Ergonomic Design of the Snow Shovel
Brad Coffiner, 11/25/97
In spite of increased automation (i.e. snow blowers), there is still a need for muscular power and manual tools, such as shovels, in the task of snow removal. Some of the frequently used tools require considerable muscle forces and stressful working postures (Degani et al., 1993). The musculoskeletal load on a person shoveling often may be high and may result, in the short term, in muscle fatigue and reduced capacity for work. In the long term, the consequences may be cumulative and result in musculoskeletal trauma disorders and chronic muscle pain (Mital et al., 1993).
The task of shoveling was first examined scientifically as early as 1898 (Taylor, 1913) and has been studied in many laboratory and field studies. A review of the literature is reported by Freivalds (1986a). The main task has been the efficiency and energy expenditure of shoveling as a function of work parameters such as shoveling rate and size of the handled load. An example is a modern study made by GrandJean (1988), who ranks shoveling among the least efficient working tasks, with a total efficiency of 6% for shoveling in upright posture.
The ergonomic and biomechanical effects of shoveling, and especially shovel design, are studied in much less detail (Degani et al., 1993). But Freivalds (1986b) describes a study on the effects of shovel design parameters such as shaft angle, size and shape of the blade and the hollow, and the closed-back design. The results indicated that the compression loads when handling heavy loaded tools under low-lift conditions could prove to be very stressful for the operators.
A modified shovel design with two perpendicular shafts was studied by Delgani et al. (1993). The results indicate a significant reduction in EMG values of the lumbar paraspinal muscles and a consistent reduction in perceived exertion ratings, when using the modified tool.
Additionally, P.A. Hansson and K. Oberg (1996) completed an analysis of biomechanical load when using differently designed shovels to move material from the ground to a higher vertical level. Their main purpose, consistent with the intent of this article, was to find tool designs that decrease loads in normal working conditions. The effects of the shaft mounting angle and length were analyzed. The effects of using a tool with a higher and angled shaft were also analyzed, as were the effects of varying operator anthropometry.
When performing working tasks including heavy lifts, for example when handling heavy snow with a shovel, the L5/S1 disc has been identified as the weakest link in the body segment chain (Ayoub and Mital, 1989). The most severe injuries and pain are likely to occur in this back region (Delgani et al., 1993). Therefore, the reported study was focused on the shear and compression forces at the L5/S1 disc and on the load at the lower back muscles.
In most situations when working with a shovel, the empty load is pushed into the material that is to be moved, for example snow, and then lifted in order to place the material on a higher level and/or to move the material also in the horizontal plane. The hard part of the job is when the blade is loaded and especially if the handled material is heavy (Hansson & Oberg, 1996).
Handling heavy material with a shovel results in disc compression and shear forces that may be harmful to the operator. The normally repetitive nature of the work compounds the problem. A shovel with a longer shaft than normal decreases the operator's trunk flexion when beginning to lift the shovel from the ground. The maximum shear forces at the spine are also decreased. The lateral moment loading the trunk is, however, increased and the maximum force at the right erector spinae muscle is also increased. Shovels with the shaft angled decrease the resulting maximum spine compression and shear forces when lifting the loaded shovel from the ground. When lifting the shovel, the load on the spine and on the back muscles is much greater for a tall person and heavy operator when compared with the load on a short and light person (Hansson & Oberg, 1996).
The analysis of the influence of the tool design variables on the biomechanical load is very useful when attempting to invent a practical solution to overcome situations resulting in biomechanical load. But perhaps the most important factor needed to be considered when deciding tool design is that the tool must be well suited for the specific working operation for which it is intended. Therefore, the goal is to invent a shovel that is to be specifically used for shoveling snow.
