Peter Vi,
Hon. B.Sc.(Ergonomics), M.Eng., Project Coordinator, CSAO
Construction Safety Association of Ontario
In Ontario,
rodworkers have a higher proportion of lost-time musculoskeletal injuries
to the back and upper limbs than all other construction trades combined
(Figure 1). The total cost of their lost-time injuries and the amount
of their time off work are also greater than for all other construction
trades combined.
Figure 1: Non-traumatic musculoskeletal
injury by construction rate group (WSIB data: 1994-1998).
CSAO
research has shown how to improve this situation: reduce the frequency
of awkward trunk postures, particularly during ground-level rebar
installation.
One
way to improve posture is to use an automatic rebar-tying machine
or "gun." This is an electric tool (cord or battery) that
can be applied where bars cross. When you press the trigger, the
machine feeds the wire around the bars, twists it, and cuts it (Figure
2).
Figure
2: Notice the difference: working posture while
manually tying rebar (left) and while working with the
rebar-tying machine (right).
The
WSIB Research Advisory Council (RAC) has allocated research funds
to study
- the
effectiveness of the rebar-tying gun in reducing risk of injuries
- the
potential use of the gun as a rehabilitation tool for injured
workers.
The
research project is divided into three phases. The first phase focused
on a controlled laboratory experiment investigating the biomechanical
differences between manual tying and using the rebar-tying machine.
In the second phase, field experiments will investigate the long-term
health benefits of using the gun. The final phase will field-test
the machine as a rehabilitation device to assist injured workers
in their return to work. This article presents the results of the
first phase of the study.
Phase
1 Study -
Controlled Experiment
To evaluate the risk of low-back injury and the benefits
of using the rebar-tying machine, CSAO conducted a controlled experiment
with nine apprentices. The experiment took place at the International
Association of Bridge, Structural, Ornamental, and Reinforcing Ironworkers
Local 721 Training Centre in Toronto.
To evaluate
rebar-tying tasks and determine the potential for reducing the risk
of injury, the research team employed electromyography to measure
low-back muscle activity. This activity was used to quantify low-back
compression at the L4/L5 disc joint.
Results
Working with the rebar-tying gun significantly decreased peak loading
in the lower back at the L4/L5 disc joint (Figure 3). Cumulative
loading on the back was also significantly less than during manual
tying with pliers (Figure 4). These reductions in low-back loading
were mainly due to the workers' upright position while using the
gun with an extension (Figure 2). Numerous studies have shown that
reducing peak and cumulative forces on the lower back can significantly
decrease the risk of low-back injury.
Figure 3: Using the rebar-tying machine
resulted in significantly less peak loading on the lower back
(L4/L5 disc).
Figure 4: Using the rebar-tying machine
resulted in significantly less cumulative loading on the
lower back (L4/L5 disc).
Conclusion
Rodworkers have a high rate of lost-time claims due to musculoskeletal
injury. The high rate may be related to the frequency and repetition
of two factors:
- the manual
handling of heavy material, and
- the static,
awkward posture connected with ground-level rebar tying.
To lower the
risk of musculoskeletal injuries, control measures must be designed
to reduce physical exertion, such as frequent heavy rebar handling
and awkward trunk postures, particularly during ground-level work.
Phase 1 of
this study indicates that one way to improve the situation is to
use automatic rebar-tying machines. Results indicate that working
with the machine can decrease repetitive wrist activities such as
the bending, twisting, and lateral bending associated with manual
tying. Furthermore, using the gun with an extension can decrease
static bending of the trunk, which in turn decreases peak and cumulative
compression forces on the lower back.
The research
team concluded that using the automatic rebar-tying machine can
significantly decrease the risk of musculoskeletal injuries to rodworkers.
Limitations
have become apparent, however, in real job situations.
- The MAX
RB392 can only tie two rebar having a combined area of 150 mm
sq. to 300 mm sq. This allows tying of only about 40%-60% of
the bar used on a typical project.
- The gun
requires regular maintenance. After two to three days of use,
the tie-wire that spools out and along the jaw of the gun constantly
jams on its inner mechanics. Once jammed, it is difficult to
clear the wire without the assistance of the manufacturer.
MAX Tools (www.maxusacorp.com)
has developed a bigger rebar-tying gun (RB650) that can tie a combined
area of 58 mm sq. to 750 mm sq. Preliminary tests show that many
of the problems with the smaller gun have been solved. CSAO will
conduct additional research in real job situations during Phases
2 and 3 of the study.
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