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Falls from height during the floor slab formwork of buildings: Current situation in Spain
Journal of Safety Research 40 (2009) 293–299
Contents lists available at ScienceDirect
Journal of Safety Research j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j s r
Falls from height during the floor slab formwork of buildings: Current situation in Spain Jose M. Adam a,⁎, Francisco J. Pallarés b, Pedro A. Calderón a a b
ICITECH, Departamento de Ingeniería de la Construcción y Proyectos de Ingeniería Civil, Universidad Politécnica de Valencia, Camino de Vera s/n, 46071 Valencia, Spain Departamento de Física Aplicada, Universidad Politécnica de Valencia, Camino de Vera s/n, 46071 Valencia, Spain
a r t i c l e
i n f o
Available online 4 August 2009 Keywords: Construction industry Occupational safety Formwork Accident prevention Injuries Fatalities Concrete slabs
a b s t r a c t Problem: One of the phases with the highest risk of falls from a height in the construction of a building is during the floor slab formwork stage. This paper analyzes this particular risk, as well as the most frequently used fall-protection systems. Method: A survey was carried out to define the current situation in Spain with regard to falls from a height during floor slab formwork and the fall-protection systems used to prevent such a risk. Results: The results of the survey clarified the current situation in Spain with regard to this risk, and made it clear that there is considerable risk of falling from a height during the floor slab formwork stage. Discussion: All the safety systems analyzed presented a series of weak points that should be studied in detail before they can be used on building sites. Impact on industry: The risk of falling associated with floor slab formwork and the most frequently used protection systems are analyzed. As no research had been carried out to date on this type of risk, we consider the research presented in this article to be a pioneer in the field. © 2009 National Safety Council and Elsevier Ltd. All rights reserved.
1. Introduction Due to its particular nature, the construction industry is among those with the highest risk of accidents in the world (Jannadi & Assaf, 1998; Jannadi & Bu-Khamsin, 2002), and in most countries the rate of fatal accidents in the construction industry is higher than in any other sector (Alves, 1999; Suraji, Duff, & Peckitt, 2001). According to data gathered by Camino López, Ritzel, Fontaneda, and González Alcántara (2008) and Müngen and Gürcanli (2005), Spain has some of the highest accident rates in the European Union. The most recent data available in Spain (Instituto Nacional de Seguridad e Higiene en el Trabajo, 2007) show that the construction industry accounts for 27.3% of occupational accidents in this country and that 34.6% of all serious accidents and 33.9% of all fatal accidents in Spain occur in the construction sector. Camino López et al. (2008) analyzed the factors involved in the Spanish situation. Seventy-four percent of the construction work in Spain involves the construction of buildings (Instituto Nacional de Seguridad e Higiene en el Trabajo, 2003), which is where the majority of fatal accidents occur, accounting for 43% of all accidents and 35.2% of fatalities (Instituto Nacional de Seguridad e Higiene en el Trabajo, 2003). The problem, of course, is not only confined to Spain but exists on a worldwide scale. This hazard has been studied by various authors (e.g., Hinze, Pedersen, & Fredley, 1998; Janicak, 1998; Jeong, 1998; Kines, 2002; Larsson & Field, 2002; Huang & Hinze, 2003; Macedo &
⁎ Corresponding author. Tel.: +34 963877562; fax: +34 963877568. E-mail address: [email protected] (J.M. Adam).
Silva, 2005; Müngen & Gürcanli, 2005), all of whom agree that falls from a height are among the most frequent accidents in the construction industry and a major cause of fatalities. Jannadi and Assaf (1998) and Zambianchi (2007) concluded that the preparation of formwork for concrete structures was the most dangerous stage in relation to falls, and Adam, Pallares, Calderon and Payá (2007) found that the highest risk of all occurred during the preparation of the floor slab formwork. As no research has to date examined the danger of falls from a height during the floor slab formwork stage, a study was carried out with the objective of reducing this risk as far as is practically possible. 2. Risk of falls from a height during the laying of floor slab formwork 2.1. General Of all the fatal accidents caused by falls in China in 1999, a total of 34 cases were identified as having occurred during the preparation of formwork for concrete structures, accounting for 6% of all fatalities attributed to falls (Tam, Zeng, & Deng, 2004). Huang and Hinze (2003) pointed out that the risk of falling is often present when provisional / temporary structures are being used, such as when floor slab formwork is being laid. Jannadi and Assaf (1998) and Zambianchi (2007) also identify the setting up of formwork as one of the stages with the highest risk of accidents, especially falls. This risk is more apparent during the formwork stage prior to the reinforcement and pouring of concrete for the floor slab of a building (Adam, Pallarés, Calderón & Payá, 2007). The work involved in laying out formwork is described in the following sub-section, where the
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construction process is explained; many of these actions involve a high risk of a fall. A total of 161,136,800 m2 of concrete formwork were constructed in Spain in 2006 (Asociación de Empresas Constructoras de Ámbito Nacional, 2006). It is therefore evident that there is a great risk of falls for workers that are engaged in the floor slab formwork process.
3) Assembly of the formwork boards on auxiliary metal structures (shores and steel beams). 4) When the formwork is complete, the reinforcement is assembled and the floor slab concrete is poured.
2.3. Analysis of the risk of falls 2.2. Description of the floor slab formwork process The assembly of floor slab formwork that is common in Spain includes the stages described in Fig. 1. There are other methods for the construction of slabs, but they are not used a great deal in Spain. The most commonly used method in Spain includes the following stages: 1) Assembly of shores and steel beams. 2) Positioning of steel beams (laid over the structure built in Stage 1).