Shoveling large amounts of snow can significantly boost heart rate and blood pressure (Healthwatch, 1997). Shoveling snow puts a lot of strain on the body. The area most vulnerable to injury is the lower back. Shoveling can cause disc compression and shear forces that are harmful to the operator (Hansson & Oberg, 1996). This task is also a repetitive motion, which increases the risk for injury. (St. Lukes - Shoveling Snow Safety, 1997). However, shoveling snow is also a sound aerobic activity. Liz Schorn, a physical therapist and orthopedic manual therapist with Physical Therapy Orthopedic Specialists Inc., stated that shoveling snow can be beneficial to the user if people warm up their hamstrings, calves and upper back before shoveling. Then they should go for an upright, erect stance while shoveling, with feet wide apart. Afterward, they should cool down with the same stretches performed in the warm-up (Fukushima, 1997).
Beyond paying attention to posture and preparation, it's important to have the right type of implement for a positive shoveling experience. Therefore, I present the ergonomic snow shovel:
The shovel blade will be plastic. Why? Well, there are three choices of materials for shovels: plastic, aluminum, or steel. Steel shovels are the most durable, but they're the heaviest. Aluminum shovels are lighter and softer, though some have steel-reinforced edges which add weight. Plastic (or poly) shovels are lightweight, but abrade rapidly (Fukushima, 1997). Plastic is the optimum material to use because the shovel blade can bend repeatedly with no damage. In the case of aluminum, forces strong enough to bend it will quickly break it. In addition, plastic is the lightest material. The lighter the shovel is, the easier it will be to lift. In contrast, the toughest, most expensive shovels, the hefty ones with steel blades that can cut through ice, look impressive but can be tiring to use (Dawson, 1997).
The dimensions of the shovel blade will vary based on the anthropometric variability of possible users. For a taller and heavier person, a 18" x 16" blade should be used. 18" blades take up about 3/4 the width of most sidewalks and are optimum for maximizing the load while taking into account the limitations of the human body (Carter, 1997). The shaft of the shovel should be 52" with a 1 1/4" handle (see Figure 2). For a shorter and lighter person, a 16 1/2" x 14 1/2" blade is best. The shaft should be 42" and a 1 1/2" handle (Rugg Companies: Backsaver Tools, 1997). As stated earlier, the relatively long length of the shaft will decrease the operator's trunk flexion when beginning to lift the shovel from the ground. In addition, the maximum shear forces at the spine are decreased. However, the lateral moment loading the trunk and the maximum force at the right erector spinae muscle is increased (Hansson & Oberg, 1996). As a result, the shaft length of the ergonomic snow shovel will not be fixed. The shaft will be slide adjustable so that the user can maximize the length to fit his height and weight, if it is not already compatible with the shovel. This will allow the user to gain more leverage, and reduce spinal compression when shoveling.
The ergonomically correct shovel will also have an angular shaft to keep the body more upright and minimize stress on the back when shoveling (Carter, 1997). Shovels with the shaft angled decrease the resulting maximum spine compression and shear forces when lifting the loaded shovel from the ground. The shaft should be angled at 60 degrees towards the bottom of the shaft, and at 35 degrees for the upper portion of the shaft. For each shovel, the bend in the shaft should occur at the 2/3 mark of the shaft when measuring from the top of the handle (see Figure 1).
The handles of the shovels will allow the user to grip the handle with mittens. Cushioned "D" grip handles provide the best grip and comfort. In addition, the handles will be made of fiberglass. Fiberglass handles are up to three times stronger than wood handles for the most demanding shoveling. And because they are water-proof, fiberglass handles won't splinter, warp, or dry rot (Ames Lawn and Garden, 1997).
With a shovel like this, the user can thankfully proclaim "Who needs a snowblower?" Of course, snowblowers might make the job of clearing snow easier, but they are expensive, noisy, smelly, and can cause numbness in the hands (Fukushima, 1997). The ergonomic shovel will allow the operator to breathe clean air and experience healthy physical exercise. The chances for injury will be reduced as will the snow in the driveways and on the sidewalks of America.
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Fukushima, Rhoda. November 15, 1997. Clear the path: Before you go after the snow, follow a few hints to baby your back. Pioneer Planet.
Grandjean, E. 1988. Fitting the Task to the Man. New York, N.Y.: Taylor & Francis.
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