HEAT_STRESS.pdf

HEAT STRESS

Dr. Y. Denny Ardyantto W. Ir. Ms

A. Siswanto

2010

TEKANAN PANAS

3 Suhu kering (Dry-bulb temperature)

Adalah suhu udara yang ditunjukkan oleh suatu

termometer yang akurat setelah panas radiasi

yang dapat mempengaruhi hasil pembacaan

dikoreksi.

Suhu basah (Wet-bulb temperature)

Adalah suhu yang menunjukkan bahwa udara

telah jenuh dengan uap air.

Suhu basah psikrometrik adalah suhu

yang ditunjukkan oleh termometer

berbola basah dari suatu psikrometer

(psychrometric wet-bulb temperature).

4

Kelembaban atau kelembaban udara dapat

dibedakan menjadi: kelembaban absolut dan

kelembab nisbi (relative humidity).

Kelembaban absolut adalah berat uap air per

unit volume udara (misalnya sekian gram uap

air dalam satu liter udara).

5

Kelembaban nisbi/relatif adalah rasio dari

banyaknya uap air dalam udara pada suatu

temperatur terhadap banyaknya uap air pada

saat udara telah jenuh dengan uap air pada

temperatur tersebut (dinyatakan dalam %).

6

Hasil perpaduan antara suhu, kelembaban,

kecepatan gerakan udara dan panas radiasi

dengan tingkat pengeluaran panas yang

dihasilkan oleh tubuh /metabolic heat. (Heat

stress is the load on the man and heat strain

is the effect of the load).

7

Suhu bola adalah suhu yang ditunjukkan

oleh termometer yang dipasang di bagian

tengah dari suatu bola (globe) yang

terbuat dari tembaga dengan diameter 15

cm atau 4,4 cm dan permukaan luarnya di

cat hitam.

8

Tubuh manusia selalu akan menghasilkan

panas sebagai akibat dari proses pembakaran

zat-zat makanan dengan oksigen.

Bilamana proses pengeluaran panas oleh tubuh

terganggu, maka suhu tubuh akan meningkat.

Antara tubuh dan lingkungan sekitarnya selalu

terjadi pertukaran panas dan proses pertukaran

panas ini tergantung dari suhu lingkungan.

9

Mekanisme pertukaran panas antara tubuh dan

lingkungan sekitarnya dapat terjadi melalui:

Konduksi

Konveksi

Evaporasi

Radiasi

Dari keempat cara tersebut diatas, konveksi

dan evaporasi memegang peranan yang

paling utama dalam pengeluaran panas tubuh.

10

Ilustrasi :

Evaporasi Respirasi

Radiasi

Konduksi

Radiasi

Konveksi

konduksi

M Kd C Rad - Evaporasi = 0

Cara-cara tubuh mempertahankan suhunya

agar selalu normal (kurang lebih 37C) adalah

sebagai berikut:

Peningkatan aliran darah ke kulit

Peningkatan sekresi (pengeluaran) keringat.

Peningkatan produksi panas oleh tubuh

dengan cara menggigil (bila suhu udara

lingkungan sekitar tubuh rendah/sangat

rendah).

12

Pertukaran panas secara konduksi terjadi

bilamana tubuh kontak dengan udara, cairan

atau benda padat. Udara adalah suatu

konduktor yang kurang baik sehingga dalam

rumus persamaan keseimbangan panas

tidak ikut diperhitungkan.

Namun peranan konduksi tidak dapat diabaikan bila kulit kontak dengan logam karena logam umumnya merupakan konduktor yang baik.

13

Antara tubuh dan udara sekitarnya selalu terjadi

pertukaran panas dan proses pertukaran panas

ini disebut konveksi.

Faktor-faktor yang mempengaruhi konveksi ini

adalah perbedaan suhu kulit dan suhu udara

sekitarnya serta kecepatan aliran udara/angin.

14

RADIASIKONVEKSI

KONDUKSI

KONDUKSI

KONDUKSI

Panas radiasi adalah suatu gelombang

elektromagnetik.

Pertukaran panas dengan cara radiasi

antara tubuh dan benda-benda

sekitarnya yakni dengan cara menyerap

atau memancarkan panas.

16

Pertukaran panas dengan cara radiasi

(radiative heat exchange) tidak dipengaruhi

oleh suhu dan kecepatan aliran udara, tetapi

oleh perbedaan suhu kulit dan suhu dari

benda padat yang berada disekitar tubuh.

Panas radiasi tidak menyebabkan pemanasan

secara langsung pada udara.

17

PANAS RADIASI

Tubuh dapat kehilangan panas melalui

penguapan keringat. Terdapat berbagai faktor

yang dapat mempengaruhi banyaknya

penguapan keringat dan faktor-faktor tersebut

adalah:

Kecepatan aliran udara

Perbedaan tekanan uap air pada suhu kulitdan tekanan parsial uap air dalam udara

atmosfer.

19

Penguapan keringat oleh tubuh akan

terganggu bila suhu dan kelembaban

udara lingkungan sekitarnya sangat tinggi

karena udara telah jenuh dengan uap air.

Sebagai akibat dari terganggunya

evaporasi ini, maka suhu tubuh akan

meningkat.

20

Indeks ini semula digunakan untuk menentukan tingkat tekanan panas yang dialami oleh prajurit yang melakukan latihan fisik yang berat dan terpapar panas radiasi yang tinggi.

Sekarang ISBB digunakan untuk menentukan tingkat tekanan panas yang dialami oleh pekerja karena tidak banyak membutuhkan ketrampilan, cara atau metodenya tidak sulit dan besarnya tekanan panas dapat ditentukan dengan cepat.

21

TLVs of Heat Stress

22

TLV ini hanya berlaku bila pakaian kerja yang dipakai oleh pekerja terbuat dari katun (pakaian musim panas).

Bilamana pakaian kerja dibuat dari bahan yang dapat menghambat penguapan keringat atau yang mempunyai nilai isolasi yang tinggi, maka toleransi pekerja terhadap panas akan menurun sehingga TLV ini tidak dapat dipergunakan.

Diluar gedung (outdoor) :

ISBB = 0,7 Sba + 0,2 Sg + 0,1 Sk

Sba : suhu basah alami

Sg : suhu globe

Sk : suhu kering

Didalam gedung (Indoor) :

ISBB = 0,7 Sba + 0,3 Sg

23

Light work (up to 200 kcal/hour) e.g., sitting

or standing to control machines, performing

light hand or arm work.

Moderate work (200-350 kcal/hour) e.g.,

walking about with moderate lifting and

pushing.

