 65.5 65.9 90
Health Hazard Evaluation Report 2003-0311-3052 Page 5

Results and Discuss

(continued

to produce approximately 186 kcal/hour, corresponding to a light 

workload rate. The WBGT results and metabolic rate estimates 

for a standard male were then compared to those listed in the 

NIOSH RELs to determine a work/rest schedule [NIOSH 1986]. 

This comparison yields a recommendation of continuous work 

for acclimatized and unacclimatized workers when environmental 

conditions are similar to those on the day we evaluated.

The metabolic rate estimates were also assigned a light workload 

category and compared to the ACGIH screening criteria [ACGIH 

2006]. The ACGIH screening criteria for heat stress also provides 

recommendations on work/rest schedules according to WBGT 

temperatures measured in the work areas. These criteria also 

suggest a continuous work schedule for acclimatized workers with 

light workloads in environments with a WBGT between 81.5°F 

and 83.3°F, which is similar to temperatures measured in the 

forming department at the time of our visit. Both the NIOSH 

REL and ACGIH TLV assume a normal work/rest regimen of a 

5-day workweek and an 8-hour workday with short morning and 

afternoon breaks (approximately 15 minutes each) and a longer 

lunch break (approximately 30 minutes).

These metabolic heat rate estimates reflect work/rest regimens 

that would be applicable had the employees rested in the same 

temperature as the work environment and were tending to the 

forming machine for the entire hour. However, this may not be the 

case for all employees. Some employees were observed performing 

maintenance work that may be classified as a moderate or high 

workload. It is important to remember that the NIOSH RELs were 

calculated for a standard worker, these work/rest regimens vary 

from employee to employee, and an hourly estimate of metabolic 

heat rate and WBGT provides a more accurate recommendation 

for work/rest regimens.

On September 13, 2006, we interviewed all 18 forming department 

employees working first and second shifts. The average age of 

the workers was 45 years (range: 21 to 60 years) and the average 

number of years worked in the hot end of the plant was 20 years 

(range: 3 months to 35 years). None of the 18 workers reported 

consulting a medical provider for a heat-related illness. During the 

3 months prior to the site visit, two employees reported having 
Page 6 Health Hazard Evaluation Report 2003-0311-3052

Results and Discuss

(continued

experienced heat-related symptoms on a hot day during their shift 

(one experiencing an episode of heart racing and lack of sweating, 

the other experiencing persistent headache). One employee 

reported having experienced symptoms consistent with heat 

exhaustion in the summer of 2005, and going outside to cool off. 

Another employee reported having experienced heat exhaustion 

during his shift in the summer of 2004, going home, and was off 

work for 2–3 days. Neither employee sought medical care. Two 

additional employees experienced heat-related cramping and 

nausea at work 15 and 27 years ago, but not recently. 

Ten of the 18 interviewed employees had no problems with the 

heat in the hot end. Employees reported that when the weather 

gets hot, the company generally provides electrolyte-containing 

fluids and heat breaks for employees. However, some workers 

mentioned that because of the lack of company guidelines to 

trigger heat stress prevention procedures, employees have to ask 

that these procedures be initiated. Employees reported that the 

swamp coolers, while more effective than the man coolers, were 

not well maintained and some were not functional. 

When asked about heat stress training, employees gave a wide 

range of answers. New employees reported watching a 3-hour safety 

training video that included heat stress prevention information. 

Other employees reported getting heat stress information from 

the senior employees as part of their on-the-job training. Others 

reported having no heat stress training. 

A few workers reported that lack of sufficient staffing on second 

shift (4 p.m.–12 midnight) during the summer months or when 

machines were changed to a different product, led to fewer breaks. 

Additionally, employees mentioned that new hot end employees 

typically started in June and were not given enough time to 

acclimatize to the heat, resulting in some quitting the job.

Logs of Work-Related Injuries and Illnesses (OSHA’s Form 300) 

were reviewed for years 2004, 2005, and 2006. Of the 43 entries in 

2004, one involved heat exhaustion in June with no lost work days. 

The logs contained no heat-related illness entries for 2005 or 2006.
Health Hazard Evaluation Report 2003-0311-3052 Page 7

Although environmental temperature measurements and workload 

assessments on the day of the NIOSH evaluation showed that 

workers in the forming department were not exposed to heat stress 

in excess of the occupational screening criteria, some interviewed 

workers reported that they had developed heat strain symptoms 

during their shifts on previous hot summer days; one reported 

missing days of work due to heat exhaustion.

