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Ergonomics evaluation and redesign of a hospital meal cart
Applied Ergonomics 33 (2002) 309–318
Ergonomics evaluation and redesign of a hospital meal cart Biman Dasa,*, Julia Wimpeeb, Bijon Dasc a
Department of Industrial Engineering, Dalhousie University, Nova Scotia, 5269 Morris Street, MC 1607, Halifax, Nova Scotia, Canada B3J 3K5 b Aladdin Synergetics Incorporated, Advance Meal Systems, Nashville, TN, USA c Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada Received 6 July 1998; accepted 22 February 2002
Abstract The ergonomic, design and other problems of a conventional hospital meal cart were evaluated with a view to redesign a hospital meal cart by incorporating ergonomic principles and data. The operators encountered difficulty in setting the cart in motion, seeing over the cart, turning the cart and stopping the cart while in motion. The operators expressed postural discomfort in the shoulder, neck, back, lower back, knee and leg, and ankle and foot. The cart with meal trays and food was found to exceed the acceptable initial turning push force requirement of 5th percentile females. Recommendations were made for proper placement of cart handles and handle diameter, provision of large-diameter cart wheel made of hard rubber tire, reduction of cart height, use of plastic material for cart construction, provision of emergency brake, provision of individually (electrically) heated plates for soup and main meal, provision of thick air-tight transparent plastic doors, and reduction of the meal tray size. Several recommendations were adopted by the manufacturer in the new model. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Hospital meal cart; Ergonomics evaluation; Equipment design; Worker survey; Push–pull forces; Ergonomic design; Ergonomic principles; Engineering anthropometry
1. Introduction Hospital meal carts are used to deliver hot meals, breakfast, lunch and dinner, on trays to the patients often in a multi-floor hospital building. Conventional hospital meal carts are equipped to deliver 24 trays. They are moved manually over floors and vertically through the use of elevators by one or two operators and generally two operators serve the meals on trays to the patients. The operators working with the hospital meal carts are both male and female. They perform other duties during the shift and continue to work in a standing posture throughout the work shift. Considerable pushing and pulling forces are involved in moving the hospital meal carts. Bending and lifting are also required in handling the meal trays. To date, no formal study has been conducted to evaluate the design and operation of a hospital meal cart from an ergonomics viewpoint. Consequently, no published information is available. The design and operation of a hospital meal *Corresponding author. Tel.: +1-902-494-3296; fax: +902-4207858. E-mail address: [email protected] (B. Das).
cart should give due consideration to the problems associated with manual materials handling and, in particular, pushing and pulling activities. It is necessary to evaluate the design and operation of a hospital meal cart from an ergonomics viewpoint to minimize operator discomfort and resulting injury. The ergonomic guidelines and principles are meant to provide an orientation towards the physiological and psychological needs of the operator. The design is essentially a compromise between the operators biological needs, as determined by the ergonomics guidelines and physical requirements of the equipment. The design is primarily accomplished by considering the mutual effects of anthropometry and location of the equipment elements on posture, strength, reach, vision, clearance, and interference of the body segments with the equipment elements. All these design factors determine the postural requirements during work or task performance (Das and Grady, 1983; Das and Sengupta, 1996). In the design of work, the working height is of critical importance. The height of the working surface should maintain a definite relationship with the operator’s elbow height depending upon the type of work. Konz
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(1990) maintains that work height, in general, should be set at 5 cm below the elbow level. However, the working height can vary several centimeters, up or down, without any significant effect on performance (Konz, 1967). A proper working height will allow a comfortable working posture. The posture of the operator is largely determined by the geometric relationship between the length of appropriate body segments, body position and the layout of the various components of the equipment. Other than segment lengths of the human body, the interference of the equipment elements with body segments and the visual requirements of the work also dictate the posture. Improperly designed equipment results in poor posture and this in turn causes static efforts. The postural or static efforts will eventually manifest in acute localized muscle fatigue and consequently decrease performance and enhance the possibility of operator-related health hazards (Corlett et al., 1982; Grandjean et al., 1983). The manner by which manual lifting, pushing or pulling is carried out in the work environment is a major concern of the ergonomist, since they attempt to make an efficient use of the work force and to prevent unnecessary injury and illness (Chaffin and Andersson, 1991). In the past, sagittal plane lifting has been studied extensively. However, pushing and pulling capabilities have been studied only in a very limited scope (Chaffin and Andersson, 1991). The vertical height of the handle against which one pushes and pulls is of critical importance (Ayoub and McDaniel, 1974; Davis and Stubbs, 1978). In the study conducted by Ayoub and McDaniel (1974), the elbows and rearward knee were kept straight for the exertions. They stated that the optimal height for a handle to be pushed or pulled should be about 91–114 cm (i.e., about hip height for males) above the floor. For pushing and pulling, Davis and Stubbs (1978) developed recommendations based on abdominal pressure measurements. They also found a larger force capability when the hands were at hip height than when raised to shoulder or above. Snook (1978a, b) made recommendations for push and pull forces that could be exerted initially and sustained by males and females for occasional performance. Snook and Ciriello (1991) subsequently up-dated the data for push and pull forces based on additional research. The recommendations are made in terms of handle height, frequency and distance. The initial and sustained pushing capabilities decreased with distance. The pushing force capabilities were greatest at 95 cm vertical height for males and at 89 cm height for females. The pulling force capabilities decreased with increased vertical height. The maximum pull forces were exerted by males and females at 64 and 57 cm vertical height. Snook and Ciriello (1991) have provided data for initial and sustained two-handed push and pull forces for
males and females, which are used extensively for design guidelines. Maximization of the push–pull forces in moving a hospital meal cart is not the only criterion for its design. Utmost consideration should be given to a comfortable (erect/slump) posture in moving the cart to reduce or minimize back problem. Also, vision over the cart, while moving it, is important, so that the operator is able to see in front of the cart to minimize traffic hazards. A comfortable erect/slump posture and a cart handle height of about 5 cm below elbow height (approximately hip height) would allow optimum (not necessarily maximum) push force to move the cart and facilitate vision above the cart. It is desirable to push the cart using both hands to minimize health hazards. Damon et al. (1966) have recommended a handle diameter of 2–4 cm, based on anthropometric considerations. Eastman Kodak (1983) recommends 3–4 cm with an optimum of 4 cm for power grips and 1.2 cm for precision grips. Drury et al. (1975) conducted field experiments with ‘‘wheeled pedestrian operated vehicles’’ in hospitals. They found that reducing the wheel size from 25 to 7.5 cm decreased mean speed by 14% and the introduction of carpeting reduced it by 18%. Consequently, they recommended using larger diameter wheels and not specifying carpets to reduce forces required for materials handling. Vehicle weight (empty 52.8 kg versus 81.8 kg) had no significant effect on vehicle movement (speed). For the evaluation of equipment, discomfort analyses have been shown to be advantageous (Corlett and Bishop, 1976; Bhatnager et al., 1985; Sthoenmarklin and Marras, 1989). Worker surveys through questionnaires are often used to evaluate the design characteristics, physical fatigue and postural discomfort. This input would be useful in the modification of an existing equipment design through the application of ergonomics principles and data. The objectives of this study are to: (1) make an ergonomics evaluation of a hospital meal cart in terms of: (a) identification of ergonomic, design and other problems, (b) conduct a worker survey to obtain operator ratings of design and other factors and postural discomfort rating and (c) determine initial push, pull and turning forces, and (2) recommend modifications to the conventional hospital meal cart for the purpose of redesigning a hospital meal cart based on ergonomic/anthropometric principles and data.
2. Identification of ergonomic, design and other problems of the conventional hospital meal cart Through direct observation and one-to-one interviews with experienced operators and supervisors, relevant information on task performance, equipment, and
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Fig. 1. Front and side elevations of the conventional (four wheel) hospital meal cart. All dimensions in centimeters.