Heavy work (350-500 kcal/hour) e.g., pick

and shovel work. (ACGIH, 2005)

24

Permissible Heat Exposure TLV WBGT

Work-rest

regimen

Light work load

Moderate work load

Heavy work load

Continuous

work

30.0 oC 26.7 oC 25.0 oC

75% work

25% rest,

each hour

30.6 oC 28.0 oC 25.9 oC

50% work

50% rest,

each hour

31.4 oC 29.4 oC 27.9 oC

25% work

75% rest,

each hour

32.2 oC 31.1 oC 30.0 oC

TLV WBGT Correction Factors in oC for Clothing

Clothing type Clo value WBGT correction

Summer uniform 0,6 0

Cotton coveralls 1,0 - 2

Winter work

uniform

1,4 - 4

Water barrier,

permeable

1,2 - 6

Metabolic Rate During Different Activities

Type of

work

Light/mode-

rate/heavy

Average

kcal/min

Range

kcal/min

Hand work light

heavy

0,4

0,9

0,2 - 1,2

Work with one arm

light

heavy

1,0

1,7

0,7 - 2,5

Work with both arms

light

heavy

1,5

2,51,0 - 3,7

Work with body

light

moderate

heavy

very heavy

3,5

5,0

7,0

9,0

2,5 15,0

Heat stress adalah besarnya beban pada

manusia, sedangkan heat strain adalah efek

dari beban tersebut. Beberapa index yang

digunakan untuk menentukan besarnya heat

strain (respon fisiologis terhadap panas) antara

lain adalah banyaknya keringat yang dihasilkan,

banyaknya keringat yang menguap, denyut

jantung dan suhu tubuh.

28

Banyaknya keringat yang dihasilkan oleh tubuh

akan ditentukan oleh jumlah kelenjar keringat

yang aktif dan banyaknya keringat yang

diproduksi (disekresi) oleh kelenjar keringat

tersebut. Seseorang yang telah beraklimatisasi

dapat mengeluarkan keringat sebanyak 1 1,5

kg keringat per jam dan keadaan ini dapat

berlangsung sampai beberapa jam.

29

Denyut jantung seseorang dapat dipengaruhioleh berbagai faktor diantaranya yaitu bebanfisik dan beban tambahan misalnya teknanpanas.

Denyut jangutng akan terus meningkat kecualibila pekerja tang bersangkutan telahberaklimatisasi terhadap suhu udara yang tinggi. Denyut jantung maksimum untuk orangdewasa adalah 180 200 denyut per menit dankeadaan ini biasanya hanya dapat berlangsungdalam waktu beberapa menit saja.

30

Aklimatisasi adalah suatu proses adaptasi

Fisiologis yang ditandai dengan pengeluaran

keringat yang meningkat, penurunan

denyaut jantung dan suhu tubuh (bila

dibandingkan dengan denyut jantung dan

suhu tubuh pada hari pertama).

31

Proses aklimasi ini biasanya memerlukan waktu selama 7 10 hari dan aklimatisasi yang telah didapat ini dapat pula menghilang dngan cepat yaitu bilamana pekerja tidak masuk kerja selama satuminggu.

Untuk menimbulkan aklimatisasi, faktor pembebanan dan lamanya kerja perlu diperhatikan.

32

Cara terjadinya proses aklimatisasi adalahsebagai berikut: Pada hari pertama kerja, pembebanan fisik

dan lamanya kerja diusahakan agar tidakmelebihi 50 % dari beban dan lama kerjayang sebenarnya.

Pada hari kedua, beban dan lama kerjaditambah 10 % ( = 60 %).

Demikian seterusnya hingga pada hari keenam pembebanan fisik dan lama kerjaditambah 10 % setiap harinya sehingga padahari tersebut akan tercapai 100 %.

33

Heat acclimatization is acquired

only gradually being fully achieved

over up to 3 weeks of continued

physical activity under heat stress

conditions.

Proses aklimatisasi perlu dilakukan bila

suhu basah tempat kerja = 25 28C, hal ini

tergantung dari keadaan aklimatisasi alami

pekerja yang bersangkutan.

Walaupun prosedur seleksi telah dilakukan

dimana mereka yang berusia setengah

lanjut/lanjut dan pekerja dengan kapasitas

yang rendah telah dieliminasi, kurang lebih

3 5 % dari populasi ditemukan tidak toleran

terhadap panas.

35

Pada proses aklimatisasi, denyut jantungdapat mencapai lebih dari 180 denyut/menit

pada hari pertama kerja dan pada hari

ketiga/keempat, detak jantung mulai stabil dan

turun sampai dibawah 140 denyut/menit.

Maximal oxygen intake dari seorang pekerja

(ditentukan secara langsung melalui uji treadmill

atau bicycle ergometer) merupakan suatu faktor

yang paling penting dalam menentukan

kemampuan pekerja tersebut untuk bekerja di

tempat yang panas.

36

Pekerja yang berusia diatas 40 tahun

sebaiknya tidak ditempatkan di tempat

kerja yang panas karena kelenjar

keringat mereka menunjukkan respon

yang lebih lambat terhadap beban panas

metabolik dan lingkungan.

37

Kerentanan Individu

Mereka yang berusia lanjut mulai mensekresikankeringat 20 menit setelah masuk ke dalam suaturuang yang panas, sedangkan orang muda hanyamembutuhkan 15 menit. Selain itu, maximaloxygen intake juga menurun jika usia seseorangbertambah sehingga kedua hal ini akanmenyebabkan pekerja yang berusia setengahlanjut/lanjut secara fisiologis tidak dapat bekerjaditempat kerja yang panas dengan beban fisik yang cukup berat.

38

Kerentanan Individu

Kerentanan Individu

Demikian pula, pada kondisi dimana panas

radiasi di tempat kerja tinggi, pekerja yang

berusia lanjut juga akan menyerap lebih banyak

panas dari lingkungan daripada orang muda

terutama karena pembuluh pembuluh darah

mereka yang terdapat pada atau dekat dengan

permukaan kulit lebih banyak terpajan panas.

39

Bila suatu pekerjaan harus dilakukan di suatu

tempat keja yang panas, maka mereka yang

bertubuh kecil dengan luas permukaan tubuh

yang kecil dan individu yang terlalu gemuk

dengan ratio luas permukaan tubuh/berat

badan yang kecil adalah rentan terhadap

pengaruh tekanan panas.

Hasil penelitian menunjukkan bahwa pekerja

yang berat badannya kurang dari 50 kg selain mempunyai maximal oxygen intake yang rendah, tetapi juga kurang toleran terhadap panas daripada mereka yang mempunyai berat badan rata-rata.

40

Walaupun telah dilakukan seleksi dan aklimatisasi, diperhatikan adalah intake cairan dan makanan. Mereka yang bekerja di tempat kerja yang panasharus minum sesering mungkin (200 300 ml air atau minuman lainnya paling sedikit setiap 30 menit sekali) dengan tujuan agar cairan tubuh tetapdalam keadaan seimbang.