Environmental temperatures may be warmer than those on the 

days of the NIOSH evaluation [NOAA 2004]. During periods of 

higher temperatures, NIOSH and ACGIH screening criteria are 

more likely to be exceeded, thereby raising the potential for heat 

stress and strain among employees. Employee reports of heat strain 

symptoms on previous hot days confirm that this is a potential 

hazard at this facility. 

The following recommendations help identify potential heat stress 

and strain risks and how to limit heat-related illnesses in hot end 

workers.

1. Place the fans that supply cooler air from the basement of 

the facility (man coolers) and the evaporative cooling fans 

(swamp coolers) on a preventive maintenance schedule 

to ensure they are operational throughout the summer 

months.

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

of heat-related disorders. Such a program involves exposing 

workers to hot work environments for progressively longer 

periods. NIOSH recommends that workers 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 employees 

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 workers may be able to work a full shift before

Conclusion

Recommendatio
Page 8 Health Hazard Evaluation Report 2003-0311-3052

Recommendatio

(continued

this process is completed. The body’s acclimatization will 

continue to improve each day in that environment for up to 

3 weeks.

3. Develop continuing education programs to ensure that all 

employees potentially exposed to hot environments and 

physically demanding job activities stay current on heat 

stress and heat stress prevention information. Employees 

working in the hot end area should have continuing 

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

•	 Employee responsibilities in avoiding heat stress

•	 Medical conditions that may increase the risk of heatrelated illnesses

•	 Dangers in using drugs, including therapeutic ones,

and alcohol in hot and physically demanding work 

environments

•	 Preventive measures that can be taken to reduce heat 

stress

•	 Instructing workers to monitor themselves and 

others for heat strain signs and symptoms following 

guidelines in Appendix C

•	 Encouraging workers to take their breaks in a cool 

location such as the break room

4. Monitor environmental heat exposures during the hottest 

months using a WBGT monitor at, or as close as possible 

to, the area where the workers are exposed. Break areas 

and other areas in which the employees may be working 

that differ in temperature 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 months of the year, and when 

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

measurements exceed the applicable criteria (NIOSH RAL 

or REL, or ACGIH TLV), then work conditions should be 

modified until two more sequential WBGT measurements
Health Hazard Evaluation Report 2003-0311-3052 Page 9

Recommendatio

(continued

are within the exposure limits. On these days, administrative 

controls such as increasing the number of breaks and 

employees in the hot end, use of cooling methods, and 

additional awareness training can be implemented to help 

reduce the risk of heat-related illness.

5. 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 above, or 90°F if this is 9°F above the maximum 

reached in any of the preceding 3 days. Procedures to follow 

during the state of heat alert include: 

•	 Increase the number of workers in each team to 

reduce each worker’s metabolic rate

•	 Increase rest allowances

•	 Remind workers to drink small amounts of water 

frequently to prevent dehydration and maintain 

body weight, and to weigh themselves before and 

after the shift

•	 Check workers’ oral temperature and pulse during 

their most severe heat-exposure period

•	 Exercise additional caution on the first day of a 

shift change to make sure workers are not 

overexposed to heat, because they may have lost 

some of their acclimatization over the weekend and 

during days off

•	 Restrict overtime work 

6. Develop a heat-related illness surveillance program, which 

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. 

7. Ensure that employees 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 alcohol and 
Page 10 Health Hazard Evaluation Report 2003-0311-3052

Recommendatio

(continued

caffeinated beverages) and encourage employees 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. 

8. Create a buddy system so that employees can monitor each 

other for symptoms of heat disorders. A buddy system 

will help to ensure that each buddy has had enough water 

and food and is feeling well enough to continue. If a 

coworker appears to be disoriented or confused, or suffers 

inexplicable irritability, malaise, or flu-like symptoms, the 

employee should be removed for rest in a cool location with 

rapidly circulating air and kept under skilled observation. 

Immediate emergency care is necessary if sweating stops and 

the skin becomes hot and dry.

9. Allow employees to take unscheduled breaks if they report 

feeling weak, nauseated, excessively fatigued, confused, 

and/or irritable during hot temperatures. These heat 

strain symptoms, and any other signs of heat overexposure, 

should be reported by employees to their supervisor for 

investigation and follow-up.

ACGIH® [2006]. Documentation of the threshold limit values 

and biological exposure indices. 7th ed. Cincinnati, OH: American 

Conference of Governmental Industrial Hygienists; 2002–2006 

Suppl.

