The spine is a sensitive mechanism. Certain lifting or equivalent to lifting actions can cause irreversible damage that can lead to permanent injury.
An "equivalent to lifting" action is a muscular effort action where the voluntary muscles controlled by the brain contract and relax in a similar fashion as if a quick lifting activity was taking place. A sample of "equivalent lifting" would be when a person is cranking an old fashion Lister diesel engine. For this sample, injuries due to lifting are combined with repetitive motion injuries (RMIs), which result in damage of soft tissue like muscles and tendons.
Besides the risk of lifting heavy weights and the risk created by the posture or position of the worker's upper body in relation to the object to be lifted, there is an increase in the risk to the worker when the object to be lifted is of unstable nature, such as a bag of potatoes or a bag of grain or minerals. Back disorders can develop gradually as a result of microtrauma brought about by repetitive activity over time or can be the produce of a single traumatic event. Because of the slow and progressive onset of this internal injury, the condition is often ignored until the symptoms become acute, often resulting in disabling injury. Acute back injuries can be the immediate result of improper lifting techniques and/or lifting loads that are too heavy for the back to support. While the acute injury may seem to be caused by a single well-defined incident, he real cause is often a combined interaction of the observed stressor coupled with years of weakening of the musculoskeletal support mechanism by repetitive micro-trauma. Injuries can arise in muscle, ligament, vertebrae, and discs, either singly or in combination.
Back disorders result from exceeding the capability of the muscles, tendons, discs, or the cumulative effect of several contributors:
The National Institute for Occupational Safety and Health (NIOSH) was established within the Department of Health and Human Services under the provision of OSHA (Occupational Safety and Health Administration), U. S. Department of Labor. NIOSH has developed a mathematical formula with which to evaluate certain types of lifting tasks. These tasks involved smooth, two handed lifts in front of the body, an unrestricted lifting posture, good shoes and floor surfaces, favorable environments, minimal pushing, pulling or holding requirements and physically fit worker. A slide-rule was developed by the National Safety Council (NSC) incorporating the NIOSH formula, called ERGONOMIC LIFTING CALUCULATOR (E.L.C.). The E.L.C. allows to obtain the AL (Action Limit) expressed in pounds, which designates the load that can be lifted by most healthy workers without developing difficulties, as well as the MPL (Maximum Permissible Limit) also in pounds.
The NIOSH formula developed about 1983 was revised and improved in 1991 thru 1994 resulting in an improved Ergonomic Lifting Calculator, which includes limitations such as:
The revised lifting equation assumes that the worker/floor surface coupling provides at least 0.4 (preferably 0.5) coefficient of static friction between the shoe sole and the working surface. An adequate worker/floor surface coupling is necessary when lifting to provide a firm footing and to control accidents and injuries resulting from foot slippage. A 0.4 to 0.5 coefficient of static friction is comparable to the friction found between a smooth, dry floor and the sole of a clean, dry leather work shoe (non-slip type).
Hence, this document may not apply when lifting with unreasonable foot/floor coupling, because it may give values of allowable weights higher than what would be reasonable for the case of unsafe floors or shoes.
Other General Industry Recommendations and Publications of Interest Regarding Lifting are:
On page 15, the conclusions reached by Chafin and Park in 1973 is quoted (see 2. above).
On page 16: The information presented on this page relates to the frequency, duration and pace of lifting, and one of the conclusions is that the more frequent the lifting of maximal loads on a job can result in a "greater probability of uncoordinated muscle action during a lift.
On page 149: On this page the influence of the floor condition is discussed and the following is stated:
"3. Worker/Floor Surface Coupling. Poor worker/floor coupling will most often resulting in accidents such as slips, trips or missteps".
On page 108, the following is stated: "The general conclusion is that materials handling while walking results in horizontal inertial forces transmitted from the load being carried to the body. The carriage of weight also affects the body's learned reflexes for recovering from a trip by changing the normal weight distribution of the body and preventing the arms from being used to regain balance or recover from the fall".
