8.0 AMBIENT TEMPERATURE
RELATED INJURY
8.1 Introduction
Thermal Stress and temperature-related injuries are most likely to occur during
season transition when our body is making biological adjustment to compensate
for hot or cold changes in ambient temperatures. Extreme hot or cold
temperatures can burn or destroy human skin and flesh tissue. Hot, South Central
Texas summers ambient, daily temperature between the months of June and
September typically averages above 90 degrees Fahrenheit (90oF).
8.2 Ambient Heat-Related Injuries
A. The American Conference of Governmental Industrial Hygienists (ACGIH)
recommend workers not be permitted to work when their deep body
temperature exceeds 100.4°F (38°C). Ambient heat-related injuries are caused
by progressive stages of (heat) stress. Stages leading from concern to severe
trauma are:
(1)
(2)
(3)
(4)
Heat Cramps – sweating and muscle cramps
Heat Syncope – fainting
Heat Exhaustion - profuse sweating and tiredness
Heat Stroke – dry skin and high body temperature
B. Signs of heat-related injury and appropriate first –aid are as follows:
Symptoms and First-aid for Heat Injuries
INJURY
Heat Syncope
SYMPTOM
Fainting when standing
erect and immobile in
the heat
Heat Cramps
Active sweating, muscle
cramps.
Heat Exhaustion
Profuse sweating,
headache, weakness,
and nausea; skin cool
and moist.
High body temperature;
skin dry and hot;
unconsciousness,
Heat Stroke –
MEDICAL
EMERGENCY
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FIRST AID
1. Remove to cool area.
2. Allow to recline and provide cool
water.
3. Recovery will be prompt and
complete.
1. Remove to cool area
2. Massage extremities
3. Notify family physician at patient’s
request
4.
1. Remove to cool area.
2. Elevate feet
3. Loosen clothing and apply wet cloths
4. Call 911
THIS IS A MEDICAL EMERGENCY!
1. Dial 911.
2. Attempt to lower body temperature
convulsions, or delirium
by:
a. Removing clothing
b. Immersing in water (if
available) or sprinkling with
water and fanning to increase
evaporation of moisture on
skin.
c. Massaging extremities and
trunk to aid blood circulation.
3. Move to medical treatment facility as
quickly as possible.
C. Drinking adequate fluids like plain water or Gatorade to replace salts and
liquid lost through sweating is the single, most effective heat-related injury
avoidance action that can be taken to protect the following at-risk employees:
(1) University of Texas Police Department (UTPD) Bicycle
Patrol Officers & Guards.
(2) Facilities Management (FM) Utilities Employees.
(3) FM Grounds Maintenance Employees.
(4) FM Central Energy Plant Employees
(5) FM Maintenance Employees.
(6) Employees tasked to work outdoor during the months
of June to September when the ambient temperature is
equal to or greater than 85oF.
At a minimum, supervisors must proactively prepare to supply at-risk
employees replacement fluids at rates shown in the (Water) Hydration Guide
Chart below.
(Water) Hydration Guide
Wet Bulb Globe Temperature
(WBGT)
In Degrees Fahrenheit (oF)
Below 82
82-84
85-87
Water Intake (Quarts) per Hour
½-¾
½-1
¾ - 1 or as much as you can drink
1 or as much as you can drink
D. If left untreated, minor Heat Cramps can progress to fatal Heat Stroke. Normal
human, deep body temperature is 98.6 oF (37oC). When normal body
temperature exceeds 109oF (43oC), death from Heat Stroke can occur. The
ACGIH publishes Heat Stress (HS) Standards which are used to evaluate,
control, and prevent occupational heat stress. Workload, ambient temperature,
and Relative Humidity (RH) are major factor in determining HS intensity and
effect. Listed below, are examples of activities and their classification in
relation to HS exposure.
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(1) Light handwork: outdoor supervision, guard duty.
(2) Heavy handwork: typewriting.
(3) Heavy work with one arm: hammering nails (cabinetmaking,
upholsterer).
(5) Light work with two arms: filing metal, using power tool, raking
leaves.
