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Hazard Analysis — Whole Body Vibration
Workers who perform surface grinding or cutting may be exposed to whole body vibration.
Surface grinding or cutting, including sitting in construction machines can cause exposures to whole body vibration, which is a risk factor for low back disorders. The risk of developing a low back disorder increases with greater levels of vibration for longer durations of exposure. For example, driving off road causes greater levels of vibration than driving on a highway.
Low Back Pain and Disorders
Low back pain (LBP) is among the most common health complaints 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
- Poor job satisfaction, perception of intensified workload, lack of job control, and certain personality traits
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.
Whole-body vibration is measured with a specialized instrument called a triaxial accelerometer. Measurements of the amount of vibration must be taken at all the supporting surfaces (floor, seat, back). It is best to contact someone who has experience with measuring vibration to determine the level of exposure.
Whole-body vibration is measured in magnitude (acceleration) and frequency. Acceleration is measured with a specialized instrument called an acceleromometer. Since accelerometers measure in only one direction, an accelerometer with three axes (triaxial) must be used. The three axes of the accelerometer are at right angles to each other and the highest average acceleration is of concern. Measurements of the magnitude of vibration should be taken at all surfaces that support the body (floor, seat, back). With driving, vibration is most often measured on top of the driver's seat.
The frequency of vibration is also measured. With whole-body vibration, frequencies between 0.5 Hz and 80 HZ are the most important to measure. However, all frequencies are not equally harmful to the body. So, the frequency measurements are "weighted" to take into consideration the most harmful frequencies. Finally, the daily duration of exposure to vibration should be measured.
After the magnitude of acceleration and exposure time are known, standards can be used to determine if the vibration is potentially harmful. These standards include the International Standard (ISO) 2631-4 Whole Body Vibration in Transport, and The American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Value (TLV) for Whole Body Vibration. Guidance on how to measure vibration is provided in European Committee for Standardization (2003) Mechanical vibration — Measurement and calculation of occupational exposure to whole-body vibration with reference to health — Practical guidance. EN 14253:2003.
It is best to contact someone who has experience with measuring vibration to determine the level of exposure.
Regulations & Standards:
The American Conference of Government and Industrial Hygienists (ACGIH) has an exposure limit, for whole body vibration called the Threshold Limit Value (TLV).
The average magnitude (acceleration) and frequency of vibration must be measured, as well as the duration of exposure to the vibration. These values are then compared to tables adapted from ISO 2631. If the acceleration values are greater than the values in the tables, the TLV is exceeded for a specific amount of exposure time, indicating that an ergonomic solution should be developed. For example, the TLV would be exceeded if a worker was exposed to average accelerations > 2.12 m/s2 at a center frequency of 5.0 Hz for longer than 16 minutes.
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.
Workers exposed to excessive vibration for extended periods may be particularly susceptible to back injury when lifting, bending, or twisting immediately after leaving the vehicle. The risk of developing low back disorders increases when exposure to whole-body vibration is combined with exposure to other risk factors such as static sitting postures.
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