ERGONOMIC DESIGN OF A BARBER'S WORKSTATION. Muhammad H. AL-HABOUBI and Azam BAIG

Transcription

1 J. Human Ergol., 26: 39-50, 1997 Center.for Academic Publications Japan. Printed in Japan. ERGONOMIC DESIGN OF A BARBER'S WORKSTATION Muhammad H. AL-HABOUBI and Azam BAIG Systems Engineering Department, King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia Research Institute King Fahd University of Petroleum and Minerals, Dhahran, Saudi Arabia Long hours of work while standing have been known to cause health problems for humans. Such professions include that of the barber. A survey was conducted of barbers from different barber shops in Saudi Arabia to determine their discomfort level. A prototype workstation was then designed and constructed in which the barber sits and performs work. The workstation was tested by nine barbers in the Human Factors Laboratory in the Systems Engineering Department at King Fahd University of Petroleum and Minerals. These barbers were among those surveyed earlier in their shops. Their discomfort level was again taken and an experiment was conducted to design the shape of the footrest. The discomfort levels obtained while standing and sitting were statistically analysed. From the results, it was concluded that the mean of the discomfort levels while standing is significantly (a=0.01) higher than that while sitting. Professions which require long hours of work while standing have been known to cause health problems for humans as shown by BUCKLE et al. (1986) and HUNTING et al. (1980). Both studies have found discomfort in the legs of persons who had to stand while performing their work. The feet, in particular, were listed as the site of most discomfort by BUCKLE et al. (1986). In general, standing is considered to be a bad work posture. Therefore, work that requires prolonged standing should be avoided as much as possible in the design of workstations. However, it should be pointed out that alternate standing and sitting postures is not bad. The advantages of sitting compared to standing during work have been summed up as follows by ANDERSSON (1986): 1. Sitting provides stability for motor control tasks. 2. Sitting is less energy consuming. 3. Sitting places less stress on the joints of the lower extremities. Received for publication October 23,

2 40 M. H. AL-HABOUBI and A. BAIL In view of the above reasons, workstations have been designed for dentists and surgeons enabling them to work while sitting. Another profession which requires long hours of standing is that of the barber. The design and evaluation of a sitting workstation for the barber is presented in this paper. It is worthwhile mentioning that in countries like Saudi Arabia, Pakistan, India, Philippines, and Bangladesh, the following factors make the workload of barbers different from other workers who may also work while standing. 1. Barbers are on duty for about 12 h daily compared to the usual 8 h for factory and office workers. 2. Barbers work 62 days a week compared to the usual 5 days for other workers. (Friday being a half-day). Customers are served on a first come, first serve basis. Factors such as longer standing hours per day, longer working days, and the difficulty of scheduling haircuts to provide suitable rest breaks justifies improving the barber's workstation. In fact, even with the absence of these factors, the improvement in this regard is justifiable on its own merit. The objective of this study is to design an ergonomic workstation in which the barber can sit while working. The workstation consists basically of a customer chair, a barber chair and a footrest for the barber. The design involves the development of pertinent shapes and dimensions based on anthropometric measurement. The workstation should accommodate all customers including children and large adults. Also, it takes into account barbers of different sizes. The design parameters were chosen in relation to body parts so that populations of different anthropometric measurements may utilize the design. To test the benefit of the suggested workstation, a prototype was put together including a commercial customer chair, and a manufactured barber chair and footrest. Nine barbers completed an experiment to test the comfort level by adopting the standing posture and the sitting posture. The standing posture was done in their shops while working on actual customers and the sitting posture was done in the Human Factors Laboratory in the Systems Engineering Department at King Fahd University of Petroleum and Minerals (KFUPM), while working on customers invited for a free haircut. An attempt was made to hold the evaluation of both workstations at one place, either the laboratory or the barber workshop, but was not successful. The barbers used in the study are employed and their employers were not cooperative. The discomfort levels measured at half-hour intervals in both postures were statistically analysed. METHODS A video recording and photographs of four barbers were taken during hair cutting at the shops to study their postures. The major observation from the film and prints is that barbers keep the top of the customer's head at or just below the