working posture was obtained (Das and Sengupta, 1996). The ergonomic and other design problems associated with the conventional, four wheel, hospital meal cart were identified in terms of the: (1) maneuverability (pushing, pulling and turning) of the cart, (2) cart handle height and placement, (3) vision or eye height above the cart, (4) opening and closing of cart doors, (5) protection of the cart against damage, (6) ease of stopping the cart, (7) size of meal tray, (8) provision of hot meals, and (9) pushing versus pulling the cart. Fig. 1 shows the front and side elevations of the fourwheel conventional meal cart. A systematic evaluation of the cart is made in terms of the ergonomic design and other problems stated above. 1. Maneuverability (pushing, pulling and turning) of the cart: The front (two) wheels of the conventional meal cart do not swivel, only the two back wheels can swivel. This does not allow general maneuverability of the cart and, in particular, contributes to an increased turning radius. The additional force requirement to maneuver the cart can be a source of twisting and turning injuries especially in the low back region. 2. Cart handle height and placement: The horizontal, cylindrical cart handle is placed on both ends of the cart at a height of 121 cm from the floor (Fig. 1). The placement of the handle does not allow a comfortable posture for a small (5th percentile female) or a large (95th percentile male) person. Furthermore, adequate spacing is not provided between the handle and the cart surface, especially for a person with a large or a thick palm. The material currently used for the handle is stainless steel, which is strong but not comfortable to the hand especially in the winter time. 3. Vision or eye height above the cart: The width and the length of the meal cart do not appear to cause any vision problem while moving the cart. However, the present height of 152 cm from the floor level (Fig. 1) exceeds the permissible eye height of a small person (5th percentile female). Thus a small operator must
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stretch or assume an awkward posture to see above the cart. This is a potential source of a traffic accident hazard. Opening and closing of cart doors: The front two doors of the cart can be opened and closed easily. The doors move in and out on a hinge and while they are open, they stay inside (on the side) of the cart. This appears to be a very satisfactory design since the doors are not in the way while handling the meal trays. Protection of the cart against damage: The meal cart’s bumper is made of hard black rubber on a fender and provides a 5 cm insulation between the fender and the cart. This appears to be satisfactory to withstand any bumps or bangs that the hospital meal carts may encounter. Ease of stopping the cart: There is no provision of emergency brakes to stop the cart in the case of an emergency. A hospital is a busy place and people are always on the move. Consequently, the operator has to make panic stops. This may involve considerable energy on the part of the operator especially when the cart is loaded with full (food) trays. This is a potential source of back injury to the operator. Failure to stop immediately may cause an injury to the person in front of the cart. Furthermore, there is no parking brake when the cart is not attended by the operator. Size of meal tray: The size of the meal tray is 1939 cm2 (Fig. 2). There was considerable unutilized space on the tray. It is possible to reduce the size of the tray without causing any inconvenience to the patient. This will obviously reduce the size of the meal cart. Provision of hot meals: To keep the meal and soup hot, stainless steel covers are used. The metallic covers have poor heat insulation properties compared to insulated plastic covers. Furthermore, metallic covers are heavier than the insulated plastic covers. Pushing versus pulling the cart: Presently, the cart is moved by one operator or sometimes by two operators. They pull the cart using one hand. This is an awkward posture to move the cart. This is a source of neck and back injury and puts considerable
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stress on the trunk. The cart ought to be pushed, using both hands. This posture will minimize health hazards especially on the neck, back and trunk. 3. Hospital meal cart worker survey The hospital meal cart users are asked to participate in the ergonomics study which has been designed to measure, through the use of a questionnaire, the effect of the meal cart (four wheel) design and other factors on employee comfort, health and ease of use. The user input will be useful and supportive to the study being undertaken. The objectives of the survey were to document or record: (1) the general operator rating of various meal cart design and other factors, (2) the current level of physical fatigue induced by the job to the operators, and (3) the changes in postural discomfort in specific anatomical regions.
Fig. 2. Meal tray arrangement of the conventional (four wheel) hospital meal cart. All dimensions in centimeters.
3.1. Method For the purpose of this study, an informed consent and two separate questionnaires were developed and approved by the hospital administration. A total of 24 operators: 11 male and 13 female were surveyed in this study. The two questionnaires: (1) hospital meal cart worker survey I had 11 questions on a Likert type fivepoint scale that dealt with design and other factors (see Appendix A), and (2) hospital meal cart worker survey II that dealt with postural discomfort in specific body regions on both sides of the body (Corlett et al., 1982). The two questionnaires were administered near the end of the shift. 3.2. Hospital meal cart worker survey I Several ergonomics design and operational problems that resulted in postural discomfort were identified from a conventional hospital meal cart worker survey. Considerable pushing and pulling forces are involved in moving the hospital meal carts. Also, bending and lifting are required in handling the meal trays. These factors were identified in the survey along with other equipment design problems including: cart maneuverability, handle height and placement, vision or eye height above the cart, opening and closing of cart doors, and ease of stopping the cart. For the analysis of non-interval scale data, the nonparametric Mann–Whitney test was performed for the male and female responses to the design and other factors. The operator scores obtained for the design and other factors were analyzed separately for male and female. For each factor, median and interquartile range scores were calculated (Table 1). For males, the median score for ‘‘stopping force’’ and ‘‘parking brake’’ was 3.0. Stated otherwise, the stopping
Table 1 Operator scores obtained for the design and other factors of the conventional hospital meal cart and a Mann–Whitney test for the male and female responses to the factors Design and
Male
Female
other factors
Median
Interquartile range
Median
Interquartile range
p-value
1. Cart in motion 2. Turning cart 3. Seeing over cart 4. Handling trays 5. Handling doors 6. Handle height (pushing) 7. Handle height (pulling) 8. Stopping force 9. Emergency hand brake 10. Parking brake 11. Tiredness
2.0 2.0 2.0 2.0 2.0 2.0 2.0 3.0 2.0 3.0 2.5
1.0 2.0 2.0 1.5 1.0 0.0 0.5 1.5 0.5 1.5 1.0
3.0 2.0 3.0 2.0 2.0 2.0 2.0 3.0 3.0 4.0 3.0
1.0 1.0 2.0 1.5 2.0 1.5 2.0 1.5 2.0 1.5 1.0
0.01** 0.24 0.05* 0.71 0.50 0.18 0.31 0.44 0.11 0.33 0.01**
Note: * Significant (po0:05), ** Highly significant (po0:01).
Mann–Whitney test:
B. Das et al. / Applied Ergonomics 33 (2002) 309–318
force requirement and the need for the parking brake were of concern to the male operator. The median score for the tiredness factor was 2.5. In other words, the male operators felt some tiredness at the end of the work shift. The other factors had median scores of 2.0. Consequently, the extent of concern for the factors was less. For females, the median scores were higher for several factors than the scores obtained for the male operators (Table 1). The results are expected, since female operators, in general, have two-thirds of the strength of male operators. The female median scores for ‘‘parking brake’’ was the highest or 4.0. For the ‘‘cart in motion’’, ‘‘seeing over the cart’’, ‘‘stopping force’’ and ‘‘emergency hand brake’’, the median score was 3.0. Consequently, the female operators encountered difficulty in dealing with these factors. For the ‘‘tiredness factor’’, the median score was also 3.0. Consequently, the female operators felt more tired at the end of the work shift compared to the male operators (median score, 2.5). The other factors had a median score of 2.0. So these factors were of less concern to the operators. The Mann–Whitney test, (Table 1), revealed that there was significant (po0:05) difference between male and female operators in the perception of the factor ‘‘seeing over the cart’’. Stated otherwise, the female operators’ perception of ‘‘seeing over the cart’’ was significantly greater than the male operators. Highly significant (po0:01) difference between male and female operators was found in terms of their perception of the factors ‘‘cart in motion’’ and ‘‘tiredness’’ at the end of the work shift. The female operators found it difficult in getting the ‘‘cart in motion’’ and they were more ‘‘tired’’, when compared to the male operators.
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3.3. Hospital meal cart worker survey II The postural discomfort questionnaires were administered at the end of the work shift. The questionnaire provides a diagram of the human body which has been divided into 22 body regions equally split between the right and left half (1) shoulder, (2) arm, (3) elbow and forearm, (4) wrist and hand, (5) neck, (6) back, (7) lower back, (8) buttocks, (9) hip and thigh, (10) knee and leg, and (11) ankle and foot, for left and right sides on a 8point scale: 0, no discomfort to 7, extreme discomfort, left to right) (Corlett et al., 1982). The data were analyzed separately for the male and female. The median and interquartile range of discomfort scale rating scores for the body regions for the male and female operators are presented in Table 2. For the male operator, the back, lower back and ankle and foot in the left region had postural discomfort scores of 1.5, 1.0 and 1.0, respectively. Stated otherwise the male operators felt postural discomfort in these areas more than the other regions. In the right region, the postural discomfort score in the lower back was 1.0. Apparently, the male operators did not feel any postural discomfort in other regions. The female operators had higher postural discomfort scores than male operators in several body regions. In the left region, the postural discomfort scores for the back, lower back, knee and leg and ankle and foot were 4.0, 4.0, 1.0 and 2.0, respectively. The interquartile range values for the stated body regions were found to be high. The results revealed that the female operators encountered considerable discomfort in the back and lower back. For the right region, the postural discomfort scores for the back, lower back, knee and leg were 4.0,
Table 2 Discomfort scale scores for the body regions of the conventional hospital meal cart and a Mann–Whitney test for the male and female responses to the body region Body region
Male
Female
Left
Right
Mann-Witney test
Left
p-value
Right
Median
Interquartile range
Median
Interquartile range
Median
Interquartile range
Median
Interquartile range
Left
right
Shoulder Arm Elbow and forearm Wrist and hand
0.0 0.0 0.0 0.0
1.5 0.0 0.0 0.0
0.0 0.0 0.0 0.0
2.5 0.0 0.0 0.0
0.0 0.0 0.0 0.0
3.5 2.5 2.0 2.0
1.0 0.0 0.0 0.0
4.0 2.5 2.0 3.5
0.32 0.06 0.16 0.35
0.56 0.03* 0.20 0.17
Neck Back Lower back Buttocks
0.0 1.5 1.0 0.0
0.0 2.0 2.0 0.0
0.0 0.5 1.0 0.0
0.0 2.0 2.0 0.0
0.0 4.0 4.0 0.0
5.0 5.0 3.5 0.0
0.0 4.0 4.0 0.0
5.0 5.5 3.5 0.5
0.19 0.25 0.03* 0.31
0.11 0.06 0.03* 0.31
Hip and thigh Knee and leg Ankle and foot
0.0 0.0 1.0
0.0 0.0 1.5
0.0 0.0 0.5
0.0 0.0 1.0
0.0 1.0 2.0
1.5 3.5 4.5
0.0 1.0 0.0
1.5 3.5 4.0
0.23 0.16 0.54
0.15 0.20 0.59
Note: * Significant (po0.05), ** Highly significant (po0.01).
