Chapter 10
Thermal Stress
Heat stress
Working in hot conditions puts stress on our body's cooling system. When the heat is combined with other stress such as physical labor, loss of fluids, fatigue or preexisting medical conditions, it may lead to heat-related illness, disability and even death. This can happen to anybody--even the physically fit. The body is always generating heat and passing it to the environment. The harder the body is working, the more heat it has to lo. When the environment is hot or humid, is near a source of radiant heat (for example,
a furnace or the sun), the body must work harder to get rid of its heat. If the air is moving
(for example, from fans) and is cooler than the body, it is easier for the body to pass heat to the environment. Workers over 40 should be more careful becau of a reduced ability to sweat.
Hot work environments can be managed with an effective program including but not limited to;
•Industrial hygiene monitoring program
•Work/rest regiments
•Ventilation
•Fluids for worker hydration
•Employees trained in the signs and symptoms of heat stress
•U of appropriate clothing and PPE
The American Conference of Industrial Hygienist (ACGIH) TLV booklet is a good source to acquire better understanding of thermal stress and was ud as a reference for this chapter. It also contains more information on heat stress factors such as metabolic rates that can assist in heat stress monitoring.
Acclimatization
If an employee is not ud to working in the heat, it can take a week or two to get acclimatized or ud to the heat. If they were ill or away from work for a week or so they can lo their acclimatization.
Signs, Symptoms, Prevention and Treatment
Signs &
Symptoms
Cau Symptoms Treatment Prevention
Heat Rash Hot humid
environment;
plugged sweat
glands. Red bumpy rash with vere
itching.
Change into dry clothes
and avoid hot
environments. Rin skin
with cool water.
Wash regularly to keep skin
clean and dry.
Sunburn Too much
exposure to the
sun. Red, painful, or blistering and
peeling skin.
If the skin blisters, ek
medical aid. U skin
lotions (avoid topical
anesthetics) and work in
the shade.
Work in the shade: cover
skin with clothing; wear
suntan lotions with a sun6399
protection factor of at least
15. People with fair skin
should be especially
cautious.
Heat Cramps Heavy sweating
drains a person's
body of salt, which
cannot be replaced
assassinsjust by drinking
water.
Painful cramps in arms, legs
or stomach which occur
suddenly at work or later at
home.
Cramps are rious becau
they can be a warning of
other more dangerous heat-
induced illness.
Move to a cool area;
loon clothing and drink
cool salted water ( 1 tsp.
salt per gallon of water) or
commercial fluid
replacement beverage. If
the cramps are vere or
don't go away, ek
someone like you 翻译medical aid.
When working in the heat,
workers should put salt on
their food (if on a low-salt
diet, this should be discusd
with a doctor). This will give
the body all the salt it needs;
don't take salt tablets.
Fainting Not enough blood
flowing to the
head, causing loss
of consciousness. Sudden fainting after at least
two hours of work; cool moist
skin; weak pul.
Fainting may be due to a
teacherclub com cn
heart attack or other
illness. GET MEDICAL
ATTENTION. Asss
need for CPR.
Move to a cool area;
loon clothing; make
person lie down; and if the
system是什么意思person is conscious, offer
sips of cool water.
Reduce activity levels and/or
heat exposure. Drink fluids
regularly. Workers should
check on each other to help
spot the symptoms which
often precede heat stroke.
Heat Exhaustion Inadequate salt and
water intake caus
a person's body's
cooling system to
start to break
down.
Heavy sweating; cool moist
skin; body temperature over
38o C; weak pul; normal or
low blood pressure; person is
tired, weak, clumsy, upt or
confud; is very thirsty; or is
panting or breathing rapidly,
vision may be blurred.
GET MEDICAL AID.
This condition can lead to
heat stroke, which can kill.
Move the person to a cool
shaded area; loon or
remove excess clothing;
provide cool water to
drink (salted if possible);
fan and spray with cool
water.
Reduce activity levels and/or
heat exposure. Drink fluids
regularly. Workers should
check on each other to help
spot the symptoms which
often precede heat stroke.
Heat Stroke If a person's body
has ud up all its
water and salt, it
will stop sweating.
This can cau
accompanyingbody temperature
to ri. High body temperature (over
41o C) and any one of the
following: the person is weak,
confud, upt or acting
strangely; has hot, dry, red
skin; a fast pul; a headache
or dizziness. In later stages, a
person may pass out and have
convulsions.
CALL AMBULANCE.
This condition can kill amistake可数吗
person quickly. Remove
excess clothing; fan and
spray the person with cool
water; offer sips of cool
water if the person is
conscious.
Reduce activity levels and/or
heat exposure. Drink fluids
regularly. Workers should
check on each other to help
spot the symptoms which
often precede heat stroke.
Effective engineering controls that reduce heat exposure to employees are the first line of defen w
hen protecting workers. Below is s list of engineering, administrative, and personal protective clothing controls.
