For many people, summertime at Princeton means warm, comfortable days,
perfect for eating outside or long walks during breaks from air-conditioned
offices. But for some of us, summertime means special projects working
outside in the direct sunlight or renovating buildings with no cooling
systems. Working in hot conditions may pose special hazards to safety
and health. This document provides an overview of the variety of illnesses
and injuries associated with heat stress and gives guidance on how to
recognize and prevent them.
How Your Body Reacts to Hot Conditions
Four environmental factors affect the amount of stress a worker faces
in a hot work area: temperature, humidity, radiant
heat (such as from the sun or a furnace) and wind speed.
Individuals with high blood pressure or some heart conditions and people
who take diuretics (water pills) may be more sensitive to heat exposure.
The body defends itself from heat through three mechanisms: breathing,
sweating, and changing the blood flow. The first reaction is to circulate
blood to the skin, which increases skin temperature and allows the body
to give off some heat. During heavy work, muscles need more blood flow,
which reduces the amount of blood available to flow to the skin and
release the heat.
Sweating also helps the body to cool off, but only when the humidity
levels are low enough to allow the sweat to evaporate and if water and
salts lost through sweating are replaced.
Heat Stress Disorders (top)
When the body becomes overheated, a condition of heat stress exists.
Heat stress can lead to a number of problems, including heat exhaustion,
heat stroke, heat cramps, fainting, or heat rash. Many people confuse
these disorders, but it is important to be able to recognize each one
and know what to do when it happens. Each of these heat stress disorders
is described below.
Although not the most serious health problem, heat exhaustion is the
most common heat-related ailment at Princeton University. Heat exhaustion
happens when a worker sweats a lot and does not drink enough fluids
or take in enough salt or both. The simple way to describe the worker
is wet, white and weak.
Signs and symptoms
- Weak or tired, possibly giddy
- Normal or slightly higher body temperature
- Pale, clammy skin (sometimes flushed)
What to do
Heat stroke is the most serious health problem for people working in
the heat, but is not very common. It is caused by the failure of the
body to regulate its core temperature. Sweating stops and the body can
not get rid of excess heat. Victims will die unless they receive proper
Signs and symptoms
- Mental confusion, delirium, fainting, or seizures
- Body temperature of 106ºF or higher
- Hot, dry skin, usually red or bluish color
What to do:
- Call Public
Safety at 9-1-1 immediately and request an ambulance
- Move victim to a cool area
- Soak the victim with cool water
- Fan the victim vigorously to increase cooling
Heat cramps are painful muscle spasms. They occur when a worker drinks
a lot of water, but does not replace salts lost from sweating. Tired
muscles – those used for performing the work – are usually
the most likely to have the cramps.
Signs and symptoms:
- Cramping or spasms of muscles
- May occur during or after the work
What to do
Fainting (Heat Syncope)
Fainting usually happens to someone who is not used to working in the
hot environment and simply stands around. Moving around, rather than
standing still, will usually reduce the likelihood of fainting.
Signs and symptoms
- Brief loss of consciousness
- Sweaty skin, normal body temperature
- No signs of heat stroke or heat exhaustion
What to do:
- Lie down in a cool place
- Seek medical attention if not recovered after brief period of
Heat rash, also called prickly heat, may occur in hot and humid environments
where sweat cannot evaporate easily. When the rash covers a large area
or if it becomes infected, it may become very uncomfortable. Heat rash
may be prevented by resting in a cool place and allowing the skin to
Signs and symptoms
- rash characterized by small pink or red bumps
- irritation or prickly sensation
What to do
- keep skin clean and dry to prevent infection
- wear loose cotton clothing
- cool baths and air conditioning are very helpful
- some over-the counter lotions may help ease pain and itching
Preventing Heat Stress (top)
In most cases, heat stress can be prevented or, at least, the risk
of developing heat stress can be reduced.
