NSWP 7.1
Revision 3
February 13, 2012
Nuclear Safe Work Practice 7.1
Heat Stress
1.0
PURPOSE/SCOPE]
This Nuclear Safe Work Practice (NSWP) provides guidance for evaluating jobs that could result
in heat stress and establishes a process for determining stay times.
2.0
DEFINITIONS

Acclimatization – physiological changes in the body usually gained over a period of time of
working in heat stress conditions that enable the body to adapt and respond to the heat
stress conditions.

Adverse Environmental Conditions – any combination of dry bulb temperature, humidity, air
velocity, and radiant heat that contributes to an increase in body temperature. These
conditions may exist outdoors or indoors in locations such as, but not limited to, Reactor
Buildings, Doghouses, High Pressure Injection Pump Rooms, and some parts of the Turbine
Building.

Radiant Heat – electromagnetic heat transferred from a higher temperature mass to a lower
temperature mass without coming in contact.

Recovery Time – the recommended amount of time necessary for an individual’s
physical state to return to its pre-exposure condition.

Self Determination- the method by which an individual may begin to recognize the
early warning signs of heat-related disorders and terminate the exposure. Selfdetermination may shorten, but never lengthen stay times.

Stay Times – the recommended amount of time that an employee is expected to safely work
in a moderate to high heat stress environment, based on environmental conditions such as
type of clothing being worn and individual health and metabolism.
Wet Bulb Globe Temperature (WBGT) – a combination of temperature, humidity, and air
movement that characterizes the environmental effects on the body, sometimes referred to
as heat index.

