versión On-line ISSN 0718-5073
Rev. ing. constr. vol.26 no.3 Santiago dic. 2011
Revista Ingeniería de Construcción Vol. 26 N°3, Diciembre de 2011 www.ing.puc.cl/ric PAG. 284-298
Musculoskeletal risks analysis related to steel reinforcement works. Good practices
Análisis de los riesgos musculoesqueléticos asociados a los trabajos de ferrallas. Buenas prácticas
Mónica López Alonso*1, Ma Dolores Martínez Aires*, Esther Martín González*
* Universidad de Granada, Granada. ESPAÑA
The MSD -musculoskeletal disorders- represent 45% of labour injuries. Specifically, construction workers involved in the different activities linked to steel reinforcement for an insitu concrete are exposed to a high rate of such injuries. This paper reviews in detail the physical risks of the iron worker, installing steel reinforcement for an insitu concrete pour. This study has revealed that the Spanish legislation, enforced since 1997 (transposing the European Directive on the implementation of minimum safety and health requirements at temporary or mobile construction sites) is not correcting the multiple musculoskeletal risk factors of these workers. It's proposed for the analysis of such risks musculoskeletal, the use of different ergonomic methodologies. In one hand, the load handling guide from the Spanish National Health and Safety Institute, and in the other, the method ERGO/ IBV, developed by the Biomecanics Institute of Valencia for the repetitive tasks analysis. The use of these tools allows the design of new working methods that reduce the risks discussed. Subsequently, after the identification of the large number of risks musculoskeletals, it's defined a set of better practices for these workers, exposed to very demanding work conditions and with low culture of prevention.
Keywords: Ergonomics, musculoskeletal Risk, steel reinforcement worker
According to Eurostat (European Commission 2011), in the EU15 (Austria, Belgium, Denmark, Finland, France, Germany, Great Britain, Greece, Ireland, Italy, Luxembourg, Netherlands, Portugal, Spain and Sweden), Spain is the head of accidents with more than 3 days lost in the construction sector 2006.
In 2009, according to data from the Spanish National Statistics Institute (INE, 2011), in this sector occurred a total of 129,234 accidents with sick leave.
Latest data provided by OSHA (OSHA, 2011) indicate that workers in the construction sector have increased exposure to biological, chemical, muscle skeletal, as well as noise and temperature changes; 45% of workers say their work affects their health. Similarly, the data indicate that back musculoskeletal disorders, in the long run produce permanent damage to these workers in a percentage between 60% and 90% while in the day to day, it is between 15% and 42%.
In Spain, as deduced from the VI National Survey on Working Conditions (INSHT, 2007), construction presents a higher prevalence of musculoskeletal disorders that global sectors (3.160 compared to 2.650 per 100.000 workers), being the sector in which there is a 47.5% of the risks related with musculoskeletal problems associated with effort, posture or movement.
The significance of the risks inherent to the absence of good habits to adopt the proper body mechanics, implementing suitable ergonomic strategy in the construction sector is growing (Ferreras R., C. Piedrabuena 2007) given that physical overexertion is the leading cause of accidents with loss in the sector (over 25% of all accidents), followed at some distance from those caused by blows with blunt objects or tools, and falls.
According to OSHA (OSHA, 2000, OSHA, 2004), the risks associated with inadequate mechanical body postures have their origin in the application of brute force at work, the repetition of tasks, positions, whether forced or static, rapid movements, contact compression or tension, vibration and cold temperatures. This paper discusses these risks, specifically in the case of steel reinforcement workers and the musculoskeletal disorders caused.
2. General causes of ergonomic problems in the construction sector
As derived from the VI National Survey on Working Conditions (INSHT, 2007), in the construction sector the main psychosocial risk is given by the need of permanence in a high or very high degree of attention, as required by the tasks developed by 70.5% of the workers. In addition to this risk should be noted that, in percentages very important, workers are frequently exposed to risk caused by the lack of proper ergonomics strategy in their work performance such as highly repetitive and very short tasks (47.8%), the need to work very fast (45.6%) or tight or very short deadlines (38.1%) and dealing with clients (the 36.3%).
