Ergonomics And Environment- 2008 (1)

ENVIRONMENTAL ERGONOMICS

SITI ZAWIAH MD. DAWAL Dept. of Engineering Design and Manufacture Faculty of engineering University of Malaya 1

Workstation Environment

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TEMPERATURE Most workers are exposed to excessive heat at one time or another. In many situations, artificially hot climates are created by the demands of the particular industry. Miners are subjected to hot working conditions due to the increase of temperature with depth, as well as a lack of ventilation. Textile workers are subjected to the hot, humid conditions needed for weaving cloth. Steel and aluminum workers are subject to intense radioactive loads from open hearth furnaces and refractory ovens. Such conditions, while present for only a limited part of the day, may exceed the climatic stress found in the most extreme, naturally occurring climates. 3

THEORY The human is typically modeled as a cylinder with a shell, corresponding to the skin, surface tissues, and limbs, and with a core, corresponding to the deeper tissues of the trunk and head. Core temperatures exhibit a narrow range around a normal value of 98.6° F (37 C). At values between 100-102° F (37.8-38.9° C), physiological performance drops sharply. 4

At temperatures above 105° F (40.6°C), the sweating mechanism may fail, resulting in a rapid rise in core temperature and eventual death.

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The heat exchanges between the body and its environment can be represented by the following heat balance equation: S=M±C±R–E Where: M = Heat gain of metabolism. C = Heat gained (or lost) due to convection. R = Heat gained (or lost) due to radiation. E = Heat lost through evaporation of sweat. S = Heat storage (or loss) of the body. For thermal neutrality, S must be zero. If the summation of the various heat exchanges across the body result in a heat gain, the resulting heat will be stored in the tissues of the body, with a concomitant increase in core temperature and a potential heat stress problem. 6

Measurement Of Thermal Conditions

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There are five basic components: Air Temperature or Dry-Bulb Temperature Relative Humidity Wet-Bulb Temperature Radiant Temperature Air Velocity

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WBGT Probably the most commonly used index in industry today establishes heat exposure limits and work-rest cycles based on the wet bulb globe temperature, or WBGT (Yaglou and Minard, 1957), and the metabolic load. In slightly different forms it is recommended by ACGIH (1985), NIOSH (1986), and ASHRAE (1991). For outdoors with a solar load, the WBGT is defined as: WBGT = 0.7 NWB + 0.2 GT + 0.1 DB and indoors or outdoors with no solar load, the WBGT is: WBGT = 0.7 NWB + 0.3 GT 9

Thermal Comfort Many attempts have been made to combine into one index the physiological manifestations of these heat exchanges with environmental measurements. Such attempts have centered around designing instruments intended to simulate the human body, or devising formulas and models based on theoretical or empirical data to estimate the environmental stresses or the resulting physiological strains.

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Once the WBGT is measured it can be used with metabolic load of workers to establish the amount of time an unacclimatized worker and acclimatized worker are allowed to work under the given conditions

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Acclimatization Continuous or repeated exposure to hot or cold conditions bring about a gradual adjustment of body functions, resulting in a better tolerance of the climatic stress. Acclimatization to heat is demonstrated by increased sweat production, lowered skin and core temperature, reduced heart rate.

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The process- acclimation is very pronounced within about a week and full acclimatization is achieved within about two weeks. Interrupting heat exposure for just a few days reduces the effects of acclimatization and return to a moderate climate is entirely lost after about two weeks. 15

A healthy person can adjust to dry or humid heat. Acclimatization to heat does not depend on the type of work performed or whether the work is heavy and of short duration or moderate and continuous. A healthy and well trained person acclimates more easy than someone in poor physical condition 16

Effect of heat Cardiovascular effects - increase blood flow from core to skin - increase heart rate Effects on muscles - competition for blood b/w skin and muscle –lack oxygen- lactic acid build up – muscle fatigue 17

Dehydration -loss water –sweating – dehydration –rise of core tempt – muscles cramp Effect of mental performance -?

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EXERCISE Consider an unacclimatized construction worker at 400kcal/hr with a thermal load of WBGT = 25 O C. How long the worker would be able to work in such condition?

