Cold Environments

Many industrial workplaces are located in cold environments, such as cold stor­age, meat packing areas, and outdoor sites. In cold environments, clothing is the

TABLE 6.8 Reference Values for the Different Criteria of Thermal Stress and Strain

Acclimatized

Subjects

Warning Danger

Non-acclimatized subjects

Warning

Danger

Cold Environments

Criteria

 

Maximum skin wettedness, «/ Maximum sweat rate Rest: At < 65 W/m Sw1TWX, W/ m~ g/h

Work: M > 65 W/m2 Sw„m, W7 m" g/h

Maximum heat storage,

Wh/m!

Maximum water loss,

, W h/m2 g

 

0.85

 

0.85

 

1.0

 

150 390

250

650

60

1250

3250

 

200

520

300

780

50

1500

3900

 

100

260

200

520

50

1000

2600

 

300

780

400

1040

60

2000

5200

 

Most important factor in obtaining an acceptable thermal environment. Based on the heat balance equation (6.1), an analytical method has been proposed by CEN and ISO: required clothing insulation, /req (ISO/TR ENV 11079). The method calculates the insulation of the clothing necessary to keep a heat balance

TABLE 6.9 Required Sweat Rate Index SWreq W/m2, and Wettedness (wreq) as a Function of Clothing, Temperature, Air Speed, and Humidity at an Activity Level M Equal to 70 W/m2

Relative Clothing humidity,

/C|, clo %

Operative

Temperature

T °C

Air velocity va,

M/s

<0.1

0.2

0.5

1.0

2.0

0.50 20

25

10(,03)

8(.02)

2(.01)

30

37(. 13)

36(.12)

33(.09)

29 (.06)

24(.04)

35

65 (.24)

64{.22)

64(.18)

63 (.14)

62(.ll)

40

93 (.37)

94(.34)

95 (.29)

98 (.24)

101 (.20)

50

169(.78)

165(.72)

165(.62)

171 (.52.)

182(.45)

50

60

*(1.00)

(1.00)

*(1.00)

-"(1.00)

S (1.00)

25

10 (.04)

8(.03)

2(.01)

29 (.08)

24 (.05)

30

37(.17)

35(J 5)

3 3 (. 12)

63 (.22)

62. (.17)

35

65 (.37)

65 (.34)

64(.28)

99 (.47)

) 02 (.39

40

102 (.74)

99( .69)

98 (.57)

29(.12)

24 (.08)

80

30

37(.26)

36 (.23)

33 (.18)

64 (.48)

63 (.38)

35

76(.82)

71(.75)

66(.61;

In a given cold environment given the activity level, air and mean radiant tem peratures, air velocity, and humidity according to the following equations:

. hk ~ fci________

.in

;req-M_W_Јsk_Cres_Јms

M-W — Esk — Crcs — Ercs — C + R

(6.

The relationship between activity level, operative temperature, and In, q may be calculated with this new method; however, it has not been widely used, and little experience is available. Therefore, the method has been proposed in the form of a technical report, which in the future may be published as an ISO standard.

The index value may be used to select a clothing ensemble that will pro­vide the required insulation. The clothing insulation can, as shown in Table 6.10, be predicted either as a minimum, where some strain may be imposed on the people, or as a neutral value, where people are expected to feel neutral. It is important when selecting the actual clothing (ISO 9920) to allow for indi­vidual adjustment of the insulation. Also, the clothing insulation values listed in ISO 9920 are valid for people engaged in standing and sedentary work. For people at higher activity levels, the clothing values from the tables in ISO 9920 should be reduced by approximately 20% owing to body movements (pump­ing effect).

If it is not possible to use a clothing ensemble with enough insulation, the method includes a procedure for calculation of a recommended exposure time. The basis for the calculations are the physiological requirements listed in Table 6.10.

For outdoor work there may be a risk of frostbite in the wintertime. The report uses the wind chill temperature, WCI, calculated as

, _ 33 — WCI

*cli ■

/6.

25.5

WCI = 1.16(10,45 + Jva — /’.j)(33 — ta) (W/irT) , (6.14′

Where ta — outside air temperature (°C), WCI = wind chill index (W/m-^), and va — relative air velocity (m s_1). Table 6.11 shows the values depending on the outside temperature and wind velocity, and Table 6.12 shows the ex­pected effect.

TABLE 6.10 Proposed Physiological Criteria for Determination of /req, OLE, and Local Cooling (ISO 7R 11079)

Type of

Cooling Parameter

Minimal /req (high strain)

Neutral /req (low strain)

(Jen era! /r

30

35.7-0.028.5M

Tik (°C)

0.06

0.0001 M

W ;n. d.)

DLE

Qhm h m’2)

-40

-40

L ocal Hand temperature (°C)

15

24

WCI (W h nr2)

1600

Respiratory tract and eye temp. (°C)

Ta < -40

TABLE 6.11 Cooling Power of Wind on Exposed Flesh Expressed as a Chilling Temperature, teh, under Almost Calm Conditions

Actual thermometer reading

Wind

Speed

(m s" )

0

-5

-10

-IS

-10

-IS

-30

-35

-40

-45

50

1.8

0

-5

-10

-15

-20

-25

-30

-35

-40

-45

— 50

7

-1

-6

-11

-16

-21

-27

-32

-37

-42

-47

— 52

3

-4

-10

-15

-21

-27

-32

-38

-44

-49

-55

-60

5

-9

-15

-21

-28

-34

-40

-47

-53

-59

— 66

-72

S

-13

-20

-27

-34

-41

-48

-55

-62

-69

-76

-83

11

-16

-23

-31

-38

-46

-53

-60

-68

-75

-83

-90

15

-18

-26

-34

-42

-49

-57

-65

-73

-80

-88

-96

20

-20

-28

-36

-44

-52

-60

-68

-76

-84

-92

100

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