Ergonomic and Hygiene Interventions to Improve the Health and Safety of Drywall Finishing Workers
| Principal investigator(s): | Greg Smith (International Union of Painters & Allied Trades, D.C. 46) |
| Co-investigator(s): | Hugh Laird (Interior Systems Contractors Association of Ontario); Peter Vi, Dru Sahai (Construction Safety Association of Ontario) |
| Sponsoring Institution: | International Union of Painters & Allied Trades, D.C. 46 |
Purpose and Objectives
- To determine the potential reduction in the risk of musculoskeletal injuries to drywall finishing workers when using a pneumatic drywall finishing system.
- To determine the potential reduction in dust exposure and ergonomic-related hazards while using a powered drywall sanding system.
- To share the results with drywall finishers and construction firms so that exposure to hygiene and ergonomic hazards can be eliminated or reduced.
Methods
Objective 1: Reducing physical load and work time using a pneumatic drywall finishing machine
Seven drywall-finishing journeymen and three apprentices participated in this experiment. To evaluate the biomechanic loads, participants performed simulated drywall plastering tasks. All experiments were conducted in a newly constructed home at the Interior Finishing Systems Training Center in Toronto. A 582 ft 2 (54 m 2 ) master bedroom was used to conduct the experiment. All participants were asked to apply drywall compound onto the flat and corner joints using both the manual method and using the pneumatic finishing machine. While the participants were performing the experimental tasks, videotapes of the participants’ working postures were recorded. Muscle activities (EMG) were also collected at the same time. Participants were also asked to fill out a usability questionnaire after each experimental trial.
Objective 2: Reducing Dust Exposures in Drywall Finishing Using a Shrouded Ventilated Rotary Sander (SVRS)
Eleven subjects - seven journeymen and four apprentices from the International Brotherhood of Painters and Allied Trades, District Council 46 - were selected to participate in this research study. This research study was conducted in a newly constructed home at the Interior Finishing Systems Training Center in Toronto, Ontario. Two very similar rooms were selected for comparing dust concentrations generated by traditional pole sanding with those generated by an SVRS, which uses a portable vacuum system attached to a sanding head which removes dust at the source. Subjects were instructed to sand as they would normally on the job. For each subject, two test runs were conducted: 1) for the respirable fraction using the pole sander in one room; 2) for the respirable fraction using the SVRS in the other room. A TSI, model AM510, SidePak™ in conjunction with a Dorr-Oliver cyclone was used to measure respirable dust concentrations for each test run. After the comparison testing involving the eleven subjects was completed, air sampling for respirable dust was conducted while sanding with the SVRS at various speed control settings (one through five). Bulk (dry) and drywall dust samples were taken to determine silica content and particle size distribution.
Objective 3: Ergonomic evaluation of drywall sanding tasks using a drywall sanding machine
Seven drywall-finishing journeymen and three apprentices participated in this experiment, thanks to the International Union of Painters & Allied trades. To evaluate the biomechanic loads, participants performed simulated drywall sanding tasks. All experiments were conducted in a newly constructed home at the Interior Finishing Systems Training Center (IFTC) in Toronto, Ontario. Using two separate rooms, participants sanded the joint compound using both the manual method and the SVRS. To investigate drywall sanding tasks for potential reduction in risk of injury, electromyography (EMG) were applied on the skin surface above the following four muscles: (1) left and (2) right upper trapezius, and (3) left and (4) right flexor digitorum superficialis to estimate muscle loads on the shoulders and forearm.
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Results
Objective 1: Reducing physical load and work time using a pneumatic drywall finishing machine
- On average, using the traditional method (i.e. using a hawk and trowel) the participants finished with an average total time period of 31.62 min to apply joint compound. Using the Apla-Tech pneumatic drywall system, the participants finished with a total time of 11.05 min - a decrease of 65% in comparison to the traditional method.
- There were no significant differences in the duration and frequency of GAP were observed for the left and right Trapezius muscles, and the right flexor muscles when comparing between the two plastering methods. Significantly (p<0.05) higher muscular rest and rest frequency were observed however, for the left forearm flexor muscles when the participants used the Apla-Tech pneumatic finishing tools.