During assembly of the floor slab formwork, there is a stage during which the risk of falling is significantly high. This is when the metal structure supporting the formwork (i.e., shores and steel beams) has been assembled and workers have to climb onto the structure to position the boards that make up the formwork (Stage 3 in Fig. 1). This risk is shown in Fig. 2. Since the risk of falling during this process is clearly apparent, it follows that workers should use a safety system when carrying out these tasks, so as to eliminate, or at least minimize, the risk of falling.
Fig. 1. Assembly process of floor slab formwork.
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Fig. 2. Risk of fall from height during floor slab formwork (note the position of the worker).
3. Fall protection systems commonly used during floor slab formwork 3.1. General approach A great many falls are caused by suitable safety equipment not being available (Huang & Hinze, 2003). Many falls could be prevented through the use of suitable fall protection systems. Those involved in occupational safety have recently started to look more closely at methods for preventing falls from height in the construction industry (Buckley, Chalmers, & Langley, 1996). There are several fall-protection systems that can be used during the floor slab formwork stage. The intention is to prevent the fall, or to reduce the consequences that it may have for the worker. Zambianchi (2007) lists the most common protection systems as: a) b) c) d)
Safety lines Auxiliary scaffolding Alsina anti-fall systems Safety nets underneath floor slabs
which workers can stand to lay formwork boards. This scaffolding is at a lower height than the formwork being built. The use of auxiliary scaffolding is mentioned by Johnson, Singh, and Young (1998) for the construction of roofs. Zambianchi (2007) mentions the possibility of using these items for the assembly of floor slab formwork. Fig. 4 shows the formwork process using this method. When correctly used, this scaffolding prevents falls.
3.4. The Alsina anti-fall system Another major safety system is the Alsina anti-fall system. This system provides the worker with an attachment point, totally eliminating the risks of a fall during the floor slab formwork stage. The system consists of a foldable steel support and a sliding section that brakes on sensing a sudden acceleration, so that in the event of a fall the device will support the weight of the worker.
A detailed description of the above protection systems follows. 3.2. Safety lines The use of safety lines is based on attaching cable/ropes to the structure being built, or to some auxiliary item. When a worker has to work at a height above the ground (as when assembling floor slab formwork), he/she will be attached to the safety line, thus preventing a possible fall. The worker's safety harness is attached to a safety line by an auxiliary device, which in a large number of cases is a retractable item. An illustration of a worker attached to a safety line and carrying out formwork can be seen in Fig. 3. As indicated by Zambianchi (2007), one method of attaching the safety line is by placing a steel tube inside the still wet concrete of a column. Then, a steel bar is inserted inside this tube to which the safety line is fitted. This system, when correctly used, prevents the worker from falling. 3.3. Auxiliary scaffolding Another way of preventing or reducing the effects of a fall during the floor slab formwork stage is the use of auxiliary scaffolding on
Fig. 3. Worker laying formwork boards while attached to a safety line.
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Fig. 4. Worker laying formwork boards from auxiliary scaffolding.
The device is installed as follows: a) A conical steel tube is inserted into the wet concrete of the column to hold the safety device in place. b) When the concrete of the column has reached the required strength, the steel support is placed in position within the conical holder. The worker then attaches his/her harness to the system and can work safely. If the columns are made of steel, the safety system is attached to the columns by a mechanical device. Fig. 5 shows a worker attached to the Alsina anti-fall system, while laying the boards that make up the floor slab formwork.
Fig. 5. Worker laying formwork boards while attached to the Alsina anti-fall system.
experts on the risks of falls from heights on building sites. The five sections of the questionnaire addressed the following areas: a) b) c) d) e)
Risk of falls from a height. Comparison of different safety systems in terms of Comparison of different safety systems in terms of Comparison of different safety systems in terms of Comparison of different safety systems in terms of
safety. installation. cost. choice.
3.5. Safety nets underneath the floor slabs In Spain safety netting is frequently placed under floor slabs as an anti-fall protection system. This netting is attached to the shores that form part of the formwork system, cushioning a possible fall. Fig. 6 shows a worker laying the boards for the formwork while protected by the netting. Although this safety system does not actually prevent workers from falling, it does mean that the possible consequences of the fall are reduced.
Some of the results of the survey are used in this section to determine the current situation in Spain related to the risk of falls from a height. The results of the remaining sections of the
4. Current situation in Spain 4.1. Method In order to determine the current situation in Spain, a survey was carried out on falls involving workers laying the formwork boards for the floor slab. This survey was conducted by sending questionnaires via e-mail to qualified experts (a total of 193) in the field of health and safety in the construction industry throughout Spain. Many construction company's were contacted randomly and their safety managers also filled out the form. Most of those surveyed were in charge of safety for their company’s construction contracts (data obtained from the survey), ensuring that all safety measures are taken to minimize risks (technicians acting as safety officers, assessing safety levels at work sites, and preventing possible job-related hazards). The questionnaires contained 12 questions (see Appendix A), in five sections, related to the phase involving the laying of formwork boards for the floor slab, in order to draw on the experience and opinions of these
Fig. 6. Worker laying formwork boards with a protective net underneath the formwork.
