A duct lift is a lifting device used to raise duct systems to the desired level for installation.
Hazard Analysis — Lifting and Carrying (Manual materials Handling)
Workers who install heating and air conditioning duct hangers and ductwork may face hazards from lifting and carrying (manual materials handling).
Lifting heavy materials during the installation of heating and air conditioning duct hangers and ductwork can cause injury to muscles, nerves, discs and ligaments of the low back. Non-specific low back pain is not the result of a fall or some other acute traumatic injury, so it can be difficult to identify a specific event that led to the injury. Repetitive lifting can lead to low back muscle strain, ligament sprain, a bulging or herniated disc, or other back problems.
Low Back Pain and Disorders
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. 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 or numbness at times.
Work-Related Risk Factors
- Work-related lifting and forceful movements
- Whole body vibration
- Awkward postures (bending and twisting)
- Heavy physical work
Development and Progression
The low back may be injured due to either a sudden stressful event or the cumulative effect of stressful activities. Strains of the muscle or sprains of the ligaments surrounding the spinal joints occur most commonly. Injuries to the low back may also involve the intervertebral disc.
The intervertebral disc is composed of a ring of fibers surrounding a sac of fluid or gel-like material. Discs may be damaged due to a sudden stress (e.g. a fall, slip, or catching an unexpected load), or due to cumulative problems when stressful activities stretch, tear, or unravel the protective fibers surrounding the sac of fluid. When the fibers can no longer contain the fluid, small leaks or bulges can occur or the disc may flatten. The most commonly injured low back discs are between the 4th and 5th lumbar vertebrae (L4-L5), and between the 5th lumbar vertebrae and the sacrum (L5-S1). Disc problems may lead to a pinched nerve.
The causes of many episodes of LBP are unclear. Even with clinical tests and imaging procedures, about 85% of patients cannot be given a precise diagnosis. The pain in these cases is presumed to be related to muscle, ligament, or tendon injury or degenerative changes.
Individuals with low back problems typically experience pain in the low back (lumbar spine). Leg pain or numbness may accompany low back pain. Often, leg pain is localized to the side or back of the thigh, but sometimes the pain may go all the way to the foot. This leg pain is called "sciatica." Individuals may also have tenderness in the low back and a limited range of motion for bending forward, backward, sideways, or twisting. Bending forward tends to increase pain levels.
Initial treatment for most episodes of low back pain includes avoidance of stressful activities and occasionally one to two days of bed rest. Nonsteroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofen or naproxen) are often helpful, and stronger drugs may be prescribed (muscle relaxants or narcotics) for more severe, acute pain. Other treatment options may include application of heat and cold, physical therapy, spinal manipulation, or injections. Some LBP cases may require surgery (ruptured disc or severe trauma cases).
Most workers with occupational LBP get better. Half of workers improve in one week and 90% improve in 30 days, regardless of treatment. Light duty work activities may be prescribed by the physician during the recovery period. The remaining 10% of workers may have a chronic condition and may not be able to return to their previous jobs. Many workers may suffer from residual pain that may affect work or activities of daily living.
Level of Risk:
Lifting or carrying heavy loads, frequent bending or twisting, and heavy physical work may cause low back disorders. Lifting or carrying heavy loads has been linked to low back disorders in numerous publications. Epidemiological research has identified that the risk of injury increases when lifting loads from low heights, holding the load away from the body, or lifting while the torso is twisted or flexed. Biomechanical research supports these findings by demonstrating that loading of the spine increases in all of those conditions. Intervention studies have determined that lift tables, lifting hoists, lightening loads, and other engineering interventions can lower the risk of developing back injuries among workers.
Lifting or carrying heavy loads, frequent bending or twisting, and heavy physical work are common in construction work. In 2002, over 29% of lost work days in the construction industry were due to back injuries. Epidemiologic studies also show that back injury prevalence among construction workers is high, 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 relationship between manual material handling and the development of back disorders among sheet metal workers. However, the strong evidence cited above regarding lifting as a risk factor, and high rates of back disorders in the construction industry, show that the risk of back injury among sheet metal workers from manual material handling is considerable.