- When comparing between the traditional method and using the Apla-Tech, significant lower static load level was observed for the left forearm flexor muscles when the participants used the Apla-Tech method. Unlike the left forearm flexor muscles, the right forearm flexor muscles were exposed to a significantly higher median load level when the participants used the Apla-Tech pneumatic tools.
- Significantly (p<0.05) higher peak load level in the left and right forearm flexor muscles were observed when participants used the pneumatic drywall finishing tools.
- Generally, working with the Apla-Tech pneumatic tool were the preferred work method when comparing to the manual method on several items on the questionnaire.
Objective 2: Reducing Dust Exposures in Drywall Finishing Using a Shrouded Ventilated Rotary Sander (SVRS)
- The data indicate that the SVRS was very effective in capturing most of the respirable airborne dust1. When using the SVRS, the eleven subjects reduced their respirable dust exposures by an average 96%, compared to exposures during conventional pole sanding.
- As the speed of the sanding disc increased, personal exposure levels increased, except at the highest setting. Even though exposure levels generally increased with disc speed, the sanding process was still very well controlled.
- Analysis by infrared spectrophotometry for silica in various bulk and dust samples revealed an average concentration of over 5%. For the dust generated during SVRS sanding, particle sizing by optical light microscopy revealed that particles less than 5 ìm (projected area diameter) were about 81% of the inhalable mass, of which 52% was less than 1 ìm in diameter. Almost the same particle size distribution was noted for the dust generated during pole sanding, except that 41% of the particles were less than 1 ìm in diameter.
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Objective 3: Ergonomic evaluation of drywall sanding tasks using a drywall sanding machine
- Generally, the SVRS sanding trial requires less muscular activity in the shoulder and forearm muscles.
- Significantly higher muscular rest duration were observed for the right and left trapezius muscles, and the left forearm flexor muscles in the SVRS sanding trial when compared to the manual sanding condition. For the rest frequency variable, only the right trapezius muscle was found to be significantly higher when working with the SVRS.
- Working with the SVRS was found to require significantly less static load levels in the left and right trapezius muscles, and the right forearm flexor when compared to manual pole sanding. The median load level (dynamic work) was also found to involve significantly less muscle activity in the left and right trapezius muscles, and in the right forearm flexor muscle when working with the SVRS.
Conclusions
Objective 1: Reducing physical load and work time using a pneumatic drywall finishing machine
- Productivity, as measured by the time required to plaster 582 ft2, was very much dependent on the type of work method used. In this study, the Apla-Tech pneumatic tool was found to be a superior tool for apply joint compound than the traditional hand method using a hawk and trowel. The increase in productivity when using the pneumatic tool is positive because it allows more rest period between work task, which in turn can decrease risks of musculoskeletal disorders.
- Working with the pneumatic drywall finishing system resulted in a significantly higher muscular rest period (average accumulated EMG gap time) for the left forearm flexor muscle. Significant increase in frequency and duration of gap period would indicate the reduction in risk of injury for the left forearm when working with the Apla-Tech pneumatic tool.
- The static load level of the left forearm flexor muscle was found to be significantly lower when working with the pneumatic drywall finishing tool. This study found an average static load level of 2.23% MVC and 0.75% MVC when work with the traditional manual method and pneumatic tool, respectively. The large differences in the static load level may be due to the constant holding of the drywall hawk. The high static load level in the left flexor muscles when using the manual plastering method can put workers at risk of upper limb musculoskeletal disorders.
- The median load level for the right forearm flexor muscles were found to be significantly higher when working with the pneumatic tool. Average median load level for the right forearm flexor muscle while working with the Apla-Tech was 11.2% MVC. The increase in median load level in the right forearm flexor muscles is significant because the EMG load level was well above the recommended level of 10% MVC suggested by Johnson (1982).
