Civil Engineering Reference
In-Depth Information
30.3.2 Causes
Solutions of Falls
Falls can occur from slips (unexpected horizontal foot movement), trips (restriction of foot movement)
and stepping-on-air (unexpected vertical foot movement). In addition, people can fall as a result of
alcohol or drug use, fainting, and so on.
/
30.3.2.1 Slips
Slips occur primarily during foot push off and heel strike. During pushoff, the person falls forward (less
common and less dangerous); in addition, during pushoff, most of the weight has already been trans-
ferred to the other foot.
During heel strike, the person falls backward.
Slips also can occur when the “ground” slopes (front to back or side to side). Examples are ramps and
ladder rungs. Slips also can occur, with stationary feet, during pushing and pulling, but there does not
tend to be a fall and injury.
During a slip, a lubricant (water, oil, grease, dust, ice, snow) usually is present, either on the surface or
on the shoe heel. Table 30.2 has some coefficients of friction. In the special outdoors circumstances of
snow and ice, slipping can be common. The most danger occurs when the ice is “wet” (i.e., close to
the freezing point). Chang et al. (2001) give 0.67 for the static coefficient of friction for shoes on ice
at
40
8
C, but 0.01 as the dynamic coefficient at
1
8
C (when there is a thin film of water).
2
2
Table 30.3 summarizes how to reduce slips.
30.3.2.2 Trips
Trips occur during foot swing. As the foot swings forward, it hits an obstacle and the person falls forward;
the problem is lack of leg movement. Usually there is a visual problem. Indoor trips tend to be from
obstacles on the floor. Outdoor trips often occur from uneven surfaces (e.g., walkways, parking lots)
that the person expects to be even.
30.3.2.3 Stepping-on-air
Unexpected vertical movement can occur on stair steps when the distance between steps is not equal;
when there is a hole in the ground; or when there is no ground (e.g., “cliff,” edge of scaffold, unexpected
step, step on spiral stairs, unexpected curb or ramp). “Single steps” (small changes in elevation such as
curbs or one-step changes in floor level) are dangerous. Steps descending from large trucks and off-road
vehicles can present problems; for such vehicles use the “three-contact rule” (at least three limbs should
be in contact with steps or handles at all times). On steps, the fall usually occurs when descending; the fall
can be for a considerable distance.
TABLE 30.2 Coefficients of Friction of Floors and Shoes.
Floor
Coefficient
of Friction
Floors
Clean
Soiled
Shoe: Soles
1.0
Soft rubber pad
0.8
0.6
Rubber-cork
0.8
End grain wood
0.75
0.55
U.S. Army
/
Air Force
standard
0.7
Concrete, rough finish
0.7
0.5
Rubber-crepe
0.65
Working decorative, dry
0.6
0.4
Neoprene
0.5
Working decorative,
soiled
0.5
0.3
Leather
0.4
Steel
Shoes: Heels
0.7
0.5
Neoprene
0.65
0.55
Nylon
Source: From Kroemer, K. 1974. Applied Ergonomics, 5(2):94-102. With permission.
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