Thursday, January 31, 2008

NIOSH Lifting Equation

'Safe Lifting' Guidelines
Lifting safely will protect your back while you lift. Before you lift an object ask yourself the following questions:
• Do you think you can lift it alone?
• Is the load too big or too awkward?
• Does the load have good handles or grips?
• Is there anything to obstruct proper lifting?
• Could the contents of the load shift while being lifted?
For safe lifting, remember to:
• Stand as close to the load as possible
• Bend at your knees NOT your waist
• Hug the load close to your body, don't hold it away from you
• Raise yourself up with the strong thigh muscles.

Low back pain risks increase when the compressive force at the L5-S1 (lumbar 5 sacral 1) disc exceeds 770 lbs.

NIOSH Lifting Equation
1981 Equation
In 1981 the National Institute of Occupational Safety and Health(NIOSH) issued a Work Practices Guide for Manual Lifting that used 770 lbs. of L5-S1 compressive force as one of the criteria for establishing an Action Limit (AL). Exceeding the action limit required implementation of administrative controls or job redesign. The AL is the weight that can safely be lifted by 75% of the female and 99% of the male population. A Maximum Permissible Limit (MPL is 3 times the action limit) was also set that was equivalent to a compressive force of 770 lbs on the lumbar spine.
The 1981 NIOSH lifting equation is as follows:
Action Limit (AL) = 90lbs. (6/H)(1-.01[V-30])(.7+3/D)(1-F/Fmax)
H = horizontal location of the load forward of the midpoint between the ankles at the origin of the lift (in inches)
V = vertical location of the load at the origin of the lift (in inches)
D = vertical travel distance between the origin and the destination (in inches)
F = average frequency of lifts (lifts/minute)
Fmax = maximum frequency of lifting which can be sustained (from a NIOSH table)
The Maximum Permissible Load (MPL) = 3 (AL)
1991 Equation
In 1991 the NIOSH equation was revised to account for the effects of other variables, such as asymmetrical lifting, good or poor handles, and the total time spent lifting during the workday. Another lifting equation, based on the 1981 equation, was developed that yields a Recommended Weight Limit (RWL) as follows:

Recommended Weight Limit (RWL) = LC x HM x VM x DM x AM x FM x CM
LC = load constant (51 lbs.)
HM = horizontal multiplier = 10/H
VM = vertical multiplier = (1- (0.0075 [V-30])
DM = distance multiplier = (0.82 + (1.8/D))
AM = asymmetric multiplier = (1 - (0.0032A))
FM = frequency multiplier (from a table)
CM = coupling multiplier (from a table)
A = angle of asymmetry = angular displacement of the load from the saggital plane, measured at the origin and destination of the lift
and where H,V,D and F are identical to the 1981 equation.
The RWL protects about 85% of women and 95% of men.
Ways to Protect Your Back
• Give yourself a lot of support. For stability, spread your feet at least as for apart as your shoulder width. Distribute weight evenly throughout the soles of both feetand keep your feet firmly planted, with your center of gravity in your abdominal cavity.
• Tighten your abdominal muscles.The abdominal cavity, consists of the abdominal muscles in front, the diaphragm and ribs above the pelvic floor below. Pressure in the abdomen that helps share the loads placed upon the spine.
• Bend form your knees. Alwways bend from our knees, so the legs can serve as shock absorbers. The pelvis to find its balance over the hips when the knees are slightly bent, so that weight comes first into the thighs and hips instead of the spine. Don't lift with locked knees because they tighten the hamstring muscles and lock the pelvis into an unbalanced position. Don't bend from the waist because it puts tremendous pressure on the lumbar vertebrae.
• Keep your spine in balance. Balance your shoulders and chest over the lower spine, to lessen the force placed on it.A balanced back, with its normal 3 curves, keeps the spinal muscles active so they can share the load placed on the bones, ligaments and discs.