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4.0 and 1.0, respectively. For the right region, the maximum postural discomfort was felt in the back and lower back. Similar results were found for the left region. The Mann-Whitney test results (Table 2) revealed that there was a significant difference in the responses to postural discomfort between the male and female operators in terms of right arm and left and right lower back. Stated otherwise, the female operators felt significantly greater discomfort than the male operators in the right arm, and left and right lower back. The postural discomfort between male and female operators in the left arm almost reached a significant level (po0:06). 4. Determination of weights and forces of hospital meal cart For the purpose of this study, it was necessary to weigh the conventional meal cart. The cart was weighed by employing a hanging weighing scale. The chains and ropes were used to lift the cart by means of an electric hoist. The weight of the empty (without meal trays) conventional meal cart was 186.0 kg (Table 3). Actual weights were used for the crockery, cutlery and insulating covers. Table 3 summarizes the weight of the cart in terms of the meal trays with food. The total weight of the conventional meal cart with 24 meal trays and food was 320.4 kg. The push, pull and turning (push) forces of the conventional hospital meal cart were determined by using a hand dynamometer. For determining the push force, the dynamometer was placed approximately at the (horizontal) handle height of the conventional cart. The dynamometer was placed at the middle of the cart width. For pulling force determination, an attachment (with rope) was made from the handles of the cart to the dynamometer. The height of the pull force was basically the same as the push force. The turning force was applied at the same height and manner as the pushing force. The dynamometer was placed close to the (front) edge of the cart. The turning (right or left) forces represented the forces while the cart was in forward motion or mode.
Table 3 Weight (kg) of conventional hospital meal cart: Empty and with 24 meal trays and food Items
Empty
With 24 trays and food
Weight of meal cart Weight of 24 meal trays at the rate of 3.6 kg/tray Weight of food on 24 meal trays at the rate of 2.0 kg/tray Total weight of cart
186.0 —
186.0 86.4
— 186.0
48.0 320.4
The push, pull and turning forces (initial) on tile and carpet floors were determined for the conventional meal cart (empty and with 24 meal trays and food). Table 4 presents the summary results of the push, pull and turning forces (initial, kg) of the conventional meal cart. The higher push force (empty, 7.3 kg) of the carpet floor could be attributed to the higher coefficient of friction of the carpet compared to the tile (empty, 2.7 kg) floor. The pull forces were basically the same as the push forces in all cases. The high turning push forces (empty, 12.5 and 16.8 kg) can be attributed to the provision of only two rotating wheels in the back and two fixed wheels in the front of the conventional meal cart. As expected, the force values of the conventional meal cart with 24 meal trays and food were considerably higher than the corresponding force values for the empty cart. Similar observations were made with regard to flooring and push, pull and turning forces. The maximum acceptable capabilities of initial twohanded push and pull forces for a female operator had ranged from 17.5 (5th percentile) to 32.0 kg (50th percentile) depending on the percentile value and frequency of movement (Snook and Ciriello, 1991). For the purpose of this study, the 5th percentile values were calculated on the basis of the data and methodology provided by Snook and Ciriello (1991). The acceptable initial push force of 17.5 kg for the 5th percentile female for one push in 5 min, is usually performed by the operators. Thus the actual push forces of 20.2 and 22.7 kg on tile and carpet floors, respectively (Table 4), exceed the acceptable initial push force (Snook and Ciriello, 1991). The interpretation of the results should be made with caution. In this study, the operators feet were stationary, while executing the turning push force. In the study performed by Snook and Ciriello (1991) the operator’s feet were not stationary. The pushing and pulling tasks were simulated on a specially constructed treadmill in their study. Earlier, it was pointed out that the operators in moving the hospital meal cart and serving meals to the patients, performed other tasks (when they are not moving cart or serving meals) during the work shift. Thus, the operators did not perform the task of moving the meal carts on a sustained basis. Snook and Ciriello
Table 4 Push, pull and turning (push) forces (initial, kg) on tile and carpet floors for the conventional meal cart: Empty, without meal trays and with 24 meal trays and food Forces
Push Pull Turning (push)
Empty
With 24 meal trays and food
Tile
Carpet
Tile
Carpet
2.7 2.5 12.5
7.3 7.2 16.8
6.3 6.2 20.2
12.2 12.1 22.7
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(1991) reported the mean initial and sustained push forces for males as 37.6 and 22.3 kg, respectively, and the corresponding values for females was 23.3 and 15.0 kg, respectively. The mean initial and sustained pull forces for males are 36.4 and 26.2 kg, respectively, and the corresponding values for females are 25.0 and 16.5 kg, respectively. Thus, sustained push or pull forces are considerably less than initial push or pull forces. The sustained push or pull forces were not measured in this study. Although initial forces are important from a biomechanical viewpoint, sustained forces have physiological implications. At present, the conventional meal cart is moved by one operator or sometimes by two operators. The operators pull the cart using one hand. This can be a source of neck and back injury and cause considerable stress on the back. 5. Redesigned hospital meal cart The proposed design changes based on ergonomics principles and data are stated below: 1. Maneuverability of the cart. The redesigned hospital meal cart (Fig. 3) would be constructed with durable plastic. This will reduce weight and thus enhance maneuverability. Additionally, it will enhance aesthetic value. It is advisable to have four swivel wheels at each corner of the cart with the addition of two fixed wheels in the middle of the cart (Fig. 3). This recommendation is made with a view that in the future, hospital meal carts can be constructed with 24 and 36 meal trays. This would not only reduce the force required to turn the cart but also decrease turning radius. Presumably the bearing used in the meal cart’s wheel is a sleeve bearing. If it is changed to ball bearing, further reduction in initial push force is possible. Large-diameter (20 cm) cart wheel (4 cm width) made of hard rubber tires (Drury et al., 1975) should be provided to facilitate pushing the cart.
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Regular maintenance of cart wheels can also reduce pushing forces. 2. Cart handle height and placement. To provide comfortable posture, strength capability and vision requirement for female and male operators, the handle height should be placed to accommodate both a small (5th percentile female) and a large (95th percentile male) person. The handle height is based on a height of 5 cm below the elbow height (5th percentile females) (standing) elbow height= 99.0 5.0=94 cm and 95th percentile male (standing) elbow height=120.3 5.0=115.3 cm (Das and Grady, 1983; Das and Sengupta, 1996). A comfortable posture while pushing the hospital meal cart will reduce or minimize back problems. The proposed handle height between 94 and 115.3 cm is in close agreement with the recommendation of Ayoub and McDaniel (1974) for the optimal height for a handle to be pushed or pulled between 91 and 114 cm above the floor. The two handles should be placed 47.8 cm apart, based on the average value between 95th percentile male (51.7 cm) and female (43.8 cm) elbowto-elbow widths. It should be recognized that operators accommodated vertically would cause a decrease in the range of operators accommodated horizontally or with respect to shoulder/elbow width. Since both the above criteria cannot be satisfied at the same time, the former option is selected considering the force/strength requirement in cart movement by operators with different statures. The handle shape can be cylindrical and the diameter of the handle based on hand anthropometry is recommended at 4.0 cm (for power grip, Eastment Kodak, 1983). The handle material can be made of hard rubber or synthetic material. Since the cart is often moved by two operators, two handles could be provided on the sides of the cart. It is possible to provide a 71 bias to the handle from the vertical away from the cart, so that the orientation of the handle is in line with the forearm. This will minimize stress in the hand.
Fig. 3. Front and side elevations of the redesigned hospital meal cart. All dimensions in centimeters.
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3. Vision above the cart. A worker survey questionnaire revealed that about half of the operators had moderate to extreme difficulty in seeing over the cart. The cart height should be reduced to 143.6 cm or less based on the 5th percentile female, eye height (slump posture). This would allow proper vision and promote an improved posture and minimize traffic hazards. 4. Ease of stopping the cart. It is desirable to install emergency brakes for panic stops especially when the cart is loaded with full meal trays. An emergency hand brake can be installed between the cart handles for easy access. 5. Provision of hot meals. It is possible to provide individually (electrically) heated plates for the soup and the main meal (cost of individually heated plates about $150 US and the weight of each tray fully loaded with food, dishes etc. about 4 kg). This is an innovative idea for serving hot meals to the patients of the hospital. By using insulated plastic covers as opposed to conventional metallic covers, improved heat insulation would be provided. Furthermore, it would reduce the weight of the covers. The provision of air tight or solid transparent plastic doors will conserve heat energy and keep the meals hot and improve the aesthetic value. 6. Size of meal tray. The size of the meal tray should be reduced to 33 47 cm (Fig. 4). A compact meal tray will prevent the crockery and cutlery from sliding on the tray. 7. Pushing Versus pulling the cart. To realize optimum benefit the cart must be pushed using both hands.