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questionnaire are used in Section 5 to compare and study the suitability of fall-protection systems. All the results are condensed in graphs and the discussions are outlined below. 4.2. Results and discussion All the experts surveyed agreed that the risk of falling from a height during the floor slab formwork stage is extremely high: 27% of those interviewed believed that it was the most significant risk the of building structure stage, while 73% classified it as one of the most significant. Forty-four percent of the experts surveyed had experienced at least one case in which a worker had fallen while laying the floor slab formwork, with more or less serious consequences to the worker. Fig. 7 summarizes the number of falls recorded by each of the individuals surveyed. The survey does not inquire into the details of individual accidents, however, it is noteworthy that 38% of the cases were serious and 39% were minor (see Fig. 8). This means that 77% of the falls resulted in some kind of injury. Based on these statistics and the survey carried out, the significance of the risk of falls during the floor slab formwork stage of building becomes evident. 5. Suitability of fall-protection systems 5.1. Method Once the situation in Spain regarding falls from height during the floor slab formwork of buildings had been established, during the second stage of the research the results from the survey sections ((b) comparison of different safety systems in terms of safety; (c) comparison of different safety systems in terms of installation; (d) comparison of different safety systems in terms of cost; and (e) comparison of different safety systems in terms of choice), were used to determine the suitability of each of the safety systems proposed in Section 3. Results and discussion follow. 5.2. Results The experts surveyed were asked how many safety systems they were familiar with and, as can be seen from Table 1, it appears that the bestknown systems are the use of safety nets underneath the formwork, the Alsina anti-fall system, and safety lines. Most of the experts were not aware of the use of auxiliary scaffolding as a safety precaution, but it must be said here that many of them considered auxiliary scaffolding as an aid to laying formwork and not as a protection against falls. Regarding the the proper installation of the most commonly used safety systems (Alsina anti-fall system and safety nets), 49% of the experts considered that the Alsina system was easier to install than the safety nets (32%), as can be observed in Fig. 9. The Alsina anti-fall system also produces the lowest level of interference with the construction
Fig. 8. Seriousness of injuries arising from a fall during floor slab formwork.
work (see Fig. 10). Regarding cost, 32% considered using nets underneath the formwork to be the most economical system, while 19% considered the costs to be similar, as can be seen in Fig. 11. When asked which safety system they would adopt to prevent falls during floor slab formwork, 46% of those interviewed opted for the Alsina anti-fall system, 52% for nets underneath the formwork, and 2% for safety lines (see Fig. 12). The authors of this paper have inspected a great number of buildings under construction and can support the claim that safety nets are currently the most widely used safety system in Spain to prevent falls during the floor slab formwork process, but it must also be said that in many cases the nets are not properly installed as a safety system. Eighty-three percent of those surveyed stated that nets underneath formwork do not provide complete protection against the consequences of a possible fall from a height. This percentage fell to 36% in the case of the other safety systems. The survey also examined the weak points of each of the systems, which could mainly be described as follows: a) Safety nets underneath the formwork do not prevent falls, since the worker falls into the net itself and can thus be injured by impact with columns or shores. Given that the nets are attached to the shores, the impact caused by a fall can damage or collapse the formwork system. b) The use of auxiliary scaffolding for the assembly or formwork impedes the free movement of materials and personnel on the site. It also slows down the process of laying the formwork and the repeated and awkward movements involved frequently lead to injury and even to falls from the scaffolding itself. c) The system of attaching safety lines has not been standardized. In addition, in order for it to be effective, the safety line has to be sufficiently taut so that the height of the fall is not excessive. d) The use of the Alsina anti-fall system requires the assembly of a large number of items, such as the various parts that make up the metal elements, those necessary for fitting the attachment tube inside the support, and those required for assembling the retractable items. 5.3. Discussion Among the safety systems designed to eliminate or minimize the risk of falls during floor slab formwork, the most frequently used in Spain are: nets placed underneath the formwork, the Alsina anti-fall system, and safety lines. The great majority of the experts surveyed stated that safety nets underneath formwork do not completely prevent the consequences of Table 1 Percentage of experts familiar with each safety system. Nets under formwork
Fig. 7. Number of falls during floor slab formwork. Percentage of safety experts surveyed that have experienced them.
Percentage of experts with knowledge 100 of the safety system (%)
Alsina Anti-fall System
Safety Auxiliary Lines Scaffolding
94.1
94.1
5.9
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Fig. 9. Results of the system with the easiest installation. Fig. 11. Results on the system with the lowest cost.
possible falls from a height associated with the assembly of floor slab formwork. In spite of this, safety netting is the most common protection system used in this stage of construction. This can be explained by the low cost of the system and its ease of installation. However, it must be said that very often the nets are not installed correctly and many are placed near different objects that can cause injuries to workers in case of a fall. Furthermore, when nets are extended under the formwork, the need to motivate personnel to use safety systems is lessened. The experts were more or less equally divided between those who preferred the Alsina anti-fall system and those who preferred to use safety nets (see Fig. 12). Hardly any of them would consider using safety lines; and none would consider using auxiliary scaffolding.
6. Conclusions The risk of falls from a height associated with floor slab formwork has been analyzed in this article, as well as the most frequently used protection systems to eliminate this risk. To date, no research had been carried out to analyze the risk of this type of fall. The research presented in this article is therefore pioneering in the field. Based on the survey carried out, it has been possible to ascertain the current situation in Spain with regard to falls from height during floor slab formwork, as well as the protection systems used to eliminate such a risk. From the results it has become obvious how serious the risk of falling is during the floor slab formwork stage of construction. On the other hand, each of the safety systems analyzed does have a series of weak points that must be studied in detail before they are used on building sites. The usefulness of the different systems strongly depends on the willingness of the workers to use them, and this should be taken into consideration when making the choice. It is also clear that further research is necessary in order to reduce the number of accidents occurring during the floor slab formwork stage. This should include, for example, an analysis of prevention strategies, organizational methods, and other construction processes.
