The Lest method was developed by F. Guélaud, M.N. Beauchesne, J. Gautrat, and G. Roustang, members of the Laboratory of Economics and Sociology of Labor (L.E.S.T.), and aims to assess working conditions as objectively and comprehensively as possible. It establishes a final diagnosis indicating whether each situation considered in the workplace is satisfactory, troublesome, or harmful.
The method is of a comprehensive nature, considering every aspect of the job broadly. It doesn't delve deeply into each of these aspects but provides an initial assessment to determine if a more in-depth analysis with specific methods is required. The objective, according to the authors, is to evaluate all factors related to job content that may impact both health and personal life of the workers. Prior to applying the method, occupational health and safety risks must have been considered and addressed, as they are not covered by the method.
The information needed to apply the method has a dual objective-subjective nature. On one hand, quantitative variables such as temperature and noise level are used, and on the other, the worker's opinion regarding the tasks performed in the position is gathered to assess mental workload and psychosocial aspects. Therefore, the involvement of the personnel concerned is essential in the evaluation.
Despite being a general method, it cannot be applied to evaluate every type of position. Initially, the method was developed to assess working conditions in fixed industrial sector jobs with a low level of required qualification. Some parts of the method (physical environment, posture, physical workload, etc.) can be used to evaluate positions with a higher level of qualification in the industrial or service sectors, provided that the workplace and environmental conditions remain consistent.
To determine the diagnosis, the method considers 16 variables grouped into 5 dimensions: physical environment, physical workload, mental workload, psychosocial aspects, and working time. The evaluation is based on the scores obtained for each of the 16 variables considered. In order to facilitate application, the version of the method implemented in Ergoniza is a simplification that considers 14 of the 16 variables, thus eliminating the need for some of the hard-to-obtain data requested in the observation guide. The simplified variables include thermal environment, lighting conditions, noise, vibrations, attention, and complexity.
Remember...
The LEST method is of a comprehensive nature and assesses various risk factors in a general manner. It does not delve into each individual risk factor. If risks are detected, a deeper analysis is required using specific methods.
Remember...
Although LEST assesses different risk factors, it does not provide an overall risk assessment for the position but rather an independent assessment for each risk factor.
Remember...
The version of the method implemented in the Ergoniza software is a simplification that considers 14 out of the 16 variables, allowing for the elimination of some of the data requested in the observation guide that is difficult to obtain.
Para aplicar el método LEST debe recogerse la información requerida para valorar cada una de las 6 dimensiones que considera. Cada dimensión se subdivide en una serie de variables mostrada en la Table 1.
| Physical Environment | Physical Load | Mental Load | Psychosocial Aspects | Working Times |
|---|---|---|---|---|
| Thermal Environment | Static Load | Time Pressure | Initiative | Work Time |
| Noise | Dynamic Load | Complexity | Social Status | |
| Lighting | Attention | Communications | ||
| Vibrations | Supervisor Relationship |
The application of the method begins with the observation of the worker's activity, during which the necessary data for evaluation must be collected. In general, the collection of objective data will require the use of appropriate instruments such as: a psychrometer for measuring temperatures, a luxometer for measuring light intensity, a sound level meter for measuring sound intensity levels, an anemometer for assessing air velocity at the workstation, and instruments for measuring distances and times, such as measuring tapes and stopwatches.
The amount of information to be gathered for assessment is substantial. Table 2 provides a summary of the items to consider.