Mekanisme haus adalah sama sekali tidak adekuatuntuk membujuk pekerja minum sesuai denganjumlah cairan yang hilang dalam keringat sehinggahal ini akan menyebabkan pekerja cenderungmengalami defisit cairan.

41

Faktor nutrisi perlu pula dipertimbangkan.Mereka yang status gizinya jelek akan menunjukkan respon yang berlebihanterhadap tekanan panas dan hal ini mungkin disebabkan oleh sistem kardiovaskuler yangtidak stabil.

Pemberian minum yang mengandung sukrosatidak saja akan menguntungkan bila ditinjaudari segi metabolisme, tetapi juga akan membantu dalam pencegahan defisit cairanyang lebih besar.

42

Kerentanan Individu

Laki-laki tampaknya memiliki sweat rate response(terhadap tekanan panas) yang lebih baik dariwanita.Penurunan berat badan umumnya dapatditolerir oleh pekerja tanpa menimbulkan pengaruhyang serius. Kehilangan air sebanyak 1,5 kg atau lebih selamakerja dapat menyebabkan kenaikan denyut nadi dan bila tubuh kehilangan air sebanyak 2 4 kg (3 6 % dari berat badan), maka keadaan ini dapat menyebabkan pekerja mengalami gangguan dalam melakukan pekerjaannya.

43

Kerentanan Individu

Workers in hot environments such as

those who work around furnaces,

smelters, boilers or out in the sun can be

subjected to considerable stress.

Because of natural climatic conditions

and outdoors life and work styles,

Queensland has high potential for heat

related work illnesses.

During any activity, the body attempts

automatically to maintain a constant

working temperature range by balancing

out the heat gain and heat loss.

What Is Heat Stress ?

There are three factors that affect

thermal balance :

a. Climatic conditions of the environment

b. Work demands

c. Clothing

Thermal Stress

Thermal stress occurs when temperatures

become uncomfortably or dangerously hot or

cold.

The human body is built to withstand a certain

amount of heat or cold.

However, temperature extremes can lead to

discomfort or even severe health problems.

Thermal Stress

Heat stress is caused by a combination

of factors (affected by environment,

work, and clothing factors) and tends to

increase body temperature, heart rate

and sweating.

Heat Stress

Heat stress is the net heat load to which

a worker may be exposed from the

combined contributions of metabolic cost

of work, environmental factors (i.e., air

temperature, humidity, air movement and

radiant heat exchange) and clothing

requirements.

A mild or moderate heat stress may cause

discomfort and may adversely affect

performance and safety, but it is not harmful

to health.

As the heat stress approaches human

tolerance limits, the risk of heat-related

disorders increases.

The skin temperature

can vary widely but

the core temperature

of the body should

kept fairly constant.

The temperature of the human body is not

as often assumed, uniform throughout. A

constant temperature, which fluctuates a

little around 37oC, is found only in the

interior of the brain, in the heart, and in

the abdominal organs (core temperature).

Core body temperature is regulated by

processes controlled by the brain,

primarily by the small segment at the

lower surface of the brain called the

hypothalamus.

Heat exchange takes place by convection,

radiation, evaporative heat transfer, and

conduction.

Since the contact area between the skin

and solid objects is usually very small,

conduction is negligible, except in the case

of body-cooling garments.

Convection is the exchange of heat

between the body surface (skin and

clothing) and the surrounding air.

The rate of convective heat exchange

between the skin and the ambient air

immediately surrounding the skin is a

function of the temperature difference

between the ambient air and the mean

skin temperature as well as air velocity

over the skin.

When skin temperature is higher than

35oC, there is a gain in body heat

from ambient air by convection.

When skin temperature is lower than

35oC, heat is lost from the body to the

ambient air by convection.

Radiation is the process by which

electromagnetic energy is transmitted

through space.

Radiative exchange is a function

primarily of the difference between the

mean radiant temperature of solid

surroundings and skin temperature.

Radiant heat transfer is dependent solely on the temperature of the surrounding objects such as walls, machinery etc.; The lower their temperature the higher the rate of heat loss from the skin.

Most people including air conditioning engineers, do not realize that under comfortable conditions, radiation accounts for 60-70% of body heat loss.

Radiant heat loss decreases to zero, however, when the surrounding objects reach temperatures of about 35 oC.

The process of evaporation of water from

the skin takes place as a result of

differences in water vapor pressure

between the skin and the surrounding air.

The evaporation of 1 gram of water

dissipates about 2,4 kcal of heat.

In the evaporation of sweat, man has a most

powerful source of heat loss, as the

evaporation of 100 ml of sweat will result in

the loss 58-62 calories of heat.

It is not unusual for acclimatized workers in

hot industries to lose up to 1,5 liters of sweat

per hour, most of which will evaporate in a hot,

dry environment.

The higher the wet-bulb temperature the

greater its influence on evaporative heat loss,

and 33 oC can be regarded as the maximal

wet-bulb temperature at which the healthy

young acclimatized individual still can

maintain body temperature equilibrium while

working at a moderate, provided that the

wind flow is reasonable..

If the wind flow is less than 0,75 meters

per second, even the healthiest and

best-acclimatized man can not work at a

wet-bulb temperature of 33 oC.

Evaporative Heat Loss

If the solid objects surrounding a worker

in hot dry environment are hotter than

skin temperature, the radiant heat gain

may exceed the capacity of the sweating

mechanism to provide cooling, and body

temperature will rise.

Working creates metabolic heat, and the heat

is carried by the blood to the skin.

The work causes the heart to pump faster and

so carries the blood faster to the surface.

The body dissipates heat through the skin via

the cooling mechanism provided by evaporation

of sweat.

Heat strain is the overall physiological response

resulting from heat strain.

The physiological adjustments are dedicated to

dissipating excess heat from the body.

Acclimatization is a gradual physiological

adaptation that improves an individuals ability

to tolerate heat stress.

Acclimatization to high temperatures is the result

of processes by which the subject adapts himself

to living and working in a climate which is hot

and perhaps humid.

It is manifested as a reduction in the heart rate

and internal body temperature at the expense of

increased sweating.

An absence from work of one week may result

in the worker losing between one-quarter and

two-thirds of his acclimatization and a 3-week

absence from exposure, whether in summer or

winter, will mean virtually total loss of

acclimatization unless he is very athletic and in

good physical condition.

Heat acclimatization increases and prolongs the activity of the sweat glands. Estimated at 2.500.000 for a man of 70 kg, by reducing the number of inactive glands.

Acclimatization affects more the sweat glands of the back than those of the chest.

Where the maximum sweat rate for a non-acclimatized subject in an environment with low relative humidity is only 1,5 l/hour, this figure rises to 3 l/hour after ten days of acclimatization and 3,5 l/hour after 6 weeks.