Acknowledgements The authors would like to express their gratitude to the Spanish Ministry of Science and Technology for funding this research project,
Fig. 10. Results of the system that interferes least with construction work.
as well as to the Alsina Formworks Company and the safety managers of the different firms that kindly collaborated in the survey. Appendix A. Questions included in the questionnaire Question 1: What is your position in the company you work for? Please give a brief description of your work. A. 1. Risk of falls from a height Question 2: Do you think that the risk of falling from a height during the slab formwork stage is significant? a) b) c) d)
Yes, the most significant Yes, one of the most significant No, minor significance Non significant
Question 3: How many accidents have you experienced in which a worker has fallen whilst laying the floor slab formwork? a) b) c) d)
1 accident 2 accidents 3 or more accidents 0 accidents Question 4: What were the consequences for the worker?
a) b) c) d)
Serious / fatal consequences Minor consequences No consequences Don't know
A.2. Comparison of different safety systems in terms of safety Question 5: Which of the following safety systems are you familiar with? a) b) c) d) e)
Safety nets Alsina anti-fall system Safety lines Auxiliary scaffolding Others
Fig. 12. Safety system preferred by the respondents. Percentage of respondents that had a high opinion of each option.
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Question 6: Do you think that safety nets fully prevent the consequences of a possible fall from a height? a) Yes b) No c) Don't know Question 7: Do you think that safety lines, the Alsina anti-fall system and auxiliary scaffolding fully prevent the consequences of a fall? a) Yes b) No c) Don't know A.3. Comparison of different safety systems in terms of installation Question 8: Which of the following safety systems is the easiest to install? a) Safety nets b) Alsina anti-fall system c) Don't know Question 9: Which of the following safety systems interferes least with construction work? a) Safety nets b) Alsina anti-fall system c) Don't know A.4. Comparison of different safety systems in terms of cost Question 10: Which of the following safety systems costs least? a) b) c) d)
Safety nets Alsina anti-fall system Similar cost Don't t know
299
References Adam, J. M., Pallarés, F. J., Calderón, P. A., & Payá, I. J. (2007). A study of the conditions of use of a new safety system for the building industry. Engineering Structures, 29(8), 1690−1697. Alves, L. M. (1999). Construction safety coordination in Portugal. Proceedings, International Conference on Construction Safety Coordination in the European Union, CIB Publication 238, CIB Working Commission W99. Lisbon, Portugal. Asociación de Empresas Constructoras de Ámbito Nacional. (2006). Informe Anual de la Construcción Madrid, Asociación de Empresas Constructoras de Ámbito Nacional, Spain (in Spanish). Buckley, S. M., Chalmers, D. J., & Langley, J. D. (1996). Falls from buildings and other fixed structures in New Zealand. Safety Science, 21(3), 247−254. Camino López, M. A., Ritzel, D. O., Fontaneda, I., & González Alcántara, O. J. (2008). Construction industry accidents in Spain. Journal of Safety Research, 5(5), 497−507. doi:10.1016/j.jsr.2008.07.006. Hinze, J., Pedersen, C., & Fredley, J. (1998). Identifying root causes of construction injuries. Journal of Construction Engineering and Management, 124(1), 67−71. Huang, X., & Hinze, J. (2003). Analysis of construction worker fall accidents. Journal of Construction Engineering and Management, 129(3), 262−271. Instituto Nacional de Seguridad e Higiene en el Trabajo. (2003). Informe sobre el sector de la construcción (1999-2002). Datos socioeconómicos, condiciones de trabajo, accidentes de trabajo y enfermedades profesionales Madrid, Spain: Ministerio de Trabajo y Asuntos Sociales (in Spanish). Instituto Nacional de Seguridad e Higiene en el Trabajo. (2007). Siniestralidad laboral. Periodo Octubre 2006-Septiembre 2007 Madrid, Spain: Ministerio de Trabajo y Asuntos Sociales (in Spanish). Janicak, C. A. (1998). Fall-related deaths in the construction industry. Journal of Safety Research, 29(1), 35−42. Jannadi, M. O., & Assaf, S. (1998). Safety assessment in the built environment of Saudi Arabia. Safety Science, 29(1), 15−24. Jannadi, O. A., & Bu-Khamsin, M. S. (2002). Safety factors considered by industrial contractors in Saudi Arabia. Building and Environment, 37(5), 539−547. Jeong, B. Y. (1998). Occupational deaths and injuries in the construction industry. Applied Ergonomics, 29(5), 355−360. Johnson, H. M., Singh, A., & Young, R. H. F. (1998). Fall protection analysis for workers on residential roofs. Journal of Construction Engineering and Management, 124(5), 418−428. Kines, P. (2002). Construction workers´ falls through roofs: Fatal versus serious injuries. Journal of Safety Research, 33(2), 195−208. Larsson, T. J., & Field, B. (2002). The distribution of occupational injury risk in the Victorian Construction industry. Safety Science, 40(5), 439−456. Macedo, A. C., & Silva, I. L. (2005). Analysis of occupational accidents in Portugal between 1992 and 2001. Safety Science, 43(5–6), 269−286. Müngen, U., & Gürcanli, G. E. (2005). Fatal traffic accidents in the Turkish construction industry. Safety Science, 43(5–6), 299−322. Suraji, A., Duff, A. R., & Peckitt, S. J. (2001). Development of causal model of construction accident causation. Journal of Construction Engineering and Management, 127(4), 337−344. Tam, C. M., Zeng, S. X., & Deng, Z. M. (2004). Identifying elements of poor construction safety in China. Safety Science, 42(7), 569−586. Zambianchi, P. (2007). Solai in sicurezza.Specializzata, 168, 742−749 (in Italian).