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ILLUMINATION The basic theory applies to a point source of light (such as a candle) of a given luminous intensity, measured in candelas (cd) Light emanates spherically in all directions from the source. The amount of light striking a surface, or a section of this sphere, is termed illumination or illuminance and is measured in foot-candles (fc). The amount of illumination striking a surface drops off as the square of the distance (d) in feet from the source to the surface: illuminance = intensity/d2 Some of that light is absorbed and some of it is reflected (for translucent materials, some is also transmitted), which allows humans to "see" that object and provides a perception of brightness. The amount reflected is termed luminance and is measured infootlamberts (fL). It is determined by the reflective properties of the surface, known as reflectance: luminance = illuminance X reflectance 20

Illustration of the distribution of light source following the inverse-square law

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ILLUMINANCE Recognizing the complexity of extending the point source theory to real light sources (which can be anything but a point source) and some of the uncertainties and constraints of Blackwell's (1959) laboratory setting, the IESNA adopted a much simpler approach for determining minimum levels of illumination (IESNA, 1995). The first step is to identify the general type of activity to be performed and classify it into one of nine categories, shown in Table 6-2. A more extensive list of specific tasks for this process can be found in IESNA (1995). Note that categories A, B, and C do not involve specific visual tasks. For each category, there is a range of illuminances (low, middle, high). The appropriate value is selected by calculating a weighting factor ( - 1, 0, + 1) based on three task and worker characteristics, 22

Recommended Illumination Levels for Use in Interior Lighting Design

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Weighting factors to be considered in selecting specific illumination level within each category

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Show in table 6-3. These weights are then summed to obtain the total weighing factor. Note that since categories A, B, and C do not involve visual tasks, the speed/accuracy characteristic is not utilized for these categories, and overall room surfaces are utilized in place of task background. If the total sum of the two or three weighting factors is -2 or -3, the low value of the three illuminance is used; if - 1, 0, or + 1, the middle value is used; and if + 2 or + 3, the high value is used. 25

Example 1 For highly critical inspection for small size assembly task and worker’s age below 40 with critical accuracy and reflectance. What will be the specific illumination?

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Example 2 For surgical operation with surgeon’s age of between 40 – 55 with critical accuracy and reflectance. What will be the illumination?

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GLARE Glare is the excessive brightness in the field of vision. This excessive light is scattered in the cornea, lens, and even corrective lenses (Freivalds, Harpster, and Heckman, 1983), decreasing visibility so that additional time is required for the eyes to adapt from light to darker conditions.

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Also, unfortunately, the eyes tend to be drawn directly to the brightest light source, which is known as phototropism. Glare can be either direct, as by light sources directly in the view, or indirect, as reflected surface in the field of view.

caused field of from a 29

Direct glare can be reduced by using more luminaires with lower intensities, using baffles or diffusers on luminaires, placing the work surface perpendicular to the light source, and increasing overall background lighting so as to decrease the contrast. 30

Reflected glare can be reduced by using non-glossy or matte surfaces and reorienting the work surface or task, in addition to the modifications recommended for direct glare. Also, polarizing filters can be used at the light source as part of glasses worn by the operator 31

The other areas of the room should reflect lower and lower percentages of the light as one moves downward from the ceiling until the floor is reached, which should reflect no more than 2040 percent of the light, to avoid glare. To avoid excessive luminance, the luminaires should be evenly distributed across the ceiling. Direct lighting de-emphasizes the ceiling surface and places more of the light on the work surfaces and the floor. Direct-indirect lighting is a combination of both. 32

Reflectances recommend for room and furniture surfaces in office

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Reflectance of typical paint and wood finishes

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LIGHT DISTRIBUTION Luminaires for general lighting are classified in accordance with the percentage of total light output emitted above and below the horizontal (see Figure 6-4). Indirect lighting illuminates the ceiling, which in turn reflects light downward. Thus, the ceilings should be the brightest surface in the room (see Figure 6-5), with reflectance above 80 percent.

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Artificial Light Source

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LIGHT SOURCES Two important parameters related to artificial lighting are efficiency (light output per unit energy; typically, lumens/watt) and color rendering. Efficiency is particularly important, since it is related to cost; efficient light sources reduce energy consumption. Color rendering relates perceived colors of the perceived colors of the standard light sources.

to the closeness with which the object being observed match the same object when illuminated by

The more efficient light sources (high- and low-pressure sodium) have only fair to poor color rendering characteristics and consequently may not be suitable for certain inspection operations where color discrimination is 37 necessary.

Types of industrial ceiling-mounted luminaires

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COLOR Both color and texture have psychological effects on people. For example, yellow is the accepted color of butter; therefore, margarine must be made yellow to appeal to the appetite. • Perhaps the most important use of color is to improve the environmental conditions of the workers by providing more visual comfort. Analysts use colors to reduce sharp contrasts, increase reflectance, highlight hazards, and call attention to features of the work environment. 40

Sales are also affected or conditioned by colors. People recognize a company's products instantly by the pattern of colors used on packages, trademarks, letterheads, trucks, and buildings. Some research has indicated that color preferences are influenced by nationality, location, and climate. Sales of a product formerly made in one color increased when several colors suited to the differences in customer demands were supplied. 41

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Bright light entering from a window Solution ?

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Glare from overhead light source (Figure 3)

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Monitor with a glare screen (Figure 4)

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