Also, the same publication discusses the visual environment indicating that an illumination of 150 LUX in the area to be transited is a recommended minimum, and contrast, which depends on the difference in light reflected from two surfaces, is necessary for a safe operation.
This publication summarized the legislation and practice concerning the limitations of weight in manual lifting and carrying loads adopted by various ILO member countries.
As a sample of the values presented in the Codes of Practice, the following is extracted from the Australian Government Publishing Service, Code of Practice 415 on Manual handling (Page 25).
On page 26, the acceptable weight of lift is given: An object with a center of gravity located at 380mm (1.25') from the body, when it is lifted from knuckle height to shoulder height, could have an optimum weight of 19kg (41.8 lbs.) and a maximum weight of 24kg (52.8 lbs.).
The following are some typical cases of back disorders caused by lifting:
Sample #1: This worker was an electronic technician in excellent physical condition and used a swing rope to board a seismographic vessel where he worked repairing electronic packages of seismic buoys. The weight of the buoys was between 50 to 60 lbs. Normally a line boat loaded with 20 to 40 seismic buoys would arrive alongside the seismographic vessel at about 9:00 a.m. The buoys were about 3' - 0" in diameter and about 8" in the vertical direction, and had a counter weight and an antenna.
Upon the arrival of the line boat, the technician was requested to assist in the transfer of the seismic buoys from the line boat to the 3rd deck of the seismographic vessel. To accomplish this task, he positioned himself on the 2nd deck, to pick up each buoy being handed over by other crewmembers from the line boat, lifted the buoy above the 2nd deck until the buoy cleared the handrail, bringing the buoy over the rail and placing the buoy on the 2nd deck.
Then he would carry the buoy a few feet towards the deckhouse below the 3rd deck and handed the buoy to a crewmember positioned on the 3rd deck. This person would lift the buoy above the 3rd deck and stowed the buoy on the 3rd deck. Then, buoys that were repaired on the previous day were lowered from the 3rd deck to the line boat. The above-described activity normally would take some 3 hours, because between 20 to 40 buoys were normally moved in the morning.
Then, the technician would carry each buoy, one buoy at a time to the electronic lab, where he would take care of the electronic equipment pertaining to each buoy.
Upon completed of the electronic work, he would carry each buoy back to the 3rd deck, where he would pick up another buoy to repeat the process with all the buoys resting on the 3rd deck. Then, he would assist to move the buoys from the 3rd deck to the 2nd deck and to the line boat.
After a period of time, he started noticing pain in his neck, shoulder and back on the morning after an active day of handling buoys.
And a few days later, pain in the area of his neck, shoulder and back the next morning of a day full of the activity discussed above increased substantially, to the point that he was forced to stop working. After reporting this condition to his supervisor and after various medical examinations, the consensus of medical opinion was that repetitive lifting of excessive load triggered his pain.
After seeing various doctors, he was put on light duty and was instructed not to lift more than 20 lbs. Later he underwent surgery because he had a herniated disc and damaged in a nerve root.
The technician tried to continue working under the light duty recommendation, but the need to use the swing rope to transfer himself from line boats to the seismic vessels and vice versa, resulted in an increase from acute paint to chronic disabling pain and he was force to stop working due to his disability.
Sample #2: Two crewmembers of a towboat tried lifting a 150 pound skiff out of the water after struggling with it for a while applying a variety of attempts to retrieve it. One of the crew, at the time that the maximum effort was applied, felt a twinge in his back between his shoulder blades and became disabled by strong back pain.
Sample #3: A diver's tender working on a diving vessel was requested to carry an outboard engine weighing some 80 to 100 lbs. He was carrying the motor when his shoe contacted a hose lying on deck. Although the tripping on the hose was minor, he could not regain his equilibrium because his body started twisting to the right and fell on his back with the motor falling on his chest.
Hector Pazos, is a Naval Architect, Marine Engineer and a Registered Mechanical Engineer and has been engaged in Accident Investigation/Reconstruction for more than 40 years. He has been retained as an Expert Witness in over 1,200 Maritime cases, related to both commercial vessels and pleasure crafts, for both defense and plaintiff.
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