Ergonomics Part II - Measuring Work Hazards

This is the second part of a three part series of articles on ergonomics. In the first article, six ergonomic hazards were introduced by ErgoWorks through the acronym F.R.E.D.V.P. ©: Force, Repetition, Environment, Duration, Vibration, and Posture. These hazards cause fatigue and fatigue is often the beginning of the injury cycle.

Once the hazards have been identified, the second step is to quantify or measure the hazards that are contributing to a work-related musculoskeletal disorder. There are guidelines and recommendations for ergonomics from the Occupational Safety and Health Administration (OSHA) (particularly for noise, heat and cold, chemical exposures, air quality, etc…), the National Institute of Occupational Safety and Health (NIOSH), American National Standards Institute (ANSI) (ANSI B11), and the International Organization for Standardization (ISO) (ISO 9241). California and Washington have also passed state ergonomic rules and regulations.

OSHA passed an ergonomic standard under the Clinton administration, but was repealed by the Bush administration. The reasons for the controversy over this legislative rule are complicated and cause dilemmas! How can you create expensive mandates for all employers when there is ambiguity in the research data? Based on age, sex, race and anthropometrics of all individuals including handicapped, pregnant, and wheel-chaired, what criteria do you use to decide how much force is too much?…or how many repetitions are too many?…or what environmental conditions cause too much fatigue?…or how much rest and recovery does a muscle need when assessing duration of a task?…or how much exposure to vibration is too much?…or what postures cause injury? ErgoWorks’ experience is that successful companies will implement ergonomic solutions when we are able to demonstrate with reliable and valid data that the COST OF INJURY IS GREATER THAN THE COST OF ERGONOMIC SOLUTIONS.

The Center for Ergonomics at the University of Michigan has been a leading institution in the field of ergonomics for decades. They have developed models for biomechanical assessments. One of the earliest models is the Two-Dimensional Static Strength Prediction Program (2DSSPP, and recently updated 3DSSPP) which provides risk data based on configured anthropometrics. The risk data provided are back compressive force at L4-L5 and L5-S1 disc and the percent of the population that has the strength to perform the lift task on an occasional basis at the back, elbow, shoulder, hip, knee and ankle.

The University of Michigan’s guideline for back compressive force is no greater than 770 lbs. and for percent capable is not less than 75% for males. ErgoWorks has found a strong correlation between the 2DSSPP risk data and back injury. When the back compressive force approaches 700 lbs. and the percent capable is under 95%, the risk for back injury is significant. The 2DSSPP model’s ability to create what-if scenarios encourages further investigation of its benefits. For example, what if we raise the object to be lifted…or bring it closer…or reduce the weight…or change the anthropometrics? How does this change or reduce the risk data? Is the change statistically significant? There is controversy regarding most biomechanical models, but Ergoworks finds the objectiveness of the data useful in motivating companies to implement ergonomic solutions.

The revised NIOSH Lift Formula (www.cdc.gov/niosh/docs/94-110) provides a Recommended Weight Limit (RWL) based on a load constant of 51 lbs. being multiplied by six criteria: Horizontal Distance Multiplier, Vertical Distance Multiplier, Distance Multiplier (the vertical difference between the origin and destination of the lift), Angle of Asymmetry Multiplier (twisting), Coupling Mechanism Multiplier (how the item is grasped), and the lift Frequency Multiplier. The formula supports the industrial benchmark of lifting no more than 51 lbs. The criterion with the lowest fractional number reduces the RWL most significantly. Learning how to manipulate this formula will help guide to the best objective solution.

Other tools that supplement an ergonomic assessment include:

Dictionary of Occupational Titles
Checklists
Discomfort surveys
Job observations
Job cycle worksheets
Measuring tape, protractor and/or goniometer
Force gauges for gross lifting, pushing and pulling
Hand grip dynamometers with pinch measurement capabilities
Videotape to more accurately document frequency rates and ranges of motion
Rapid Upper Limb Assessment (RULA)
Borg Perceived Exertion Level

Further ergonomic analysis should consider:

Static loading
Quick, jerky and/or accelerated forces
End ranges of motion
Pushing and pulling forces
Pinch and grip forces
Energy expenditures
Asymmetric work
Restricted movements, particularly inability to maintain lumbar lordosis

A key point to remember is that no one assessment tool will lead to an optimal solution. Performing multiple risk assessments should identify primary hazards. The question that an employer will ask is, “What is causing injuries and what is the best and most inexpensive way to fix the problem?” A good analysis should objectively quantify the risk hazards that will lead toward ergonomic solutions. The next article will address implementing cost-effective solutions.

Glenn Orser

Ergonomics Part I

This is the first of a three part series of articles on ergonomics. Ergonomics is a multi-disciplined science that includes biomechanics, engineering, psychology, sociology, and economics, combined with human factors/error. It investigates all aspects of the mind, body, and soul connections, and analyzes/compares their functions to the tools, equipment, and methods used in the workplace. To put it simply, ergonomics looks at human ability versus the demands of one’s work, play, and daily activities.

ErgoWorks teaches three basic steps for performing an ergonomic analysis:

1) Identify ergonomic hazards.
2) Quantify the hazards and eliminate/reduce them through engineering, administrative, or work practice controls.
3) Demonstrate cost-effectiveness and implement solutions.

The first step is the easiest to teach and everyone can learn it. There are only six ergonomic hazards that cause injury. ErgoWorks has developed an acronym F.R.E.D. V.P. © as a way of remembering these causes of aches and pains:

FORCE – Lift, carry, push, pull, grasp, pinch, swing, strike, jerky/sudden movement, contact stress.
REPETITION – How many?
ENVIRONMENT – Hot, cold, wet, dry, humid, noise, bright, dark, slippery, outdoors, indoors, confined, hazardous, heights, dust, fumes, mist, negotiate irregular terrain.
DURATION – How long? How much recovery?
VIBRATION – Whole body or segmental.
POSTURE – Twisting, static, restricted movement, bending, reaching, poor seating, inadequate tool, squat, kneel, crawl, manipulates: slippery, bulky, sharp, awkward objects.

When the demands of these hazards are greater than human ability, they can cause fatigue; the beginning of the injury cycle. The one hazard that causes fatigue quickly is. . . Posture!

1) Carpal tunnel – stems from deviated wrist postures.
2) Rotator cuff injuries – elbow at, or higher than your shoulder.
3) Lateral and medial epicondylitis – wrist deviations of flexion and extension respectively combined with grasp force.
4) Postural back injuries – not maintaining lumbar lordosis posture and forward bending > 30 degrees.
5) Neck injuries – forward head posture.
6) Knee injuries – bending the knee > 90 degrees.

Posture is the one hazard that your patients usually have the greatest control over. Learn to identify these hazards and teach them to your patients for better compliance and reduce risk for re-injury.
Part II will discuss how to quantify these hazards and eliminate/reduce them through engineering, administrative, or work practice controls.

Glenn Orser - CEO of ErgoWorks