(6) Moderate work with the body: cleaning a floor, transporting and
stacking bio-hazardous waste boxes.
(7) Heavy work with the body: trenches, construction work, landscape
maintenance.
8.3 Heat Stress (HS) Evaluation, Control, and Prevention
A. Evaluation
This is an annual requirement which is best performed when outdoor
temperatures routinely rise to or exceed 90oF. HS is measured with a
Wet Bulb Globe Temperature (WBGT) instrument. WGBT is the term
used to quantify outdoor and indoor ambient heat intensity, with (outdoors
in sunlight) and without (indoors) solar (sun) load. Environmental heat
measurements should be made in, or close to, the specific exposure area.
When a worker is not continuously exposed in a single hot area but moves
between two or more areas having different levels of environmental heat,
or when the environmental heat varies substantially at a single hot area,
heat exposures should be measured in each area and for each level of heat
to which employees are exposed.
(1) The exposure limits in the table below are valid for employees
wearing light clothing. They must be adjusted for the insulation
from clothing that impedes sweat evaporation and other body
cooling mechanisms.
(2) Use the table below requires knowledge of the WBGT and
approximate workload. Workload can be estimated using the data
in Paragraph 8.2B, and formulae below.
Portable heat stress meters or monitors are used to evaluate occupational
heat exposure. These instruments can calculate both indoor (without solar
load) and outdoor (with solar load) WBGT index according to established
ACGIH Threshold Limit Value equations. Coupled with the type of work
being performed, heat stress meter information can be used to determine
how long a person can safely work or remain in a high-heat environment.
(3) Use the following formulae to calculate WBGT:
(a) Outdoor, with solar load
WBGT = 0.7NWB + 0.2GT + 0.1DB
(b) Indoor, without solar load
WBGT = 0.7NWB + 0.3GT
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Where
WBGT - Wet Bulb Globe Temperature Index
NWB
- Nature Wet-Bulb Temperature
DB
- Dry-Bulb Temperature
GT
- Globe Temperature
(4) The WBGT for continuous all-day or several hour exposures
should be averaged over a 60-minute period. Intermittent
exposures should be averaged over a 120-minute period. These
averages should be calculated using the following formula:
Average Web Bulb Globe Temperature (WBGT)
WORK/REST GUIDELINES IN INDUSTRIAL ENVIRONMENTS
Light Work
Moderate Work
Heavy Work
*WBGT
Temperature
Range in
Degrees
Heat
Fahrenheit
Category (oF)
Caution 77.0 – 86.9
Danger
87.0 – 89.9
Extreme Above 90
Danger
***Water
Intake in
Quarts/
Hour
Work/Rest
**Work/Rest (Qts/hr)
Cycle in
Cycle
minutes/hour)
No limit
0.5
45/15
No Limit
0.75
30/30
50/10
1.0
15/45
Water
Intake
Qts/Hr
0.75
0.75
1.0
Work/Rest Water
Cycle
Intake
Qts/Hr
40/20
0.75
20/40
1.0
10/50
1.0
*When wearing protective over garments like Tyvex, Rain, or Chemical
Protective Suits, add 10oF to WBGT.
**Work/Rest Cycles apply to acclimatized workers.
***Water or other fluid intake should be a maximum of 1.5 quarts per hour or 10
quarts per day.
PERMISSIBLE HEAT EXPOSURE THRESHOLD LIMIT VALUES
Work/rest regimen
Light
Work Load*
Moderate
Heavy
Continuous work
30.0°C
(86°F)
30.6°C
(87°F)
31.4°C
(89°F)
26.7°C
(80°F)
28.0°C
(82°F)
29.4°C
(85°F)
25.0°C
(77°F)
25.9°C
(78°F)
27.9°C
(82°F)
75% Work, 25% rest, each hour
(45 minutes work, 15 minutes rest)
50% Work, 50% rest, each hour
(30 minutes work, 30 minutes rest)
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25% Work, 75% rest, each hour
(15 minutes work, 45 minutes rest)
32.2°C
(90°F)
31.1°C
(88°F)
30.0°C
(86°F)
Values are in °C and °F, WBGT.