A.5. Comparison of different safety systems in terms of choice Question 11: Which safety system would you adopt to prevent falls during floor slab formwork? a) b) c) d) e)
Safety nets Alsina anti-fall system Safety lines Auxiliary scaffolding Other
Question 12: List the defects, in your opinion, of the following safety systems. a) b) c) d)
Safety nets Alsina anti-fall system Safety lines Auxiliary scaffolding
Jose M. Adam has a PhD in Civil Engineering from the Universidad Politécnica de Valencia (Spain). He works as an Associate Professor at the Civil Engineering School of the Universidad Politécnica de Valencia. His main research topics are Falls from Height in the Construction Industry, Retrofitting/Strengthening of RC Structures, and Assessment of Masonry Structures. Francisco J. Pallarés has a PhD in Civil Engineering from the Universidad Politécnica de Valencia (Spain). He works as an Associate Professor at the Civil Engineering School of the Universidad Politécnica de Valencia. His main research topics are Falls from Height in the Construction Industry, Analysis of Masonry chimneys and Belltowers, and Structural Dynamics. Pedro A. Calderón has a PhD in Civil Engineering from the Universidad Politécnica de Valencia (Spain). He has a MSc in Geotechnics from the University of California-Davis. He works as a Professor at the Civil Engineering School of the Universidad Politécnica de Valencia, where he is the Teaching Director. His main research topics are Falls from Height in the Construction Industry, Geotechnics, and Retrofitting/Strengthening of RC Structures.
Contents lists available at ScienceDirect
Journal of Safety Research j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j s r
Falls from height during the floor slab formwork of buildings: Current situation in Spain Jose M. Adam a,⁎, Francisco J. Pallarés b, Pedro A. Calderón a a b
ICITECH, Departamento de Ingeniería de la Construcción y Proyectos de Ingeniería Civil, Universidad Politécnica de Valencia, Camino de Vera s/n, 46071 Valencia, Spain Departamento de Física Aplicada, Universidad Politécnica de Valencia, Camino de Vera s/n, 46071 Valencia, Spain
a r t i c l e
i n f o
Available online 4 August 2009 Keywords: Construction industry Occupational safety Formwork Accident prevention Injuries Fatalities Concrete slabs
a b s t r a c t Problem: One of the phases with the highest risk of falls from a height in the construction of a building is during the floor slab formwork stage. This paper analyzes this particular risk, as well as the most frequently used fall-protection systems. Method: A survey was carried out to define the current situation in Spain with regard to falls from a height during floor slab formwork and the fall-protection systems used to prevent such a risk. Results: The results of the survey clarified the current situation in Spain with regard to this risk, and made it clear that there is considerable risk of falling from a height during the floor slab formwork stage. Discussion: All the safety systems analyzed presented a series of weak points that should be studied in detail before they can be used on building sites. Impact on industry: The risk of falling associated with floor slab formwork and the most frequently used protection systems are analyzed. As no research had been carried out to date on this type of risk, we consider the research presented in this article to be a pioneer in the field. © 2009 National Safety Council and Elsevier Ltd. All rights reserved.
1. Introduction Due to its particular nature, the construction industry is among those with the highest risk of accidents in the world (Jannadi & Assaf, 1998; Jannadi & Bu-Khamsin, 2002), and in most countries the rate of fatal accidents in the construction industry is higher than in any other sector (Alves, 1999; Suraji, Duff, & Peckitt, 2001). According to data gathered by Camino López, Ritzel, Fontaneda, and González Alcántara (2008) and Müngen and Gürcanli (2005), Spain has some of the highest accident rates in the European Union. The most recent data available in Spain (Instituto Nacional de Seguridad e Higiene en el Trabajo, 2007) show that the construction industry accounts for 27.3% of occupational accidents in this country and that 34.6% of all serious accidents and 33.9% of all fatal accidents in Spain occur in the construction sector. Camino López et al. (2008) analyzed the factors involved in the Spanish situation. Seventy-four percent of the construction work in Spain involves the construction of buildings (Instituto Nacional de Seguridad e Higiene en el Trabajo, 2003), which is where the majority of fatal accidents occur, accounting for 43% of all accidents and 35.2% of fatalities (Instituto Nacional de Seguridad e Higiene en el Trabajo, 2003). The problem, of course, is not only confined to Spain but exists on a worldwide scale. This hazard has been studied by various authors (e.g., Hinze, Pedersen, & Fredley, 1998; Janicak, 1998; Jeong, 1998; Kines, 2002; Larsson & Field, 2002; Huang & Hinze, 2003; Macedo &
⁎ Corresponding author. Tel.: +34 963877562; fax: +34 963877568. E-mail address: [email protected] (J.M. Adam).
