Ergonomics (Thermal stress)

PRESENTED BY:
Arundhati P Dolas
Roll No.3
M.Sc-I RM-ERGO
2013-14

CONTENT
Definition
Thermo-regulation of the human body
Variables which affect thermal sensation
Heat stress
Heat acclimatization
Factors causing heat stress
Types of heat transfer
Health effects of heat stress
Methods for measuring heat stress
Control of heat stress
Prevention of heat stress
Conclusion
Saturday, March 08, 2014

THERMAL STRESS

2

Definition
Thermal stress is defined as the
physical and physiological reactions
of the human body to temperatures
that fall outside of the human
normal comfort zone.


THERMAL STRESS

3

Thermo-Regulation Of The
Human Body
•

•

•

Humans are warm-blooded animals, meaning they maintain
their body temperature internally. This control of body
temperature is referred to as thermoregulation.
The human body regulates temperature by keeping a tight
balance between heat gain and heat loss.
Humans regulate heat generation and preservation to maintain
internal body temperature or core temperature. Normal core
temperature at rest varies between 36.5 and 37.5 Celsius
( C), which is 97.7 to 99.5 Fahrenheit ( F). Core temperature
is regulated by the hypothalamus (in the brain), which is often
called the body’s thermostat.


THERMAL STRESS

4





Temperature Detection
When met with environments that threaten the internal temperature of
the body, such as cold or hot conditions, the human body is triggered into
response. For example, nerve endings in the skin detect temperature
changes in the environment outside the body and signal the brain to either
increase or decrease the heat inside the body.
Reactions to Hot Temperatures
When the body senses warm temperatures any number of reactions
may occur. Sweating is one method for reducing body temperature. The
sweat glands in the skin excrete sweat, which contains water and some
nutrients. The process of evaporation then works to cool the body. The
drawback to perspiration is the loss of water. Maintaining water within the
body is especially important in high temperatures.


THERMAL STRESS

5

Hypothalamus Regulation of
Temperature
Hypothalamus acts as
“thermostat” that makes
thermoregulatory adjustments
to deviations from
temperature norm in the brain
(37 C 1 C or 98.6
 1.8 F ).

THERMAL STRESS

6

Variables Which Affect Thermal
Sensation


Age, weight, degree of physical fitness



Degree of acclimatization, metabolism



Use of alcohol or drugs


THERMAL STRESS

7

HEAT STRESS






Hot conditions put your
body under a lot of stress.
Heat stress is commonly
associated with warm weather.
When heat is combined with physical activity, loss of
fluids, fatigue, and other conditions it can lead to a
number of heat-related illnesses and injuries. Death is
even possible.


THERMAL STRESS

8

HEAT ACCLIMATIZATION
•
•

•
•
•

The body adapts to a new thermal environment by a process
called acclimatization.
Complete heat acclimatization generally takes six to seven
days, but some individuals may need longer. Loss of
acclimatization occurs gradually when a person is moved
permanently away from a hot environment.
Repeated exposure to heat stress during exercise improves
your ability to get rid of excess heat.
Muscle glycogen use is reduced to delay onset of fatigue.
Amount of heat acclimation depends on environmental
conditions and duration of exposure and intensity of exercise.


THERMAL STRESS

9

FACTORS CAUSING HEAT
STRESS
Environmental factors:
 Air Temperature
 Humidity
 Air Movement
 Radiant Heat



THERMAL STRESS

10

TYPES OF HEAT TRANSFER
Conduction.
 Evaporation.
 Convection.
 Radiation.



THERMAL STRESS

11

CONDUCTION


THERMAL STRESS

12

CONVECTION


THERMAL STRESS

13

RADIATION


THERMAL STRESS

14

EVAPORATION


THERMAL STRESS

15

WORKPLACES WITH HEAT
STRESS
Workplaces with heat stress conditions may include
iron and steel foundries, brick-firing and ceramic plants,
glass products facilities, rubber products factories,
electrical utilities (particularly boiler rooms), bakeries,
confectioneries, commercial kitchens, laundries, food
canneries, chemical plants, mining sites, smelters, and
steam tunnels.