- The peak load level in the right and left forearm flexor muscles were found significantly (p<0.05) higher when working with the Apla-Tech pneumatic tools. The large differences in peak load level may due to the heavy weight of the Apla-Tech tool (15 lb with full drywall compound). Although there was an increase in peak load level, the risk of injury however, remains low because it is well below the recommend load level of 90% MVC suggested by Johnson (1982).
- Majority of the items on the usability questionnaires were found to be significantly in favor of the Apla-Tech pneumatic drywall finishing tool. Although the majority of the workers prefer to work with the pneumatic tool, some workers felt uneasiness about the speed of the tool and the “deskilling” of the plastering trade when working with the tool, which they believe can lead to a loss of jobs.
- Working with the pneumatic tool can prevent fall related injuries because the use of ladders, scaffolds and benches can be reduced. However, this hypothesis should be further studied to confirm the findings.
- Based on the EMG measures, tool preference, productivity and reduction of risk of traumatic slips and falls, it is concluded that the pneumatic tool is an effective tool for applying compound onto drywall joints.
- Further studies in the field setting to verify the effectiveness of the pneumatic tool should be conducted.
Objective 2: Reducing Dust Exposures in Drywall Finishing Using a Shrouded Ventilated Rotary Sander (SVRS)
Traditional Pole sanding creates high dust levels. This dust can contain silica in significant concentrations as a natural ingredient. Usually drywall joint compound manufacturers recommend that workers wear respirators in dusty areas. Unfortunately, respiratory protection can be ineffective even when worn, if training on how to properly select, care or fit is inadequate. A far more efficient means of control is to utilize a vacuum sanding system such as the SVRS. The SVRS has many occupational health and safety benefits over pole sanding including the following:
- For sanders and nearby workers the SVRS significantly reduces exposure to drywall dust. Thus workers are much less likely to suffer adverse health effects.
- It greatly reduces the need for respiratory protection.
- Because it controls drywall dust so well, it can significantly reduce cleanup time.
- It is easy to use and not likely to cause musculoskeletal problems.
- It is ideal for situations where creating dust is a problem, for example, renovations where the building is occupied, new construction when other trades are in the area, hospital work where patients must be protected, work around dust-sensitive electronic equipment such as computers.
Objective 3: Ergonomic evaluation of drywall sanding tasks using a drywall sanding machine
- Despite the large difference in total weight between the SVRS (8 lbs) and the pole sanding tool (2 lbs), working with the SVRS generally requires less muscular activity in the upper extremity. The high muscular effort in manual pole sanding may result from the forceful and repetitive movement of the upper extremity in order to create a high friction force between the sandpaper and the wall. In the SVRS sanding condition, however, little muscular effort is required because majority of the sanding force was generated by the sanding machine.
- For manual pole sanding, the loads on the lower arm muscles were found to be at most risk for musculoskeletal injuries. The risk for musculoskeletal injuries at the trapezius muscles was found to be lower than the forearm muscles. The higher risk of injuries in the lower arm when compared to the shoulder area corresponds well with the WSIB lost-time injury (LTI) data.
- The static and median load level for the right and left trapezius muscle, and the right forearm flexor muscles were found to be significantly lower when using the SVRS. The decrease in muscular exertion can reduce the risk of musculoskeletal injuries. The reduction of risk of musculoskeletal injuries was found to be the most significant on the forearm flexor muscles.
- Working with the SVRS resulted in a significantly higher muscular rest period for the left and right trapezius muscles, and for the left forearm flexor muscle. Past studies have found a correlation between muscular rest periods and reporting of shoulder pain. Higher frequency and duration of rest periods when performing physical activities can allow improvement of blood flow, calcium re-absorption into the sarcoplasmatic reticulum, and the reduction of the extra-cellular efflux of potassium. All these factors have been found to be correlated with reduction in pain sensation.
- Based on the biomechanical measures, we conclude that using the SVRS is an effective method for drywall sanding.
- Further studies should be conducted in the field setting to verify the benefits of using the sanding machine to decrease risk of musculoskeletal disorders.
For more information: petervi@csao.org
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