There is also a change in the electrolytic content

of the sweat.

The sodium chloride loss in the first day is 15-25

gram per day, after 6 weeks acclimatization, this

loss has fallen to 3-5 gram per day.

Due to the effect of aldosterone, the sodium

chloride content of sweat decreases after

acclimatization and falls from 4 g/l to 1 g/l,

although individual variations occur.

Heat acclimatization must be carried out when

the dry-bulb and wet-bulb temperatures are

between 33-35 oC and 25-28 oC respectively.

To achieve good acclimatization for heavy work

under hot conditions, it is better to subject the

individual to very heavy work under moderately

warm conditions than to subject him to light

work under very severe climatic conditions.

Although black subjects do not become

acclimatized better than whites, it would seem

that morphology and the color of the skin may

play a part.

In this respect, it is of interest to note the tall,

thin stature of the people of the Sahelian

region where the temperatures are extremely

high. With such a build, the ratio of body

surface to volume is improved.

In the same way, the most effective cutaneous

cover would be that which contain sufficient

melanin to impede the UV rays, and not so dark

as to have a heat absorption coefficient that

would be too high;

Once again, this corresponds with the brownish

skin of some of the Sahelian populations.

Stout and obese persons are less adaptable to

heat. (stout = gemuk)

Under such conditions, they are less capable of

working and more likely to succumb (mati) to

heat stroke, which in their case would be three

to four times more likely to be fatal than in the

case of a person of normal weight.

They are also at a disadvantage because of the

low values of their maximum VO2 per kg per

body weight and of the ratio of skin surface

area to body weight.

The level of fitness of a thin or undernourished

subject is not, however, superior to that of the

stout person.

The optimum environmental conditions for

different activities can not be defined with

great precision, since there are differences

within an individual at different times and

between individuals at the same time.

Heat stress in the workplace can

be recognized by noting workplace

risk factors and by the effects it has

on workers.

The workplace risk factors, broadly

stated, are :

Hot environment;

High work demands; and

Protective clothing requirements.

Tolerable heat condition can be assessed

by using the man himself as a sensing

device. Sources of information are :

a. His opinion

b. His thermal state

c. The physiological responses; and

d. His performance

HOT ENVIRONMENT

80

HOT DRY HOT WET

Hot humid environments comprise those

in which a high dry bulb temperature is

coupled with high water vapor pressure,

the water vapor pressure being sufficient

to have an influence on the mans ability

to lose heat by evaporating sweat.

In hot dry environments, the ability to

produce sufficient sweat may limit a

mans heat dissipating capacity, the

evaporation being quite efficient due to

large vapor pressure gradient between

the skin and air.

In the industrial context hot dry environments

can be classified according to whether the

consist of the following :

1. A high dry bulb temperature with little

radiant heat.

2. a. Low dry bulb with a high omnidirectional

radiant heat component.

b. Low dry bulb with a high unidirectionalradiant heat component.

3. a. Both high dry bulb and

unidirectional radiant heat.

b. Both high dry bulb and

omnidirectional radiant heat.

Humans, like all mammals and birds, produces

heat as a result of metabolic activity.

The metabolic heat is then lost to the

environment in a controlled manner to maintain

body temperature at about 36,8o C or, if under

thermal stress. Some value normally within the

range of 36,5o 39o C.

Body temperature is maintained within close

limits by an efficient homeostatic mechanism,

though diurnal variation is observed over a

range or 0,5 1oC.

Physical exercise will increase body temperature

in proportion to oxygen consumption, the range

being 0,5o C for moderate exercise up to 4o C for

marathon running.

The dry bulb air temperature is the temperature

of the ambient air as measured with a thermometer or equivalent instrument. This is a

direct measure of air temperature.

The temperature sensor is surrounded by air, which is allowed to flow freely around the sensor. The sensor, however, can be influenced

by radiant heat sources and should therefore be shielded from them.

This measure is based on the degree of

evaporative cooling that can occur.

A wetted wick is wrapped around a

temperature sensor, and enough air (>3m/s)

is forced over the wick to maximize the rate

of evaporative cooling.

The amount of temperature reduction that

can be achieved depends directly on the

amount of water vapor in the air.

When humidity is high, the reduction in

temperature is low. As humidity decreases,

temperature reduction increases.

The instrument used for this measurement

is similar to the psychrometric wet bulb,

except that air is allowed to flow over the

sensor naturally rather than being forced.

When air flow is less than 3 m/s, the temperature

reduction is less than that achieved with a

psychrometric wet bulb at the same absolute

humidity. That is, natural wet bulb temperature is

sensitive to both humidity and air movement.

Globe Temperature

This is a measure of radiant heat from the solid surrounding and convective

heat exchange with the ambient air.

The globe temperature is classically measured using a 6-inch, thin-walled

copper sphere painted matte black on

the outside.

Globe Temperature

The temperature sensor is placed at the center of the globe. The globe is then suspended in the air in a location near the workspace.

When all the surrounding surfaces are the same temperature as the air, the globe temperature is equal to air temperature.

Globe Temperature

If one or more of the surfaces are

different, then the globe temperature

increases or decreases, depending on

the average temperature of the solid

surrounding.

Globe Temperature

Finally, for a given level of radiant heat exchange with the globe, the globe temperature differs more from air temperature when there is little air movement, and it differs less when there is significant air motion, because the globe thermometer is also sensitive to convective heat exchange with the air.

Globe temperature is used to estimate the average wall temperature of the surroundings.

The natural wet bulb temperature (NWB) is the

temperature measured by a thermometer or

equivalent sensor which is covered by a wetted

cotton wick and which is exposed only to the

naturally prevailing air movement.

Accurate measurement of NWB requires use of

a clean wick, distilled water, and shielding to

prevent radiant heat gain.

The psychrometric wet bulb temperature

(WB) is obtained when the wetted wick

covering the sensor is exposed to a high

forced air movement.

The wet bulb temperature is commonly

measured with psychrometer which

consists of two mercury in-glass

thermometers mounted alongside each

other on the frame of psychrometer.

This measure is based on the degree of

evaporative cooling that can occur.

A wetted wick is wrapped around a

temperature sensor, and enough air (>3

m/s) is forced over the wick to maximize

the rate of evaporative cooling.

The amount of temperature reduction that can be achieved depends directly

on the amount of water vapor in the air.

When humidity is high, the reduction in temperature is low.

As humidity decreases, temperature reduction increases.

This is commonly known as humidity. There two ways humidity is expressed : relative and absolute.

At any given temperature, the pressure of water vapor that can be in the air has a maximum value, which is called the saturation pressure.

At low temperatures, the saturation pressure is low, and it increases exponentially with temperature.