3 ERGONOMIC DESIGN OF A BARBER'S WORKSTATION 41 level of their shoulder during hair cutting. This is achieved by adjusting the height of the customer's chair. To determine the preferred distance between the barber's shoulder and the top of the customer's head (CD), data was collected by setting up a prototype of a barber's workstation in the Human Factors Laboratory in which the barber works while sitting. Nine barbers, were called from their barber shops to work for the whole day outside. CD was measured for the 161 customers that participated in these experiments. The statistics are summarized as follows: 5-th percentile equals 1.5 cm, average equals 6.6 cm and 95-th percentile equals 14.2 cm. A schematic diagram of the proposed workstation for the barbers is shown in Fig. 1. Some of the parameters of relevance to the proposed design are defined in the nomenclature (Appendix A). Design features of the proposed workstation were as follows. (A) Range of height adjustment. It is emphasized that the proposed workstation should be designed to accomodate large barbers and yound customers (say 5 years old) and small barbers serving adult customers. So, the need for chair height adjustment seems imperative. The range of height adjustment for the barber's footrest and the barber's chair was chosen based on the largest possible difference in body dimensions that may occur between the customer and the barber. In the first situation, a five-year-old child is considered as the customer. The age of five years is selected since it is about this age that children regularly have their hair cut. The barber serving this child is considered to be a tall individual. In the second situation, the customer is considered to be a tall person and the barber serving this customer is considered to be of short stature. These two situations can be expressed in anthropometric variables as follows. CASE1. The customer is 5 years old having a low percentile sitting height (e.g. 5-th percentile), and the barber is a tall person having a large percentile of sitting shoulder height and popliteal height (e.g. 95-th percentile). CASE2. The customer is a tall person having a large percentile sitting height (e.g. 95-th percentile), and the barber is a small person having a low percentile of sitting shoulder height and popliteal height (e.g. 5-th percentile). From Fig. 1, the following equations were obtained by inspection. Hence, Similarly, Therefore, HB+KB+F=CD+SHC+KC F=SHC+KC-KB-HB+CD (1) HB+SH=CD+SHC+KC

4 42 M. H. AL-HABOUBI and A. BAIG Fig. 1. Suggested design of barber's workstation. SH=SHC+KC-HB+CD (2) For both cases, two more extreme situations are considered: 1. The tall barber who prefers to keep the customer's head at about shoulder level (for example 5-th percentile CD); 2. The short barber who prefers to keep the customer's head at below shoulder level (for example 95-th percentile CD). Equation (1) can be represented as follows for the two given cases to obtain the range of height adjustment for the barber's footrest. CASE-1 (short customer and tall barber). F>low percentile SHE+KC(max)-large percentile KB -large percentile HB+low percentile CD (3) CASE-2 (tall customer and short barber). F<large percentile SHE+KC(min)-low percentile KB -low percentile HB+large percentile CD (4) Likewise, Eq. 2 can be represented as follows for the two given cases to obtain the range of height adjustment for the barber's chair. CASE-1 (short customer and tall barber).

5 ERGONOMIC DESIGN OF A BARBER'S WORKSTATION 43 Fig. 2. Photograph of barber's footprints. SRP: Seat reference point of customer chair. C1: center of outer circle. C2: center of inner circle. SH>low percentile SHc+KC(max)-large percentile HB +low percentile CD (5) CASE -2 (tall customer and short barber). SH<large percentile SHE+KC(min)-low percentile HB +large percentile CD (6) (B) Distance between barber and customer. While the barber works when sitting, the hips are abducted to partially embrace the customer's chair in the `V' space between the thighs. The following two distances were measured while the barbers abducted their hips at the maximum possible angle (am), and at a comfortable angle (ƒ c) Yƒ =distance from barber's shoulder joint to front of the knee at different hip abduction angles (a) D=Comfortable arm reach from barber's shoulder joint to the ears of the customer's head with the barber immediately behind the customer. The above parameters are graphically shown in Fig. 1. (C) Shape of the barber's footrest. To determine the shape and dimensions of the footrest, the barbers' footprints were recorded during actual work. For this purpose, ink stamp pads shaped to the sole of the shoe were sealed inside cellophane packing which had pin holes on one side. These stamp pads were tied to the

