Civil Engineering Reference
In-Depth Information
There are several epidemiological studies which have focused on highly repetitive lifting and comp-
lement the findings of biomechanical studies (Chaffin & Park, 1973; Kelsey et al., 1984; Kerr et al.,
2001; Liira, Shannon, Chambers & Haines, 1996; Liles, Deivanayagam, Ayoub & Mahajan, 1984;
Marras et al., 1995; Waters et al., 1999). In a case referent study of hospitalization for herniated
lumbar discs, Kelsey et al. (1984) found increased risks associated with lifting more than 25 lbs 25
times per day (RR
3.5);
lifting more than 25 lbs while twisting more than five times per day
¼
(RR
3.1); and for lifting more than 25 lbs per day while twisting and having the knee straight
¼
(RR
6.1). Similarly, Punnett et al. (1991) found an increased risk of low back disorders with frequent
lifts (more than 10 lbs more than once per minute). Liira et al. (1996) found increased odds of long-term
low back problems for those bending
¼
lifting more than 50 times per day (OR
1.7), for frequent lifts of
/
¼
less than 50 lbs (OR
1.8).
As the number of risk factors increased, so did the risk. The Marras studies (1993, 1995) quantitatively
monitored 114 different workplace variables in over 500 jobs that were classified according to historical
risk of LBD. These analyses were able to show that many, biomechanical workplace factors (such as trunk
velocities) were associated with risk. However, when a multivariate logistic model of risk was considered,
five factors in combination (lift frequency, sagittal torso bending angle, lateral velocity, twisting velocity,
and external
1.5), awkward trunk postures (OR
2.3) and whole body vibration (OR
¼
¼
¼
load moment), described the relationship with risk of reporting a LBD incidence
(OR
3.3) aver-
aged 3.77 lifts per minute and 20-lb loads. All studies provide some evidence that repetitive lifting is
hazardous, and most provide substantial evidence. The Marras et al. (1993, 1995) studies provided
the most detailed information on the most highly repetitive lifts and was used to select the weights
for the various cells in the TLV tables. The weights for cells B, D, and G primarily determined by identi-
fying weights below which there were a large proportion of low-risk jobs (i.e., with incidence rates of zero
cases) and a small proportion of the high-risk jobs (i.e., with incidence rates of 12 cases per 100 FTEs (full
time employees)). For example, the weight in cell D is 20 lbs (9.1 kg). In the OSU database on low- and
high-risk jobs, number of low jobs below 20 lbs (9.1 kg) and above 20 lbs (9.1 kg) was 49
¼
10.7) and LBD lost or restricted time (OR
¼
10.6) very well. The high-risk jobs (OR
¼
6 for low-risk
/
jobs and corresponding number was 15
30 for high-risk jobs. The weight for lifts in cell G is 15 lbs
(6.8 kg). In the OSU database on low- and high-risk jobs, number of low jobs below 15 lbs (6.8 kg) and
above 15 lbs (6.8 kg) was 20
/
21 for high-risk jobs. The data from the OSU
studies are based on experienced workers performing repetitive lifting tasks and thus is more predictive
of observed elevated risk for LBD.
4 for low-risk jobs and 2
/
/
50.3 Using the Lifting TLV
50.3.1 About the Lifting TLV
The Lifting TLVs recommend workplace lifting conditions under which it is believed nearly all workers may
be repeatedly exposed, day after day, without developing work-related low back and shoulder disorders
associated with repetitive lifting tasks (ACGIH, 2004). Appropriate control measures should be imple-
mented any time the Lifting TLVs are exceeded or lifting-related musculoskeletal disorders are detected.
The tool consists of three charts; the chart used to determine the TLV is a function of the lifting dur-
ation and lifting frequency. Then, based upon the one of four categories for height of the lift (floor to
mid-shin height, mid-shin to knuckle height, knuckle height to below shoulder, and below shoulder
to 30 cm above shoulder) and one of three categories of horizontal lift distance (close, intermediate,
and extended), a TLV for weight is given. In some cases, the tables indicate that there is no known
safe limit for repetitive lifting under those conditions.
The TLV is limited to two-handed mono-lifting tasks performed within 30
of the sagittal plane, so
tasks requiring a large amount of trunk twisting should not be analyzed with this tool. Additionally,
the ACGIH states that the guide does not apply to tasks where there are
8
360 lifts per hour, lifting
more than 8 h per day, constrained body posture, high heat or humidity, lifting unstable objects, poor
.
Search WWH ::
Custom Search