Silva, 2005; Müngen & Gürcanli, 2005), all of whom agree that falls from a height are among the most frequent accidents in the construction industry and a major cause of fatalities. Jannadi and Assaf (1998) and Zambianchi (2007) concluded that the preparation of formwork for concrete structures was the most dangerous stage in relation to falls, and Adam, Pallares, Calderon and Payá (2007) found that the highest risk of all occurred during the preparation of the floor slab formwork. As no research has to date examined the danger of falls from a height during the floor slab formwork stage, a study was carried out with the objective of reducing this risk as far as is practically possible. 2. Risk of falls from a height during the laying of floor slab formwork 2.1. General Of all the fatal accidents caused by falls in China in 1999, a total of 34 cases were identified as having occurred during the preparation of formwork for concrete structures, accounting for 6% of all fatalities attributed to falls (Tam, Zeng, & Deng, 2004). Huang and Hinze (2003) pointed out that the risk of falling is often present when provisional / temporary structures are being used, such as when floor slab formwork is being laid. Jannadi and Assaf (1998) and Zambianchi (2007) also identify the setting up of formwork as one of the stages with the highest risk of accidents, especially falls. This risk is more apparent during the formwork stage prior to the reinforcement and pouring of concrete for the floor slab of a building (Adam, Pallarés, Calderón & Payá, 2007). The work involved in laying out formwork is described in the following sub-section, where the
0022-4375/$ – see front matter © 2009 National Safety Council and Elsevier Ltd. All rights reserved. doi:10.1016/j.jsr.2009.07.003
294
J.M. Adam et al. / Journal of Safety Research 40 (2009) 293–299
construction process is explained; many of these actions involve a high risk of a fall. A total of 161,136,800 m2 of concrete formwork were constructed in Spain in 2006 (Asociación de Empresas Constructoras de Ámbito Nacional, 2006). It is therefore evident that there is a great risk of falls for workers that are engaged in the floor slab formwork process.
3) Assembly of the formwork boards on auxiliary metal structures (shores and steel beams). 4) When the formwork is complete, the reinforcement is assembled and the floor slab concrete is poured.
2.3. Analysis of the risk of falls 2.2. Description of the floor slab formwork process The assembly of floor slab formwork that is common in Spain includes the stages described in Fig. 1. There are other methods for the construction of slabs, but they are not used a great deal in Spain. The most commonly used method in Spain includes the following stages: 1) Assembly of shores and steel beams. 2) Positioning of steel beams (laid over the structure built in Stage 1).
During assembly of the floor slab formwork, there is a stage during which the risk of falling is significantly high. This is when the metal structure supporting the formwork (i.e., shores and steel beams) has been assembled and workers have to climb onto the structure to position the boards that make up the formwork (Stage 3 in Fig. 1). This risk is shown in Fig. 2. Since the risk of falling during this process is clearly apparent, it follows that workers should use a safety system when carrying out these tasks, so as to eliminate, or at least minimize, the risk of falling.
Fig. 1. Assembly process of floor slab formwork.
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Fig. 2. Risk of fall from height during floor slab formwork (note the position of the worker).
3. Fall protection systems commonly used during floor slab formwork 3.1. General approach A great many falls are caused by suitable safety equipment not being available (Huang & Hinze, 2003). Many falls could be prevented through the use of suitable fall protection systems. Those involved in occupational safety have recently started to look more closely at methods for preventing falls from height in the construction industry (Buckley, Chalmers, & Langley, 1996). There are several fall-protection systems that can be used during the floor slab formwork stage. The intention is to prevent the fall, or to reduce the consequences that it may have for the worker. Zambianchi (2007) lists the most common protection systems as: a) b) c) d)
Safety lines Auxiliary scaffolding Alsina anti-fall systems Safety nets underneath floor slabs
which workers can stand to lay formwork boards. This scaffolding is at a lower height than the formwork being built. The use of auxiliary scaffolding is mentioned by Johnson, Singh, and Young (1998) for the construction of roofs. Zambianchi (2007) mentions the possibility of using these items for the assembly of floor slab formwork. Fig. 4 shows the formwork process using this method. When correctly used, this scaffolding prevents falls.
3.4. The Alsina anti-fall system Another major safety system is the Alsina anti-fall system. This system provides the worker with an attachment point, totally eliminating the risks of a fall during the floor slab formwork stage. The system consists of a foldable steel support and a sliding section that brakes on sensing a sudden acceleration, so that in the event of a fall the device will support the weight of the worker.
A detailed description of the above protection systems follows. 3.2. Safety lines The use of safety lines is based on attaching cable/ropes to the structure being built, or to some auxiliary item. When a worker has to work at a height above the ground (as when assembling floor slab formwork), he/she will be attached to the safety line, thus preventing a possible fall. The worker's safety harness is attached to a safety line by an auxiliary device, which in a large number of cases is a retractable item. An illustration of a worker attached to a safety line and carrying out formwork can be seen in Fig. 3. As indicated by Zambianchi (2007), one method of attaching the safety line is by placing a steel tube inside the still wet concrete of a column. Then, a steel bar is inserted inside this tube to which the safety line is fitted. This system, when correctly used, prevents the worker from falling. 3.3. Auxiliary scaffolding Another way of preventing or reducing the effects of a fall during the floor slab formwork stage is the use of auxiliary scaffolding on
Fig. 3. Worker laying formwork boards while attached to a safety line.
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Fig. 4. Worker laying formwork boards from auxiliary scaffolding.
The device is installed as follows: a) A conical steel tube is inserted into the wet concrete of the column to hold the safety device in place. b) When the concrete of the column has reached the required strength, the steel support is placed in position within the conical holder. The worker then attaches his/her harness to the system and can work safely. If the columns are made of steel, the safety system is attached to the columns by a mechanical device. Fig. 5 shows a worker attached to the Alsina anti-fall system, while laying the boards that make up the floor slab formwork.