These Permissible Exposure Limits (PELs) are based on the assumption that
nearly all acclimatized, fully clothed workers with adequate water and salt intake
should be able to function effectively under the given working conditions without
exceeding a deep body temperature of 38°C (100.4° F). They are also based on
the assumption that the WBGT of the resting place is the same or very close to
that of the workplace. Where the WBGT of the work area is different from that of
the rest area, a time-weighted average should be used (consult the ACGIH 20012002 Threshold Limit Values for Chemical Substances and Physical Agents and
Biological Exposure Indices (1992).
These TLV's apply to physically fit and acclimatized individuals wearing light
summer clothing. If heavier clothing that impedes sweating or has a higher
insulation value is required, the permissible heat exposure TLVs in Table III:4-2
must be reduced by the corrections shown
Source: ACGIH 2002
B. Controlling Heat-Related (Heat Stress) Injury
Controlling workers exposure to extreme, ambient temperatures
will significantly reduce or eliminate heat stress exposure potential. The
ACGIH table above combines activity classification (workload) and Wet
Bulb Globe Temperature (WBGT) to standardize recommended work
versus rest period as ambient conditions (temperature and RH) during hot
seasons change.
C. Preventing Heat-Related Injury
Avoiding heat exposure is the best form of prevention. However the nature
of some UTHSCSA employees’ responsibilities predisposes them to high,
ambient, heat exposure for extended time periods. When heat exposure
cannot be avoided, Managers, Leaders, and supervisors should:
(1) Use Appendix H, Heat-Related Illness Hazard Assessment, to
evaluate personnel potential for heat overexposure before starting
work.
(2) Perform Health and Safety (EH&S) Heat Stress Training for shop
personnel with assistance from EH&S
(3) Insure personnel are slowly acclimatized to changing weather
conditions in preparation for extended work periods in high,
ambient heat.
(4) Insure personnel are adequately hydrated while working outdoor
or indoor in hot areas such as Utility, Mechanical, and Steam
Rooms.
(5) Schedule outdoor work during the coolest part of the day (early
morning & before 2 PM) when the ambient temperature is
comfortable and more conducive to stress-free performance.
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8.4 The Heat Index
Ambient temperature, Relative Humidity (RH), other environmental factors, and
workload are all factors used in determining the Heat Index (HSI) – the perceived
intensity of atmospheric heat on bare skin. For example, the chart below shows
an HI of 107 oF when actual (atmospheric) temperature is 95 oF and RH is 50%.
This means that to someone working outdoors, in 95oF weather, the ambient
temperature will feel like 107 oF. A mean HI above 85 oF is considered
dangerous.
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How temperature and humidity combine to increase perceived body temperature
HEAT INDEX CHART
(Read UP to the temperature on the Temperature scale and ACROSS to the current
Relative Humidity on the Relative Humidity Scale. The HEAT INDEX is the temperature
in the block where the two readings intersect).
Extreme
Danger
Danger
Extreme
Caution
Caution
RELATIVE HUMIDITY (PERCENT)
AIR TEMPERATURE (DEGREES FAHRENHEIT)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
90
95
100
140
125
135
120
128
130
117
122
131
125
111
118
123
131
141
120
107
111
118
123
130
139
148
115
103
107
111
115
120
127
135
143
151
110
99
102
105
108
112
117
123
130
137
143
150
105
95
97
100
102
105
109
113
118
123
129
135
142
149
100
91
93
95
97
99
101
104
107
110
115
120
126
132
138
144
95
87
88
90
91
93
94
96
98
101
104
107
110
114
119
124
130
136
90
83
84
85
86
87
88
90
91
93
95
96
98
100
102
106
109
113
117
122
85
78
79
80
81
82
83
84
85
86
87
88
89
90
91
93
95
97
99
102
105
108
80
73
74
75
76
77
77
78
79
79
80
81
81
82
83
85
86
86
87
88
89
91
75
69
69
70
71
72
72
73
73
74
74
75
75
76
76
77
77
78
78
79
79
80
70
64
64
65
65
66
66
67
67
68
68
69
69
70
70
70
71
71
71
71
71
72
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