HUMIDITY

Relative humidity is the ratio of the water

vapor pressure in the air to the saturation

pressure at that temperature. So 50

percent relative humidity (Rh=50%) means that

water vapor pressure in the air is 50 percent of

the saturation pressure.

Unfortunately, relative humidity is not very

useful as a tool in assessing heat stress

because the water vapor pressure

represented by a relative humidity value

varies widely, depending on the air

temperature.

Absolute humidity is expressed as

the amount of water vapor in the air

in terms of either partial pressure or

weight-per-unit volume of air.

The usual practice for heat stress evaluation

is to use the partial pressure, and the SI unit

for this is the kilopascals (kPa).

(To convert from kPa to mmHg, the value in

kPa is multiplied by 7,5.)

Usually, a psychrometric chart is used to

determine humidity from psychrometric

dry bulb temperature and psychrometric

wet bulb temperature.

TLVs OF HEAT STRESS

The TLVs of heat stress are based on the

assumption that nearly all acclimatized,

fully clothed (i.e. lightweight pants and shirt)

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 38oC.

Where there is a requirement for protection

against other harmful substances in the work

environment and additional personal

protective clothing and equipment must be

worn, a correction to the Wet Bulb Globe

Temperature (WGBT) TLV values, as

presented in the table (TLV WGBT correction

factors in oC for clothing) must be applied.

Permissible Heat Exposure TLV WBGT

Work-rest

regimen

Light work load

Moderate work load

Heavy work load

Continuous

work

30.0 oC 26.7 oC 25.0 oC

75% work

25% rest,

each hour

30.6 oC 28.0 oC 25.9 oC

50% work

50% rest,

each hour

31.4 oC 29.4 oC 27.9 oC

25% work

75% rest,

each hour

32.2 oC 31.1 oC 30.0 oC

TLV WBGT Correction Factors in oC for Clothing

Clothing type Clo value WBGT correction

Summer uniform 0,6 0

Cotton coveralls 1,0 - 2

Winter work uniform 1,4 - 4

Water barrier,

permeable

1,2 - 6

Clo is the insulation value of clothing.

One Clo unit = 5,55 kcal/m2/hr of heat exchange by radiation and convection for each oC of temperature difference between the skin and adjusted dry-bulb temperature [(the average of the ambient air dry-bulb temperature and the mean radiant temperature; t adb = (ta+tr)/2].

When WGBT-TLV criteria are exceeded

or impermeable clothing (in particular

encapsulated suits) is worn, exposure to

environmentally induced or activity-

induced heat stress is to be discontinued;

for individuals when at any time :

TLV Of Heat Stress

1. Sustained heart rate is greater than

160 beats per minute for those under

35 years of age; 140 for 35 years or

older, in subjects with assessed normal

cardiac performance; or

2. In unselected, unacclimatized workers

deep body temperature is greater than

38o C or in selected and acclimatized

personnel, 38,5oC; or

3. In conditions of regular daily exposure to the

stress, 24-hour urinary sodium excretion is

less than 50 mmoles; and for the group of

persons exposed when :

4. There are complaints of sudden and severe

fatigue, nausea, dizziness or lightheadedness.

5. Higher heat exposure than those shown in table

(Permissible Heat Exposure Threshold Limit

Values table) are given in oC and oF WBGT are

permissible if the workers have been

undergoing medical surveillance and it has

been established that they are more tolerant

to work in heat than the average worker.

Workers should not be permitted to

continue their work when their deep

body temperature exceeds 38oC.

For unacclimatized workers performing a

moderate level of work, the permissible

heat exposure TLV should be reduced by

approximately 2,5 oC.

Behavioral disorders ---- simple heat fatigue,

either chronic or transient, and often occurring

in workers from colder climate unacclimatized to

continuously hot weather.

Life styles (appropriate clothing, mid-day siesta)

or avoiding strenuous work during heat of day

and acclimatization are appropriate. (siesta =

period of rest or sleep taken in the early

afternoon, as is customary in hot countries).

Heat produced by the body and the environmental

heat together determine the total heat load.

Therefore, if work is to be performed under hot

environmental conditions, the workload categories

of each job should be established and the heat

exposure limit pertinent to the work load evaluated

against the applicable standard in order to protect

the worker exposure beyond the permissible limit.

Light work (up to 200 kcal/hour) e.g.,

sitting or standing to control machines,

performing light hand or arm work.

Moderate work (200-350 kcal/hour) e.g.,

walking about with moderate lifting and

pushing.

Heavy work (350-500 kcal/hour) e.g., pick

and shovel work. (ACGIH, 2005)

The ranking of job may be performed

either by measuring the workers

metabolic heat while performing a job or

by estimating the workers metabolic rate

with the use of tables.


Body position and

movement

kcal/minute

Sitting 0,3

Standing 0,6

Walking 2,0 -3,0

Walking up hill Add 0,8 per meter (yard)


Type of

work

Light/mode-

rate/heavy

Average

kcal/minRange

kcal/min

Hand work light

heavy

0,4

0,9

0,2 - 1,2

Work with one arm

light

heavy

1,0

1,7

0,7 - 2,5

Work with both arms

light

heavy

1,5

2,51,0 - 3,7

Work with body

light

moderate

heavy

very heavy

3,5

5,0

7,0

9,0

2,5 15,0

Work rates

Resting

Activity

Sitting quietly

Sitting with

moderate arm

movement

Light Sitting with moderate arm and leg movements

Standing with light work at machine or bench while using mostly arms

Using a table saw

Standing with light work at machine or bench and some walking about

Standing with moderate work at machine or bench with some walking about.

Moderate Scrubbing in a standing position

Walking about with moderate

lifting or pushing

Walking on level at 4 miles

per hour while carrying 5

pounds weight load

Heavy Carpenter sawing by hand Shoveling dry sand

Heavy assembly work on a noncontinuous basis

Intermittent heavy lifting with pushing or pulling (e.g., pick-and-shovel work)

Shoveling wet sand

The TLVs specified in Table is based on the

assumption that the WBGT value 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 value should be used for

both environmental and metabolic heat .

(ACGIH, 2005)

The time-weighted average metabolic rate (M)

should be determined by the equation :

t1 + t2 + . + tnwhere M1, M2, . and Mn are estimated or

measured metabolic rates for the various

activities and rest periods of the worker during

the time periods t1, t2, and tn (in minutes)

are determined by a time study.

Av. M = M1 x t1 + M2 x t2 + . + Mn x tn

WBGT1xt1 + WBGT2xt2 ++WBGTnxtn

T1 + T2 + . + Tnwhere WBGT1, WBGT2, . and WBGTn are calculated values of WBGT for the various work and

rest areas occupied during total time periods and t1,

t2, and tn are the elapsed times in minutes spent in the corresponding areas which are determined by a

time study.

