# Criteria for a Recommended Standard: Occupational Exposure to Heat and Hot Environments

Revised Criteria
Brenda L. Jacklitsch, MS 

# Paul A. Schulte, PhD Education and Information Division
Public Meeting, February 13, 2014



### Cincinnati, OH

1 This information is distributed solely for the purpose of pre dissemination peer review under applicable information quality guidelines. It has not been formally disseminated by the National Institute for Occupational Safety and Health. It does not represent and should not be construed to represent any agency determination or policy.

# Why Update the Criteria Document?

 

### Injuries, illnesses, and deaths in a large worker population.

 

### Document was last updated in 1986

.
 

### In recent years, including during the Deepwater Horizon oil spill response of 2010, questions raised regarding the need for revision.

 

### Health Hazard Evaluation (HHE) requests and CDC Info requests.

 

### Additional info relating to the physiological changes that result from heat stress.

 

### Updated info from relevant studies

.
 

### Need to redefine heat stroke and associated symptoms.

 

### Updated info on physical monitoring and Personal Protective Equipment (PPE)

.

2

# History of NIOSH Heat Stress Activities

 

### 1972

– Original Criteria Document published

 

### 1986

– Revised Criteria Document

 

### 2005

– Research activity on PPE and heat stress begins

 

### 2008

– Heat Stress Web Topic page revised; MMWR on heat

- related deaths among crop workers

 

### 2010

– NIOSH Fast Facts card; participation in the Deepwater Oil Spill Response; Start reviewing content of Criteria Document

 

### 2011

– OSHA

- NIOSH Infosheet; Medscape Article; NIOSH Blog; E

- News Director’s Desk; AIHce Table Talk; Begin work on Criteria Document

 

### 2013

– Workplace Solution document

 

### 2014

– Criteria Document Public Meeting and T entative Publication

3

# Definitions

 

## Heat Stress

 The net heat load to which a person may be exposed from the combined contributions of metabolic heat, environmental factors, and clothing requirements which may result in an increase in heat storage in the body.

 

## Heat Strain

 The physiological response to the heat load experienced by a person, which attempts to increase heat loss from the body in order to maintain a stable body temperature.

4

# Occupational Relevance of

Heat Stress

 

# Potential for worker exposure

 Outdoor workers

• Ex. Construction; Roofers; Farmers/Agricultural; Lawn care/Landscapers; Foresters; Emergency Responders



##  Indoor workers in hot environments

• Ex. Firefighters; Factory/Foundry; Bakery; Anyone in hot, confined spaces

5

# Occupational Relevance of

Heat Stress

 

## H eat

- related illness , such as:

 Heat stroke

 Heat exhaustion

 Heat cramps

 Heat rashes

 

## Increased risk of injury , resulting from:

 Sweaty palms

 Fogged

- up safety glasses

 Dizziness

 Contact with hot surfaces or steam

 

## Increased risk of death

6

# Factors Affecting Risk of Heat

- related Illness

7

# Purpose of a Criteria Document

NIOSH is mandated by the Occupational Safety and Health 

## (OSH) Act of 1970:

“...to develop criteria dealing with toxic materials and harmful physical agents and substances which will describe exposure levels that are safe for various periods of employment , including but not limited to the exposure levels at which no employee will suffer impaired health or functional capacities or diminished life expectancy as a result of his work experiences.”

8 [ OSH Act, 20 USC 22 (a)(3)]

# Updating this Criteria Document

9 Literature Search

Chapter

Updates

Internal

Review

Public

Comment

External

Peer Review

Publication

# Criteria Document Topics

10

# Fundamental Thermal Physiology Concepts and Established NIOSH Limits

 

# Heat Balance Equation

 

# Modes of H eat Exchange

 

# Thermoregulatory Pathways

 

# Basic Effects of Clothing on Heat Exchange

 

# NIOSH Recommended Alert Limit (RAL) and Recommended Exposure Limit (REL)

11

# Heat Balance Equation

 

## Normal body function requires that the deep body core temperature be maintained at about 37 ° C (98.6 ° F) ± 1 ° C 

## (1.8 ° F)

.
 

## Body temperature equilibrium requires constant exchange of heat between the body & environment.

12 Change in body heat content = Total

Metabolism - External

Work Performed 

# ( ) Convection Heat Exchange (C) Radiative

Heat Exchange (R) Evaporative

Heat Loss (E) ±
-

±

C = Difference between the ambient air & the mean weighted skin temp. & the rate of air movement over the skin.
R = Temp. gradient between the mean radiant temp. of the surroundings & the mean weighted skin temp.

E = Air motion & water vapor pressure difference between ambient air & wetted skin at skin temp.

# Major Modes of Heat Exchange

 Convection

 Transfer of heat between skin and ambient air immediately surrounding the skin.

 Rate of air movement is a factor.

 Radiation

 Transfer of heat between the radiant temperature of the surroundings and the skin.

 Ex. Heat from hot ovens or the sun.

 Evaporation

 Water evaporating from the skin resulting in heat loss.