6 44 M. H. AL-HABOUBI and A. BAIL underside of the barbers feet by strings that passed through the cellophane packing. A plywood sheet in the shape of a large horseshoe was fixed on the prototype of the footrest and plain white paper was put on top. The seat reference point (SRP) of the customer's chair was then marked on the paper, while performing work, the ink pads under the barbers feet leave ink marks of the foot on the white paper. This is shown in the photograph in Fig. 2. Using this technique, nine footprint sets were collected from the nine barbers while performing a full haircut. (D) General features of a seat. The general design features of the barber's chair such as the seat width, seat depth and backrest are not different from those recommended in literature with respect to the general design of seats. The seat pan is horizontal and no armrests are provided since they serve no purpose for the barber. RESULTS AND DISCUSSION Results and discussion related to the design of the workstation are presented here, followed by the results of the discomfort survey. Ergonomists usually adopt the 5-th percentile and 95-th percentile of concerned body dimensions in designs. For the height adjustment, the low percentile is considered to be the 5-th percentile and the large percentile is taken to be the 95-th percentile. Inequality 3 defines the lowermost limit of the barber's footrest. As an example, the lowest possible height of the footrest (F) is considered to be 0 cm, so that the footrest is on the floor. In inequality 3, all the terms except KC(max) are known. The variables KB, SHT and HB are anthropometric measurements which are available in literature such as those found in PHEASANT (1988). For example, for British adults, the 95-th percentile values for KB, HB and SHT are given as 49.0, 65.0 and 97.0 cm, respectively. Also the 5-th percentile for KB and HB are 39.5 and 54.5 cm, respectively. The 5-th percentile for SHT for a 5-year-old British child is 57.5 cm (PHEASANT, 1988). Since, Ĉ is the small backward slope angle of the customers chair, hence, SHE is approximately equal to the sitting height of the customer as SHE = cos Ĉ * SHT. The 5-th percentile of distance CD is obtained from the laboratory survey. By substituting the appropriate values into inequality 3, KC(max) is obtained as 55.0 cm. Inequality 4 defines the uppermost limit of the barber's footrest. All the terms in this inequality except F and KC(min) are known. Appropriate values for SHE, KB, HB and CD are similarly obtained as for inequality 3. Therefore, F changes as KC(min) changes while all other terms remain constant. The minimum height for the barber's footrest (F) occurs if KC(min) is kept at KC(max). Therefore, KC(min) is also equal to 55.0 cm. Hence, the customer's chair should be fixed at a height of 55.0 cm. For KC(min) equal to 55.0 cm, the uppermost height of the footrest is determined to be 72.2 cm. Since the customer's chair is above the 5-th percentile popliteal height of (British) adults, which equals 39.5 cm, a footrest for the customer's chair becomes necessary.

7 ERGONOMIC DESIGN OF A BARBER'S WORKSTATION 45 From inequalities 5 and 6, the lowermost and uppermost heights of the barber's chair from the floor (SH) are obtained respectively. All terms in these two inequalities are obtained as for inequality 3. The value 55.0 cm is substituted for KC(max) and KC(min). By substituting the appropriate values into inequalities 5 and 6, the height of the barber's chair (SH) is from 49.0 to cm. For the distance between barber and customer, details of measurements need not be shown, but the results of the measurements of the hip abduction posture show that D does not vary with hip abduction angle (a). However, Ya is a function of a and reaches a minimum at am. To ensure the feasibility of the new design, D should be greater than the Ya measured at ; to ensure that the barber can reach the customer's head. A check of both distances shows that D > Ya at o for all barbers. So, being able to comfortably reach the customer's head is not a problem. As far as the barber's footrest is concerned, the footprints were observed to form a particular horseshoe shape (Fig. 2). By using trial and error to overlap the footprints, the footprints were enclosed in two circles which were formed as follows. 1. A straight line 9 cm long was drawn on the footrest paper from the marked SRP towards the center of the seat pan of the customers chair. A circle of radius 55 cm in length was drawn from this point. This formed the outer enclosure of the foot prints. 2. The above straight line from the marked SRP on the paper was extended down 18 cm towards the center of the seat pan. A circle of radius 34 cm in length was made from this point. This formed the inner enclosure of the foot prints. All foot prints were almost completely contained by this enclosure. The two circles have different centers and the width of the footrest is narrower towards the front of the customers chair and wider at the back of the customers chair. This shape comes naturally due to the hip abduction posture of the barber since his feet are placed diagonally on the footrest. This is an advantageous shape since it saves space towards the front of the customers chair. During experimentation with the prototype, it was observed that the barber moves closer or farther from the customer's head while working. Hence, to allow the barber to move freely without any constraint, the barber's chair was not linked to the customer's chair. To allow free movement, the barber's chair is fitted with five wheels. Two square trays were placed on either side of the barber's chair in line with the horizontal level of the seat pan for an easy reach. These trays were intended to eliminate the frequent trips to the dressing counter which intensifies the barber's inconvenience. These trays can swivel in an arc of 90 degrees around the side of the chair and are 30 cm2 in size. As far as the customer's chair is concerned, an ordinary chair usually seen in barber shops is used. One modification adopted in the new design was to fix the height of the customer's chair to a lower percentile of adults. It is worth mentioning that such a suggestion is not new since the height adjustability feature for current