Av WDGT =

The time-weighted average WBGT should be

determined by the equation :

Where exposure to hot environmental conditions

is continuous for several hours or the entire

work day, the time-weighted averages should be

calculated as an hourly time-weighted average,

i.e., t1 + t2 +.+ tn = 60 minutes.

Where the exposure is intermittent, the time-

weighted averages should be calculated as two-

hour time weighted averages, i.e., t1 + t2 + .

+ tn = 120 minutes.

The TLVs for continuous work are applicable

where there is a work-rest regimen of a 5-day

work week and an 8-hour work day with a

short morning and afternoon break

(approximately 15 minutes) and a longer lunch

break (approximately 30 minutes).

Higher exposure values are permitted if

additional resting time is allowed.

All breaks, including unscheduled pauses and

administrative or operational waiting periods

during work, may be counted as rest time when

additional rest allowance must be given

because of high environmental temperatures.

HEAT DISORDERS

Three major clinical disorders can result from excessive heat stress to susceptible workers :

Heat stroke from failure of the thermoregulatory center.

Heat exhaustion from depletion of body water and/or salt.

Heat cramps from from salt loss and dilution of tissue fluid.

Heat Exhaustion/Heat Stroke

A classification of disorders caused by exposure

to high levels of environmental heat is as follows :

Systemic disorders : heat stroke

(hyperpyrexia), heat exhaustion (from

circulatory deficiency; heat syncope), water

deficiency, salt deficiency, heat cramps, or

sweating deficiency.

Continued .

Skin disorders : prickly heat (miliaria rubra),

cancer of the skin (rodent ulcer).

Psychoneurotic disorders : mild chronic

(tropical) heat fatigue, acute loss of emotional

control.

Psychoneurotic disorders ---- tropical fatigue.

Chronic effects upon Europeans of working

for long periods in the tropics have been

reported. Loss of motivation, lassitude,

irritability, sleeplessness appear to constitute

the symptoms of a condition for which little

physiological evidence has been found.

Tough the phenomena of tropical fatigue are

quite real to sufferers, it appears that their

occurrence is more closely related to

psychological factors of the individuals in

tolerance of boredom, monotony, thermal

discomfort and heat illnesses than to a

specific physical basis.

Prickly heat, painful itching may occur

if skin is constantly wet with sweat and

sweat glands become plugged.

Worker needs to allow time to dry off in

cold area, bathe or use drying powder.

Painful muscle spasms of arms, legs,

or abdominal muscles.

They occur when individuals lose

excessive amounts of salt while

sweating during hard physical labor and

high heat loads.

Heat cramps often occur in conjunction with conditions of salt depletion when levels of sodium chloride (NaCl) circulating in the blood fall below a critical level.

The attacks of severe painful spasms in limb and abdominal muscles may last for several hours, days, or even weeks.

The cramps may occur during or after work and may resolve spontaneously. If not, the

person should take lightly salted fluids by mouth.

Persons not acclimatized to heat may require additional salt.

A normally salted diet is usally adequate to prevent heat cramps.

Fainting results from insufficient blood flow to the brain.

Blood vessels expand as blood flow increases, more goes to the surfaces rather than brain

and gravity can cause pooling of blood in lower

parts of the body.

Lying the worker down will result in complete recovery.

Heat syncope is alarming (mengawatirkan) to

the person but is the least serious of the heat-

induced disorders.

Heat syncope is characterized by dizziness

and/or fainting while immobile, usually standing

in the heat for an extended period.

The condition occurs primarily in individuals who are not acclimatized to the heat, and it results from the pooling of blood in the dilated

vessels of the skin and lower extremities with a resulting decrease in blood flow to the brain.

Treatment consists of removal of the individual to a cooler area, if possible, and recumbent rest. Recovery is usually prompt and complete.

Heat fatigue is a set of behavioral response to acute or chronic heat exposure.

The behavioral responses include impairment in :

a. The performance of skilled sensorimotor

tasks

b. Cognitive performance

c. Alertness (kesigapan/kesiagaan)

These symptoms arise from the discomfort,

physiological strain, psychosocial stress,

and perhaps hormonal changes associated

with working and living in hot climates.

These aspects of heat stress are not well

understood or documented.

Heat exhaustion results from the reduction of

body water content or blood volume.

The condition occurs when the amount of

water lost by sweating exceeds the volume of

water drunk.

The major signs and symptoms of heat

exhaustion include fatigue, extreme weakness,

nausea, headache, faintness, and a cool, pale,

clammy skin.

Core body temperature, however, is usually

normal or only slightly elevated.

Treatment consists of removal to a cool area,

recumbent rest, and cool fluids by mouth.

Recovery usually occurs in less than 12 hours.

Generally there are no permanent after-effects.

Heat exhaustion occurs when body losses too

much fluid, or too much salt or both.

Worker becomes dry in mouth, thirsty, weak,

fatigued.

Remove with rest, administer fluids .

Ensure workers are acclimatized, with ability to

take water regularly during work

If environmental work factors prevent evaporative

cooling i.e. because :

a. Air temperature is too high

b. Humidity is too high

c. There is a high radiant heat load

d. Worker is constricted by insulating

clothing then the body begins to experience

physiological heat strain with different illnesses

depending on the degree of heat stress.

Heat stroke or hyperthermia is a life-threatening disorder that results from a failure of the core body temperature-regulating system which may cause core body temperature to exceed 40oC.

Heat stroke is usually accompanied by hot and dry skin, mental confusion, convulsions, and unconsciousness.

Death or irreversible damage frequently results; the fatality rate of heat stroke may be as high as 50%.

Result in hot dry skin, mottled or cyanotic

(bluish).

Can be the result of several causes including

extensive overexertion, loss of fluids, cardiac

disease.

The body fails to sweat, so evaporative cooling

does not function. Body temperature rises

uncontrollably, accompanied by convulsions,

loss of consciousness.

Heat Stroke (contd)

A core body temperature above 42oC for more than a few hours is usually fatal, depending on the persons health status.

Early recognition and treatment of heat stroke will decease the risk of death or damage to the brain, liver, kidneys or other organs.

Heat stroke is an emergency and medical assistance should be obtained immediately.

Procedures to reduce body temperature must be initiated as early as possible.

An approved first-aid method for lowering body temperature is to remove the person to a cool and protected environment, remove the outer clothing, wet the skin with water, and fan vigorously.

This procedure will maximize body cooling by evaporation and will prevent further body temperature increase while the patient is being transported to a hospital.

Unless the person is conscious and alert, one should not administer fluid by mouth.

Unless the person is conscious and alert,

one should not administer fluid by

mouth.

Body temperature should be monitored

to ensure that it is reduced but does not

fall below normal.

Prolonged increases in deep body

temperatures may also be associated

with temporary infertility for people in

both genders, and, during the first

trimester of pregnancy, may endanger

the fetus.