 Ex. Evaporation of sweat

.
 Conduction

 Transfer of heat from a warmer object to a cooler object by direct contact.

 Ex. Body contact with hot tools , working in water, or in supine positions

.

13

# Physiological Responses to Heat

14

Skin Temperature Core Temperature

Peripheral Thermoreceptors (in skin) Central Thermoreceptors (in hypothalamus, CNS, abdominal organs)

Skin Blood Vessels Sympathetic Nervous System Sweat Glands

Vasodilation Sweating

Heat Loss Heat Loss 

### Hypothalamus
(acts like thermostat)

# Effects of Clothing on Heat Exchange

 

### Clothing serves as a barrier between skin and the environment to protect against hazards (i.e., chemical, physical, and biologic 

### agents).

 

### Clothing systems alter the rate and amount of heat exchange between the skin and the ambient air by convection (C), radiation (R), and evaporation (E).

 

### The thicker, and greater the air and vapor impermeability of the clothing layers , the greater its interference with C, R, & E heat exchange

.
 

### During exertion there is an increased metabolic heat production that can be trapped inside clothing, creating a hot microenvironment.

15

# NIOSH RAL and REL

 

## Recommended Alert Limit (RAL) for unacclimatized workers.

 

## Recommended Exposure Limit (REL) for acclimatized workers.

 

## Still protective.

 

## No new data identified to use as the basis for an update.

 

## Wet Bulb Globe Temperature (WBGT)

- based threshold values for acclimatized workers are similar to OSHA, ACGIH, AIHA, and ISO.

16

# Updated Items

 

## Hydration and Fluid Requirements

 

## Urine Color C hart

 

## Psychrometric Chart

 

## Body Fat and Obesity

 

## Acclimatization

 

## Medications

 

## Caffeine Usage

 

## Exertional Heat Stroke

 

## HHE Reports and Case S tudies

 

## Physiological Monitoring

17

# Hydration and Fluid Requirements

• Drink 8 oz. of water or other fluids every 15

- 20 

# minutes (moderate activity in moderate conditions).



# • During prolonged sweating lasting several hours, drink a sports drink that contains balanced electrolytes (electrolytes/carbohydrates should not exceed 8% by volume).

18

# Urine Color Chart

Adapted from [Mayo Clinic 2011; Medline Plus 2011; Watson 2011].

19

# Addition of the Psychrometric Chart

20 Adapted from ISO [1993] and Coolerado [2012].

# Body Fat and Obesity

 

## Body fat is an insulator and alters heat exchange with the environment.

 

## Obesity predisposes individuals to heat disorders

-- heat disorders occur 3.5 times more frequently in the obese than in the lean individual (Leithead and Lind 1964; 

## Henschel 1967; Chung and Pin 1996; Kenney et al. 2010 ).

 

## More fat → More weight → Greater energy expenditure for a given task

 

## Body surface to body weight ratio.

 

## Store thermal energy at a greater rate.

21

# Acclimatization

Topics Additional Information

Acclimatization Plan

 Gradually increase exposure time in hot environmental conditions over a 7

- 14 day period.

 For new workers, the schedule should be no more than 20% on day 1 and a no more than 20% increase on each additional day.

 For workers who have had previous experience with the job, the acclimatization regimen should be no more than a 50% exposure on day 1, 60% on day 2, 80% on day 3, and 100% on day 4.

Level of Acclimatization

 Relative to the initial level of physical fitness and the total heat stress experienced by the individual.

Maintaining Acclimatization

 Can be maintained for a few days of non

- heat exposure.

 Absence from work in the heat for a week or more results in a significant loss in the beneficial adaptations leading to an increase likelihood of acute dehydration, illness, or fatigue.

 Can be regained in 2

- 3 days upon return to a hot job.

 Appears to be better maintained by those who are physically fit.

 Seasonal shifts in temperatures may result in difficulties.

 Working in hot, humid environments provides adaptive benefits which also apply in hot, desert environments, and vice versa.

 Air conditioning will not affect acclimatization.

Adapted from [ Moseley 1994; Armstrong and Stoppani 2002; TBMed 2003; Casa et al. 2009; ACGIH 2011; OSHA

- NIOSH 2011].

22

# Medications

Drug or drug class Proposed mechanism of action Anticholinergics Impaired sweating
Antihistamines Impaired sweating
Phenothiazines (Thorazine ® , Stelazine ® , Trilafon ® ) Impaired sweating, (possibly) disturbed hypothalamic temperature regulation Tricyclic antidepressants (imipramine, amitriptyline) Impaired sweating, increased motor activity and heat production

Amphetamines, cocaine, “Ecstasy” Increased psychomotor activity, activated vascular endothelium

Ergogenic stimulants (ephedrine/ephedra) Increased heat production
Lithium Nephrogenic diabetes insipidus and water loss

Diuretics Salt depletion and dehydration Antihypertensives (atenolol, carvedilol) Reduced skin blood flow and reduced blood pressure
Ethanol Diuresis, possible effects on intestinal permeability
Barbiturates Reduced blood pressure Antispasmodics Impaired sweating Haloperidol Tachycardia, altered central temperature regulation, and hyponatremia
Adapted from Heat Stress Control and Heat Casualty Management ( DOD 2003).