6. Conclusions The following conclusions and recommendations are reached from this investigation:
Fig. 4. Meal tray arrangement of the redesigned hospital meal cart. All dimensions in centimeters.
1. The operators (especially female) encountered difficulty in setting the cart in motion, seeing over the cart and stopping the cart while in motion. The subjects agreed or strongly agreed to the usefulness of an emergency hand brake. Some (female) subjects felt tired to a large or great extent at the end of the work shift. 2. There was a significant difference between male and female operators in their perception of the factors ‘‘cart in motion’’, ‘‘seeing over the cart’’ and ‘‘tiredness’’. 3. The male operators expressed postural discomfort in the back, lower back and ankle and foot in the left region and lower back in the right region. The female operators encountered postural discomfort in the back, lower back and knee and leg in both the left and right regions and ankle and foot only in the left region. The female operators had generally higher postural discomfort than the male operators. 4. There was a significant difference in postural discomfort between the male and female operators in terms of right arm and left and right lower back. 5. The weights of the conventional meal carts, empty as well as with 24 meal trays and food were determined. The push, pull and turning (push) forces (initial) on tile and carpet floors were determined for the conventional cart (empty and with 24 meal trays and food). Based on the maximum acceptable capabilities, the conventional meal cart would exceed the initial turning push force requirement of 5th percentile female. 6. The use of plastic material would reduce the weight of the hospital meal cart. This will reduce initial push/pull force requirements and enhance maneuverability. 7. The provision of four swivel wheels at each corner of the cart along with two fixed wheels in the middle of the cart would reduce the turning force and decrease the turning radius. This is desirable for meal carts with 24 meal trays and especially with 36 meal trays. Further reduction in initial push force is possible by changing the conventional sleeve bearing to ball bearing for the wheels. Large (20 cm) diameter cart wheel (4 cm width) made of hard rubber tire should be provided to facilitate pushing the cart and regular maintenance will reduce pushing forces. 8. The proposed cart would meet the initial push force requirements stated in sources (1) and (2). 9. The cart handles should be placed between 94 and 115.3 cm from the floor and the two handles should be placed 47.8 cm apart. A cart handle diameter of 4.0 cm is recommended. 10. The height of the cart should be reduced to 143.6 cm or less (preferably 140 cm) from the floor to provide
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11. 12.
13. 14. 15.
16.
317
better vision especially for the small person (5th percentile female). Individually (electrically) heated plates for the soup and main meal should be installed. Thick air-tight transparent plastic doors should be provided. This will conserve heat energy and keep the meals hot and improve the aesthetic value. An emergency hand brake should be added and located between the cart handles for easy access. The size of the meal tray should be reduced from 38 51 to 33 47 cm. The cart must be pushed using both hands to obtain optimum benefit. The meal trays on the lower level of the cart should be handled using a kinetic lift to minimize lower back pain. The operators should be trained to follow the proper work method.
7. Incorporation of the design changes in the new version of the hospital meal cart The proposed changes based on ergonomic/anthropometric principles and data were adopted by the manufacturer in the new version of the hospital meal cart. The new model incorporated design changes with regard to air tight or solid transparent plastic doors, vertical handles, 2 swivel locking and 2 stationary casters (20 cm diameter 4 cm width), individually heated plates for soup and main meals, among others. The incorporation of individually (electrically) heated plates for soup and main meals is considered innovative and a breakthrough in the design of hospital meal carts. Some of the features of the advanced meal systems (hospital meal cart) from Aladdin are highlighted below. Fig. 5 shows advanced meal systems from Aladdin Tem-Rite (R) LLC cart with tray. Meals are assembled cold, using advance prepared foods. Assembled trays are placed in carts on specially designated conduction heating elements. Hospital meal carts are then held in individual roll-in or centralized walk-in refrigerator. 36 min before meal service, meals return to serving temperatures within the refrigerator. Cart tow hitches for 16–20 shelf carts are available. Hospital meal carts are available in 16, 20 and 24 shelf carts for central and de-central applications. Face mounted high-density polymer tray supports and bumpers are provided. Heavy duty sealed non-marking casters (20 cm diameter 4 cm width) are provided. Face mounted heating elements allow for easy replacements. Fig. 5 shows a Temp-Rite II Excel C700 Series (C720) Rethermalization cart and meal tray. The physical characteristic dimensions of the Temp-RiteII cart (C720) are: weight=136.1 kg, height=142.5 cm, width=71.1 cm, and length=73.5 cm. The meal tray
Fig. 5. Advanced meal system—Aladdin Temp-Rite II Excel C700 Services (C720) (Hospital meal cart with tray).
dimensions are: height=2.9 cm, width=32.3 cm, and length=54.4 cm. It should be noted that some of the ergonomic recommendations made in this study were not incorporated in the New C700 Series, due to cost or marketing reasons. The cost or marketing implications of the ergonomics recommendations were not investigated in this study. The cart height for C724 (24 shelves or trays) of 163.3 cm, exceeds the recommended cart height of 143.6 cm or less. The New C700 Series (for 16, 20 and 24 shelves or trays) uses 2 swivel locking and 2 stationary wheels as opposed to the recommended 4 swivel wheels at each cart corner with 2 stationary wheels (casters) in the middle of the cart, especially desirable for 24 and 36 shelves. The recommended hand emergency brake was not implemented.
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8. Concluding remarks It will be desirable to conduct a study to evaluate the new model (New C700 Series Advanced Meal Systems (AMS) cart, Aladdin), especially from an ergonomics viewpoint. This will allow further improvements in the future.
Strongly Agree Neutral Disagree Agree 1 2 3 4 The 5-point scale above was placed under and 10.
Strongly disagree 5 questions 9
11. The extent to which I am tired at the end of the work shift is:
Appendix A. Hospital meal cart survey I The following questions have been developed to evaluate a number of factors associated with your four-wheel hospital meal cart. We would ask you to take a few moments and complete the questionnaire near the end of the work shift. For each question please circle the number which most closely represents your opinion about the factor under review. The results of this questionnaire will be kept confidential. 1. 2. 3. 4. 5.
Getting the four-wheel cart in motion, I have: Turning the four-wheel cart, I have: Seeing over the four-wheel cart, I have: Placing and removing the trays, I have: Opening and closing the doors, I have:
No Slight Moderate Great difficulty difficulty difficulty difficulty 1 2 3 4 The 5-point scale above was placed under 1–5.
Extreme difficulty 5 questions
6. I find the four-wheel cart’s handle height while pushing to be: 7. I find the four-wheeled meal cart’s handle height while pulling to be:
Excellent Good Fair Poor Unacceptable 1 2 3 4 5 The 5-Point scale was placed under questions 6 and 7. 8. I find the force that I must use to bring the four wheeled meal cart to a stop once it is in motion to be:
Completely acceptable Good Fair Poor Unacceptable 1 2 3 4 5
9. An emergency brake for the panic stops would be useful: 10. A parking brake on the wheels would be useful:
None 1
Little 2
Fair 3
Large 4
Great 5
References Ayoub, M.M., McDaniel, J.W., 1974. Effects of operator stance of pushing and pulling tasks. Trans. Am. Inst. Ind. Eng. 6, 185–195. Bhatnagar, V., Drury, C.G., Schiro, S.G., 1985. Postural discomfort and performance. Hum. Factors 27 (2), 189–199. Chaffin, D.B., Andersson, G.B.J., 1991. Occupational Biomechanics, 2nd Edition. John Wiley, New York. Corlett, E.N., Bishop, R.P., 1976. A technique for assessing postural discomfort. Ergonomics 19, 175–182. Corlett, E.N., Bowssenna, M., Pheasant, S.T., 1982. Is discomfort related to the postural loading of the joints? Ergonomics 25, 315–352. Damon, A., Stoudt, H.W., McFarland, R.A., 1966. The Human Body in Equipment Design. Harvard University Press, Cambridge, MA, USA. Das, B., Grady, R.M., 1983. Industrial workplace layout design: An application of engineering anthropometry. Ergonomics 26 (5), 433–447. Das, B., Sengupta, A.K., 1996. Industrial workstation design: A systematic ergonomics approach. Appl. Ergon. 27 (3), 157–163. Davis, P.R., Stubbs, D.A., 1978. Performance capacity limits. Appl. Ergon. 9, 33–38. Drury, C.G., Barnes, R.E., Daniels, E.D., 1975. Pedestrian operated vehicles in hospitals. Proceedings of the AIIE Annual Convention, Washington, DC, USA, pp. 184–191. Eastman Kodak Co., 1983. Ergonomic design for people at work. Lifetime Learning, Belmont, CA, USA, pp. 140–159. Grandjean, E., Hunting, W., Maeda, K., Landi, Th., 1998. Constrained postures at office workstations. In: Kavelseth, T.O. (Ed.), Ergonomics of Workstation Design. Butterworth, Kent, England. Konz, S., 1967. Design of work stations. J. Ind. Eng. 18, 413–428. Konz, S., 1990. Work Design: Industrial Ergonomics, 3rd Edition. Publishing Horizons, Scottsdale, AZ. Snook, S.H., 1978a. The design of manual handling tasks. Ergonomics 21, 963–985. Snook, S.H., 1978b. The design of manual handling tasks. Paper presented at Ergonomics Society Lecture, Carnfield Institute of Technology, Bedfordshire, England. Snook, S.H., Ciriello, V.M., 1991. The design of manual handling tasks: revised tables of maximum acceptable weights and forces. Ergonomics 34 (9), 1197–1213. Sthoenmarklin, R.W., Marras, W.S., 1989. Effects of handle and work orientation on hammering: II. Muscle fatigue and subjective rating of body discomfort. Hum. Factors 4 (31), 413–420.
