|
|
|
|
|
|
|
The authors ask you:
Residential construction workers record high numbers of injuries and illnesses annually (1). There is a need to measure work exposures to identify high risk tasks likely contributing to musculoskeletal disorders in this working population. Construction jobs involve highly variable tasks making exposure assessment difficult. The purpose of this study was to evaluate exposure data to identify high risk work tasks in residential framers.
Sixty-one framers provided estimates of task times and videotaped samples of tasks. Using these data, observer-rated physical exposures were calculated using a modified Hand Activity Level (HAL) (2). Based on this analysis, the highest exposure work tasks included wood assembly, followed by packing and sawing. Analysis of subtasks for assembly determined nail gun use was most problematic. Assembly task exposures were rated unsafe for 16% of the average daily workday.
Worker estimates and observer-rated exposures provide a mechanism for identifying high risk work tasks in variable jobs. This method may be used to estimate exposures in construction jobs to assess levels of risk and assist intervention efforts.
High rates of musculoskeletal disorders (MSDs) occur in the construction sector (3). Carpal tunnel syndrome rates of 10% shown in construction exceed rates of one to five percent found in the normal population (4). These higher rates are even more striking given the significant under-reporting of injuries and illnesses of construction workers (5). Most construction workers are subject to project-based employment. This leads to frequent periods of unemployment and increases the difficulty of assigning financial responsibility for the injury. Often injured workers resort to unpaid days off or job change in response to the symptoms. Recognizing the tasks that contributed to these injuries is difficult given the dynamic nature of the industry (6).
Residential carpenters perform highly variable work tasks throughout the course of a house build. Quantification of physical exposures that may be associated with MSDs is difficult to assess for jobs with tasks performed intermittently within a single day or from one day to the next. Recently developed tools used to assign risk levels for upper extremity exposures were designed for mono-task jobs. The American Conference of Governmental Industrial Hygienists (ACGIH) proposed a hand activity level threshold limit value (HAL-TLV) that combines two physical exposures: the hand force required for a task and the frequency and speed of the hand movements. The results may categorize the overall job into a safe, caution or unsafe level of risk. Although the HAL-TLV scale was intended for use in mono-task jobs, it may be applied to variable task jobs. By separating the job into primary task components and using the HAL-TLV rating scales, the exposures and associated risk levels may identify the high risk tasks or task components. Prioritizing these high risk tasks will identify activities that may be associated with chronic injuries. Developing feasible interventions for these targeted high risk tasks may impact injury rates and severity. For the construction industry jobs that universally contain variable tasks, this method provides an opportunity to focus on decreasing worker’s risk. This task component method of risk assessment does not determine the risk of the overall job but further investigation of methods may show a useful way to combine exposures from task components that represents an overall rating of worker risk. The purpose of this study was to evaluate exposure data to identify the high risk work tasks performed by residential framers.
Worksite visits were conducted at residential construction sites as part of an ongoing study investigating the development of carpal tunnel syndrome in apprentice carpenters. The one-hour onsite visits involved taking videotape samples of work tasks that were being performed by the worker at the time of the visit. The brief videotape samples did not include mock-up of tasks that were not regularly performed during the stage of construction. Following the videotape, workers completed a brief interview to obtain estimates of total task times and worker’s ratings of hand force for all primary work tasks. Workers rated peak hand force for the most common task and the most difficult task using a modified Borg scale for perceived exertion (8). After completing the worksite visit, observers used the worksite data to rate each worker’s physical exposures on recommended exposure scales for repetition, peak hand force and arm/hand postures for each primary task (8). Analysis of data included frequency distributions of key work tasks, worker hand force ratings and exposure threshold levels of safe, caution and unsafe for work tasks based on the Hand Activity Level-Threshold Value Limit (HAL-TLV).
Sixty-one apprentice carpenter framers completed residential worksite visits. Wood assembly with use of the nail gun was the most common task reported (61% of the workers) and packing lumber was the most difficult task (39% of the workers) reported by the framers. Framers performed different tasks during their work day. Wood assembly using a nail gun was performed for 3.7 hours on average by those who reported this task (75% of the workers). Wood assembly using the hammer occurred half as often compared to use of the nail gun. Peak hand force ratings on a 0 to 10 point scale (10= highest force) showed worker and observer-rated exposure estimates were both highest for the packing task, followed by wood assembly using a hammer.