THERMAL STRESS

16


THERMAL STRESS

17

HEALTH EFFECTS OF HEAT
STRESS
Heat Stroke
 Heat Exhaustion
 Heat Syncope
 Heat Cramps
 Heat Rash



THERMAL STRESS

18

HEAT STROKE (Hyperthermia)


Symptoms

•

•

Hot, dry skin or profuse sweating
Hallucinations
Chills
Throbbing headache
High body temperature
Confusion/dizziness
Slurred speech



Causes

•

Due to the failure of the heat-regulating
mechanisms of the body.
Due to high heat and humidity.

•
•
•
•
•

•


THERMAL STRESS

19



First Aid

•

Move the sick worker to a cool shaded area.
Cool the worker using methods such as:

•

•
•

•

Soaking their clothes with water.
Spraying, sponging, or showering them
with water.
Fanning their body.


THERMAL STRESS

20

HEAT EXHAUSTION


Symptoms
• Heavy sweating
• Extreme weakness or fatigue
• Dizziness, confusion
• Nausea
• Clammy, moist skin
• Pale or flushed complexion
• Muscle cramps
• Slightly elevated body temperature
• Fast and shallow breathing


THERMAL STRESS

21



Causes

•

•

Loss of water/or salt
Loss of blood plasma
Strain on circulatory system



First Aid

•

Have them rest in a cool,
shaded or air-conditioned area.
Have them drink plenty of
water or other cool,
nonalcoholic beverages.
Have them take a cool
shower, bath, or sponge bath.

•

•

•


THERMAL STRESS

22

HEAT SYNCOPE

•
•
•

•
•

•

Symptoms
Light-headedness
Dizziness
Fainting
Causes
Pooling of blood in legs causing drop in blood
pressure.
Lack of acclimatization.
Loss of body fluid from sweating.


THERMAL STRESS

23



•

•

First Aid
Sit or lie down in a cool place when they begin
to feel symptoms.
Slowly drink water, clear juice, or a sports
beverage.


THERMAL STRESS

24

HEAT CRAMPS


Symptoms

•

Muscle pain or spasms usually
in the abdomen, arms, or legs.



Causes

•

This normally happens after exercise.
Most often to people who aren’t used
to the heat, who sweat a lot or don’t
drink enough fluids.

•


THERMAL STRESS

25







First Aid
Stop all activity, and sit in a cool place.
Drink clear juice or a sports beverage.
Do not return to strenuous work for a few
hours after the cramps subside because further
exertion may lead to heat exhaustion or heat
stroke.


THERMAL STRESS

26

HEAT RASH


Symptoms





Heat rash looks like a red cluster of
pimples or small blisters.
It is more likely to occur on the neck and
upper chest, in the groin, under the breasts,
and in elbow creases.



Causes



Heat rash normally happens most often in hot, humid
conditions, particularly wearing heavy clothing and with
excessive sweating.
Fair skinned individuals are more prone to develop heat rash.




THERMAL STRESS

27



First Aid

•

Try to work in a cooler, less humid environment
when possible.
Keep the affected area dry.
Dusting powder may be used to increase comfort.

•
•


THERMAL STRESS

28

METHODS FOR MEASURING
HEAT STRESS


WBGT
The Wet-Bulb Globe Temperature device
(WBGT) takes into account four variables: air
temperature, humidity, radiant heat and air
movement. This reading gives a more
accurate measurement of heat stress than any
one reading alone.


THERMAL STRESS

29

The WBGT is measured by a simple
three-temperature element device:


The natural wet-bulb temperature (Tw),
which consists of a thermometer with its bulb
covered with a wettened cotton wick supplied
with distilled water from a reservoir.
The cotton wick will always be wet, allowing
continuous evaporative cooling of the
thermometer's bulb, simulating the evaporation
of sweat. This thermometer represents the
integrated effect of humidity, wind and radiation.


THERMAL STRESS

30





The black globe temperature (Tg), which usually consists of
a 150 mm (6 inch) black globe with a thermometer located at
the center. The black globe temperature represents the
integrated effects of radiation and wind.
The (shade) air temperature (Ta), which consists of a
thermometer shielded from radiation - generally by being
placed in a weather screen. It is the standard temperature
normally quoted in weather observations and forecasts.


THERMAL STRESS

31

For outdoor use in sunshine:
 WBGT out = 0.7(T nwb )+0.2(T g )+0.1(T
db ) in ˚F or ˚C
For indoor measurements or outdoor
measurements in the shade:
 WBGT=0.7(T nwb )+0.3(T g ) in ˚F or ˚C


THERMAL STRESS

32

HEAT STRESS INDEX






The Heat Stress Index (HSI)
was developed by Belding
and Hatch (1995).
The HSI is the ratio of the body’s
heat load from metabolism, convection, and
radiation to evaporate cooling capacity of the
environment.
It is predicted on the assumption that the heat
load must be dissipated through evaporation.