8 46 M. H. AL-HABOUBI and A. BAIG Fig. 3. Photograph of the suggested workstation. customer's chairs is made to suit the height of the barber. The required height adjustment for the customer's head is accomplished via the barber's chair as discussed above. The prototype with the design features described above was used by nine of the fourteen barbers who participated earlier in this study to compare the discomfort level during standing and sitting. The prototype workstation is shown in Fig. 3. In order to discover if barbers experience discomfort during work, a survey was carried out to determine their discomfort level. The aim of this survey was to substantiate the opinion that the barbers experience discomfort due to standing for long hours, and hence, to establish a need for a sitting workstation for them. Fourteen volunteer barbers from five different countries (India, Pakistan, Phillipines, Indonesia and Bangladesh) living in the Eastern province of Saudi Arabia, were initially surveyed so that the obtained data was not restricted to persons of any particular origin. However, only nine barbers were able to complete the experiment, three dropped because their employers were reluctant to send them to the laboratory, one left the country because of end of contract and the input of one barber was excluded after informing the experimenter that he experienced physical stress in the day preceding the experiment. The average age of the remaining barbers is 28 years, the average height is cm, and the average weight is 65.1 kg. All the surveyed subjects were professional barbers and had been working in barber shops in Saudi Arabia for at least one year. Almost all of the surveys were conducted on Thursday since this is part of the weekend break and thus more customers are expected. This day was selected so that the discomfort level of the barbers could be assessed under the maximum possible workload. According to the barbers, they experience approximately similar

9 ERGONOMIC DESIGN OF A BARBER'S WORKSTATION 47 Table 1. Discomfort levels during sitting and standing. discomfort on other days of the week also, although Thursday is the most hectic day for them. Postural discomfort is assessed via a technique developed by CORLETT and BISHOP (1976). It consists of a questionnaire and sampling the discomfort of the worker at regular intervals throughout the work period. For overall discomfort in the body, the worker ranks his discomfort according to a discomfort scale. The overall discomfort scale is not restricted to any one body part but represents the collective discomfort felt all over the body as suggested by CoRLETT and BISHOP (1976). The discomfort scale used in the present study varies from 0 to 5 as follows:- 0: Extremely comfortable, 1: No noticeable discomfort, 2: Slight discomfort, 3: Moderate discomfort, 4: Heavy discomfort and 5: Extreme discomfort On the day of the survey, each barber was observed from the opening time of the shop to its close. The discomfort level of the barber was sought at half-hour intervals as in the CORLETT and BISHOP study. The results of the survey for standing posture are shown in Table 1. The average and the standard error of the overall body discomfort rating for the nine barbers are shown against the period of the day. The increasing trend in average discomfort level against time is clearly demonstrated. The discomfort level averages 1.0 at the beginning of work and