Ergonomics evaluation and redesign of a hospital meal cart Biman Dasa,*, Julia Wimpeeb, Bijon Dasc a
Department of Industrial Engineering, Dalhousie University, Nova Scotia, 5269 Morris Street, MC 1607, Halifax, Nova Scotia, Canada B3J 3K5 b Aladdin Synergetics Incorporated, Advance Meal Systems, Nashville, TN, USA c Faculty of Medicine, Dalhousie University, Halifax, Nova Scotia, Canada Received 6 July 1998; accepted 22 February 2002
Abstract The ergonomic, design and other problems of a conventional hospital meal cart were evaluated with a view to redesign a hospital meal cart by incorporating ergonomic principles and data. The operators encountered difficulty in setting the cart in motion, seeing over the cart, turning the cart and stopping the cart while in motion. The operators expressed postural discomfort in the shoulder, neck, back, lower back, knee and leg, and ankle and foot. The cart with meal trays and food was found to exceed the acceptable initial turning push force requirement of 5th percentile females. Recommendations were made for proper placement of cart handles and handle diameter, provision of large-diameter cart wheel made of hard rubber tire, reduction of cart height, use of plastic material for cart construction, provision of emergency brake, provision of individually (electrically) heated plates for soup and main meal, provision of thick air-tight transparent plastic doors, and reduction of the meal tray size. Several recommendations were adopted by the manufacturer in the new model. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Hospital meal cart; Ergonomics evaluation; Equipment design; Worker survey; Push–pull forces; Ergonomic design; Ergonomic principles; Engineering anthropometry
1. Introduction Hospital meal carts are used to deliver hot meals, breakfast, lunch and dinner, on trays to the patients often in a multi-floor hospital building. Conventional hospital meal carts are equipped to deliver 24 trays. They are moved manually over floors and vertically through the use of elevators by one or two operators and generally two operators serve the meals on trays to the patients. The operators working with the hospital meal carts are both male and female. They perform other duties during the shift and continue to work in a standing posture throughout the work shift. Considerable pushing and pulling forces are involved in moving the hospital meal carts. Bending and lifting are also required in handling the meal trays. To date, no formal study has been conducted to evaluate the design and operation of a hospital meal cart from an ergonomics viewpoint. Consequently, no published information is available. The design and operation of a hospital meal *Corresponding author. Tel.: +1-902-494-3296; fax: +902-4207858. E-mail address: [email protected] (B. Das).
cart should give due consideration to the problems associated with manual materials handling and, in particular, pushing and pulling activities. It is necessary to evaluate the design and operation of a hospital meal cart from an ergonomics viewpoint to minimize operator discomfort and resulting injury. The ergonomic guidelines and principles are meant to provide an orientation towards the physiological and psychological needs of the operator. The design is essentially a compromise between the operators biological needs, as determined by the ergonomics guidelines and physical requirements of the equipment. The design is primarily accomplished by considering the mutual effects of anthropometry and location of the equipment elements on posture, strength, reach, vision, clearance, and interference of the body segments with the equipment elements. All these design factors determine the postural requirements during work or task performance (Das and Grady, 1983; Das and Sengupta, 1996). In the design of work, the working height is of critical importance. The height of the working surface should maintain a definite relationship with the operator’s elbow height depending upon the type of work. Konz
0003-6870/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 3 - 6 8 7 0 ( 0 2 ) 0 0 0 1 8 - 2
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(1990) maintains that work height, in general, should be set at 5 cm below the elbow level. However, the working height can vary several centimeters, up or down, without any significant effect on performance (Konz, 1967). A proper working height will allow a comfortable working posture. The posture of the operator is largely determined by the geometric relationship between the length of appropriate body segments, body position and the layout of the various components of the equipment. Other than segment lengths of the human body, the interference of the equipment elements with body segments and the visual requirements of the work also dictate the posture. Improperly designed equipment results in poor posture and this in turn causes static efforts. The postural or static efforts will eventually manifest in acute localized muscle fatigue and consequently decrease performance and enhance the possibility of operator-related health hazards (Corlett et al., 1982; Grandjean et al., 1983). The manner by which manual lifting, pushing or pulling is carried out in the work environment is a major concern of the ergonomist, since they attempt to make an efficient use of the work force and to prevent unnecessary injury and illness (Chaffin and Andersson, 1991). In the past, sagittal plane lifting has been studied extensively. However, pushing and pulling capabilities have been studied only in a very limited scope (Chaffin and Andersson, 1991). The vertical height of the handle against which one pushes and pulls is of critical importance (Ayoub and McDaniel, 1974; Davis and Stubbs, 1978). In the study conducted by Ayoub and McDaniel (1974), the elbows and rearward knee were kept straight for the exertions. They stated that the optimal height for a handle to be pushed or pulled should be about 91–114 cm (i.e., about hip height for males) above the floor. For pushing and pulling, Davis and Stubbs (1978) developed recommendations based on abdominal pressure measurements. They also found a larger force capability when the hands were at hip height than when raised to shoulder or above. Snook (1978a, b) made recommendations for push and pull forces that could be exerted initially and sustained by males and females for occasional performance. Snook and Ciriello (1991) subsequently up-dated the data for push and pull forces based on additional research. The recommendations are made in terms of handle height, frequency and distance. The initial and sustained pushing capabilities decreased with distance. The pushing force capabilities were greatest at 95 cm vertical height for males and at 89 cm height for females. The pulling force capabilities decreased with increased vertical height. The maximum pull forces were exerted by males and females at 64 and 57 cm vertical height. Snook and Ciriello (1991) have provided data for initial and sustained two-handed push and pull forces for
males and females, which are used extensively for design guidelines. Maximization of the push–pull forces in moving a hospital meal cart is not the only criterion for its design. Utmost consideration should be given to a comfortable (erect/slump) posture in moving the cart to reduce or minimize back problem. Also, vision over the cart, while moving it, is important, so that the operator is able to see in front of the cart to minimize traffic hazards. A comfortable erect/slump posture and a cart handle height of about 5 cm below elbow height (approximately hip height) would allow optimum (not necessarily maximum) push force to move the cart and facilitate vision above the cart. It is desirable to push the cart using both hands to minimize health hazards. Damon et al. (1966) have recommended a handle diameter of 2–4 cm, based on anthropometric considerations. Eastman Kodak (1983) recommends 3–4 cm with an optimum of 4 cm for power grips and 1.2 cm for precision grips. Drury et al. (1975) conducted field experiments with ‘‘wheeled pedestrian operated vehicles’’ in hospitals. They found that reducing the wheel size from 25 to 7.5 cm decreased mean speed by 14% and the introduction of carpeting reduced it by 18%. Consequently, they recommended using larger diameter wheels and not specifying carpets to reduce forces required for materials handling. Vehicle weight (empty 52.8 kg versus 81.8 kg) had no significant effect on vehicle movement (speed). For the evaluation of equipment, discomfort analyses have been shown to be advantageous (Corlett and Bishop, 1976; Bhatnager et al., 1985; Sthoenmarklin and Marras, 1989). Worker surveys through questionnaires are often used to evaluate the design characteristics, physical fatigue and postural discomfort. This input would be useful in the modification of an existing equipment design through the application of ergonomics principles and data. The objectives of this study are to: (1) make an ergonomics evaluation of a hospital meal cart in terms of: (a) identification of ergonomic, design and other problems, (b) conduct a worker survey to obtain operator ratings of design and other factors and postural discomfort rating and (c) determine initial push, pull and turning forces, and (2) recommend modifications to the conventional hospital meal cart for the purpose of redesigning a hospital meal cart based on ergonomic/anthropometric principles and data.
