What are ergonomic assessment methods?
The risk assessment required by Law 31/1995 and Royal Decree 39/1997 must use procedures that provide confidence in their results and, in case of doubt, recognized methods. In physical ergonomics, assessment methods translate observations of actual work (postures, frequencies, durations, weights, forces, grip conditions, and organization) into a score or risk level that guides the priority and type of intervention. Each method is designed for a specific risk factor and a particular body part, and therefore they are not interchangeable.
The general process begins with an initial identification of positions and tasks with potential risks, continues with an assessment using the appropriate method for the dominant factor, and concludes with a proposal for redesigning the workstation, the organization, or mechanical aids, followed by a reassessment. The INSST publishes Technical Prevention Notes that describe the most widely used methods and a specific technical guide for manual handling of loads.
Observational methods have limitations: they depend on the quality of the observation, oversimplify the variability of tasks, and do not replace technical judgment. Therefore, they must be applied with training, supplemented with measurements when necessary, and corroborated with information from the people performing the work.
Methods according to the risk factor
- Postural load: RULA and REBA. RULA (Rapid Upper Limb Assessment) assesses the upper limbs, neck, and trunk in seated or standing tasks with minimal movement; REBA (Rapid Entire Body Assessment) extends the assessment to the entire body, including the legs, and is suitable for dynamic tasks involving loads. Both generate a score with action levels. Described in INSST NTP 452 and 601.
- Postures in variable tasks: OWAS . Posture sampling method that classifies combinations of back, arms, legs and load throughout the day, useful in jobs with a wide variety of postures such as construction, agriculture or maintenance.
- Manual handling of loads: INSST technical guide and NIOSH equation. The technical guide of Royal Decree 487/1997 proposes an evaluation method with acceptable weight calculated from correction factors; the NIOSH equation calculates the recommended weight limit and the lifting index; the UNE-EN 1005-2 and ISO 11228-1 standards address lifting, and ISO 11228-2 addresses pushing and pulling.
- Repetitive movements: OCRA and UNE-EN 1005-5. The OCRA index and its checklist assess repetitiveness, force, upper limb postures, recovery times, and additional factors; UNE-EN 1005-5 and ISO 11228-3 incorporate it as a reference method. NTP 629 describes its application.
- Application of forces. The UNE-EN 1005-3 standard sets recommended force limits for the use of machines; the Strain Index method assesses the effort in the hand and wrist.
- Global methods and checklists. The INSST method for ergonomic job assessment, initial identification lists, and tools such as Ergo/IBV integrate several factors into a single application.
How to choose and apply the method
- Identify the dominant factor: posture, repetition, load, force, or a combination thereof, through observation and consultation with the workers.
- Check the scope of validity. Each method defines the type of task, the population, and the conditions for which it was designed.
- Record the actual task. Direct observation or recording of representative cycles, with times, frequencies, weights and forces measured.
- Interpret with sound judgment. The scores guide the priority; the proposed measures require analysis of the causes in the job design and in the organization.
- Re-evaluate after the measures. Apply the method again to verify the risk reduction and document the result.
Organizational application: how to integrate ergonomic assessment
- Perform an initial identification of positions with ergonomic risk based on checklists, damage data (musculoskeletal disorders, absenteeism) and consultation with the staff.
- For each position, select the method appropriate to the dominant risk factor and document the justification.
- Observe and record the actual tasks, with measurements of weights, forces, frequencies and times, and with the participation of the people who perform them.
- Apply the method, obtain the risk level, and prioritize interventions.
- Design measures regarding the workstation (heights, reach, tools, mechanical aids), the organization (rotation, breaks, rhythms) and training.
- Re-evaluate after the intervention and record the before-and-after comparison.
- Integrate the results into risk assessment, preventive planning, and health surveillance.
Preventive management software allows you to link the results of ergonomic assessments with workstations, plan measures and monitor their effectiveness along with indicators of musculoskeletal damage.
Limits and common mistakes
- Applying a method outside its scope of validity, for example RULA in tasks with displacements and loads or the NIOSH equation in one-handed lifts.
- Evaluate a posture or cycle that is not representative of the actual work.
- Using the score as a final conclusion without analyzing the causes or proposing redesign measures.
- Entrusting the evaluation to personnel without training in the method or in the specialty of ergonomics.
- Forgetting to reassess after implementing measures to verify their effectiveness.
- Setting universal weight or force limits without considering correction factors and the exposed population.
The methods and technical standards are updated; the current versions of the INSST NTPs and the applicable UNE-EN and ISO standards should be consulted.
Practical example
Situation: A fresh produce packaging company with 70 people detects an increase in shoulder and wrist ailments on the packaging line.
- Identification. Initial checklist and health surveillance data pointing to repetitiveness and elevated shoulder posture.
- Method. OCRA checklist because the dominant factor is the repetition of upper limbs, complemented with REBA in the palletizing task.
- Result. OCRA index at high risk level due to lack of recovery and high frequency; REBA medium in palletizing due to stacking height.
- Measures. Rotation between positions every two hours, recovery breaks, palletizing lift table and redesign of the belt height; re-evaluation at three months with reduction of the index to an acceptable level.
Regulatory and technical framework in Spain
- Royal Decree 39/1997, article 5. Evaluation procedure: recognized methods or criteria when the regulations do not establish them.
- Royal Decree 487/1997, of April 14. Manual handling of loads, with the INSST technical guide as the reference method.
- INSST technical guide on manual handling of loads . Method for evaluating lifting, carrying, pushing and pulling.
- NTP 452 of the INSST . Evaluation of working conditions: postural load (RULA method).
- NTP 601 of the INSST . Evaluation of working conditions: postural load. REBA method.
The UNE-EN 1005 (machinery safety, human physical capacity) and ISO 11228 (manual handling) standards are international references; Directive 90/269/EEC regulates the manual handling of loads in the European Union.