NIOSH [1986]. Criteria for a recommended standard: 

occupational exposure to hot environments, rev. Cincinnati, 

OH: U.S. Department of Health and Human Services, Public 

Health Service, Centers for Disease Control, National Institute for 

Occupational Safety and Health, DHHS (NIOSH) Publication No. 

86-113.

NOAA [2004]. Climatography of the United States report No. 20: 

Anderson Sewage Plant, Indiana. Asheville, NC: U.S. Department 

of Commerce, National Oceanic and Atmospheric Administration, 

National Environmental Satellite, Data, and Information Service.

Referenc
Health Hazard Evaluation Report 2003-0311-3052 Page 11

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 workers 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 workers 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 pre-existing 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 worker 

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 U.S., 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, worker 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 U.S. include the TLVs 

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

Industrial Hygiene Association, another professional organization. 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 2007]. WEELs have been established for some chemicals “when no 

other legal or authoritative limits exist” [AIHA 2007]. 

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 

Appendix A: Occupational Exposure Limits & He
Page 12 Health Hazard Evaluation Report 2003-0311-3052

Appendix A: Occupational Exposure Limits & He

(continued

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).

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 a worker with a CBT exceeding those levels will necessarily experience 

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

stress illnesses [NIOSH 1986].

NIOSH recommends controlling total heat exposure so that unprotected healthy workers 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 criteria. These criteria state that most healthy employees who work in 

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

NIOSH RALs for non-acclimatized workers (Appendix D, Figure 1) or the NIOSH RELs for acclimatized 

workers (Appendix D, Figure 2), 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 metabolic 

and environmental heat combinations exceeding the applicable ceiling limits of Figures 1 or 2 without 

being provided with and properly using appropriate and adequate heat-protective clothing and equipment 

[NIOSH 1986].
Health Hazard Evaluation Report 2003-0311-3052 Page 13

Appendix A: Occupational Exosure  Limits & He

(continued

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 2006]. ACGIH WBGT screening criteria factor in the ability of the body to cool itself (clothing 

insulation value, humidity, and wind) and, like the NIOSH criteria, can be used to develop work/rest 

regimens for acclimatized and unacclimatized 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 workers 

may be 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 2006]. 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, it is important to note that the TLVs are not directed toward controlling these 

[ACGIH 2006].

NIOSH and ACGIH criteria can only be used when WBGT data for the immediate work area are 

available and must not be used when workers 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 while NIOSH and ACGIH guidelines distinguish 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].

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 (fainting) results from blood flow being directed to the skin 

for cooling, resulting in decreased supply to the brain, and most often strikes workers 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 
Page 14 Health Hazard Evaluation Report 2003-0311-3052

Appendix A: Occupational Exposure Limits & He

(continued

hard work, hot environment, and dehydration overload the body’s capacity to cool itself. This thermal 

regulatory failure (heat stroke) is a life-threatening 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 2006]. 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].

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 workers, 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 are 

recovering from recent use, people in poor physical condition, and those recovering from illness. With 

regard to prescribed medications, ß-adrenergic receptor blockers and calcium-channel blockers, used to 

treat hypertension, limit maximal cardiac output and alter normal vascular distribution of blood flow in 

response to heat exposure. Diuretics, such as caffeine, can limit cardiac output and affect heat tolerance 

and sweating; antihistamines, phenothiazines, and cyclic antidepressants can impair sweating. A CBT 

increase of only 1.8°F above normal encroaches on the brain’s ability to function [ACGIH 2006].

Acclimatization

When workers 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. On repeated 

exposure there is 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 worker 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 2006].
Health Hazard Evaluation Report 2003-0311-3052 Page 15

Appendix A: Occupational Exosure  Limits & He

(continued

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, workers 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 worker’s 

capacity to acclimatize [ACGIH 2006].

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, workers 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. Caffeinated beverages and 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.

References

ACGIH® [2006]. Documentation of the threshold limit values and biological exposure indices. 7th ed. 

Cincinnati, OH: American Conference of Governmental Industrial Hygienists; 2002–2006 Suppl.

ACGIH® [2007]. 2007 TLVs® and BEIs®: threshold limit values for chemical substances and physical 

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

Industrial Hygienists.

AIHA [2007]. 2007 Emergency response planning guidelines (ERPG) & workplace environmental 

exposure levels (WEEL) handbook. Fairfax, VA: American Industrial Hygiene Association.