2. Identification of ergonomic, design and other problems of the conventional hospital meal cart Through direct observation and one-to-one interviews with experienced operators and supervisors, relevant information on task performance, equipment, and
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Fig. 1. Front and side elevations of the conventional (four wheel) hospital meal cart. All dimensions in centimeters.
working posture was obtained (Das and Sengupta, 1996). The ergonomic and other design problems associated with the conventional, four wheel, hospital meal cart were identified in terms of the: (1) maneuverability (pushing, pulling and turning) of the cart, (2) cart handle height and placement, (3) vision or eye height above the cart, (4) opening and closing of cart doors, (5) protection of the cart against damage, (6) ease of stopping the cart, (7) size of meal tray, (8) provision of hot meals, and (9) pushing versus pulling the cart. Fig. 1 shows the front and side elevations of the fourwheel conventional meal cart. A systematic evaluation of the cart is made in terms of the ergonomic design and other problems stated above. 1. Maneuverability (pushing, pulling and turning) of the cart: The front (two) wheels of the conventional meal cart do not swivel, only the two back wheels can swivel. This does not allow general maneuverability of the cart and, in particular, contributes to an increased turning radius. The additional force requirement to maneuver the cart can be a source of twisting and turning injuries especially in the low back region. 2. Cart handle height and placement: The horizontal, cylindrical cart handle is placed on both ends of the cart at a height of 121 cm from the floor (Fig. 1). The placement of the handle does not allow a comfortable posture for a small (5th percentile female) or a large (95th percentile male) person. Furthermore, adequate spacing is not provided between the handle and the cart surface, especially for a person with a large or a thick palm. The material currently used for the handle is stainless steel, which is strong but not comfortable to the hand especially in the winter time. 3. Vision or eye height above the cart: The width and the length of the meal cart do not appear to cause any vision problem while moving the cart. However, the present height of 152 cm from the floor level (Fig. 1) exceeds the permissible eye height of a small person (5th percentile female). Thus a small operator must
4.
5.
6.
7.
8.
9.
stretch or assume an awkward posture to see above the cart. This is a potential source of a traffic accident hazard. Opening and closing of cart doors: The front two doors of the cart can be opened and closed easily. The doors move in and out on a hinge and while they are open, they stay inside (on the side) of the cart. This appears to be a very satisfactory design since the doors are not in the way while handling the meal trays. Protection of the cart against damage: The meal cart’s bumper is made of hard black rubber on a fender and provides a 5 cm insulation between the fender and the cart. This appears to be satisfactory to withstand any bumps or bangs that the hospital meal carts may encounter. Ease of stopping the cart: There is no provision of emergency brakes to stop the cart in the case of an emergency. A hospital is a busy place and people are always on the move. Consequently, the operator has to make panic stops. This may involve considerable energy on the part of the operator especially when the cart is loaded with full (food) trays. This is a potential source of back injury to the operator. Failure to stop immediately may cause an injury to the person in front of the cart. Furthermore, there is no parking brake when the cart is not attended by the operator. Size of meal tray: The size of the meal tray is 1939 cm2 (Fig. 2). There was considerable unutilized space on the tray. It is possible to reduce the size of the tray without causing any inconvenience to the patient. This will obviously reduce the size of the meal cart. Provision of hot meals: To keep the meal and soup hot, stainless steel covers are used. The metallic covers have poor heat insulation properties compared to insulated plastic covers. Furthermore, metallic covers are heavier than the insulated plastic covers. Pushing versus pulling the cart: Presently, the cart is moved by one operator or sometimes by two operators. They pull the cart using one hand. This is an awkward posture to move the cart. This is a source of neck and back injury and puts considerable
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stress on the trunk. The cart ought to be pushed, using both hands. This posture will minimize health hazards especially on the neck, back and trunk. 3. Hospital meal cart worker survey The hospital meal cart users are asked to participate in the ergonomics study which has been designed to measure, through the use of a questionnaire, the effect of the meal cart (four wheel) design and other factors on employee comfort, health and ease of use. The user input will be useful and supportive to the study being undertaken. The objectives of the survey were to document or record: (1) the general operator rating of various meal cart design and other factors, (2) the current level of physical fatigue induced by the job to the operators, and (3) the changes in postural discomfort in specific anatomical regions.
Fig. 2. Meal tray arrangement of the conventional (four wheel) hospital meal cart. All dimensions in centimeters.
3.1. Method For the purpose of this study, an informed consent and two separate questionnaires were developed and approved by the hospital administration. A total of 24 operators: 11 male and 13 female were surveyed in this study. The two questionnaires: (1) hospital meal cart worker survey I had 11 questions on a Likert type fivepoint scale that dealt with design and other factors (see Appendix A), and (2) hospital meal cart worker survey II that dealt with postural discomfort in specific body regions on both sides of the body (Corlett et al., 1982). The two questionnaires were administered near the end of the shift. 3.2. Hospital meal cart worker survey I Several ergonomics design and operational problems that resulted in postural discomfort were identified from a conventional hospital meal cart worker survey. Considerable pushing and pulling forces are involved in moving the hospital meal carts. Also, bending and lifting are required in handling the meal trays. These factors were identified in the survey along with other equipment design problems including: cart maneuverability, handle height and placement, vision or eye height above the cart, opening and closing of cart doors, and ease of stopping the cart. For the analysis of non-interval scale data, the nonparametric Mann–Whitney test was performed for the male and female responses to the design and other factors. The operator scores obtained for the design and other factors were analyzed separately for male and female. For each factor, median and interquartile range scores were calculated (Table 1). For males, the median score for ‘‘stopping force’’ and ‘‘parking brake’’ was 3.0. Stated otherwise, the stopping
Table 1 Operator scores obtained for the design and other factors of the conventional hospital meal cart and a Mann–Whitney test for the male and female responses to the factors Design and
Male
Female
other factors
Median
Interquartile range
Median
Interquartile range
p-value
1. Cart in motion 2. Turning cart 3. Seeing over cart 4. Handling trays 5. Handling doors 6. Handle height (pushing) 7. Handle height (pulling) 8. Stopping force 9. Emergency hand brake 10. Parking brake 11. Tiredness
2.0 2.0 2.0 2.0 2.0 2.0 2.0 3.0 2.0 3.0 2.5
1.0 2.0 2.0 1.5 1.0 0.0 0.5 1.5 0.5 1.5 1.0
3.0 2.0 3.0 2.0 2.0 2.0 2.0 3.0 3.0 4.0 3.0
1.0 1.0 2.0 1.5 2.0 1.5 2.0 1.5 2.0 1.5 1.0
0.01** 0.24 0.05* 0.71 0.50 0.18 0.31 0.44 0.11 0.33 0.01**
Note: * Significant (po0:05), ** Highly significant (po0:01).
Mann–Whitney test:
B. Das et al. / Applied Ergonomics 33 (2002) 309–318
force requirement and the need for the parking brake were of concern to the male operator. The median score for the tiredness factor was 2.5. In other words, the male operators felt some tiredness at the end of the work shift. The other factors had median scores of 2.0. Consequently, the extent of concern for the factors was less. For females, the median scores were higher for several factors than the scores obtained for the male operators (Table 1). The results are expected, since female operators, in general, have two-thirds of the strength of male operators. The female median scores for ‘‘parking brake’’ was the highest or 4.0. For the ‘‘cart in motion’’, ‘‘seeing over the cart’’, ‘‘stopping force’’ and ‘‘emergency hand brake’’, the median score was 3.0. Consequently, the female operators encountered difficulty in dealing with these factors. For the ‘‘tiredness factor’’, the median score was also 3.0. Consequently, the female operators felt more tired at the end of the work shift compared to the male operators (median score, 2.5). The other factors had a median score of 2.0. So these factors were of less concern to the operators. The Mann–Whitney test, (Table 1), revealed that there was significant (po0:05) difference between male and female operators in the perception of the factor ‘‘seeing over the cart’’. Stated otherwise, the female operators’ perception of ‘‘seeing over the cart’’ was significantly greater than the male operators. Highly significant (po0:01) difference between male and female operators was found in terms of their perception of the factors ‘‘cart in motion’’ and ‘‘tiredness’’ at the end of the work shift. The female operators found it difficult in getting the ‘‘cart in motion’’ and they were more ‘‘tired’’, when compared to the male operators.