THERMAL STRESS

33

The HSI compares the amount of sweat
that must be evaporated to balance the heat
loss equation for given a set of environmental
conditions to the maximum amount of sweat
that can actually be evaporated for these
conditions.
HSI= 100 Ereq / Emax
Where HSI = a dimension less index number
Ereq = evaporative heat loss required (kcl/hr)
Emax = maximum evaporative heat loss
(kcl/hr)

THERMAL STRESS

34

EFFECTIVE TEMPERATURE
OR CORRECTIVE EFFECTIVE
TEMPERATURE
Effective Temperature (ET) Or
Corrective Effective Temperature (CET) can
be determined from the nomogram.
WBGT can be approximated from effective
temperature by using the following
relationship:
 WBGT = 1.102ET - 9.1 in ˚F

THERMAL STRESS

35


THERMAL STRESS

36

SLING PSYCHROMETER
The sling psychrometer
measures dry-bulb
temperature (Tdb )
and thermodynamic
wet-bulb temperature
(T wb ).


THERMAL STRESS

37

PREDICTED FOUR HOUR
SWEAT RATE
The predicted four hour sweat rate (P4 SR)
index was developed by Mac Ardle et al (1947).
The index taken into account metabolic level and
two types of clothing (shorts and overall), in
addition to the climate factors.


THERMAL STRESS

38

CONTROL OF HEAT STRESS
Reducing Metabolic Heat Production (heat
produced by the body)
 Reducing the Humidity
 Insulating Hot Surfaces
 Shielding
 Ventilation and Air Conditioning
 Reducing the Radiant Heat Emission from Hot
Surfaces



THERMAL STRESS

39

 Changing

the rate of work
 Schedule hot jobs to cooler times of the day.
 Increase the frequency and length of rest breaks if possible
 Allow for slower-paced work during the hottest periods of
the day.
 Limiting duration of exposure time.
 Rotate work activities.
 Take breaks in cool shaded areas.
 Avoid eating large meals before working in hot
environments.
 Avoid caffeine and alcohol (these beverages make the body
lose water and increase your risk for heat illnesses).


THERMAL STRESS

40

 Protective




Clothing

In some workplaces, insulated gloves, insulated suits, reflective clothing, or infrared
reflecting face shields may be needed.
Thermally conditioned clothing might be used for extremely hot conditions; for example:
 A garment with a self-contained air conditioner in a
backpack.
 A garment with a compressed air source that feeds
cool air through a vortex tube.
 A plastic jacket whose pockets can be filled with dry ice
or containers of ice.


THERMAL STRESS

41

Prevention of Heat Stress
Learn to recognize the symptoms of heat stress. Change work
location, taking adequate rest periods (in shade or cooler
environment).
 Become familiar with the hazards associated with working in
hot environments
 Use adequate fans for ventilation and cooling, especially when
wearing personal protective equipment (PPE).
 Wear light colored, loose (unless working around equipment
with moving parts) clothing.
 Keep shaded from direct heat where possible (e.g., wear a hat
in direct sunlight).
 Drink plenty of water. In hot environments the body requires
more water than it takes to satisfy thirst.



THERMAL STRESS

42

CONCLUSION







Heat stress cannot be eliminated completely.
Simple precautionary measures can
considerably reduce heat strain to acceptable
levels
Proper thermal control helps a long way in
success of missions.
There is a necessicity for maintaining a
suitable temperature to protect the health of
the workers and maximize efficiency and
productivity .


THERMAL STRESS

43

BIBLIOGRAPHY






http://www.osha.gov
http:// www.cdc.gov
en.wikipedia.org/wiki
www.osach.ca
National workshop on Ergonomics retrospective and
prospective.
July 1993, Andhra University, Visakhapatnam.


THERMAL STRESS

44


THERMAL STRESS

45

Ergonomics (Thermal stress)

Recommandé

Recommandé

Contenu connexe

Tendances

Tendances (20)

En vedette

En vedette (20)

Similaire à Ergonomics (Thermal stress)

Similaire à Ergonomics (Thermal stress) (20)

Ergonomics (Thermal stress)