Worker and observer-rated peak hand force and estimated work hours by primary tasks for 61 residential framers
Estimated work hours |
Worker Ratings |
Observer Ratings |
|||
|---|---|---|---|---|---|
Ave (SD) |
n |
Peak force Ave (SD) |
n |
Peak force Ave (SD) |
|
| Assembly with nail gun | 3.7 (1.2) |
47 |
4.1 (2.6) |
46 |
5.2 (1.5) |
| Assembly with hammer | 1.9 (1.2) |
34 |
4.7 (2.2) |
7 |
6.6 (1.4) |
| Packing lumber | 2.0 (0.7) |
41 |
6.5 (2.5) |
37 |
7.1 (1.5) |
| Saw | 2.5 (1.4) |
31 |
3.9 (2.2) |
17 |
5.1 (1.6) |
For each primary task or group of tasks, the observers rated exposures based on the scales for the HAL-TLV. The observer-rated hand activity and peak hand force exposures were combined as described by the HAL-TLV and then classified as safe, caution or unsafe risk levels. The results show that all framers performed tasks classified in the caution category with 41% of the workers exposed for more than 1 hour per day. Ninety-eight percent of the framers performed tasks classified in the unsafe category with 31% of the workers performing these unsafe tasks for more than 1 hour per day. Five percent of the workers performed tasks with unsafe exposures for 4 or more hours per day.
HAL-TLV ratings of the specific tasks show that wood assembly was rated “unsafe” on average for 16% of the daily work time with wood assembly tasks most often performed using a pneumatic nail gun. The tasks reported as most common and difficult by workers were verified as such by observer ratings.
The HAL-TLV threshold scale for physical exposures provides a mechanism for
identifying high risk tasks in jobs with variable task. By combining worksite
data and exposure ratings, this method enabled identification of high risk tasks
performed by residential framers. Wood assembly with nail gun use was the most
common task performed and packing lumber was reported as the most difficult
task by workers. The observers concurred and rated packing with the highest
peak hand force. Most framers were exposed to “unsafe” exposure
levels for one hour or less of the work day. All framers were exposed to work
tasks with exposures in the caution category. These results provide physical
exposures for several framing tasks. Comparison of exposure levels gives a way
to prioritize high risk tasks among a wide range of tasks commonly performed
by workers. Although most of the high risk exposures are for short periods of
time, it would be prudent to decrease exposures to acceptable levels for all
tasks if possible.
In the absence of a sophisticated method for rating physical exposures in variable
task jobs, breaking the job into component tasks and rating exposures provides
a useful means of prioritizing tasks for risk assessment and interventions.
This study showed wood framing with nail gun use, a common task for most framers,
has some exposure time in the “unsafe” category. A more detailed
investigation into the physical exposures of task components may highlight the
task component contributing to the risk level. This would be a feasible area
to explore with other collaborators. Pneumatic nail guns may weigh 9 pounds
or more and are often held in awkward arm positions from fully extended overhead
to work at floor height. Alternative tools or methods may decrease physical
exposures. Nail gun weight, type and weight of hose, swivel attachment of hose,
battery operated tool, alternative attachments or alternative assembly methods
may decrease exposures in some contexts. Following implementation of an intervention,
re-evaluation of physical exposures would be assessed.
Although the task component method is useful for variable task jobs, there remains the need to develop a risk assessment rating for the overall job. Strategies for combining exposure scores of tasks using time-weighted averages of exposures or selected weightings for peak exposures may produce a valid measure of overall job exposure. Further investigation is needed in this area.
We would welcome communication and collaboration with other researchers who have experience in physical exposures, interventions or best practice methods related to residential construction. A specific collaboration could target high risk residential tasks such as wood assembly with use of nail gun, using a task component assessment to evaluate the risk outcome. At a broader level, we would invite comment from other researchers who have developed simple methods for identifying and quantifying exposures in variable task jobs in the construction industry. Our group is currently exploring tasks distributions and individual and group variability of physical exposures in residential construction workers. We are interested in examining various methods of combining risk levels from component tasks to produce a valid overall job risk score in the variable tasks for residential construction.
The findings and conclusions in this poster are those of the author(s) and do not necessarily represent the views of the National Institute for Occupational Safety and Health. Citations to Web sites external to NIOSH do not constitute NIOSH endorsement of the sponsoring organizations or their programs or products. Furthermore, NIOSH is not responsible for the content of these Web sites.