23

# Caffeine Usage

 

## Past : Caffeine is a mild diuretic and may contribute to heat stress by reducing fluid volume and resulting in 

## cardiovascular strain during exposure to the heat (Serafin 1996 ).

 

## Update: Recent studies suggest that caffeine may have 

## less effect on heat tolerance than previously suspected (Roti et al. 2006; Armstrong, Casa, Maresh et al. 2007; Ely et al. 2011).

24

# Heat Stroke: Classical vs. Exertional

Adapted from Heat Stress Control and Heat Casualty Management [DOD 2003].

25 Characteristic Classical Heat Stroke Exertional Heat Stroke Age Young children or elderly 15

- 45 years Health Chronic illness common Usually healthy Activity Sedentary Strenuous exercise Sweating Usually absent Often present Prevailing weather Frequent in prolonged heat waves Variable

Rhabdomyolysis Seldom severe Common, may be severe Acute renal failure Fairly rare Common

# HHE Reports and Case Studies

 

# HHE Reports

 Aluminum Smelter Potrooms (NIOSH 2006)

 Automobile Parts Manufacturing Facility (NIOSH 2003)

 Glass Bottle Manufacturer (NIOSH 2003)

 National Park (NIOSH 1999)

 

# Case Studies

 Landscaping (NIOSH 2002)

 Migrant Farm Workers (NIOSH 2006, CDC 2008)

 Construction (NIOSH 2004)

 Fire Fighter (NIOSH 1997)

26

# Physiological Monitoring

Monitoring Method When

Assessed How Assessed Additional Information

Heat Exposure History  Before work begins  Interview or questionnaire  A history of heat

- related illness increases the risk of a repeat occurrence, so worker should be monitored more closely.

 Some workers might choose to alert their employers of medical conditions which increase the risk of heat

- related illnesses.
Heart Rate (Pulse Rate)  Before work begins to determine baseline and then after heat exposure (e.g., 1 st minute and 3 rd minute after the work period ends)  Count the number of beats per minute (use a watch), or monitor with heart
rate sensor  The heart rate should fall rapidly, approaching the baseline.

 Heart rate will remain elevated in a worker experiencing a heat

- related illness.

Temperature  Increased temperature indicates that the body is not cooling itself as rapidly as necessary.

 Initial baseline and again after the work period  Oral temperature

– measure with an oral thermometer  Oral temperature is inaccurate if the workers drinks cool beverages frequently (as is recommended).

 Initial baseline and again after the work period.  Tympanic temperature

– measure with an infrared thermometer  Tympanic temperature is a more reliable indicator of core temperature than oral.

 Continuous sensing devices measure temperature during both work and rest periods  Core temperature

– measure with electronic or color

- changing sensing devices (e.g., ingestible, in

- ear, or part of skin patches)  Core temperature is the most reliable measure of body temperature.

 Modern advances in sensing technology are making core temperature measurements increasingly practical

.

27

# Future Research Needs

 

# Effects of climate change on outdoor workers.

 Increased ambient temperatures.

 Extreme weather.

 Reduced work capacity and productivity in heat

exposed jobs.

 

# How heat stress affects toxic response to chemicals

.

 Heat can affect absorption of chemicals into the body.

28

# Timeline

 

## Federal Register Notice requesting public comments posted on December 27, 2013

.

 

## Public meeting on February 13, 2014

.

 

## Receive all public comments by February 25, 2014

.

 

## Receive all peer review comments by March 28, 2014

.

 

## Anticipate completion of FINAL Criteria Document in 2014

.

29

# Charge to Peer Reviewers

 

## The following questions should be considered:

 Is worker acclimatization clearly explained and presented?

 Are there any additional recommendations that should be made?

 Is there any additional information on hydration that should be considered?



###  Are there any additional risk factors for heat

- related illnesses that should be discussed?

 Are there any additional examples of auxiliary body cooling and protective clothing that should be included?



###  Are there any additional research needs that should be mentioned?

 Are there any additional references that should be included?

30

# Criteria Document Update Team

 

### Authors

 W . Jon Williams (NPPTL)

 Nina Turner (NPPTL)

 Aitor Coca (NPPTL)

 Jung

- Hyun Kim (NPPTL)

 Kristin Musolin (DSHEFS)  

### Support

 Thomas J. Lentz (EID)

 Kathleen MacMahon (EID)

 Ralph Zumwalde (EID)

 Lauralynn Taylor McKernan (EID)

 HeeKyoung Chun

 Barbara Dames (EID)

 Sherry Fendinger (EID)

31

## For updates visit the NIOSH Docket Heat Stress web page: http:// www.cdc.gov/niosh/docket/review/docket266/default.html

Written comments may be submitted by : Federal eRulemaking Portal: http://www.regulations.gov Enter: CDC

- 2013

- 0025

Mail : NIOSH Docket Office Robert A . Taft Laboratories 4676 Columbia Parkway , MS C

– 34 Cincinnati , OH 45226 

# Thank you!

32