No work can be performed by patients

with a water loss deficit of about 10%

of body weight.

Death occurs when depletion of blood

volume (oligaemic shock) results from

water loss in excess of 15% of body

weight.

A mild thirst reflects uncorrected water loss of

less than 5% of body weight.

There may be increases in pulse rate and body

temperature. A decrease in output of urine

(oliguria), loss of working efficiency,

complaints of restlessness, irritability, lassitude

or drowsiness and of thirst when uncorrected

water loss amounts to 5-8% of body weight.

Liquids should be taken in small quantities and often from the start of exposure to high temperatures : 100 to 150 ml of water every 15 to 20 minutes.

The quantities to be drink should be calculated on the basis of the fluid loss, since the thirst mechanism does not at all furnish an

appropriate basis for compensating the important factor, which is fluid loss.

Drinking Water

Recommended drinks are plain (non-

carbonated) cool water (9-12 oC); Cool

lemon tea, well diluted fluid juice, etc.

Carbonated drinks, undiluted fluid juice,

milk and especially any alcoholic drinks

should be forbidden.

Drinks

Intolerance to high temperature due to

dehydration disappears completely by the

addition of 100 g of sugar to the drinking

water distributed during the working day.

when, for example, miners exposed to a

wet-bulb temperature of more than 29 oC

drink at least 3 liters of water per shift;

Drinks

Coffee and tea can inhibit absorption of some

nutrient, particularly iron.

In addition, caffeines ability to increase

urination by as much as 30% for up to 3

hours after ingestion can cause such nutrient

as calcium, magnesium, and sodium to be

flushed from the body.

Heavy caffeine use is also associated with

high cholesterol levels, but the reason for this

is unknown.

Nearly all of the caffeine found in soft drinks

is added during manufacture.

Soft drinks usually contain about one-

fourth of the caffeine normally found in an

equivalent amount of coffee and about half

that normally found in an equivalent amount

of tea.

Caffeinism is the name given to symptoms associated with very heavy daily caffeine use.

These symptoms include frequent urination,

jitter(gelisah), agitation, irritability, muscle

twithching lightheadedness, rapid

breathing, rapid heartbeat, palpitations,

upset stomach, loose stools, and heartburn.

Binge (pesta minum minuman keras) type

alcohol consumption results in the production of quantities of dilute urine.

The individual is now much more susceptible to dehydration working in a hot environment, and therefore to heat stroke.

As a CNS depressant, alcohol interferes with heat adaptation.

Alcoholic Drinks

The intake of fatty foodstuffs should be reduced.

The administration of additional salt is only

justified in the case of unacclimatized workers

who are newly assigned to a hot workplace.

Food

Binge (pesta minum minuman keras) type

alcohol consumption results in the production of quantities of dilute urine.

The individual is now much more susceptible

to dehydration working in a hot environment,

and therefore to heat stroke.

As a CNS depressant, alcohol interferes with

heat adaptation.

Alcoholic Drinks

Heavy exposure to heat could lead to a significant loss in zinc, thus impairing normal

growth, development, health, and ossification.

Potentially, the same applies to magnesium (Mg), the relevance of which should be viewed

against the relationship between deaths

ascribed (yang dianggap berasal) to ischemic

heart disease and low magnesium intake.

Nutrition

Prolonged, strenuous work is also likely to induce iron deficiency to the extent that

supplementation becomes essential.

Iron deficiency leads to a measurable decline in work capacity; conversely, a significant

increase in work productivity has been

demonstrated following iron supplementation

in iron-depleted individuals.

Nutrition

Men working moderately hard for 6 hours show a fall in respiratory quotient from 0,94 to 0,80 indicating switch from a predominantly carbohydrate metabolism to a fat metabolism.

The change in metabolic substrate results in an increase in oxygen consumption, heart rate and body temperature.

A midshift feed of 100 grams of sucrose in water was shown to cause an immediate improvement in these parameters.

Nutrition

RQ (respiratory quotient) : the steady state

ratio of CO2 produced by tissue metabolism to

oxygen consumed in the same metabolism; for

the whole body, normally about 0,82 under

basal conditions; In the steady state, the RQ

is equal to the respiratory exchange ratio.

Nutrition

A supplementary dose of 100 mg of

thiamin, 8 mg of riboflavin, 5 mg of

piridoxin, 25 mg of cobalamin, 100 mg of

niacin and 30 mg of pantothenic acid will

delay appearance of fatigue during work

in high ambient temperatures.

Vitamin

In the same way a daily supplementary

dose of 250 mg of vitamin C during 10

days or so will enable a man to withstand

heat better and will hasten the process of

acclimatization.

Vitamin

Environmental Monitoring

The thermal environment around the body which

affects the rate of heat flow, is expressed by four

parameters :

The dry bulb temperature of the air

The moisture content or water vapor pressure

of the air

The air velocity

The radiant heat exchange between the

skin and surrounding surfaces

CONTROL MEASURES

Alternative measures for controlling heat stress

Item Possible actions

Metabolic heat load

(M)

Mechanization of some or all tasks

Sharing workload with

others(particularly during heat period)

Increasing rest time

Radiant heat load

(R)

Minimizing line-of sight to source

Insulating furnace walls

Using reflective screens

Wearing reflective aprons (particularly

valuable when workers face source)

Covering exposed parts of body



Convective heat

load (C)

If air temperature is above 35 oC, reduce

C by : lowering air temperature, lowering

air velocity, wearing clothing.

If air temperature is below 35 oC, reduce

C by lowering air temperature, increasing

air velocity and removing clothing

Evaporation

(Emax)

Increase by : increasing air velocity,

decreasing humidity.



Work schedule Duration : shorten duration of each

exposure, use more frequent rest periods.

Recovery : use nearby air conditioned space

for rest area, adjust air velocity in rest area

for effective cooling.

Other : allow worker to self-limit exposure on

basis of signs and symptoms of heat strain,

and provide cool, potable water containing

0,1%$ salt.



Clothing For extreme conditions, use cooled (by

vortex tube or other means) clothing.

Wear type of clothing to obtain

E max > E req with minimum sweating.

Relative efficiencies of common shielding materials

Surface Reflectivity of radiant heat

incident upon surface (%)

Emissivity of

radiant heat from

surface (%)

Aluminum,

bright

95 5

Polished

aluminum

92 8

Zinc, bright 90 10

Zinc,

oxidized

73 27

Aluminum,

paint, new,

clean

65 35

187

Radiation shielding can be categorized

into reflecting, absorbing, transparent and

flexible shields.

Radiant heat passes through air without

heating the air; it heats only the objects in

its path that are capable of absorbing it.

188

Reflective shields are constructed from sheets

of aluminum, stainless steel, or other bright

surface metallic materials.