CFR. Code of Federal Regulations. Washington, DC: U.S. Government Printing Office, Office of the 

Federal Register.
Page 16 Health Hazard Evaluation Report 2003-0311-3052

Appendix A: Occupational Exposure Limits & He

(continued

Cohen R [1990]. Injuries due to physical hazards. In: LaDou J, ed. Occupational medicine. East Norwalk, 

CT: Appleton & Lange.

Minard D [1961]. Prevention of heat casualties in Marine Corps recruits. Mil Med 126(44):261–272.

NIOSH [1986]. Criteria for a recommended standard: occupational exposure to hot environments, rev. 

Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for 

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

86-113.

NIOSH [1992]. Recommendations for occupational safety and health: compendium of policy documents 

and statements. Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, 

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

DHHS (NIOSH) Publication No. 92-100.

NIOSH [2005]. NIOSH pocket guide to chemical hazards. Cincinnati, OH: U.S. Department of Health 

and Human Services, Centers for Disease Control and Prevention, National Institute for Occupational 

Safety and Health, DHHS (NIOSH) Publication No. 2005-149. 

OSHA [1999]. Heat stress. In: OSHA technical manual. Sec 3 Chap 4. Washington, D.C. U.S. 

Department of Labor, Occupational Safety and Health Administration, TED 1-0.15A.

Roetzheim R [1991]. Overhydration. Physician Sports Med 19:32.

Rolls BJ, Kim S, Federoff IC [1990]. Effects of drinks sweetened with sucrose or aspartame on hunger, 

thirst and food intake in men. Physiol Behav 48 (1):19–26.

Rolls BJ [1993]. Palatability and fluid intake. In: Mariott BM, ed. Fluid and heat stress. Washington DC: 

National Academy Press, pp. 161–167.

Singer GG, Brenner BM [1998]. Fluid and electrolyte disturbances. In: Fauci AS, Brunwald E, Isselbacher 

KJ, Wilson JD, Martin JB, Kasper DL, Hauser SL, Longo DL, eds. Harrison’s principles of internal 

medicine, 14th ed. New York: Mc-Graw Hill.

WHO [1969]. Health factors involved in working under conditions of heat stress. Geneva, Switzerland: 

World Health Organization. Technical Report Series No. 412.
Health Hazard Evaluation Report 2003-0311-3052 Page 17

Appendix B: Estimating Metabolic Heat Produc

A. Body Position and Movement kcal/min

Sitting 0.3

Standing 0.6

Walking (uphill) 2.0–3.0 (add 0.8 kcal/meter rise 

in elevation) 

B. Type of Work Average

(kcal/min)

Range

(kcal/min)

Hand work: 0.2–1.2

Light 0.4

Heavy 0.9

Work, one arm: 0.7–2.5

Light 1.0

Heavy 1.8

Work, both arms: 1.0–3.5

Light 1.5

Heavy 2.5

Work, whole body: 2.5–9.0

Light 3.5

Moderate 5.0

Heavy 7.0

Very heavy 9.0

C. Basal Metabolism 1.0

Sample calculation for forming department employees: 

Task kcal/min

A. Standing 0.6

B. Light, work with both arms 1.5

C. Basal metabolism 1.0

Metabolic rate total per minute 3.1 kcal/min 

Metabolic rate total per hour 186 kcal/hour 

 

The sum of A, B, and C is equal to the estimated metabolic production per task. Estimates are for a 

standard male worker of 154 lbs body weight and 19.4 square feet body surface.

by Task Anal
Page 18 Health Hazard Evaluation Report 2003-0311-3052

Appendix B: Estimating Metabolic Heat Produ

by Task Analysis (conti

References

NIOSH [1986]. Criteria for a recommended standard: occupational exposure to hot environments, rev. 

Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for 

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

No. 86-113.
Health Hazard Evaluation Report 2003-0311-3052 Page 19

A ppendix C: Use of Personal Monitoring Methods 

Heat-Related Illn

Periodic monitoring of the heart rate, oral temperature, extent of body weight loss, 

and/or recovery heart rate should always include the determination of baseline values for

 deciding whether individuals are fit to continue work that day.

Heart Rate: Calculate your heart rate limit by subtracting your age from 180. Your heart rate at peak work 

effort should not exceed this number for more than 3 or 4 minutes. If it does, stop work immediately, find 

some shade, drink, and rest until your heart rate returns to a more normal pace. Repeat as necessary.