3.0
RESPONSIBILITIES
1. Work Supervisors / Job Sponsors:
a. Utilize this work practice to identify jobs that could expose employees to heat stress.
b. Evaluate team members to ensure they are capable of working in adverse environmental
conditions prior to assigning work in those areas.
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February 13, 2012
c. Utilize this work practice to obtain the WBGT and recommended stay times.
d. Utilize this work practice to determine methods for reducing heat stress.
e. Interface with Operations, Radiation Protection, EHS and other groups, as appropriate,
to ensure that all reasonable measures have been taken to reduce temperatures in the
work area or to determine if protective clothing can be reduced.
f.
Assign employees to work in teams, when possible, so they can observe each other for
heat related disorders and terminate jobs if a team member develops signs or symptoms
of any of these disorders.
g. Assure employees are aware of the estimated stay times and observe them.
h. Assure employees have adequate recovery time between heat stress exposures.
i.
Arrange for coolers with ice and water for long duration projects.
j.
Determine if heat stress training is required for work group employees based on work
activities performed and ensure that they are trained to CBT HS0328.
Note: Before taking water coolers into an RCA obtain approval from RP
k. Incorporate this information into pre-job briefings.
2. Employees
a. Inform supervision of any health concerns, prescriptions or over-the-counter drugs being
taken, or any physical problems encountered during past or current heat stress
exposures.
b. Inform supervision of any current or previous off-the-job heat stress exposures so that
recovery times from that exposure can be considered.
c. Know the signs and symptoms of heat related disorders described in the Physical Heat
Related Disorders section and how to monitor themselves and coworkers for the
development of any signs / symptoms.
d. Stop work and leave the area when heat related disorders develop or assist teammates
who show signs of heat related disorders.
e. Know the estimated times for the job to be performed and follow the recommended stay
times.
f.
4.0
1.
2.
3.
4.
Know recovery times and the expectations for a recovery area.
SECTIONS
Physical Heat Related Disorders
General Safe Work Practices For Heat Stress Areas
Guidelines For Using The Heat Stress Monitors And Determining Stay Times
Stay Time Chart
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February 13, 2012
Section 1.
Physical Heat Related Disorders
1.
Heat Rash – occurs when sweat is not removed from the surface of the skin and the skin
remains wet most of the time. The sweat ducts become plugged and a skin rash
develops. The individual can prevent this condition by resting in a cool place, allowing
sweat to evaporate, and by regularly bathing and drying the skin.
2.
Fainting (Heat Syncope) – can occur in persons not accustomed to the heat who stay in
one position for periods of time. This allows the blood to pool in enlarged blood vessels
and lower parts of the body. Insufficient blood is returned to the heart and brain.
3.
Heat cramps – are painful muscle spasms caused by insufficient salt replacement
(usually due to low potassium, but can include sodium and others).
4.
Heat Exhaustion – is caused by the loss of large amounts of fluid, sometimes with
excessive salt loss. The affected employee still sweats, but experiences extreme
weakness or fatigue, giddiness, nausea, and / or headache and may vomit or lose
consciousness. The skin is clammy and moist, the complexion is pale or flushed and the
body temperature is normal or slightly elevated.
5.
Heat Stroke – occurs when the body’s temperature regulating system fails and sweating
is inadequate. The affected employee’s skin is hot, usually dry, red or spotted. Body
temperature is 105 F or higher. Unless the victim receives quick and appropriate
treatment brain damage or death can occur.
Section 2. General Safe Work Practices for Heat Stress Areas
1. Things To Do
a. Maintain good physical condition for work in heat stress environments by exercising,
eating a balanced diet and getting sufficient rest.
b. Frequently drink small amounts of water before becoming thirsty to maintain good
hydration, During moderate activities, in moderately hot conditions, at least one pint of
water per hour is needed. Drink about 8 ounces every 15 minutes. Urine should be clear
or lightly colored when well hydrated.
Note: Dehydration prevention is the goal and a sufficient amount of water must be consumed
to achieve this. (Caution: Employees who have high blood pressure should not consume liquids
heavy in salt content.) The nuclear sites will not purchase sports drinks such as Gatorade for
supervisors nor stock them in the warehouse.
c. Take adequate breaks.
Note: The temperature in the work area, type of work being performed and the physical
condition of the employee should determine the number of breaks.
d. Dress appropriately for the environmental conditions.
e. Take precautions to protect from overexposure to the sun (e.g., clothing, eye protection,
and sunscreen).
f. During extended exposures covering several days it is important to know your body
weight before exposure and check it daily to determine if sufficient fluids are being
consumed to maintain it.
g. Work at a deliberate pace to avoid over-exerting yourself.
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February 13, 2012
2. Things To Avoid
a. Drinks that contain alcohol. Alcohol leads to dehydration and nervous system
depression.
b. Smoking. Smoking reduces the size of blood vessels limiting the ability to carry away
heat and provide oxygen to the muscles. It also has other interactions that reduce the
body’s ability to respond to heat stress.
3. Medical Conditions
a. Illnesses such as colds, flu, high blood pressure, diabetes, or any illness that may cause
weakness, dizziness, or fever may render an employee unfit for exposure to heat stress.
b. Prescription or over-the-counter medication, alcohol consumed, and / or a history of heat
stress intolerance should be considered in determining assignment to work in heat
stress environments.
c. Additional personal monitoring to determine effects of heat can be done by checking
heart rate, body temperature, or extent of body weight loss.
4. Methods To Reduce Heat Stress
a. Erect or place a shield between radiant heat and the immediate work area (e.g.,
insulation blanket, welder’s flash guards).
b. Use Kool Vests when available. For additional guidance, reference Nuclear Safe Work
Practice 8.0 section on “Body Protection”, for information on Ice Vests / Thermal Wear
(Kool Vests).
Note: Before taking water coolers into an RCA, obtain approval from RP group.
c. Set up coolers of ice water in or near the work area.
Note: Before using fans in an RCA/RCZ, obtain approval from RP group.
d. Use fans when appropriate to help sweat evaporate and cool the body.
e. Schedule jobs during cooler periods when able.
f. Perform mockup / practice training to improve efficiency and reduce stay times.
g. Ensure adequate recovery time in a cool environment between exposures. A cool
environment is considered to be <77 F while wearing light, dry clothing. Recovery time
can be calculated by the following formula:
Recovery Time = (Time Spent in Heat Stress Area ÷ Stay Time) X 60 Minutes
h. Maximum Stay time can be determined from the table in Section 4, Stay Time Chart.
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Revision 3
February 13, 2012
Section 3. Guideline For Using Heat Stress Monitors
Quest Heat Stress Monitors
Note: Historical heat stress data exists for many plant areas if needed, contact EHS. Historical
data may be used if conditions are the same.
Follow these guidelines to use this monitor.
Note: Prior to going to the work area, check the “LOBAT” indicator on the display to determine
if the battery needs to be replaced. The battery compartment is located on the rear of
the monitor. To replace the battery, open the compartment by lifting one end of the
cover. This will expose the battery and connector. Replace with a standard 9-volt.
Note: The Quest Area Heat Stress Monitor may be used for multiple shifts if the steps listed
below are followed.
1. Guidelines for using the Quest Heat Stress Monitors:
a. Ensure instrument has been calibrated, check calibration sticker on back of instrument.
b. Some Quest monitors require DEMIN water in the middle top basin, wet the sponge and
wick thoroughly, if applicable. Contact EHS or Chemistry to obtain DEMIN water.
c. Turn the monitor on by pressing the ON / OFF button.
d. Set the instrument to display the Wet Bulb Globe Temperature (WBGT) in °F to
determine Heat Stress temperature.
e. Place the instrument in the immediate work area to be measured approximately at chest
level and allow 5 minutes to stabilize.
f.
Use the WBGT and the Stay Time Chart (Section 4) to determine your
RECOMMENDED stay time.
Note: The recommended stay time may be too long for employees in poor physical condition
or with a previous history of heat related illness.
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February 13, 2012
SPER Scientific Heat Stress Meter
1. Operation guideline for using the SPER:
a. Slide the clear sensor cover down.
b. Turn on the meter, press the SET button
c. Press the MODE button until WBGT is displayed
d. Press and hold the MODE button to change from WGBT IN and WBGT OUT. Use
WBGT IN for indoor and WBGT OUT for outdoor areas.
e. To change from Celsius to Fahrenheit press the Mode and NEXT buttons simultaneously
f.
Use the WBGT reading and the Stay Time Chart (Section 4) to determine your
RECOMMENDED stay time.
Note: The recommended stay time may be too long for employees in poor physical condition
or with a previous history of heat related illness.
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February 13, 2012
Botsball Thermometer
i.
Guidelines for using the Botsball Thermometer:

Add water to the reservoir located within the aluminum sleeve to wet the black cloth
around the base
 Place instrument within work area and allow the instrument to stabilize (5 minutes)
before taking a reading
 Use the following chart to convert the Botsball’s reading to a WBGT. Then use the Stay
Time Chart (Section 4) to determine your Recommended stay time.
Note: The recommended stay times listed on the "Stay Time Chart" may be too long for
employees in poor physical condition or with a previous history of heat related illness.
BOTSBALL WBGT BOTSBALL WBGT
75
79.3
89
98.5
76
80.5
90
100.1
77
81.7
91
101.7
78
83.0
92
103.3
79
84.3
93
104.9
80
85.6
94
106.5
81
87.0
95
108.2
82
88.3
96
109.9
83
89.7
97
111.6
84
91.1
98
113.3
85
92.6
99
113.3
86
94.0
100
116.6
87
95.5
101
118.7
88
97.0
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February 13, 2012
Section 4.
Stay Time Chart
The number within the box is the worker’s stay time in minutes.
Work in Street Clothes
Work in single layer
cotton or OREX
Work in double layer
cotton or OREX
Work in
Plastics/Rainsuits
111°F
60
25
45
20
45
15
30
10
108°F
104°F
100°F
97°F
93°F
90°F
86°F
82°F
79°F
75°F
90
90
120
240
480
NL
NL
NL
NL
NL
30
45
45
60
90
120
240
NL
NL
NL
60
90
90
120
240
480
NL
NL
NL
NL
25
40
45
45
60
100
120
240
NL
NL
45
60
90
90
120
240
480
NL
NL
NL
20
25
30
45
45
60
90
120
140
NL
45
45
60
90
90
120
240
480
NL
NL
15
20
25
30
45
45
60
90
120
240
10
20
30
40
45
60
120
240
Heavy
Work
10
15
20
10
25
30
45
50
90
180
480
NL
Moderate
Work
20
30
Light
Work
10
15
Heavy
Work
Moderate
Work
30
45
10
20
30
40
45
60
120
240
480
NL
Moderate
Work
Light
Work
15
20
Light
Work
Moderate
Work
45
45
Heavy
Work
Light
Work
118°F
115°F
Heavy
Work
WBGT
10
20
30
40
45
60
120
NL = no limit (stay times given in minutes)



Light Work is sitting or standing with moderate arm or trunk movement, stationary welding,
bench work, monitor equipment, minimal walking and climbing.
Moderate Work is walking with some lifting or ladder climbing, floor cleaning, painting,
surveys with occasional climbing, insulation removal or installation, or easy manual valve
alignments.
Heavy work is pushing or pulling, frequent ladder or stair climbing, scaffold erection, lead
blanket removal or installation, mopping and sweeping, difficult manual valve alignments.
To determine the stay time when using an ice vest / thermal wear (Kool Vest), multiply the stay
time by 1.5.
Recovery time is the recommended amount of time necessary for an individual’s physical state to
return to its pre-exposure condition.
Recovery Time = (Time Spent in Heat Stress Area ÷ Stay Time) X 60 Minutes
Recovery areas need to be in locations that are <77° F.
NSWP 7.1-8