Differentiate between subjective and objective measures when assessing ergonomic risk, providing examples of each, and explaining how they are used in identifying problem areas in the workplace.
In ergonomic risk assessment, both subjective and objective measures are essential tools that provide different yet complementary insights into workplace conditions and their impact on workers. These measures are used to identify problem areas, evaluate the extent of risks, and inform the development of effective control measures. Subjective measures rely on personal perceptions and experiences, while objective measures involve observable and quantifiable data. Understanding the difference between the two, and how they can be used effectively, is essential for a thorough ergonomic assessment.
Subjective measures capture the worker's personal experience, opinions, feelings, and perceptions related to their job. These are qualitative data and are often gathered through interviews, questionnaires, and self-assessments. While subjective data can be influenced by individual biases, they provide valuable insights into issues like comfort, fatigue, and pain, which are not always easily measurable through objective methods. Examples of subjective measures include:
1. Discomfort Surveys: These questionnaires ask workers to rate their discomfort or pain levels using numerical or descriptive scales. For example, a worker might rate their back pain on a scale of 1 to 10, where 1 is no pain and 10 is the most severe pain. A body map may also be used, which is a diagram where workers can indicate on which parts of the body they are experiencing pain or discomfort. Discomfort surveys can identify specific areas of the body that are most affected by work, allowing for targeted intervention. For instance, if multiple workers report high levels of neck and shoulder pain, an ergonomic investigation focusing on workstation setups would be warranted.
2. Perceived Exertion Scales: These scales measure how hard workers feel they are working. One common scale is the Borg Rating of Perceived Exertion (RPE), which ranges from 6 (no exertion at all) to 20 (maximal exertion). Workers use this scale to indicate how physically demanding a task feels, and this can be very useful in evaluating the physical load of manual handling and repetitive tasks. For example, if workers consistently rate a task at 15 or higher, it suggests that the task is too physically demanding and may require ergonomic modifications.
3. Interviews and Focus Groups: These methods allow workers to describe their experiences in their own words. They can provide valuable insights into subtle issues that might be missed by objective measures alone. For example, workers may describe feeling mentally strained from constant interruptions, or having to make repeated reaching motions to get supplies, which might not show up in the data collected in other ways. The qualitative information gathered during the interview process often gives the human context of how a person is feeling at their job.
4. Self-Assessment Checklists: These checklists ask workers to assess their own workstations and work habits. They can highlight issues related to workstation setup, lifting techniques, or use of tools and equipment. For example, a worker might use a checklist to note that their monitor is positioned too low or that they do not use a footrest. Such self assessments can empower workers to proactively participate in making changes that are relevant to their own ergonomic needs.
Objective measures, on the other hand, involve direct observation and quantification of workplace conditions and worker actions. These are often quantitative data, gathered using instruments, observation, or checklists to provide measurable data of risk factors. Examples of objective measures include:
1. Posture Analysis: This involves measuring the worker's body positions using observation, photos or videos, and sometimes special measurement tools. For example, a posture analysis might quantify the degree of neck flexion, wrist extension, or back bending while performing a specific task. Direct observation of workers throughout their work day is important to identifying awkward postures that may lead to musculoskeletal disorders. Posture analysis tools such as the Rapid Entire Body Assessment (REBA) or Rapid Upper Limb Assessment (RULA) can help to quantify ergonomic risks based on postures, and provide a score that can be used for tracking purposes.
2. Force Measurements: This uses instruments such as force gauges to measure the amount of force exerted by workers during tasks. For example, a force gauge can measure the force needed to push or pull a cart, turn a valve, or grip an object. Comparing these measurements to accepted ergonomic limits helps identify high force tasks that require modification. Force measurements are especially important in evaluating the risks associated with manual handling, or repetitive use of hand tools.
3. Time Motion Studies: These studies measure the time it takes to perform tasks, the frequency of movements, and the cycle times for different work processes. For example, a time-motion study might quantify the number of repetitions a worker performs in an hour, or the duration of a specific task. These measurements can help identify tasks with excessive repetition, or insufficient recovery periods, which are both known causes of injuries.
4. Environmental Measurements: This involves assessing factors such as lighting levels, noise levels, and temperature, that can contribute to discomfort or fatigue. These measurements are obtained using light meters, sound level meters, and thermometers. For example, measuring the lighting at a computer workstation will reveal if there are issues with glare or improper illumination which can cause eye strain. These types of issues need to be addressed through workplace design or other control methods.
5. Workstation Assessments: Using checklists or direct measurements to determine the dimensions of workstations, including desk height, chair adjustability, and monitor placement, to ensure proper fit. Direct measurements are often taken to determine if a workstation is within recommended ergonomic dimensions, and to determine if adjustments need to be made.
These subjective and objective measures are used in a coordinated and complementary manner to identify problem areas in the workplace:
Initial Assessment: An initial assessment typically begins with subjective data to gather a broad understanding of workers' experiences. This provides insight into where problems are mostly likely to exist.
Targeted Investigations: Subjective feedback helps to pinpoint areas where more detailed objective measurements should be focused. For example, if workers report high discomfort in the lower back, then the ergonomic assessment should prioritize evaluating lifting tasks, postures, or the design of the workstations.
Quantifying Risks: Objective measurements are then used to quantify these risks. Posture measurements can show the specific degree of awkward postures and force gauges can measure the forces exerted, which provides solid data that backs up the subjective data and clarifies the extent of the problem.
Informing Solutions: Both subjective and objective data are then used to develop suitable control measures. For example, if both subjective reports and objective measurements indicate that computer workstations have issues with monitor heights, then adjustable monitor arms can be implemented.
Evaluation of Effectiveness: After changes are made, both subjective and objective measures are taken again to determine the effectiveness of the implemented controls, and whether changes made have had the intended effects. For example, the initial data taken from workers showed that there was significant back pain during lifting. Then after ergonomic training and the implementation of lifting aids, subjective data from workers shows reduced pain and objective data shows a decrease in the amount of weight lifted manually.
By using both subjective and objective measures, ergonomic assessments become more comprehensive and are much more effective in identifying and addressing problem areas in the workplace, and making the workplace a safer and more comfortable environment.