10 48 M. H. AL-HABOUBI and A. BAIG reached an average of 3.57 towards the end of work. Generally, an increase in the discomfort level against time is observed with the exception of the three half-hour periods after the lunch break. Apparently, the lunch break was effective in relieving the muscles from the morning shift, which resulted in having equivalent discomfort levels at the beginning of work in the morning and immediately after the lunch break. However, the discomfort level increased steeply in the afternoon hours. This is considered a substantial increase, which warrants the suggested improvement of the present workstation design. The participants stated that the discomfort is basically a result of the long standing hours. The same nine barbers were asked to replicate hair cutting in the laboratory using the prototype barber's workstation (Fig. 3). The work schedule of each barber, from the previous survey, was duplicated in the laboratory in order to reduce variation. The customers in the experiment were individuals from the KFUPM community invited for a free haircut. The discomfort level of the barbers was again taken as half-hour intervals and the average and the standard error is presented in Table 1. Discomfort levels during sitting in the morning hours were maintained as the initial level except during the sixth period when a slight increase is noticed. However, the lunch break dissipated the tiny discomfort. Again, the discomfort level started to increase as the work continued. Comparing the discomfort levels at the same period, it was found that the values during sitting are consistently less than or equal to the levels during standing. However, the discomfort levels for both postures in the morning, are fairly similar since the barbers are still fresh. As the working day progresses, the standing posture causes more discomfort and the difference between the discomfort level during standing and during sitting becomes larger. Towards the end of the day, the discomfort felt by all the barbers during sitting reached an average of 2.29, which is classified between slight discomfort and moderate discomfort but is inclined to the former. On the other hand, the standing posture caused an average of 3.57 in the same period, which is classified between moderate and heavy discomfort. These results show that sitting caused some reduction in the discomfort level and the prototype workstation reduced muscle fatigue. Comparison between both postures is treated by analysis of variance using randomized complete block design for two-factor experiments. The factors in this context are the posture (P) and time interval (T), while the blocks represent the subjects (S). Only seventeen intervals were included in the analysis as scores for intervals 5, 6 and 20 were omitted because of incomplete data due to some barbers leaving for lunch or closing the barbershop earlier. The results of the ANOVA are presented in Table 2. These results show a highly significant effect of posture at a = 0.01, which means the sitting posture is highly favored by barbers while performing the job. The effect of the time interval is also significant at ƒ =0.01, which means as the time of the day advances toward the evening hours, the barbers feel the discomfort due to cumulative working hours. It is noted that there is a

11 ERGONOMIC DESIGN OF A BARBER'S WORKSTATION 49 Table 2. Anova for the discomfort score. * Significant at a = subject effect as well, which may be explained by the standard error for each time interval as shown in Table 1. An advantage of adopting the randomized block design is removing the subject effect to reduce the experimental error. Also, it is noted that there is an interaction effect between the time interval and the posture treatments at a = This interaction is basically due to the equivalence of scores during early morning hours and immediately after lunch hours from one side and the increase of scores for the standing posture during the rest of the working hours on the other side. CONCLUSION The current method of hair cutting causes discomfort to barbers basically as a result of the standing posture. This paper introduces a design of a barber's workstation which was tested experimentally. The results of the test showed a significant reduction in discomfort levels when the new workstation was used. Such a reduction is translated to mean less pain during off-work hours and fresher barbers on the next day of work. It should be noted that the cost of the new design is not considerable. The cost of the footrest and the barber's chair are not high compared to the current cost of the customer's chair. In the new design, since the height of the customer's chair is not adjustable, the cost of the customer's chair decreases and may well offset the increase in total cost due to the addition of a barber's chair and the footrest. Thus the new design would appear to be economically feasible. The authors would like to acknowledge King Fahd University of Petroleum and Minerals for supporting this research. Special thanks are extended to the barbers who participated in this study. REFERENCES ANDERSSON, G. (1986) Loads on the spine during sitting. In The Ergonomics of Working Postures, Taylor and Francis Ltd., London, England. BUCKLE, P., STUBBS, D., and BATY, D. (1986) Musculoskeletal disorders (and discomfort) and associated work factors. In The Ergonomics of Working Postures, Taylor and Francis Ltd., London,

12 50 M. H. AL-HABOUBI and A. BAIG England. CORLETT, E. and BISHOP, P. (1976) A technique for assessing postural discomfort. Ergonomics, 19(2): HUNTING, W., GRAND.IEAN, E., and MAEDA, K. (1980) Constrained postures in accounting machine operators. Applied Ergonomics, 11(3): PHEASANT, S. (1988) Body Space: Anthropometry, Ergonomics & Design, Taylor and Francis Ltd., London, England. APPENDIX-A NOMENCLATURE CD: distance between shoulder level of barber and top of customer's head F: height of the footrest from the floor HR: sitting shoulder height of the barber KB: popliteal height of the barber ƒà : backward seat pan angle of customer's chair SRPB : seat reference point of barber chair SRPB : seat reference point of customer chair KC: height of SRPC from the moor SH: height of SRPB from the floor SHT: sitting height of the customer SHE: CosƒÀ ESHT T: height from the floor to top of customer's head