Ergonomic risk assessment tools

You cannot control what you have not assessed. Ergonomic risk assessment identifies which jobs and tasks put workers at risk of MSDs, how serious the risk is, which risk factors drive it, and which changes would make the biggest difference. Many tools exist, from simple checklists anyone can use to detailed methods that require training. This lesson explains how to plan an assessment, how to gather information, and how the most widely used tools work. The general process of hazard identification and risk assessment is covered in the hazard recognition and risk assessment course; this lesson focuses on what is special about ergonomic assessment.

A staged approach

Most organizations use a staged approach. First, screen all jobs quickly to find those with obvious or likely MSD risk. Second, assess the jobs flagged by screening in more detail, using a tool suited to the main risk factors. Third, for complex, high-risk or disputed jobs, bring in a qualified ergonomist for specialist analysis. This avoids wasting effort on detailed analysis of low-risk jobs and makes sure the highest risks get attention first.

Jobs should be screened and assessed when there are reports of discomfort or injury, when new jobs, equipment or processes are introduced, when existing jobs change, when workers raise concerns, and periodically as part of a regular program. In several jurisdictions, an MSI report or reported symptoms trigger a legal duty to review the job.

Gathering information

Good assessments draw on several sources of information:

• Injury and first aid records, compensation claims and absence data, showing where MSDs have occurred.
• Worker reports, interviews and discomfort surveys, showing where people feel strain before injuries occur.
• Direct observation of the job over several cycles and at different times of the shift, since tasks often vary.
• Video recordings, which allow postures and frequencies to be measured accurately and reviewed with workers.
• Measurements: weights of loads, push and pull forces using a force gauge, heights and reach distances with a tape measure, joint angles, cycle times and the number of repetitions.
• Production data such as quotas, line speeds, overtime and the number of units handled per shift.

Involve the workers who do the job. They know which parts of the task are hardest, how the task varies, what shortcuts people take and what has been tried before. Always explain that the assessment is of the job, not the person.

Discomfort surveys

A discomfort survey asks workers to mark on a body map where they have felt ache, pain, numbness or tingling over a recent period, such as the last week or year, and to rate how often and how severe it is. The Nordic Musculoskeletal Questionnaire is a widely used standardized version. Surveys are cheap, quick and confidential, and they reveal problems before claims appear. Repeating the same survey after changes shows whether the changes helped.

Screening checklists

Checklists ask yes or no questions about the presence of risk factors, often with thresholds of duration. A typical checklist asks whether a worker lifts more than a certain weight more than a certain number of times per day, works with hands above the head or elbows above the shoulders for more than two hours a day, kneels or squats for more than two hours a day, repeats the same motion with the neck, shoulders, elbows, wrists or hands for more than two hours a day, grips with force, or uses vibrating tools for long periods. A yes answer flags the job for more detailed assessment.

WorkSafeBC publishes an MSI risk factor identification worksheet and an assessment worksheet for use under the BC regulation, and other provinces and safety associations, such as WSPS in Ontario, CNESST in Quebec and WorkSafe Saskatchewan, offer similar checklists. The Ontario MSD Prevention Guideline toolbox includes a hazard identification tool and links to the assessment methods described below.

Checklists are good at finding jobs that need attention, but they do not tell you how much risk there is or which change would reduce it most. For that, you need the methods that follow.

Observational posture methods: RULA and REBA

The Rapid Upper Limb Assessment (RULA), published in 1993, is an observational method for jobs where the upper body and arms are the main concern, such as assembly, computer work and many manufacturing tasks. The analyst observes the job, selects the posture that is held longest or is most extreme, and scores each body part using diagrams on a one-page worksheet: upper arm, lower arm and wrist (group A), and neck, trunk and legs (group B). Additional points are added for muscle use (static postures or repetitive actions more than four times a minute) and for force or load. Lookup tables combine the scores into a grand score from 1 to 7.

The Rapid Entire Body Assessment (REBA), published in 2000, uses a similar approach but is designed for whole-body tasks with unpredictable postures, such as health care, warehousing and service work. It scores the trunk, neck and legs, and the upper arms, lower arms and wrists, adds points for load or force, coupling and activity, and gives a final score from 1 to 15.

RULA and REBA are quick and need only a worksheet, which makes them popular. Their limitations are that they assess a single posture rather than the whole shift, and they do not account well for duration or recovery. Use them to compare postures before and after a change, and combine them with frequency and duration information.

Tools for repetitive hand and arm work

For jobs dominated by repetitive hand and arm motions, several methods consider force, repetition, posture and duration together. The Strain Index, developed by Moore and Garg in 1995 and later revised, multiplies ratings for intensity of exertion, duration of exertion, efforts per minute, hand and wrist posture, speed of work and duration per day to estimate risk for distal upper limb disorders. The OCRA method, widely used in Europe and the basis of ISO 11228-3, compares the actual number of technical actions per shift with a recommended number adjusted for force, posture, repetitiveness, recovery and other factors.

The ACGIH, a scientific organization that publishes threshold limit values (TLVs) for chemical and physical agents, publishes a TLV for hand activity. It combines a hand activity level (HAL), rated on a scale of 0 to 10 based on the frequency of exertions and recovery time, with the normalized peak force of the hand, rated on the same scale. Plotting the two on a chart shows whether a job is below the action limit, between the action limit and the TLV, or above the TLV. Lesson 10 returns to repetitive work and tools.

Several Canadian jurisdictions, including British Columbia and Alberta, base their exposure limits for chemical and physical agents largely on ACGIH TLVs, and Canadian ergonomists commonly use the ACGIH hand activity and lifting TLVs as assessment benchmarks, although these ergonomics TLVs are not generally adopted as legal limits.

Tools for lifting, pushing, pulling and carrying

For manual material handling, the most widely used tool is the revised NIOSH lifting equation, which calculates a recommended weight limit for a specific two-handed lifting task. It is covered in detail in Lesson 6. Other tools include:

• The ACGIH lifting TLV, which gives recommended weight limits for zones defined by the horizontal distance of the load from the body and its vertical height, for different durations and frequencies. The highest values apply to loads lifted close to the body between knuckle and shoulder height, and they fall sharply for loads far from the body, near the floor or above the shoulders.
• The Liberty Mutual manual materials handling tables, first published by Snook and Ciriello in 1991 and since updated, which give the maximum acceptable weights for lifting, lowering and carrying and the maximum acceptable forces for pushing and pulling, based on studies of what percentage of male and female workers find a task acceptable for a full shift. They allow you to estimate what percentage of the working population could perform a task without excessive fatigue.
• ISO 11228-1 and ISO 11228-2, international standards for lifting, carrying, pushing and pulling, which incorporate methods similar to the NIOSH equation and the Liberty Mutual tables.
• Push and pull force gauges, which measure the initial force needed to start a cart moving and the sustained force needed to keep it moving, for comparison with the Liberty Mutual tables or other guidelines (Lesson 8).

Choosing the right tool

No single tool fits every job. Choose the tool that matches the main risk factors and the decision you need to make:

From assessment to action

An assessment is only useful if it leads to action. A good assessment report states the job and task assessed, who did the assessment and when, the information gathered, the tool used and the scores obtained, the main risk factors identified, and recommended controls ranked by the hierarchy of controls. It should set priorities based on the level of risk, the number of workers exposed and the availability of practical solutions, and it should name who is responsible for each action and by when. After controls are in place, reassess the job using the same tool to confirm that the risk has fallen, and ask workers whether the change works for them.