The problems associated with lack of appropriate ergonomic conditions at work are becoming increasingly important. An increase in the number of musculoskeletal disorders among such workers is being produced, associated mainly to inadequate ergonomic conditions. According to Attwood (Attwood et al. 2004) a musculoskeletal disorder involves damage to bones, muscles and other parts of the body related to the joint tissues. According to Piedrabuena et al., (Piedrabuena et al. 2005), musculoskeletal injuries are those that affect muscles, tendons, bones, ligaments and intervertebral discs.
Table 1 shows the distribution of musculoskeletal ailments in workers of the construction sector according to the VI National Survey of Working Conditions (INSHT). Likewise, Table 2 shows the factors that are commonly associated to ergonomic problems in the construction sector in Spain.
Table 1. Musculoskeletal diseases (INSHT, 2007)
Table 2. Working physical demands according to activity branch (INSHT. 2007)
The most influential factors in musculoskeletal problems include age, duration of employment contract, time of the accident, company size and day of week (Burdorf et al. 2007), although other factors exist (INSHT, 2003; Piedra et al. 2005) such as:
1. - Environmental conditions in the workplace. Environmental conditions of the workplace, in particular temperature and air velocity, humidity and radiation, along with the "intensity" or the work activity level and clothing used, can lead to risky situations for the health of workers, known as temperature stress either by heat or cold.
2. - Tools and equipment management. Several factors can affect health and work efficiency when using hand tools: time-use tool, awkward postures for handling, the weight of the tool vibration and repeatability.
3.- Machinery management. Workers who handle heavy machinery on irregular land are likely to have problems in the lower part of their back. Continuous vibration and leaps as well as bounds in the seat can compress and damage intervertebral disc and back joints.
4. - Loads manual handling. The manipulation of materials includes several stages that involve a high effort to reach the load through bending or kneeling, lifting the load, transferring the weight of the object to a load position and, finally, transport the load to the desired location.
5. - Order and cleanliness in the workplace. Keep the work area neat is pretty complex in the construction sector, as the movement of materials and the generation of residues are very frequent Obstacles in the work area can cause slips or setbacks, disordered areas may prevent the use of trolleys and lack of order in the workplace increases ergonomic hazards.
6. - Psychosocial risks. Workers may respond differently to an unexpected event, and these responses can trigger pathophysiological mechanisms of a disease (Díaz D.L., 2011).
3. Analysis methods
One can distinguish two large groups of musculoskeletal disorders according to the affected body area: back injuries, mainly in the lower back zone and upper limb injuries as well as neck and shoulders.
The main cause of back disorders, especially in the lumbar segments of the spine and associated muscles and ligaments, are the manual activities upon handling loads. However, most of these diseases are not caused by accidents or unique or isolated attacks, but as a result of repeated small injuries. Some simple, repetitive movements, such as grabbing, pushing or reach-tasks are repeated in the construction sector up to 25,000 times a day (INSHT, 2009).
The ergonomic analysis often used several methods, the end result being a combination of the results of various tests. In the first phase, the experimental information is collected through manuals, articles, previous studies on the subject and other available documents. Once this process has been done, the method(s) that best meet the objectives of the study in accordance with available resources, time, population size, etc.. is choosed.
Ergonomic evaluation methods, based on the classification criteria of Buck Lehto (Lehto B., 2008), are physical, quantitative, and mixed with a component of objectivity and subjectivity (as they are based on subjective observations of objects to be scored according to predefined tables). For example, the estimate of the position through observation is a subjective method as previous studies have shown different degrees of validity and reliability, providing little information about the conditions necessary to achieve acceptable reliability (Bao et al., 2009).
