Industrial Engineering Department Methods Engineering Chapter 6: Work Environment Design

1. Industrial Engineering DepartmentMethods EngineeringChapter 6: Work Environment Design Eng. Suleiman Daifi

2. KEY POINTS • Provide both general and task lighting—avoid glare. • Control noise at the source. • Control heat stress with radiation shielding and ventilation. • Provide both overall air movement and local ventilation for hot areas. • Dampen tool handles and seats to reduce vibration exposure. • Use rapid, forward-rotating shifts, if shiftwork can’t be avoided

3. Methods analysts should provide good, safe, comfortable working conditions for the operator. • Advantages of Plants with good working conditions • increasing production • improve the safety record; • reduce absenteeism التغيب, tardiness التأخر, and labor turnover; • raise employee morale المعنوية; • and improve public relations. Acceptable levels for working conditions and the recommended control measures for problem areas Should be set by the analysts

4. 1( ILLUMINATION • Light is captured by the human eye and processed into an image by the brain. • The basic theory of illumination applies to a point source of light (such as a candle) of a given luminous intensity, measured in candelas(cd) (see Figure 6.2). Light emanates ينبعspherically in all directions from the source with 1-cd sources emitting 12.57 lumens (lm) (as determined from the surface area of a sphere, 4pr2). The amount of light striking a surface, or a section of this sphere, is termed illumination or illuminance and is measured in footcandles (fc). • Some of that light is absorbed and some of it is reflected (for translucent ma- terials, 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 in foot-lamberts(fL). It is determined by the reflective properties of the surface, known as reflectance: • Reflectance is a unitless proportion and ranges from 0 to 100 percent. High- quality white paper has a reflectance of about 90 percent, newsprint and con- crete around 55 percent, cardboard 30 percent, and matte black paint 5 percent. The reflectances for various color paints or finishes are presented in Table 6.1.

5. VISIBILITY • Definition: Visibility: The clarity with which the human sees something • The three critical factors of visibility are: • visual angle: the angle subtended at the eye by the target • contrast:النقيضthe difference in luminance between a visual target and its background • and most important, illuminance. • Other less important factors for visibility are exposure time, target motion, age, known location, and training, • Although increasing the amount of illumination is the simplest approach to improving task visibility, it can also be improved by increasing the contrast or increasing the size of the target.

6. ILLUMINANCE Approach for determining minimum levels of illumination : • 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. • For each category, there is a range of illuminances (low, middle, high). The appropriate value is selected by calculating a weighting factors which lead to (High – Medium – Low) • In practice, illumination is typically measured with a light meter (similar to one found on cameras, but in different units), while luminanceإنارةis measured with a photometer

7. LIGHT SOURCES AND DISTRIBUTION After determining the illumination requirements for the area under study, analysts select appropriate artificial light sources. Two important parameters related to artificial lighting are: • Efficiency: efficient light sources reduce energy consumption • Color rendering: the closeness with which the perceived colors of the object being observed match the perceived colors of the same object when illuminated by standard light sources • 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 necessary. • Table 6.4 provides efficiency and color rendering information for the principal types of artificial light. • Typical industrial lighting sources, that is, luminaires, are shown in Figure 6.4. • To avoid excessive luminance, the luminaires should be evenly distributed across the ceiling. The purpose of this is to avoid glare and problems in adaptation.

8. GLARE • Definition: It is the excessive brightness in the field of vision. This excessive light can leads to decreasing visibility ,so that additional time is required for the eyes to adapt from light to darker conditions. 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 caused by light sources directly in the field of view, or indirect, as reflected from a surface in the field of view. • 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. • Reflected glare can be reduced by using nonglossy غير لامعةor matte surfaces and reorienting the work surface or task, in addition to the modifications recommended for direct glare.

9. COLOR • Both color and texture have psychological effects on people. • Example: employees in an air-conditioned Midwestern plant complained of feeling cold, although the temperature was maintained at 72°F (22.2°C). When the white walls of the plant were repainted in a warm coral مرجانيcolor, complaints ceased. • 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. • 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. • Table 6.5 illustrates the typical emotional effects and psychological significances of the principal colors.

10. 2) NOISE • Definition: Noise is any unwanted sound. • Sound waves originate from the vibration of some object, which in turns sets up a succession of compression and expansion waves through the transporting medium (air, water, and so on). Thus, sound can be transmitted not only through air and liquids, but also through solids, such as machine tool structures.

11. Noise Measurement • Because of the very large range of sound intensities encountered in the normal human environment, the decibel (dB) scale has been chosen. • dB Decibel: it is the logarithmic ratio of the actual sound intensity to the sound intensity at the threshold of hearing of a young person.