Fig. 5. Worker laying formwork boards while attached to the Alsina anti-fall system.
experts on the risks of falls from heights on building sites. The five sections of the questionnaire addressed the following areas: a) b) c) d) e)
Risk of falls from a height. Comparison of different safety systems in terms of Comparison of different safety systems in terms of Comparison of different safety systems in terms of Comparison of different safety systems in terms of
safety. installation. cost. choice.
3.5. Safety nets underneath the floor slabs In Spain safety netting is frequently placed under floor slabs as an anti-fall protection system. This netting is attached to the shores that form part of the formwork system, cushioning a possible fall. Fig. 6 shows a worker laying the boards for the formwork while protected by the netting. Although this safety system does not actually prevent workers from falling, it does mean that the possible consequences of the fall are reduced.
Some of the results of the survey are used in this section to determine the current situation in Spain related to the risk of falls from a height. The results of the remaining sections of the
4. Current situation in Spain 4.1. Method In order to determine the current situation in Spain, a survey was carried out on falls involving workers laying the formwork boards for the floor slab. This survey was conducted by sending questionnaires via e-mail to qualified experts (a total of 193) in the field of health and safety in the construction industry throughout Spain. Many construction company's were contacted randomly and their safety managers also filled out the form. Most of those surveyed were in charge of safety for their company’s construction contracts (data obtained from the survey), ensuring that all safety measures are taken to minimize risks (technicians acting as safety officers, assessing safety levels at work sites, and preventing possible job-related hazards). The questionnaires contained 12 questions (see Appendix A), in five sections, related to the phase involving the laying of formwork boards for the floor slab, in order to draw on the experience and opinions of these
Fig. 6. Worker laying formwork boards with a protective net underneath the formwork.
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questionnaire are used in Section 5 to compare and study the suitability of fall-protection systems. All the results are condensed in graphs and the discussions are outlined below. 4.2. Results and discussion All the experts surveyed agreed that the risk of falling from a height during the floor slab formwork stage is extremely high: 27% of those interviewed believed that it was the most significant risk the of building structure stage, while 73% classified it as one of the most significant. Forty-four percent of the experts surveyed had experienced at least one case in which a worker had fallen while laying the floor slab formwork, with more or less serious consequences to the worker. Fig. 7 summarizes the number of falls recorded by each of the individuals surveyed. The survey does not inquire into the details of individual accidents, however, it is noteworthy that 38% of the cases were serious and 39% were minor (see Fig. 8). This means that 77% of the falls resulted in some kind of injury. Based on these statistics and the survey carried out, the significance of the risk of falls during the floor slab formwork stage of building becomes evident. 5. Suitability of fall-protection systems 5.1. Method Once the situation in Spain regarding falls from height during the floor slab formwork of buildings had been established, during the second stage of the research the results from the survey sections ((b) comparison of different safety systems in terms of safety; (c) comparison of different safety systems in terms of installation; (d) comparison of different safety systems in terms of cost; and (e) comparison of different safety systems in terms of choice), were used to determine the suitability of each of the safety systems proposed in Section 3. Results and discussion follow. 5.2. Results The experts surveyed were asked how many safety systems they were familiar with and, as can be seen from Table 1, it appears that the bestknown systems are the use of safety nets underneath the formwork, the Alsina anti-fall system, and safety lines. Most of the experts were not aware of the use of auxiliary scaffolding as a safety precaution, but it must be said here that many of them considered auxiliary scaffolding as an aid to laying formwork and not as a protection against falls. Regarding the the proper installation of the most commonly used safety systems (Alsina anti-fall system and safety nets), 49% of the experts considered that the Alsina system was easier to install than the safety nets (32%), as can be observed in Fig. 9. The Alsina anti-fall system also produces the lowest level of interference with the construction
Fig. 8. Seriousness of injuries arising from a fall during floor slab formwork.
work (see Fig. 10). Regarding cost, 32% considered using nets underneath the formwork to be the most economical system, while 19% considered the costs to be similar, as can be seen in Fig. 11. When asked which safety system they would adopt to prevent falls during floor slab formwork, 46% of those interviewed opted for the Alsina anti-fall system, 52% for nets underneath the formwork, and 2% for safety lines (see Fig. 12). The authors of this paper have inspected a great number of buildings under construction and can support the claim that safety nets are currently the most widely used safety system in Spain to prevent falls during the floor slab formwork process, but it must also be said that in many cases the nets are not properly installed as a safety system. Eighty-three percent of those surveyed stated that nets underneath formwork do not provide complete protection against the consequences of a possible fall from a height. This percentage fell to 36% in the case of the other safety systems. The survey also examined the weak points of each of the systems, which could mainly be described as follows: a) Safety nets underneath the formwork do not prevent falls, since the worker falls into the net itself and can thus be injured by impact with columns or shores. Given that the nets are attached to the shores, the impact caused by a fall can damage or collapse the formwork system. b) The use of auxiliary scaffolding for the assembly or formwork impedes the free movement of materials and personnel on the site. It also slows down the process of laying the formwork and the repeated and awkward movements involved frequently lead to injury and even to falls from the scaffolding itself. c) The system of attaching safety lines has not been standardized. In addition, in order for it to be effective, the safety line has to be sufficiently taut so that the height of the fall is not excessive. d) The use of the Alsina anti-fall system requires the assembly of a large number of items, such as the various parts that make up the metal elements, those necessary for fitting the attachment tube inside the support, and those required for assembling the retractable items. 5.3. Discussion Among the safety systems designed to eliminate or minimize the risk of falls during floor slab formwork, the most frequently used in Spain are: nets placed underneath the formwork, the Alsina anti-fall system, and safety lines. The great majority of the experts surveyed stated that safety nets underneath formwork do not completely prevent the consequences of Table 1 Percentage of experts familiar with each safety system. Nets under formwork
Fig. 7. Number of falls during floor slab formwork. Percentage of safety experts surveyed that have experienced them.