313
3.3. Hospital meal cart worker survey II The postural discomfort questionnaires were administered at the end of the work shift. The questionnaire provides a diagram of the human body which has been divided into 22 body regions equally split between the right and left half (1) shoulder, (2) arm, (3) elbow and forearm, (4) wrist and hand, (5) neck, (6) back, (7) lower back, (8) buttocks, (9) hip and thigh, (10) knee and leg, and (11) ankle and foot, for left and right sides on a 8point scale: 0, no discomfort to 7, extreme discomfort, left to right) (Corlett et al., 1982). The data were analyzed separately for the male and female. The median and interquartile range of discomfort scale rating scores for the body regions for the male and female operators are presented in Table 2. For the male operator, the back, lower back and ankle and foot in the left region had postural discomfort scores of 1.5, 1.0 and 1.0, respectively. Stated otherwise the male operators felt postural discomfort in these areas more than the other regions. In the right region, the postural discomfort score in the lower back was 1.0. Apparently, the male operators did not feel any postural discomfort in other regions. The female operators had higher postural discomfort scores than male operators in several body regions. In the left region, the postural discomfort scores for the back, lower back, knee and leg and ankle and foot were 4.0, 4.0, 1.0 and 2.0, respectively. The interquartile range values for the stated body regions were found to be high. The results revealed that the female operators encountered considerable discomfort in the back and lower back. For the right region, the postural discomfort scores for the back, lower back, knee and leg were 4.0,
Table 2 Discomfort scale scores for the body regions of the conventional hospital meal cart and a Mann–Whitney test for the male and female responses to the body region Body region
Male
Female
Left
Right
Mann-Witney test
Left
p-value
Right
Median
Interquartile range
Median
Interquartile range
Median
Interquartile range
Median
Interquartile range
Left
right
Shoulder Arm Elbow and forearm Wrist and hand
0.0 0.0 0.0 0.0
1.5 0.0 0.0 0.0
0.0 0.0 0.0 0.0
2.5 0.0 0.0 0.0
0.0 0.0 0.0 0.0
3.5 2.5 2.0 2.0
1.0 0.0 0.0 0.0
4.0 2.5 2.0 3.5
0.32 0.06 0.16 0.35
0.56 0.03* 0.20 0.17
Neck Back Lower back Buttocks
0.0 1.5 1.0 0.0
0.0 2.0 2.0 0.0
0.0 0.5 1.0 0.0
0.0 2.0 2.0 0.0
0.0 4.0 4.0 0.0
5.0 5.0 3.5 0.0
0.0 4.0 4.0 0.0
5.0 5.5 3.5 0.5
0.19 0.25 0.03* 0.31
0.11 0.06 0.03* 0.31
Hip and thigh Knee and leg Ankle and foot
0.0 0.0 1.0
0.0 0.0 1.5
0.0 0.0 0.5
0.0 0.0 1.0
0.0 1.0 2.0
1.5 3.5 4.5
0.0 1.0 0.0
1.5 3.5 4.0
0.23 0.16 0.54
0.15 0.20 0.59
Note: * Significant (po0.05), ** Highly significant (po0.01).
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4.0 and 1.0, respectively. For the right region, the maximum postural discomfort was felt in the back and lower back. Similar results were found for the left region. The Mann-Whitney test results (Table 2) revealed that there was a significant difference in the responses to postural discomfort between the male and female operators in terms of right arm and left and right lower back. Stated otherwise, the female operators felt significantly greater discomfort than the male operators in the right arm, and left and right lower back. The postural discomfort between male and female operators in the left arm almost reached a significant level (po0:06). 4. Determination of weights and forces of hospital meal cart For the purpose of this study, it was necessary to weigh the conventional meal cart. The cart was weighed by employing a hanging weighing scale. The chains and ropes were used to lift the cart by means of an electric hoist. The weight of the empty (without meal trays) conventional meal cart was 186.0 kg (Table 3). Actual weights were used for the crockery, cutlery and insulating covers. Table 3 summarizes the weight of the cart in terms of the meal trays with food. The total weight of the conventional meal cart with 24 meal trays and food was 320.4 kg. The push, pull and turning (push) forces of the conventional hospital meal cart were determined by using a hand dynamometer. For determining the push force, the dynamometer was placed approximately at the (horizontal) handle height of the conventional cart. The dynamometer was placed at the middle of the cart width. For pulling force determination, an attachment (with rope) was made from the handles of the cart to the dynamometer. The height of the pull force was basically the same as the push force. The turning force was applied at the same height and manner as the pushing force. The dynamometer was placed close to the (front) edge of the cart. The turning (right or left) forces represented the forces while the cart was in forward motion or mode.
Table 3 Weight (kg) of conventional hospital meal cart: Empty and with 24 meal trays and food Items
Empty
With 24 trays and food
Weight of meal cart Weight of 24 meal trays at the rate of 3.6 kg/tray Weight of food on 24 meal trays at the rate of 2.0 kg/tray Total weight of cart
186.0 —
186.0 86.4
— 186.0
48.0 320.4
The push, pull and turning forces (initial) on tile and carpet floors were determined for the conventional meal cart (empty and with 24 meal trays and food). Table 4 presents the summary results of the push, pull and turning forces (initial, kg) of the conventional meal cart. The higher push force (empty, 7.3 kg) of the carpet floor could be attributed to the higher coefficient of friction of the carpet compared to the tile (empty, 2.7 kg) floor. The pull forces were basically the same as the push forces in all cases. The high turning push forces (empty, 12.5 and 16.8 kg) can be attributed to the provision of only two rotating wheels in the back and two fixed wheels in the front of the conventional meal cart. As expected, the force values of the conventional meal cart with 24 meal trays and food were considerably higher than the corresponding force values for the empty cart. Similar observations were made with regard to flooring and push, pull and turning forces. The maximum acceptable capabilities of initial twohanded push and pull forces for a female operator had ranged from 17.5 (5th percentile) to 32.0 kg (50th percentile) depending on the percentile value and frequency of movement (Snook and Ciriello, 1991). For the purpose of this study, the 5th percentile values were calculated on the basis of the data and methodology provided by Snook and Ciriello (1991). The acceptable initial push force of 17.5 kg for the 5th percentile female for one push in 5 min, is usually performed by the operators. Thus the actual push forces of 20.2 and 22.7 kg on tile and carpet floors, respectively (Table 4), exceed the acceptable initial push force (Snook and Ciriello, 1991). The interpretation of the results should be made with caution. In this study, the operators feet were stationary, while executing the turning push force. In the study performed by Snook and Ciriello (1991) the operator’s feet were not stationary. The pushing and pulling tasks were simulated on a specially constructed treadmill in their study. Earlier, it was pointed out that the operators in moving the hospital meal cart and serving meals to the patients, performed other tasks (when they are not moving cart or serving meals) during the work shift. Thus, the operators did not perform the task of moving the meal carts on a sustained basis. Snook and Ciriello
Table 4 Push, pull and turning (push) forces (initial, kg) on tile and carpet floors for the conventional meal cart: Empty, without meal trays and with 24 meal trays and food Forces
Push Pull Turning (push)
Empty
With 24 meal trays and food
Tile
Carpet
Tile
Carpet
2.7 2.5 12.5
7.3 7.2 16.8
6.3 6.2 20.2
12.2 12.1 22.7
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(1991) reported the mean initial and sustained push forces for males as 37.6 and 22.3 kg, respectively, and the corresponding values for females was 23.3 and 15.0 kg, respectively. The mean initial and sustained pull forces for males are 36.4 and 26.2 kg, respectively, and the corresponding values for females are 25.0 and 16.5 kg, respectively. Thus, sustained push or pull forces are considerably less than initial push or pull forces. The sustained push or pull forces were not measured in this study. Although initial forces are important from a biomechanical viewpoint, sustained forces have physiological implications. At present, the conventional meal cart is moved by one operator or sometimes by two operators. The operators pull the cart using one hand. This can be a source of neck and back injury and cause considerable stress on the back. 5. Redesigned hospital meal cart The proposed design changes based on ergonomics principles and data are stated below: 1. Maneuverability of the cart. The redesigned hospital meal cart (Fig. 3) would be constructed with durable plastic. This will reduce weight and thus enhance maneuverability. Additionally, it will enhance aesthetic value. It is advisable to have four swivel wheels at each corner of the cart with the addition of two fixed wheels in the middle of the cart (Fig. 3). This recommendation is made with a view that in the future, hospital meal carts can be constructed with 24 and 36 meal trays. This would not only reduce the force required to turn the cart but also decrease turning radius. Presumably the bearing used in the meal cart’s wheel is a sleeve bearing. If it is changed to ball bearing, further reduction in initial push force is possible. Large-diameter (20 cm) cart wheel (4 cm width) made of hard rubber tires (Drury et al., 1975) should be provided to facilitate pushing the cart.
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Regular maintenance of cart wheels can also reduce pushing forces. 2. Cart handle height and placement. To provide comfortable posture, strength capability and vision requirement for female and male operators, the handle height should be placed to accommodate both a small (5th percentile female) and a large (95th percentile male) person. The handle height is based on a height of 5 cm below the elbow height (5th percentile females) (standing) elbow height= 99.0 5.0=94 cm and 95th percentile male (standing) elbow height=120.3 5.0=115.3 cm (Das and Grady, 1983; Das and Sengupta, 1996). A comfortable posture while pushing the hospital meal cart will reduce or minimize back problems. The proposed handle height between 94 and 115.3 cm is in close agreement with the recommendation of Ayoub and McDaniel (1974) for the optimal height for a handle to be pushed or pulled between 91 and 114 cm above the floor. The two handles should be placed 47.8 cm apart, based on the average value between 95th percentile male (51.7 cm) and female (43.8 cm) elbowto-elbow widths. It should be recognized that operators accommodated vertically would cause a decrease in the range of operators accommodated horizontally or with respect to shoulder/elbow width. Since both the above criteria cannot be satisfied at the same time, the former option is selected considering the force/strength requirement in cart movement by operators with different statures. The handle shape can be cylindrical and the diameter of the handle based on hand anthropometry is recommended at 4.0 cm (for power grip, Eastment Kodak, 1983). The handle material can be made of hard rubber or synthetic material. Since the cart is often moved by two operators, two handles could be provided on the sides of the cart. It is possible to provide a 71 bias to the handle from the vertical away from the cart, so that the orientation of the handle is in line with the forearm. This will minimize stress in the hand.