Engineering Controls
•Control the heat at source through the u of insulating and reflective barriers (insulate furnace walls).
•Exhaust hot air and steam produced by specific operations.
•Reduce the temperature and humidity through air cooling.
•Provide air-conditioned rest areas.
•Reduce physical demands of work task through mechanical assistance (hoists, lift-tables, etc.).
Administrative Controls
•Schedule hot jobs to cooler times of the day.
•Work/rest regiment.
职称英语考试查询•Make available cool drinking water or other fluids for workers and remind them to drink a cup every 20 minutes.
•Assign additional workers or slow down work pace.
•Make sure everyone is properly acclimatized.
•Train workers to recognize the signs and symptoms of heat stress.
•Pregnant workers and workers with a medical condition should discuss working in the heat with their doctor.
Clothing & PPE
•Light clothing should be worn to allow free air movement and sweat evaporation.
•Outside, wear light-colored clothing.
•In a high radiant heat situation, reflective clothing may help.
•For very hot environments, air, water or ice-cooled insulated clothing should be considered.
•Vapor barrier clothing, such as acid suits, greatly increas the amount of heat stress on the body, and extra caution is necessary.
Monitoring Equipment
Two commonly ud monitoring tools are the Wet Bulb, Globe Temperature
(WBGT) device and the personal heat stress monitor. The WBGT offers a uful
index of environmental contribution to heat stress. It is influenced by air
temperature, radiant heat and humidity. It can be ud to determine heat stress
exposure before it occurs. Personal heat stress monitors indicate body core
temperature. The heat stress monitor in the example below us an ear lug device to
calculate body core temperature. The heat stress monitor gives a reading of heat
stress exposure during or after the exposure has occurred.
Wet Bulb, Globe Temperature (WBGT)
The WBGT us three nsors (nsor array) to take measurements which compute the WBGT index; wet bulb thermometer, globe temperature, and dry bulb thermometer. The WBGT index is an excepted method of determining the heat stress level impod on an individual in a given environment. Although the formulas for the WBGT index are
included in this chapter, the WBGT monitor will give an index reading temperature that can be uful in determining the potential for heat stress exposure. The ACGIH screening criteria for heat stress exposure table is included as well. The values from the WBGT can be compared to this table to determine an appropriate work/rest regiment.
The WET BULB THERMOMETER gives an indication of the effects of humidity on an individual. Relative humidity and wind speed are taken into account by measuring the amount of evaporative cooling taking place at a thermometer covered with a moistened
wick.
socialcurityThe GLOBE THERMOMETER gives an indication of radiant heat exposure to an
individual due to either direct light or hot objects in the environment. This is
accomplished by placing a temperature nsor inside a blackened copper sphere and
measuring the temperature ri.
The DRY BULB THERMOMETER measures the ambient air temperature. This
measurement is ud in the outdoor WBGT calculation when a high solar radiant heat load may be prent.
The WBGT us the wet bulb and globe temperatures readings to monitor the indoor environment. Outdoor measurements include the dry bulb temperature reading where a high solar radiant heat load may be prent. The WBGT index is a weighted average of the measurements according to the formulas:
WBGT indoor = 0.7 wet bulb + 0.3 globe
WBGT Outdoor = 0.7 wet bulb + 0.2 globe + 0.1 dry bulb
Monitoring with a Wet Bulb, Globe Temperature (WBGT)
Some WBGT units are available with more than one
nsor array. The can be ud to monitor more than one
area at a time or ud together at ankle, abdomen, and head
height when the temperature in an area is variable (e
illustration). When ud in a temperature variable
environment the WBGT can weight or average the
readings. Most WBGT units can be t to automatically
weight the readings together using formula below.
WBGT= (WBGT head + (2 x WBGT abdomen) + WBGT feet)
4
Basic Operating Instructions:
•Depending on the memory capabilities, you may need to clear the WBGT data from previous monitoring. The unit may append the data or start a new ssion.
•Place the WBGT at a height of 3.5 ft. for standing individuals or 2.0 ft. for sitting individuals. Tripod mounting is recommended to get unit away from anything that
may block radiant heat or airflow.
•Fill the wet bulb rervoir with distilled water. After adding water or moving the unit to a new locatio
n, allow 10 minutes for the globe and wet bulb readings to
stabilize.
•Set the instrument to WBGT-in for indoor application or WBGT-out for outdoor u.
•Start the unit’s data recording for the monitoring ssion.
See the instruction book for the WBGT you are using for details on data logging,
programming start and stop times, alarm options, data out-put, printing options, etc.
Becau the WBGT is only an index of environment, the screening criteria are adjusted for the contributions of the work demands and clothing as well as state of acclimation. The following tables are ud in conjunction with WBGT measurements to asss the work environment. Table 1 provides WBGT criteria suitable for screening purpos, table 2 provides additions to measured WBGT values for some clothing enmbles, and table 3 provides examples of activity levels. The values are bad on preventing fit, acclimatized workers' core temperatures from rising above 38o C (100o F).
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