Percentage of experts with knowledge 100 of the safety system (%)
Alsina Anti-fall System
Safety Auxiliary Lines Scaffolding
94.1
94.1
5.9
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Fig. 9. Results of the system with the easiest installation. Fig. 11. Results on the system with the lowest cost.
possible falls from a height associated with the assembly of floor slab formwork. In spite of this, safety netting is the most common protection system used in this stage of construction. This can be explained by the low cost of the system and its ease of installation. However, it must be said that very often the nets are not installed correctly and many are placed near different objects that can cause injuries to workers in case of a fall. Furthermore, when nets are extended under the formwork, the need to motivate personnel to use safety systems is lessened. The experts were more or less equally divided between those who preferred the Alsina anti-fall system and those who preferred to use safety nets (see Fig. 12). Hardly any of them would consider using safety lines; and none would consider using auxiliary scaffolding.
6. Conclusions The risk of falls from a height associated with floor slab formwork has been analyzed in this article, as well as the most frequently used protection systems to eliminate this risk. To date, no research had been carried out to analyze the risk of this type of fall. The research presented in this article is therefore pioneering in the field. Based on the survey carried out, it has been possible to ascertain the current situation in Spain with regard to falls from height during floor slab formwork, as well as the protection systems used to eliminate such a risk. From the results it has become obvious how serious the risk of falling is during the floor slab formwork stage of construction. On the other hand, each of the safety systems analyzed does have a series of weak points that must be studied in detail before they are used on building sites. The usefulness of the different systems strongly depends on the willingness of the workers to use them, and this should be taken into consideration when making the choice. It is also clear that further research is necessary in order to reduce the number of accidents occurring during the floor slab formwork stage. This should include, for example, an analysis of prevention strategies, organizational methods, and other construction processes.
Acknowledgements The authors would like to express their gratitude to the Spanish Ministry of Science and Technology for funding this research project,
Fig. 10. Results of the system that interferes least with construction work.
as well as to the Alsina Formworks Company and the safety managers of the different firms that kindly collaborated in the survey. Appendix A. Questions included in the questionnaire Question 1: What is your position in the company you work for? Please give a brief description of your work. A. 1. Risk of falls from a height Question 2: Do you think that the risk of falling from a height during the slab formwork stage is significant? a) b) c) d)
Yes, the most significant Yes, one of the most significant No, minor significance Non significant
Question 3: How many accidents have you experienced in which a worker has fallen whilst laying the floor slab formwork? a) b) c) d)
1 accident 2 accidents 3 or more accidents 0 accidents Question 4: What were the consequences for the worker?
a) b) c) d)
Serious / fatal consequences Minor consequences No consequences Don't know
A.2. Comparison of different safety systems in terms of safety Question 5: Which of the following safety systems are you familiar with? a) b) c) d) e)
Safety nets Alsina anti-fall system Safety lines Auxiliary scaffolding Others
Fig. 12. Safety system preferred by the respondents. Percentage of respondents that had a high opinion of each option.
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Question 6: Do you think that safety nets fully prevent the consequences of a possible fall from a height? a) Yes b) No c) Don't know Question 7: Do you think that safety lines, the Alsina anti-fall system and auxiliary scaffolding fully prevent the consequences of a fall? a) Yes b) No c) Don't know A.3. Comparison of different safety systems in terms of installation Question 8: Which of the following safety systems is the easiest to install? a) Safety nets b) Alsina anti-fall system c) Don't know Question 9: Which of the following safety systems interferes least with construction work? a) Safety nets b) Alsina anti-fall system c) Don't know A.4. Comparison of different safety systems in terms of cost Question 10: Which of the following safety systems costs least? a) b) c) d)
Safety nets Alsina anti-fall system Similar cost Don't t know
299
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A.5. Comparison of different safety systems in terms of choice Question 11: Which safety system would you adopt to prevent falls during floor slab formwork? a) b) c) d) e)
Safety nets Alsina anti-fall system Safety lines Auxiliary scaffolding Other
Question 12: List the defects, in your opinion, of the following safety systems. a) b) c) d)
Safety nets Alsina anti-fall system Safety lines Auxiliary scaffolding
Jose M. Adam has a PhD in Civil Engineering from the Universidad Politécnica de Valencia (Spain). He works as an Associate Professor at the Civil Engineering School of the Universidad Politécnica de Valencia. His main research topics are Falls from Height in the Construction Industry, Retrofitting/Strengthening of RC Structures, and Assessment of Masonry Structures. Francisco J. Pallarés has a PhD in Civil Engineering from the Universidad Politécnica de Valencia (Spain). He works as an Associate Professor at the Civil Engineering School of the Universidad Politécnica de Valencia. His main research topics are Falls from Height in the Construction Industry, Analysis of Masonry chimneys and Belltowers, and Structural Dynamics. Pedro A. Calderón has a PhD in Civil Engineering from the Universidad Politécnica de Valencia (Spain). He has a MSc in Geotechnics from the University of California-Davis. He works as a Professor at the Civil Engineering School of the Universidad Politécnica de Valencia, where he is the Teaching Director. His main research topics are Falls from Height in the Construction Industry, Geotechnics, and Retrofitting/Strengthening of RC Structures.