Fig. 3. Front and side elevations of the redesigned hospital meal cart. All dimensions in centimeters.
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3. Vision above the cart. A worker survey questionnaire revealed that about half of the operators had moderate to extreme difficulty in seeing over the cart. The cart height should be reduced to 143.6 cm or less based on the 5th percentile female, eye height (slump posture). This would allow proper vision and promote an improved posture and minimize traffic hazards. 4. Ease of stopping the cart. It is desirable to install emergency brakes for panic stops especially when the cart is loaded with full meal trays. An emergency hand brake can be installed between the cart handles for easy access. 5. Provision of hot meals. It is possible to provide individually (electrically) heated plates for the soup and the main meal (cost of individually heated plates about $150 US and the weight of each tray fully loaded with food, dishes etc. about 4 kg). This is an innovative idea for serving hot meals to the patients of the hospital. By using insulated plastic covers as opposed to conventional metallic covers, improved heat insulation would be provided. Furthermore, it would reduce the weight of the covers. The provision of air tight or solid transparent plastic doors will conserve heat energy and keep the meals hot and improve the aesthetic value. 6. Size of meal tray. The size of the meal tray should be reduced to 33 47 cm (Fig. 4). A compact meal tray will prevent the crockery and cutlery from sliding on the tray. 7. Pushing Versus pulling the cart. To realize optimum benefit the cart must be pushed using both hands.
6. Conclusions The following conclusions and recommendations are reached from this investigation:
Fig. 4. Meal tray arrangement of the redesigned hospital meal cart. All dimensions in centimeters.
1. The operators (especially female) encountered difficulty in setting the cart in motion, seeing over the cart and stopping the cart while in motion. The subjects agreed or strongly agreed to the usefulness of an emergency hand brake. Some (female) subjects felt tired to a large or great extent at the end of the work shift. 2. There was a significant difference between male and female operators in their perception of the factors ‘‘cart in motion’’, ‘‘seeing over the cart’’ and ‘‘tiredness’’. 3. The male operators expressed postural discomfort in the back, lower back and ankle and foot in the left region and lower back in the right region. The female operators encountered postural discomfort in the back, lower back and knee and leg in both the left and right regions and ankle and foot only in the left region. The female operators had generally higher postural discomfort than the male operators. 4. There was a significant difference in postural discomfort between the male and female operators in terms of right arm and left and right lower back. 5. The weights of the conventional meal carts, empty as well as with 24 meal trays and food were determined. The push, pull and turning (push) forces (initial) on tile and carpet floors were determined for the conventional cart (empty and with 24 meal trays and food). Based on the maximum acceptable capabilities, the conventional meal cart would exceed the initial turning push force requirement of 5th percentile female. 6. The use of plastic material would reduce the weight of the hospital meal cart. This will reduce initial push/pull force requirements and enhance maneuverability. 7. The provision of four swivel wheels at each corner of the cart along with two fixed wheels in the middle of the cart would reduce the turning force and decrease the turning radius. This is desirable for meal carts with 24 meal trays and especially with 36 meal trays. Further reduction in initial push force is possible by changing the conventional sleeve bearing to ball bearing for the wheels. Large (20 cm) diameter cart wheel (4 cm width) made of hard rubber tire should be provided to facilitate pushing the cart and regular maintenance will reduce pushing forces. 8. The proposed cart would meet the initial push force requirements stated in sources (1) and (2). 9. The cart handles should be placed between 94 and 115.3 cm from the floor and the two handles should be placed 47.8 cm apart. A cart handle diameter of 4.0 cm is recommended. 10. The height of the cart should be reduced to 143.6 cm or less (preferably 140 cm) from the floor to provide
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11. 12.
13. 14. 15.
16.
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better vision especially for the small person (5th percentile female). Individually (electrically) heated plates for the soup and main meal should be installed. Thick air-tight transparent plastic doors should be provided. This will conserve heat energy and keep the meals hot and improve the aesthetic value. An emergency hand brake should be added and located between the cart handles for easy access. The size of the meal tray should be reduced from 38 51 to 33 47 cm. The cart must be pushed using both hands to obtain optimum benefit. The meal trays on the lower level of the cart should be handled using a kinetic lift to minimize lower back pain. The operators should be trained to follow the proper work method.
7. Incorporation of the design changes in the new version of the hospital meal cart The proposed changes based on ergonomic/anthropometric principles and data were adopted by the manufacturer in the new version of the hospital meal cart. The new model incorporated design changes with regard to air tight or solid transparent plastic doors, vertical handles, 2 swivel locking and 2 stationary casters (20 cm diameter 4 cm width), individually heated plates for soup and main meals, among others. The incorporation of individually (electrically) heated plates for soup and main meals is considered innovative and a breakthrough in the design of hospital meal carts. Some of the features of the advanced meal systems (hospital meal cart) from Aladdin are highlighted below. Fig. 5 shows advanced meal systems from Aladdin Tem-Rite (R) LLC cart with tray. Meals are assembled cold, using advance prepared foods. Assembled trays are placed in carts on specially designated conduction heating elements. Hospital meal carts are then held in individual roll-in or centralized walk-in refrigerator. 36 min before meal service, meals return to serving temperatures within the refrigerator. Cart tow hitches for 16–20 shelf carts are available. Hospital meal carts are available in 16, 20 and 24 shelf carts for central and de-central applications. Face mounted high-density polymer tray supports and bumpers are provided. Heavy duty sealed non-marking casters (20 cm diameter 4 cm width) are provided. Face mounted heating elements allow for easy replacements. Fig. 5 shows a Temp-Rite II Excel C700 Series (C720) Rethermalization cart and meal tray. The physical characteristic dimensions of the Temp-RiteII cart (C720) are: weight=136.1 kg, height=142.5 cm, width=71.1 cm, and length=73.5 cm. The meal tray
Fig. 5. Advanced meal system—Aladdin Temp-Rite II Excel C700 Services (C720) (Hospital meal cart with tray).
dimensions are: height=2.9 cm, width=32.3 cm, and length=54.4 cm. It should be noted that some of the ergonomic recommendations made in this study were not incorporated in the New C700 Series, due to cost or marketing reasons. The cost or marketing implications of the ergonomics recommendations were not investigated in this study. The cart height for C724 (24 shelves or trays) of 163.3 cm, exceeds the recommended cart height of 143.6 cm or less. The New C700 Series (for 16, 20 and 24 shelves or trays) uses 2 swivel locking and 2 stationary wheels as opposed to the recommended 4 swivel wheels at each cart corner with 2 stationary wheels (casters) in the middle of the cart, especially desirable for 24 and 36 shelves. The recommended hand emergency brake was not implemented.
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8. Concluding remarks It will be desirable to conduct a study to evaluate the new model (New C700 Series Advanced Meal Systems (AMS) cart, Aladdin), especially from an ergonomics viewpoint. This will allow further improvements in the future.
Strongly Agree Neutral Disagree Agree 1 2 3 4 The 5-point scale above was placed under and 10.
Strongly disagree 5 questions 9
11. The extent to which I am tired at the end of the work shift is:
Appendix A. Hospital meal cart survey I The following questions have been developed to evaluate a number of factors associated with your four-wheel hospital meal cart. We would ask you to take a few moments and complete the questionnaire near the end of the work shift. For each question please circle the number which most closely represents your opinion about the factor under review. The results of this questionnaire will be kept confidential. 1. 2. 3. 4. 5.
Getting the four-wheel cart in motion, I have: Turning the four-wheel cart, I have: Seeing over the four-wheel cart, I have: Placing and removing the trays, I have: Opening and closing the doors, I have:
No Slight Moderate Great difficulty difficulty difficulty difficulty 1 2 3 4 The 5-point scale above was placed under 1–5.
Extreme difficulty 5 questions
6. I find the four-wheel cart’s handle height while pushing to be: 7. I find the four-wheeled meal cart’s handle height while pulling to be:
Excellent Good Fair Poor Unacceptable 1 2 3 4 5 The 5-Point scale was placed under questions 6 and 7. 8. I find the force that I must use to bring the four wheeled meal cart to a stop once it is in motion to be:
Completely acceptable Good Fair Poor Unacceptable 1 2 3 4 5
9. An emergency brake for the panic stops would be useful: 10. A parking brake on the wheels would be useful:
None 1
Little 2
Fair 3
Large 4
Great 5
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