12. Hearing Loss • The chances of damage to the ear, resulting in “nerve” deafness الصمم العصبي, increase as the frequency approaches the 2,400- to 4,800-Hz range. • This loss of hearing is a result of a loss of receptors in the inner ear, which then fail to transmit the sound waves further to the brain. Also, as the exposure time increases, especially where higher intensities are involved, there will eventually be an impairment in hearing. • Nerve deafness is due most commonly to excessive exposure to occupational noise. • Individuals vary widely in their susceptibility قابلية to noise-induced deafness. • In general, noise is classified as either broadband noise or meaningful noise. • Broadband noise is made up of frequencies covering a significant part of the sound spectrum. This type of noise can be either continuous or intermittent. • Meaningful noise represents distracting information that impacts the worker’s efficiency. • Reducing the time of exposure to excessive noise during the work shift reduces the probability of permanent hearing impairment. • The OSHA (1997) limits for permissible noise exposure are contained in Table 6.6.

13. NOISE DOSE: • OSHA uses the concept of noise dose, with the exposure to any sound level above 80 dBA causing the listener to incur a partial dose. If the total daily exposureconsists of several partial exposures to different noise levels, then the several partial doses are added to obtain a combined exposure. • Thus, 90 dBA is the maximum permissible level for an 8-h day, and any sound level above 90 dBA will require some noise abatementحد. All sound levels between 80 and 130 dBA must be included in the noise dose computations (al- though continuous levels above 115 dBA are not allowed at all). Since Table 6.6 provides only certain key times, a computational formula can be used for inter- mediate noise levels. • The noise dose can also be converted to an 8-h time-weighted average (TWA) sound level. This is the sound level that would produce a given noise dose if a worker were exposed to that sound level continuously over an 8-h workday. • Today, OSHA also requires a mandatory hearing conservation program, including exposure monitoring, audiometric testing, and training, for all employees who have occupational noise exposures equal to or exceeding TWA of 85 dB. • Although noise levels below 85 dB may not cause hearing loss, they contribute to distractionإلتهاءand annoyanceإنزعاج, resulting in poor worker performance. For example, typical office noises, although not loud, can make it difficult to concentrate, resulting in low productivity in design and other creative work. Also, the effectiveness of telephone and face-to-face communications can be considerably distracted by noise levels less than 85 dB

14. PERFORMANCE EFFECTS • Generally, performance decrements are most often observed in difficult tasks that place high demands on perceptualإدراك حسي, information processing, and short-term memory capacities. Surprisingly, noise may have no effect, or may even improve performance, on simple routine tasks. Without the noise source, the person’s attention may wander due to boredom.

15. NOISE CONTROL • Management can control the noise level in several ways such as: 1)The best, and usually the most difficult, is to reduce the noise level at its source. 2)If the noise cannot be controlled at its source, then analysts should investigate the opportunity to isolate the equipment responsible for the noise; that is, control the noise that emanates from a machine by housing all or a substantial portion of the facility in an insulating enclosure.

16. 3) Temperature • Exposure: 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, coke, and aluminum workers are subject to intense radiative 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. • THEORY: The human is typically modeled as a cylinder with a shell, corresponding to the skin, surface tissues, and limbsأطراف, and with a core, corresponding to the deeper tissues of the trunkجذعand head. Core temperatures exhibit a narrow range around a normal value of 98.6°F (37°C). At values between 100 and 102°F (37.8 and 38.9°C), physiological performance drops sharply. At temperatures above 105°F (40.6°C), the sweatingتعرقmechanism may fail, resulting in a rapid rise in core temperature and eventual death. The shell tissues of the body, on the other hand, can vary over a much wider range of temperatures without serious loss of efficiency, and can act as a buffer to protect core temperatures. Clothing, if worn, acts as a second shell to insulate the core temperature further.

17. CONTROL METHODS • Heat stress can be reduced by implementing either engineering controls, that is, modifying the environment, or administrative controls. • Modifying the environment :the workload should be reduced by mechanization of the operation. • Administrative measures, though less effective, include modifying work schedules to decrease the metabolic load, using work/rest schedules

18. 4) Ventilation • If a room has people, machinery, or activities in it, the air in the room will deteriorate due to the release of odors, the release of heat, the formation of water vapor, the production of carbon dioxide, and the production of toxic vapors. Ventilation must be provided to dilute these contaminants, exhaust the stale قديمair, and supply fresh air. • This can be done in one or more of three approaches: general, local, or spot. • General Ventilation: General or displacement ventilation is delivered at the 8- to 12-ft (2.4- to 3.6-m) level and displaces the warm air rising from the equipment, lights, and workers. Recommended guidelines for fresh air requirements, based on the room volume per person, are shown in Figure 6.15 (Yaglou, Riley, and Coggins, 1936). A rough rule of thumb is 300 ft3 (8.5 m3) of fresh air per person per hour. • Local Ventilation: In a building with only a few work areas, it would be impractical to ventilate the whole building. In that case, local ventilation can be provided at a lower level, or perhaps in an enclosed area, such as a ventilated control booth or crane cab. Accept- able air velocities at the worker are specified in Table 6.9 (ASHRAE, 1991). A rough rule of thumb is that at a distance of 30 fan diameters, the fan velocity drops to less than 10 percent of its face velocity (Konz, 1995). • Spot Ventilation: in areas with localized heat sources, such as refractory ovens, spot cooling with a direct high-velocity airstream at the worker will increase convective and evaporative cooling.