| Dimension | Variable | Required Data |
|---|---|---|
| Physical Load | Static Load | The most frequently adopted postures by the worker and their duration in minutes per hour of work |
| Dynamic Load | Weight in kilograms of the load causing exertion | |
| If the exertion performed at the workstation is Continuous or Brief but repetitive | ||
| If the exertion is continuous, indicate the total duration of exertion in minutes per hour | ||
| If exertions are brief but repetitive, indicate the frequency per hour of exertion | ||
| When handling materials, the distance traveled with the load in meters, frequency per hour of transportation, and weight transported in kilograms | ||
| Physical Environment | Thermal Environment | Wind speed at the workstation |
| Dry and wet bulb air temperature | ||
| Duration of daily exposure to these conditions | ||
| Number of temperature variations experienced by the worker during the day | ||
| Noise | The level of attention required by the task | |
| Number of impulsive noises to which the worker is exposed | ||
| Lighting Environment | Lighting level at the workstation | |
| General workshop average lighting level | ||
| Contrast level at the workstation | ||
| Perception level required for the task | ||
| Whether artificial lighting is used | ||
| If there are glare issues | ||
| Vibrations | Duration of daily exposure to vibrations | |
| Nature of the vibrations | ||
| Mental Load | Time Pressure | Time required to reach the normal work pace |
| Method of worker compensation | ||
| If the worker can take breaks | ||
| If the work is on an assembly line | ||
| If delays need to be made up | ||
| If the worker can stop the machine or assembly line in case of an incident | ||
| If the worker can briefly leave their workstation outside of scheduled breaks | ||
| If the worker needs to be replaced by another worker | ||
| Consequences of the worker's absences | ||
| Attention | Level of attention required for the task | |
| Duration the level of attention must be maintained | ||
| Significance of the risks associated with a lack of attention | ||
| Frequency of risks due to lack of attention experienced by the worker | ||
| Technical feasibility of talking at the workstation | ||
| Time the worker can divert their gaze from work per hour, given the level of attention | ||
| Number of machines the worker must attend to | ||
| Average number of signals per machine per hour | ||
| Different interventions the worker must perform | ||
| Total duration of all interventions per hour | ||
| Complexity | Average duration of each repeated operation | |
| Average duration of each cycle | ||
| Psychosocial Aspects | Initiative | If the worker can change the order of operations they perform |
| If the worker can control the pace of operations they perform | ||
| If the worker can work ahead | ||
| If the worker controls the pieces they produce | ||
| If the worker occasionally makes adjustments | ||
| Quality standard for the manufactured product | ||
| If there is a positive influence of the worker on the product quality | ||
| Possibility of making errors | ||
| In case of an incident, who should intervene | ||
| Who regulates the machine | ||
| Communication with Other Workers | Number of people visible to the worker within a 6-meter radius | |
| If the worker can leave their workstation | ||
| Regulations regarding the right to speak | ||
| Technical possibility of speaking at the workstation | ||
| Necessity to speak at the workstation | ||
| If organized workers' expression exists | ||
| Supervisor Relationship | Frequency of instructions received from the supervisor during the day | |
| Extent of front-line supervision | ||
| Intensity of hierarchical control | ||
| Dependency on non-hierarchical higher-ranking positions | ||
| Social Status | Duration of worker training for the position | |
| Required general education level for the position | ||
| Working Times | Quantity and Organization of Work Time | Weekly duration of work time in hours |
| Worker's schedule type | ||
| Regulation regarding overtime hours | ||
| Tolerance for schedule delays | ||
| If the worker can determine break times | ||
| If the worker can determine the end of their workday | ||
| Break times |
Once the data is collected, a series of scoring tables must be consulted to obtain assessments for each variable and dimension. The number of tables that need to be consulted is quite high, making the application of the method labor-intensive without the use of specific software like that offered by Ergoniza. The assessment obtained for each dimension ranges from 0 to 10, and the interpretation of these scores is done according to Table 3.
| SCORE | ASSESSMENT |
|---|---|
| 0, 1, 2 | Satisfactory Situation |
| 3, 4, 5 | Mild Discomfort. Some improvements could provide more comfort to the worker. |
| 6, 7 | Moderate Discomfort. Risk of Fatigue. |
| 8, 9 | Severe Discomfort. Fatigue. |
| 10 | Harmful Situation. |
The final assessment is represented in the form of a histogram. This graphical representation allows for a quick overview of working conditions and facilitates an initial diagnosis. By knowing which elements are less favorable in the working conditions, priorities can be established when intervening in the various evaluated factors.
Diego-Mas, J.A., Poveda-Bautista, R. y Garzon-Leal, D.C., 2015. Influences on the use of observational methods by practitioners when identifying risk factors in physical work. Ergonomics, 58(10), pp. 1660-70.
Guelaud, F., Beauchesne, M.N., Gautrat, J. Y Roustang G., 1977. Pour une analyse des conditions du travail ouvrier dans l'entreprise. Paris: A. Colin.
NTP 175, Evaluación de las condiciones de trabajo: el método L.E.S.T. Instituto Nacional de Seguridad e Higiene en el Trabajo. Ministerio de Trabajo y Asuntos Sociales. España.
Diego-Mas, Jose Antonio. Global ergonomic analysis using LEST method. Ergonautas, Universidad Politécnica de Valencia, 2023. Available online: https://www.ergonautas.upv.es/ergoniza/app_en/land/index.html?method=lest
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