Aluminum offers the advantage of 85-95%

reflectivity. It is used also as shielding in the

form of foil with insulative backing, and in

aluminized paint, with reduced effectiveness.

189

Successful use of aluminum as shielding requires

an understanding of certain principles :

There must be an aluminum-to-air surface; the

shield can not be embedded in other materials.

The shield should not be painted or enameled.

The shield should be kept free of oil, grease, or

dirt, to maximize reflectivity.

190

When used to enclose a hot source, the shield

should be separated from the source by several

inches.

Corrugated sheeting should be arranged so that

the corrugations run vertically rather than

horizontally, to help maintain a surface free of

foreign matter.

191

Absorption shielding absorbs infrared radiation readily. This type of shielding, preferably flat block, is constructed typically of two or three

sheets separated by air spaces.

Heat can then removed by causing water to flow between two metal plates in the shield, transferring heat from the shield by conduction.

The surfaces of absorptive shielding exposed to work areas should be constructed of aluminum

or aluminized to reduce emissivity.

192

Transparent shielding consists of two general types : special glass and metallic mesh.

Special glass reduces transmission of infrared radiation because it is either heat absorptive or infrared reflecting.

Infrared reflecting glass is used commonly in the windows of control rooms amid (berdiri ditengah-tengah) excessive heat sources.

Metallic mesh shielding involves the use of chains and wire mesh to provide partial reflectance and to help reduce the amount of radiant heat reaching an operator.

193

Flexible shielding utilizes fabric treated with aluminum.

When worn as aprons or other items of clothing, they protect against radiant heat by reflecting

up to 90%.

Reflective garments are useful for protection against very localized and directional radiant sources.

194

Reduce work load factor by mechanization

Reduce radiant heat load by :

a. Lowering temperature of hot processes or

changing emissivity of the hot surface

b. Relocating hot processes.

c. Using heat seals, reflective protective

equipment, and heat shielding clothing.

Increase air speed with fans if air temperature

is less than 35oC and shed (melepas) clothing.

Decrease air speed if air temperature is

greater than 35o C and wear protective

clothing.

Dehumidify air to increase evaporative

cooling from sweating (e.g. eliminate all

sources of water vapor from leaks in steam

lines, water evaporating from floors).

Limit the time exposure to the hot work

a. Carry out hot task in cool of morning

or evening.

b. Provide cool areas for recovery.

c. Use extra manpower to reduce

exposure time for each worker.

Attention should be paid to the heat

acclimatization, appropriate levels of

physical fitness, liquid replacement

schedule should be followed, electrolyte

balance of body fluids must be

maintained, especially for unacclimatized

workers.

Supervisors and workers should be trained in recognition of various heat illnesses.

Workers to be alerted to effects of drugs, alcohol, obesity on heat illnesses.

Screen workers for heat intolerance

(particularly previous episodes)

Be aware of seasonal factors relating to climate.

Restrict overtime work in hot environments

Provide specialized vortex air-cooled or ice suits for some continuous demand tasks.

Training and selection of workers.

WORKER SELECTION

People who are least endangered

while working in heat stress conditions

are young and appropriately clothed, in

good general health and physical

condition, not obese, and adequately

hydrated with electrolyte concentrations

in normal ranges.

There are individual differences in acclimatization

to high temperatures. These are mainly

dependent on age and sex. Subjects of more

than 60 years of age are more likely to suffer

from heat stroke than those are younger.

After the age of 40, the onset of sweating is

distinctly retarded, the volume of sweat is less

and the cardiovascular system has a reduced

capability for adaptation.

Women are less able to stand heat than men

as they commence (begin) to sweat later, while

both their skin and internal body temperatures

are higher;

Women also sweat less even though they have

an increased number of sweat glands both in

absolute term and per cm2 of skin than men;

After acclimatization, the amount of sweat

produced is half that of a man.

In general, there are four major physiologic

parameters to consider when selecting men

for heat tolerances :

1. The maximal oxygen intake

2. Age

3. Body size, composition and surface area

4. Race and sex differences

The maximal oxygen intake of an individual as directly determined on the treadmill or the bicycle ergometer is a most important factor in his ability to work in heat.

Those with high maximal oxygen intake capacities should be located to hard work (oxygen cost = 1,4 l/min), those with low capacities to light work (oxygen cost = 0,6 l/min) and the intermediate group should be put on moderate work (oxygen cost = 1,0 l/min).

Significant age trends in heat adaptation have

been observed, and men over 40 years of

age are at a distinct disadvantage when

exposed to work in heat.

The sweat gland of these older men show a

more sluggish response to environmental and

metabolic heat load.

The older men started to secrete sweat 29

minutes after entering a hot room as

compared to 15 minutes for young men,

Under high radiant heat conditions, older men

also absorb more heat from the environment

than do young men mainly due to the fact that

their blood vessels on and near the skin

surface are more exposed.

Maximal oxygen intake also decreases

with age, and the older man, therefore, is

physiologically not well equipped to work

moderately hard in heat.

When the work has to done under high

environmental stress conditions, the

small or underdeveloped worker with a

small body surface area and the

overweight individual with a low body

surface/weight ratio will both be at a

disadvantage.

Research has indicated that men weighing less than 50 kg not only have a low maximal oxygen

intake but are also less tolerant to heat than

men of average weight.

When doing the same absolute work, men with small surface areas have a higher metabolic

heat production per unit area than do large

men, yet they have similar rate of cooling.

Studies on race and sex differences to

heat exposure showed that the major

contributory causes to any observed

difference are physical activity level,

nutritional state, body size and the extent

of natural acclimatization.

On the average, adult males have plus minus

48 ml O2 ml/kg/min available against only plus

minus 38 ml O2/kg/min in females.

This does not mean that females should not be

used for manual labor at all; it only show that

they should not be required to work as hard as

males, and that at any set work intensity, they

will experience more physiologic strain than will

males.

Provide accurate verbal and written

instructions, frequent training programs,

and other information about heat stress

and strain.

Provide work settings with good

ventilation both for general air movement

and for removal of process heat and water

vapor, with shielding from radiant sources.

Encourage drinking small volumes of cool,

palatable (enak/lezat) drinks about every 20

minutes.

Monitor WBGT-TLVs and guidelines for heat

exposure limiting conditions.

Pay extra attention to those who take medications

that compromise (membahayakan)

cardiovascular, blood pressure, body temperature

regulation, renal, or sweat gland functions.

Use pre-placement medical screening

to determine those susceptible to

systemic heat injury.

Pay extra attention to those returning to

work after absence from hot exposure

situations, or who abuse or are

recovering from the abuse of alcohol or

other intoxicants.

SEKIAN DAN TERIMA KASIH

Documents

HEAT_STRESS.pdf