Bernard, B. (Ed.). (1997). Musculoskeletal disorders and workplace factors: A critical review of epidemiologic evidence for work-related disorders of the neck, upper extremity, and low back (Vol. No. 97-141). Cincinnati: National Institute for Occupational Safety and Health.
Cook, TM, Rosecrance, JC, & Zimmermann, C L (1996). The University of Iowa construction survey. Report e1-96. Washington, DC: The Center to Protect Workers' Rights.
Goldsheyder, D, Nordin, M, Weiner, SS, & Hiebert, R (2002). Musculoskeletal symptom survey among mason tenders. American Journal of Industrial Medicine, 42(5), 384-396.
Latza, U, Karmaus, W, Strumer, T, Steiner, M, Neth, A, & Rehder, U. (2000). Cohort study of occupational risk factors of low back pain in construction workers. Occupational and Environmental Medicine, 57, 28-34.
Merlino, LA, Rosecrance, JC, Anton, D, & Cook, TM. (2003). Symptoms of musculoskeletal disorders among apprentice construction workers. Applied Occupational and Environmental Hygiene, 18, 57-64.
National Research Council - Institute of Medicine. (2001). Musculoskeletal disorders and the workplace. Washington, DC: National Academy Press.
Stürmer, T, Luessenhoop, S, Neth, A, Soyka, M, Karmaus, W, Toussaint, R, et al. (1997). Construction work and low back disorder. Preliminary findings of the Hamburg construction worker study. Spine, 22(21), 2558-2663.
Liberty Mutual Manual Material Handling Guidelines can be helpful in determining maximum acceptable weight limits for lifting and carrying tasks along with suggested solutions for minimizing the risk of injury from lifting or carrying. Washington State LNI also has some useful tables that can help determine weight limits.
There is no easy way to measure the actual load on the lumbar spine in the workplace or to correlate measured load with risk of back pain. For a job analysis one should, as much as possible, quantify the worker's exposure to factors found to be associated with increased risk of back pain.
Liberty Mutual recently published updated tables that can be used to determine the maximum acceptable weights for men or women during different types of MMH tasks (lifting, carrying, pushing, pulling, etc.). These tables can be used to identify hazardous lifting activities and to help design engineering solutions to minimize the risk of injury associated with MMH.
The NIOSH Lifting Equation is also a useful tool, but can only be used to analyze lifting that does not including carrying or changing hand movements. Based on the NIOSH Lifting Equation, lifting a load of more than 51 lbs. is not recommended in any circumstance. For infrequent lifts, the Liberty Mutual tables may allow loads of 89 lbs. Practically speaking, the Liberty Mutual tables will be useful in more settings.
Eight variables should be evaluated for any lift:
- The weight of the object being lifted.
- Hand height of the worker at the start of the lift.
- Hand height of the worker at the end of the lift.
- The distance of the hand from the body during the lift.
- The quality of the container in terms of how easy it is to grasp (coupling or type of handholds, box, bag, etc.).
- The angle of the object from the midpoint of the worker's body (twisting angle).
- The lifting frequency (lifts/minute).
- The amount of time spent lifting by the worker during a regular workday.
Avoid these activities because doing them will increase the risk for injury during MMH tasks:
- Beginning or ending a lifting at a level below the knuckle height of the worker.
- Twisting the back.
- Holding the load far away from the body.
- One-handed lifts.
- Catching items.
- Throwing items.
OSHA has an Ergonomics eTool for MMH at http://www.osha.gov/SLTC/etools/electricalcontractors/materials/heavy.html
NIOSH provides guidance for the design of safer lifting jobs at http://www.cdc.gov/niosh/topics/ergonomics/
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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