19. 5) Vibration • Vibration can cause detrimental effects on human performance. Vibrations of high amplitude and low frequency have especially undesirable effects on body organs and tissue. The parameters of vibration are frequency, amplitude, velocity, Displacement and maximum acceleration are the principal parameters used to characterize the intensity of vibration. • There are three classifications of vibration exposure: 1. Circumstances in which the whole or a major portion of the body surface is affected, for example, when high-intensity sound in air or water excites vibration. 2. Cases in which vibrations are transmitted to the body through a supporting area, for example, through the buttocks of a person driving a truck, or through the feet of a person standing by a shakeout facility in a foundry. 3. Instances in which vibrations are applied to a localized body area, for example, to the hand when holding and operating a power tool.

20. The human tolerance for vibration decreases as the exposure time increases. Thus, the tolerable acceleration level increases with decreasing exposure time. The limits for whole-body vibration have been developed by both the International Standards Organization (ISO) and the American National Standards Institute (ANSI) (ASA, 1980) for transportation and industrial applications. • The vibration may be reduced by modifying the speed, feed, or motion, and by properly maintaining the equipment, balancing and/or replacing worn parts. Analysts can place equipment on ant-vibrationmountings (springs, shear-type elastomers, compression pads) or alter workers’ body positions to lessen the disturbing vibratory forces. They can also reduce the time workers are exposed to the vibration by alternating work assignments within a group of employees. Last, they can introduce supports that cushion the body and thus dampen higher-amplitude vibrations. Seat suspension systems involving hydraulic shock absorbers, coil or leaf springs, rubber shear-type mountings, or torsion bars may be used. In standing operations, a soft, elastomer مطاط صناعيfloor mat usually proves helpful.

21. 6) Radiation • Although all types of ionizing radiation can damage tissue, beta and alpha radiation are so easy to shield that most attention today is given to gamma ray, X-ray, and neutron radiation. • The roentgen (R) is a unit of exposure that measures the amount of ionization produced in air by X or gamma radiation. • Tissue located at a point where the exposure is 1 R receives an absorbed dose of approximately 1 rad. Very large doses of ionizing radiation—100 rads or more—received over a short time span by the entire body can cause radiation sickness. • An absorbed dose of about 400 radsto the whole body would be fatal to approximately one- half of adults. Small doses received over a longer period may increase the probability of contracting various types of cancers or other diseases.

22. 7) Shiftwork and Working Hours • SHIFTWORK: working other than daytime hours, is becoming an ever- increasing problem for industry. Traditionally, the need for continuous services from police, fire, and medical personnel, or for continuous operations in the chemical or pharmaceutical industries, has required the use of shiftwork. • The problem with shiftwork is the stress on circadianالساعة البيولوجيةrhythms, which is affected by the daily light–dark changes, social contacts, work, and clock time. The most marked cyclic changes occur in sleep, core temperature, heart rate, blood pressure, and task performance, such as critical tracking capability (see Figure 6.18). • Typically, bodily functions and performance start increasing upon awakening, peak in midafternoon, then steadily decline to a low point in the middle of the night. There may also be a dip تراجعafter midday, typically known as the postlunch dip. Thus, individuals who are asked to work on night shift will exhibit a marked degradation in performance, from truck drivers falling asleep at the wheel to gas inspectors reading meters (Grandjean, 1988). • Night workers also experience health problems, such as appetite loss, digestive problems, ulcers, and increased sickness rates. The problems become even worse as the worker ages. • Typically, a three-shift system has an early (E) shift from 8 A.M. to 4 P.M., a late afternoon to 12 P.M. (midnight), and a night (N) shift from 12 P.M. to 8 A.M.. In the simplest case, because of short-term increased production demands, a company may go from just an early shift to both an early and a late afternoon shift.

23. Definite health and accident risks are associated with shiftwork. However, if shiftwork is unavoidable, due to manufacturing process considerations, the following recommendations should be considered: 1. Avoid shiftwork for workers older than 50. 2. Use rapid rotations as opposed to weekly or monthly cycles. 3. Schedule as few night shifts (three or less) in succession as possible. 4. Use forward rotation of shifts if possible (e.g., E-L-N or D-N). 5. Limit the total number of working shifts in succession to seven or less. 6. Include some free weekends, with at least two successive full days off. 7. Schedule rest days after night shifts. 8. Keep the plans simple, predictable, and equitable for all workers.

24. Over Time • Many studies have shown that changes in the length of the workday or workweek have a direct effect on work output. Unfortunately, the result is not typically the direct proportionality expected. • The following guidelines should be followed: 1. Avoid overtime for heavy manual work. 2. Reevaluate machine-paced work for appropriate rest periods or lowered rates. 3. For continuous or long periods of overtime, rotate the work among several workers, or examine alternate shift systems. 4. In choosing between extending a series of workdays by 1 or 2 h versus extending the workweek by 1 day, most workers will opt for the former, to avoid losing a weekend day with the family (Eastman Kodak, 1986).