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.
References
Ames Lawn and Garden. 1997. World Wide Web.
Ayoub, M.M. and A. Mital. 1989. Manual Materials Handling. London,
England: Taylor & Francis.
Carter, Tom. 1996. Dig through snow shovels to find one right for you. Lexington
Herald-Leader.
Dawson, Lou. 1997. Shovel. World Wide Web.
Degani, A., S.S. Asfour, S.M. Waly and J.G. Koshy. 1993. A comparative study
of two shovel designs. Applied Ergonomics 24(5): 306-312.
Freivalds, A. 1986a. The ergonomics of shoveling and shoveling design -
A review of the literature. Ergonomics 29(1): 3-18.
Freivalds, A. 1986b. The ergonomics of shoveling and shoveling design -
A review of the literature. Ergonomics 29(1): 19-30.
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.
Hansson, P-A and K. Oberg. 1996. Analysis of Biomechanical Load when Shoveling.
Journal of Agricultural Safety and Health 127-142.
HealthWatch: Snow Shoveling Hazards. 1997. World Wide Web.
Mital, A., A.S. Nicholson and M.M. Ayoub. 1993. A Guide to Manual Materials
Handling. London, England: Taylor & Francis.
Rugg Companies: Backsaver Tools. 1997. World Wide Web.
St. Luke's - Shoveling Snow Safety. 1997. World Wide Web.
Taylor, F.W. 1913. The Principles of Scientific Management. New York,
N.Y.: Harper & Bro.