In the case of risk assessment and prevention of disorders that cause skeletal muscles associated with repetitive tasks can be applied, at the present moment, different methods (see Table 3). The practical application of these methods is based primarily on gathering information on various risk factors such as the repeatability of upper limb movements, the positions taken by the arms, neck, wrists and hands, or duration of exposure to different positions/jobs.
Table 3. Main methods of ergonomic evaluation. Own elaboration
4. Effects on workers
The effects on the worker that has each of the risks from inadequate ergonomic strategy (see Table 2) are the following:
1.- The extreme positions of the spine and joints (eg, push-ups and twists) done at work is detrimental to the back, neck, arms and legs, especially if sustained for a long time or performed repeatedly. Body postures very common in the construction sector (Piedrabuena et al., 2005).
2.- As for heavy loads several studies claim that about 20% of all injuries at workplace are back injuries, and nearly 30% are due to overexertion. These data provide an idea of the importance of correct evaluation of tasks involving lifting loads and proper maintenance of jobs involved (Waters et al., 1994).
3.- The injuries caused by handling of loads correspond to a high percentage (about 20% of total), being the most common injury the ones of skeletal muscle type, particularly those affecting the back.
4.- Injuries from heavy lifting may originate as a result of inadequate ergonomic conditions for handling loads (unstable loads, inadequate clamping, ...), slippery due to the characteristics of the worker who performs it (lack of information about the ideal conditions for lifting, improper outfit, etc.) or by excessive weight lifting. All aspects gathered by the method (INSHT, 2003).
5.- Environmental conditions of the job: the days of physical labor, as well as outdoor work situations can lead to muscle fatigue and thermal stress.
Figure 1 shows how a large percentage of workers in the construction sector have discomfort in their lower back zone.
Figure 1. Distribution of slight muscular-skeletal pains undergone by construction workers. (INSHT. 2007)
5. Brief ergonomic analysis of steel reinforcement workers job
In Spain, according to Real Decreto 2010/1996, the main tasks of steel reinforcement workers are:
- To prepare materials with the conditions of shape, length and geometric characteristics suited to each armor.
- To build armor in the workshop, which involves measuring, cutting and bending steel bars, as needed.
- To install and assemble on site the armor built at the workshop and other made-in site for its subsequent concreting.
- To organize steel storage (wires, rods, mesh and molded parts) and control the quality of these materials.
What kind of problems arise from an improper ergonomics strategy at work, at steel reinforcement jobs?
Skeletal muscle risk factors at steel reinforcement jobs
Table 4 shows, schematically, a summary of the various risk factors derived from skeletal muscles with an improper body mechanics developed in the construction activities or procedures that are performed on steel reinforcement jobs.
Table 4. Muscular-skeletal risks according to main tasks developed during reinforcement matting stage (Instituto Navarro de Seguridad Laboral, 2008)
Figure 2. Laying of curbs (Bust et al., 2005)
6. Good practices
From the data provided by the VI National Survey on Working Conditions good practices are also deduced in the construction sector:
1° In more than 50% of the cases, measures were taken in order to improve working conditions aimed to reduce the risks of musculoskeletal disorders.
2 ° Only 21.7% of the cases decided to introduce changes in working methods.
3 ° In more than 30% of the cases, measures taken only made changes in the machinery and equipment, without addressing the underlying causes of workplace design, as has been said before, are those that give rise to more risk and more difficult to change because, in most cases, are part of the habit of work.
In addition to the above, there is progress in the industrialization of the construction sector and the design of mechanisms, which among other benefits, prevent musculoskeletal risks to the worker (see Figure 2d and 3) which must be considered as good practices. In the field of steel rods, the use of prefabricated reinforcement is increasingly common, and not only in welded steel mesh (see Figure 4).
