A motorized screed consists of a blade, or plow, that floats on and vibrates the concrete during screeding operations.
Hazard Analysis — Stooped postures
Problem:Workers that finish concrete may face hazards from stooped postures.
Prolonged bending of the back during the process of finishing concrete can cause injuries to muscles, nerves, discs and ligaments of the low back. The cumulative effects of stooped postures may lead to LBP or low back disorders, such as strains of the muscles, sprains of the ligaments surrounding the spine, or intervertebral disc problems.
Low back pain (LBP) is among the most common health complaint in working-aged populations worldwide. In the U.S., 70%-80% of adults will experience a significant episode of LBP at least once in their lives. Low back disorders are conditions associated with lifting and other forceful movements of the back. Episodes of LBP are characterized by varying levels of pain and symptoms in the low back (lumbar spine). Low back disorders can even cause leg pain at times.
- Work-related lifting and forceful movements
- Whole body vibration
- Awkward postures (bending and twisting)
- Heavy physical work
Level of Risk:
The 'stooped' position, characterized by prolonged periods of forward bending of the back, is considered one type of awkward back posture that is a risk factor for low back pain (LBP). Several scientific studies have found that stooped postures may cause low back pain compared to work that does not require stooping. Furthermore, it appears that the risk for LBP increases when more time is spent in the awkward postures or if forward bending is more pronounced. Biomechanics research shows that forces within the lumbar spine are higher when the lumbar spine is bent forward fully. In these postures, the spine is weaker and is supported by the ligaments instead of the back muscles. Research has shown that reliance on ligaments instead of muscles may increase the risk for LBP.
Stooped postures are common in construction work. In 2002, over 29% of lost work days in the construction industry were due to back injuries. Studies also show that back pain is common among construction workers, with over 50% of workers reporting low back pain in a year. In 1996, the University of Iowa surveyed 2,929 workers representing 13 different construction trades and found that 70% of workers experienced low back pain in the previous 12 months.
There has not been specific research on the development of back disorders among structural steel workers due to work in stooped postures. However, the evidence cited above on stooped posture as a risk factor, and high rates of back disorders in the construction industry, show that there is an increased risk of LBP among any structural steel workers who often works in stooped postures.
Cook TM, Rosecrance JC, Zimmermann CL (1996). The University of Iowa Construction Survey. Report E1-96. Washington, DC: The Center to Protect Workers' Rights.
Gallagher S. (2005). Physical limitations and musculoskeletal complaints associated with work in unusual or restricted postures: A literature review. Journal of Safety Research, 36, 51-61.
To assess exposure to stooped postures, determine how many hours per day the worker spends in with their back bent forward >30°, bent forward >45°, or twisted >30°. Also, visit Thomas Bernard's website for a host of practical ergonomic tools.
To assess the exposure to stooped postures, it is necessary to observe a worker drilling, grinding and sawing materials. Look for:
- Time spent with the back bent forward more than 30°
- Excessive trunk twisting more than 30°
The risk of injury increases with more time spent in a bent forward posture and a greater degree of forward bending. General guidelines include:
- Working with the back bent forward >30° for more than 2 hours a day is a moderate risk
- Working with the back bent forward >30° for more than 4 hours a day is a significant risk
- Working with the back bent forward >45° for more than 2 hours a day is a significant risk
Quantitative methods of measuring back posture are available (e.g. Lumbar Motion Monitor) but require technical expertise.Thomas Bernard's website has a host of practical ergonomics tools, including the Washington Department of Labor and Industries Checklist and the Rodgers Muscle Fatigue Assessment.
Thomas Bernard's website has a host of practical ergonomics tools, including three Microsoft Excel® based analysis tools based on the Liberty Mutual Manual Material Handling Tables.
Regulations & Standards:
There is no Federal OSHA standard specifically for this hazard. However, hazardous work activities or exposures that are not covered by a specific standard are covered by the general duty clause, which requires each employer to provide a safe and healthful workplace.
Regulations adopted by a state must be at least as protective as the corresponding federal standard. Work may also be subject to rules of other federal, state and local agencies. Even where there is no hazard specific standard, OSHA provides a general duty for the employer to provide a work site free from recognized hazards.
The American National Standards Institute (ANSI) has a standard which applies to construction work where there may be risk factors for musculoskeletal disorders. ANSI standard A10.40 is not a regulation, but implementing this standard can help reduce the risk of MSDs. The standard is available for purchase from the American Society of Safety Engineers: http://www.asse.org/departments/standards/
Federal OSHA Standards are enforced by the U.S. Department of Labor in 26 states. There are currently 22 states and jurisdictions operating complete State plans (covering both the private sector and state and local government employees) and 5 - Connecticut, Illinois, New Jersey, New York and the Virgin Islands - which cover public employees only. If you are working in one of those states or jurisdictions you should ensure that you are complying with their requirements.
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