Dru Sahai and Peter Vi
Construction Safety Association of Ontario
Health
Almost every construction project
involves installation of drywall for
interior walls. One step in drywall
finishing is sanding the drywall
compound.
Currently, workers sand the
compound manually using a handheld
block or a long-handled pole
(Figure 1) with a piece of sandpaper
at the end of a swivel plate.
Stress
To create sufficient friction for
sanding, the worker applies
pressure to the manual sander. This
results in stress on the back, arms,
and wrist.
Dust
Sanding also generates high levels
of dust including respirable silica.
Inhaling this dust causes eye,
nose, throat, and respiratory tract
irritation, coughing, phlegm
production, and breathing
difficulties. Worse, it increases the
risk of silicosis and lung cancer.
Sander
One way to control these health
hazards is to use an electric
shrouded ventilated rotary sander
(SVRS).
The SVRS collects particulates by
drawing air through the space
between a) the outer circumference
of the rotating abrasive pad and
b) the inner surface of the shroud
covering the abrasive pad. The dust
then passes into a vacuum
collection system equipped with a
high-efficiency filter.
Study
Three partners undertook a study
to document the potential
ergonomic and hygiene benefits of
using an SVRS to prevent
musculoskeletal injuries and dustrelated
illness. The partners were
the International Brotherhood of
Painters and Allied Trades District
Council 46, the Interior Systems
Contractors Association, and the
Construction Safety Association of
Ontario.
The study took place in a newly
constructed home at the Interior
Finishing Systems Training Centre
in Toronto. We selected two very
similar rooms—Aand B—to
compare dust concentrations
generated by conventional pole
sanding with those generated by an
SVRS. The total sanding area for
room A was 256 ft2, and for room B,
286 ft2.
Eleven subjects participated in the
study: seven journeymen and four
apprentices from the Painters’
Union. While all participated in the
dust measurement portion of the
study, only ten participated in the
ergonomic portion.
Each subject participated in two
test runs for dust measurement:
1) using the pole sander in one
room
2) using the SVRS in the other
room.
Room and method of sanding were
randomly selected.
To measure respirable dust
concentrations, we used a TSI, model
AM510, SidePak™ in conjunction
with a Dorr-Oliver cyclone. The
aerosol monitor is a small, directreading,
data-logging unit.
While measuring respirable dust,
we also measured muscle activity
using electromyography (EMG).
EMG signals were recorded by
attaching surface electrodes to the
skin above the following four
muscles, selected to estimate
muscle loads on the shoulders and
forearm:
–– left upper trapezius
–– right upper trapezius
–– left flexor digitorum superficialis
–– right flexor digitorum
superficialis.
Results: Respirable Dust
The research data indicate that the
SVRS was very effective in capturing
most of the respirable airborne dust.
Pole-sanding exposures ranged
from 0.394 to 3.767 mg/m3 with a
mean value of 1.686 mg/m3. SVRS
exposures ranged from below
background levels to 0.458 mg/m3
with a mean of 0.073 mg/m3. The
difference between the two sanding
methods was found to be highly
significant (p<0.05) and represents
a 96% reduction in respirable dust
exposure.
This finding is consistent with other
studies involving similar sanders.
From bulk samples, we detected an
average concentration of 5% silica
in the drywall compound used in
this study—demonstrating that
dust control is a continuing concern
for drywall finishers.
Results: Ergonomics
Despite the large differences in
weight between the SVRS (8 lbs)
and the pole sander (2 lbs),
working with the SVRS required
significantly (p<0.05) less static
load levels in the left and right
trapezius muscles and the right
forearm flexor. The median load
level (dynamic work) involved
significantly less muscle activity in
the left and right trapezius muscles
and in the right forearm flexor
when a worker used the SVRS.
With the SVRS, there were
significantly higher muscular rest
durations for the right and left
trapezius muscles and the left
forearm flexor muscles than with
the manual sander. Only the right
trapezius muscle was found to
have a significantly higher rest
frequency with the SVRS.
With a manual pole sander,
workers expend great muscular
effort to create a high friction force
between the sanding paper and the
wall. Using the SVRS, however,
requires comparatively little
muscular effort because most of the
sanding force is generated by the
machine. In this case, the muscular
effort observed in workers’ upper
extremities served to support and
guide the SVRS along the wall.
Amplitude domain analysissummaries of sanding using manual and machine methods |
|
SVRS |
Manual Pole Sanding |
P-Value |
|
Mean |
SD |
Mean |
SD |
|
Static level (p: 0.10) |
|
|
|
|
|
Left trapezius |
0.964 |
0.60 |
1.57 |
1.31 |
0.05* |
Right trapezius |
0.876 |
0.528 |
1.57 |
0.88 |
0.036* |
Left forearm flexor |
1.82 |
1.17 |
2.82 |
1.38 |
0.065 |
Right forearm flexor |
2.08 |
1.21 |
4.13 |
2.14 |
0.008* |
Median level (p: 0.50) |
|
|
|
|
|
Left trapezius |
7.05 |
3.03 |
8.79 |
4.21 |
0.024* |
Right trapezius |
7.32 |
2.94 |
10.62 |
4.48 |
0.009* |
Left forearm flexor |
7.6 |
3.95 |
10.18 |
4.91 |
0.10 |
Right forearm flexor |
9.74 |
3.70 |
13.07 |
4.98 |
0.034* |
Peak level (p: 0.90) |
|
|
|
|
|
Left trapezius |
21.16 |
7.49 |
23.38 |
8.03 |
0.287 |
Right trapezius |
24.94 |
10.02 |
25.83 |
8.88 |
0.556 |
Left forearm flexor |
23.90 |
11.13 |
22.83 |
12.87 |
0.786 |
Right forearm flexor |
23.53 |
6.48 |
26.94 |
8.86 |
0.279 |
* Significant at p<0.05 |
Comparing Muscle Use
Based on the ergonomic and
hygiene measures, we conclude
that the SVRS is an effective
method for drywall sanding and
recommend that the SVRS be used
to control drywall dust. The SVRS
has many advantages over pole
sanding.
Some advantages of the SVRS - It significantly reduces exposure
to drywall dust. Workers are
much less likely to suffer
adverse health effects.
- It greatly reduces the need for
respiratory protection.
- It can significantly reduce
cleanup time because it controls
drywall dust so well.
- It is easy to use and unlikely to
cause musculoskeletal problems.
- It is ideal for situations where
creating dust is a problem—
for example, renovations in
occupied buildings, new
construction when other trades
are in the area, work in hospitals
or medical facilities where
patients must be protected, or
work around dust-sensitive
electronic equipment.
Some disadvantages of the SVRS - The vacuum is not portable
enough to be used in some
circumstances—e.g., on a scaffold.
- The vacuum hose can create a
tripping hazard.
- The round shape of the sanding
head means it cannot fully sand
corners.
- The vacuum and sander require
electrical power that is not
always available, especially on
new construction sites.
Acknowledgements
This project was funded by a
research grant from the Workplace
Safety and Insurance Board
(Ontario). The authors are grateful
to the International Brotherhood
of Painters and Allied Trades
District Council 46 and the Interior
Finishing Systems Training Center
for their support.
|