Figure 3. Different systems for cobblestones placement
Figure 4. Pre-fabricated reinforcement mat
Figure 5. Tools for tying up reinforcement bars, with extension handle (Albers E., 2007)
Finally, it should be presented a series of good practices to prevent or reduce musculoskeletal risks steel reinforcement workers described in the previous section. In general, the phase of selection and purchase of steel rods products, must provide the purchase of materials in such ways that are acquired as needed, that is, trying to reduce the stored material. This eliminates the need to maneuver and to make unnecessary movements around the materials.
Forced postures of trunk and arms
- Use aids that maintain an adequate level of work. In work at ground level, bend the legs and crouch, avoiding keeping the legs straight, then bend the back.
- Use of fixing tools that reduce crouched positions and tools to tie reinforced bars and rods (see Figure 7).
- The use of platforms to support columns and other components can reduce back flexion.
Manual handling of loads
- Handle the loads close to the body, at a height between the elbows and knuckles to reduce tension in the lumbar region and avoid having to make unnecessary handling (see Figure 6).
- While analyzing the load prior to lifting it, make a "lifting plan" (shape and size, weight, grip areas, potential danger points, stability, etc.. ) If materials weigh more than 25 kg, they should not be lifted by one person, it is necessary to use mechanical aids or seek the help of another worker.
- Separate the feet to provide a stable and balanced position for lifting.
- Bend the legs at all times keeping the back straight.
- Stretching and warm up before and after work and during breaks to be made when working long time in an awkward position.
- Place materials as close as possible to the work area. This reduces transport distances of the same.
- Estimate the rotation of the trunk in determining the angle formed by lines connecting the heel to the shoulder line (see Figure 6). Whenever possible, tasks should be designed so that the loads are handled without making turns. The turns of the trunk increases the compressive forces in the lumbar area.
- Activity tied to the knees, we recommend alternating positions of the sword inclined squatting and kneeling positions.
Figure 6. Posture and position adequate (INSHT, 2003)
Figure 7. Power tool for steel rods
Force, repetitive and forced postures of hand tools
- Use Ergonomic Hand Tools: with proper termination of the handle of adequate roughness and tools which push or twist exercise it may be desirable that the surface is mottled or grooves in the opposite direction to the movement.
- Use power tools instead of hand whenever possible for tying and knotting of the bars.
- Change task, perform stretching and take breaks from repetitive tasks.
- Plan job rotation positions of different types.
- When welding, push the mask up and down with the hand, avoiding sudden movement of neck to lower it.
Work over irregular and unstable surfaces
- If there is no choice but to work at floor level, follow the following instructions:
. If you must work on your knees, to minimize contact stress of the knees with the surfaces of the bars, use padded knee.
. Take short breaks every 20 minutes of work with the trunk flexed. Place the back straight and stretch, take a few steps and continue working.
- Maintain a good level of fitness and flexibility.
- Sort the materials as close as possible to where they have to be placed.
- Make sure that the soil is dry and there are no obstacles. Back injuries occur mostly when the person slips or trips.
Disorders resulting from poor ergonomic practices are not as obvious as accidents at work or a traffic accident while traveling. Furthermore, prevention of these risks is not as eloquent as in those in which the risk is reduced by placing a collective protection or by the use of PPE. Such risks are part of the standard technique of the employee or are problems inherent from the use of certain machines (as in the case of vibration tools handheld). It is important therefore to be aware of existing ergonomic risks the post of work and to try to avoid them.
The agents involved in the production process must observe the working methods and habits of employees and watch the ergonomic measures. Prevention of injuries musculo-skeletal at work is now one of the biggest challenges for European countries.
The activity of a steel rods has certain risk factors that may cause MSDs if not follow adequate work habits. It is therefore important to pay attention to the positions of work, perform repetitive movements and cargo handling, in particular the general objectives theoreticaly studied, which are:
- Try to facilitate or improve the environment of cargo transportation in this sector.
- Improve the development of tasks that require repetition during its work.
- Improving environmental working conditions so that these are not harmful to the health of workers or for the performance of their work.
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Fecha de recepción: 01/ 07/ 2011 Fecha de aceptación: 01/ 09/ 2011