NIOSH Lifting Equation submitted by William A. Groves

C.6.b

Introduction• NIOSH first developed a lifting equation in

1981 to aid in evaluating lifting demands

• Original equation was widely used by occupational health practitioners since it provided an empirical method for estimating a weight limit for different manual lifting tasks

– Useful for identifying lifting tasks that posed a risk for developing low back pain

– Limited to sagittal plane lifting tasks – no asymmetry or rotation out of longitudinal plane

Introduction

• A revised lifting equation was developed and initially presented in 1991– Documentation and an application manual

were subsequently developed and released in 1993-94.

– Based on more recent research

– Provided methods for evaluating asymmetrical lifting tasks, and lifts of objects with less than optimal coupling between object and worker’s hands

Introduction• NIOSH Lifting Equation represents

only one tool in a comprehensive effort to prevent work-related low back pain and disability

– Lifting is only one of the causes of low back pain

– Psychosocial factors, medical treatment, and job demands can also play an important role

Criteria Used in Developing Equation

1. Physiological

• limit energy expenditure (3.5 Kcal/min)

2. Biomechanical

• limit compression on L5/S1 disc (770 lb)

3. Psychophysical

• 75% of female population capable of lift

4. Epidemiological

• consider risk to “fit” and “susceptible” populations

NIOSH Lifting Equation Limitations

• Does NOT apply to:

– Lifting/lowering with one hand

– Lifting/lowering for over 8 hrs

– Lifting/lowering while seated or kneeling

– Lifting/lowering in a restricted work space

– Lifting/lowering unstable object

– Lifting/lowering while carrying, pushing, or pulling

NIOSH Lifting Equation Limitations (cont)

• Does NOT apply to:

– Lifting/lowering with wheelbarrows or shovels

– Lifting/lowering with high speed motion (faster than 30 in./sec)

– Lifting/lowering with poor foot/floor coupling (< 0.4 coefficient of friction)

– Lifting/lowering in an unfavorable environment (high or low temperature / humidity)

Required Input

• Load weight

• Horizontal distance from load to low back

• Vertical location of load at beginning and end of lift

• Degrees from midline where load is located at beginning and end of lift

• Frequency of lifting in lifts per minute

• The duration of the task

• The quality of any handles or hand-holds

Revised Lifting Equation

• The revised equation for calculating the recommended weight limit (RWL) is a multiplicative model that incorporates weighting factors (multipliers) corresponding to six task variables:

RWL = LC x (HM x VM x DM x AM x FM x CM)

Load Constant 6 Weighting Factors(maximum weight for ideal lift)

NIOSH Equation Multipliers

1)

2)

3)

4)

5)

6)

Task Variables

Task Variables

Frequency Multiplier

Coupling Multiplier

Coupling Multiplier Decision Tree

Procedure1. Measure horizontal distance (H1) and vertical

distance (V1) at the origin of lift

2. Estimate asymmetry at origin (A1)

3. Measure horizontal distance (H2) and vertical distance (V2) at the destination of lift

4. Estimate asymmetry at destination (A2)

5. Select hand-hold category (good, fair, or poor)

6. Count the number of lifts in a given time frame, and convert to lifts per minute

7. Select the duration of the task: 1 hr, 2 hr, or 8 hr

• Multipliers < 1.0 indicate non-optimal conditions for that task variable

• Table 8 outlines design strategies for each task variable to improve the lift geometry (adjust multiplier toward value of 1.0)

Lifting Index (LI)

Example Problem 1

ANKLE LOCATION ASSUMESSTEP FORWARD WITH LOAD

H ORIGIN = 23"

V ORIGIN = 15"

H DESTINATION = 23"

30" DIAMETER

V DESTINATION = 63"

44 LB REEL

Example #1: Loading Punch Press Stock

Example Problem 1

Example 1

Example 1

Review Questions (Answers on the next slide)

1. The maximum load that should be lifted according to the revised NIOSH equation is ?

a. 23 lbsb. 43 lbsc. 37 lbsd. 51 lbs

2. The maximum value for any of the six task multipliers is ?

a. 100b. 1c. -1d. 10

3. Which of the following design techniques would not be used to decrease the lifting index (LI) ?

a. increase lift frequencyb. reduce lift durationc. bring load closer to workerd. reduce vertical distance between origin and destination

4. The coupling type for an optimally sized container, with non-optimal handles, that allow for 90 o finger flex would be ?

a. optimalb. goodc. faird. poor

Answers to the Review Questions

1. The maximum load that should be lifted according to the revised NIOSH equation is ?

d. 51 lbs

2. The maximum value for the six task multipliers is ?

b. 1

3. Which of the following design techniques would not be used to decrease the lifting index (LI) ?

a. increase lift frequency

4. The coupling type for an optimally sized container, with non-optimal handles, that allow for 90o finger flex would be ?

c. fair

References1. Applications Manual for the Revised

NIOSH Lifting Equation; T.R. Waters, V. Putz-Anderson, and A. Garg, DHHS (NIOSH) Publication No. 94-110.

http://www.cdc.gov/niosh/94-110.html

2. Waters, T.R.; Putz-Anderson, V.; Garg, A.; and Fine, L.J. Revised NIOSH Equation for the Design and Evaluation of Manual Lifting Tasks, Ergonomics, 1993, Vol 36(7), 749-776.