Oral Temperature: Use a clinical thermometer right after stopping work but before drinking anything. Try 

to avoid open-mouth breathing prior to inserting the thermometer. If the oral temperature taken under 

the tongue exceeds 99.7°F, shorten the next work cycle by one third, and maintain the same rest period. 

An oral temperature of 100.4°F (deep body temperature of 102.2°F) should be considered reason to 

terminate exposure even when temperature is being monitored.

Body Weight: Monitor hydration status on a regular basis. Thirst is a poor indicator of hydration because 

significant dehydration has already taken place when the thirst sensation occurs. Workers should be 

familiar with their weight when they are fully hydrated and should strive to maintain this weight. Weight 

loss should not exceed 1.5% of total body weight in a work day. If it does, fluid and food intake should 

increase. Alcohol and caffeinated beverages should always be avoided when working under heat stress 

conditions. Workers should attempt to rehydrate themselves until they achieve their baseline weight. Body 

water loss can be measured by weighing the worker at the beginning and end of each work day and by 

using this equation:

(pre-activity weight – post-activity weight) ÷ pre-activity weight x 100 = percent body weight loss

Recovery Heart Rate: Following a normal work cycle, compare a pulse rate taken after 3 minutes of seated 

rest, P3, with the pulse rate taken after 1 minute of rest, P1. Interpret the results using the following table:

References

NIOSH [1986]. Criteria for a recommended standard: occupational exposure to hot environments, rev. 

Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for 

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

86-113.

ACGIH® [2006]. Documentation of the threshold limit values and biological exposure indices. 7th ed. 

Cincinnati, OH: American Conference of Governmental Industrial Hygienists; 2002–2006 Suppl.

Heart Rate Recovery Pattern P3 P1 minus P3 

Excessive heat strain: > 90 BPM and < 10 BPM 

Moderate strain: > 90 BPM and > 10 BPM 

Sufficient recovery: <90 BPM and >10 BPM 
Page 20 Health Hazard Evaluation Report 2003-0311-3052

 : Appendix D: NIOSH-Recommended Heat-Stres

Heat-Stress Exposure 

 Figure 1. Recommended Heat-Stress Alert Figure 2. Recommended Heat-Stress 

 Limits (unacclimitized workers) Exposure Limits (acclimatized workers)

The figures’ curves indicate recommended work/rest regimens of external heat (measured as wetbulb globe temperatures) and internal (metabolic) heat. The ‘C’ curve is the Ceiling Limit, indicating 

that workers should not be exposed to such conditions without adequate heat-protective clothing and 

equipment.

References

NIOSH [1986]. Criteria for a recommended standard: occupational exposure to hot environments, rev. 

Cincinnati, OH: U.S. Department of Health and Human Services, Public Health Service, Centers for 

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

86-113.
Health Hazard Evaluation Report 2003-0311-3052 Page 21

Acknowledgements a

Availability

 Report 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.

This report was prepared by Chad H. Dowell and Loren C. Tapp 

of HETAB, Division of Surveillance, Hazard Evaluations and Field 

Studies (DSHEFS). Industrial hygiene field assistance was provided 

by Andrea M. Markey. Medical field assistance was provided by 

Bich Dang. Desktop publishing was performed by Robin Smith. 

Editorial assistance was provided by Ellen Galloway.

Copies of this report have been sent to employee and management 

representatives at Owens-Illinois; Glass, Molders, Pottery, Plastics 

and Allied Workers International Union Local 207; 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: http://www.cdc.gov/niosh/

hhe. Copies may be purchased from the National Technical 

Information Service (NTIS) at 5825 Port Royal Road, Springfield, 

Virginia 22161.
This is a recommended citation for this report.

NIOSH [2007]. Health Hazard Evaluation Report: evaluation of heat stress at a 

glass bottle manufacturer, Owens-Illinois, Lapel, Indiana. Cincinnati, OH: U.S. 

Department of Health and Human Services, Public Health Service, Centers for 

Disease Control and Prevention, National Institute for Occupational Safety and 

Health, NIOSH HETA No. 2003-0311-3052.

To receive NIOSH documents or information about 

occupational safety and health topics, contact NIOSH at:

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

TTY: 1-888-232-6348

E-mail: cdcinfo@cdc.gov

or visit the NIOSH web site at www.cdc.gov/niosh

For a monthly update on news at NIOSH, subscribe to 

NIOSH eNews by visiting www.cdc.gov./niosh/eNews

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Safety and Health