A number of engineering controls can help reduce heat exposure. These
- general and local exhaust ventilation in areas of high heat
- shielding of radiant heat sources, such as furnaces or hot machinery
- elimination of steam leaks
- use of cooling fans or personal cooling devices, such as cooling
- use of power tools to reduce manual labor
- Clothing: Wear loose-fitting, lightweight
clothing, such as cotton, to allow sweat to evaporate. Light colors
absorb less heat than dark colors. When working outside, wear a lightweight
hat with a good brim to keep the sun off your head and face.
- Drinking: Drink plenty of liquids, especially
if your urine is dark yellow, to replace the fluids you lose from
sweating – as much as one quart per hour may be necessary. Water
and/or sports drinks are recommended. Since caffeine is a diuretic
(makes you urinate more), beverage such as cola, iced tea and coffee
should be avoided. Thirst is not a reliable sign that your body needs
fluids. When doing heavy work, it is better to sip rather than gulp
- Work Schedule: If possible, heavy work
should be scheduled during the cooler parts of the day. Otherwise,
alternate heavy work in the heat with lighter work or work in cooler
areas. When the temperature humidity index (see next page) is between
84 and 93 (Warning Zone), try to minimize the amount of time working
in the heat such that approximately half of each hour is spent doing
heavy work in the heat. When the temperature humidity index is 94
or higher (Danger Zone), this should be further minimized to approximately
one quarter of each hour spent doing heavy work in the extreme heat.
- Acclimatization: New employees and workers
returning from an absence of two weeks or more should have 5 days
to get used to the heat. Begin with 50 percent of the normal workload
and time exposure the first day and gradually build up to 100 percent
on the fifth day.
- Body Weighing: Workers may be at greater
risk of heat stress if they lose more than 1.5% of their body weight
in a single day from sweating.
Personal Protective Equipment
When work must proceed in hot conditions at Princeton, personal cooling
systems may help reduce the risk of heat stress. There are several systems
available through health and safety catalogs, including the following:
- Heat reflective clothing may alleviate
the problem of radiant heat sources, such as furnaces. However, if
the worker is fully covered, he or she will have trouble evaporating
- Ice vests or cooling vests remove heat
from the skin. They are relatively inexpensive and allow freedom of
- Liquid cooling systems also remove heat
from the skin. Cool liquid flows in the suit around the body and carries
the heat away.
Employees and supervisors need to be trained to be able to detect early
signs of heat stress. Employees must understand the need to replace
fluids and salt from sweat and recognize the signs of dehydration, fainting,
heat cramps, heat exhaustion, and heat stroke.
Supervisors should watch for signs of heat stress and allow workers
to interrupt their work if they are extremely uncomfortable. Supervisors
should also ensure that work schedules allow appropriate rest periods
and ensure liquids are available. They should use appropriate engineering
controls, personal protective equipment and work practices to reduce
the risk of heat stress.
Temperature-Humidity Index (top)
A useful guide to summertime comfort is the Temperature-Humidity Index
(THI). This table gives an approximation of how most people react to
heat and humidity. To use the table, find out the temperature and relative
humidity of the work area. Start at the temperature listed on the left,
and read across to the number under the relative humidity level (round
up to the higher percentage). This number is the temperature-humidity
index. The values are for people wearing the right amount of clothing
doing light work, with very little wind.
The lightly highlighted area is uncomfortable for everyone. For moderate
to heavy activity, workers should be concerned about heat stress and
should alternate time working in the heat and time in cooler areas or
light work. When the THI is in the darkly highlighted area, extreme
caution is indicated. Workers should try to schedule work to allow only
25% of time performing heavy work in such an environment. Workers should
be encouraged to drink plenty of fluids and be on the lookout for signs
of heat stress.
For more information (top)
Contact Environmental Health and Safety at 258-5294 or Employee
Health at McCosh
Health Center at 258-5068 for more information.
In an emergency, call
Public Safety at 9-1-1.