Occupational risk of building construction

Reliability Engineering and System Safety 105 (2012) 36–46

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Occupational risk of building construction O.N. Aneziris a,n, E. Topali b, I.A. Papazoglou a a b

National Centre for Scientific Research ‘‘DEMOKRITOS’’, Aghia Paraskevi 15310, Greece Hellenic Open University, 18, Parodos Aristotelous St., 26 335 Patra, Greece

a r t i c l e i n f o

a b s t r a c t

Article history: Received 31 March 2011 Received in revised form 23 October 2011 Accepted 10 November 2011 Available online 20 November 2011

This paper presents the quantification of occupational risk of a building construction project. Risk assessment is based on the Occupational Risk Model (ORCA) developed under the Workgroup Occupational Risk Model project (WORM), in the Netherlands, for quantifying occupational risk. This model assesses occupational risk of a worker, by taking into account his various tasks, activities and their hazards. Risk is evaluated for three types of consequences: recoverable injury, permanent injury and death. The occupational risk model is based on a set of 63 bowties, which assess risk owing to different hazards such as fall from ladder, scaffold, roofs, falling object, struck by moving vehicle, contact by moving parts, etc. ORCA calculates the risk profile of a building construction site, consisting of thirty-eight workers in different job positions, such as operators of excavators, loaders, compaction equipment, workers in excavation and framing phases, etc. All risk profiles of workers have been quantified and jobs have been ranked according to their risk. Workers installing timber formworks have the highest fatality risk (1.57  10  3/yr), followed by the workers installing reinforcement (1.52  10  3/yr). & 2011 Elsevier Ltd. All rights reserved.

Keywords: Occupational risk Construction sector Probabilistic occupational safety analysis Risk assessment model

1. Introduction Occupational health and safety is a major concern to many countries since occupational accidents represent a major source of risk. In 2007, accidents at work killed 3782 workers in Europe (EU-15) and 5527 in EU-27, while 3882435 workers were injured in EU-15, with absence of work more than three days [1]. The building and construction industry has a high contribution to overall occupational accidents, since in 2007, 703389 accidents occurred in EU-15 among which 1083 were fatal, out of 29% of total fatal accidents [1]. The construction section is very hazardous worldwide [2–4], owing to its unique dynamic nature [5], poor conditions and tough environment. The International Labour Organisation recorded 60,000 fatalities in the construction section, out of a world total of 355,000, (nearly 17%), while one in six fatal accidents at work occurred in construction, in 2003 [6]. Traditional occupational safety methods are legislation, regulation, standards, safety guidelines, collection of best practices, accident statistics, investigations and inspections, analysis of safety management systems and personal behaviour. Various accident studies have examined the causes of occupational injuries and fatalities such as those performed by the National Institute of Occupational Safety [6] and OSHA [7,8] This research investigated accident reports, analysed

n

Corresponding author. Tel.: þ302106503703; fax: þ302106545496. E-mail address: [email protected] (O.N. Aneziris).

0951-8320/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.ress.2011.11.003

the epidemiology of accidents, recommended elements for an effective accident preventive programme and identified common risk factors such as technical, organisational and managerial. Researchers have analysed several types of accidents in the construction section such as falls from height [9–12], electrical accidents [13,14] and crane related accidents [15,16] and in various countries, such as in the US [17,18], the UK [19], the Netherlands [20], Spain [21], Taiwan [22], China [23] and Kuwait [24]. The main focus was on types of accidents, injuries, age of victim and the major causes of accidents in terms of technical barrier failures. Statistical methods have been extensively used to analyse injuries and fatalities in the construction sector using descriptive statistics [9], factorial analysis [25], variance analysis [26] and multiple regression [27]. In occupational safety research, root causes influencing safety performance have been analysed, by interviewing site managers and safety officers [28], safety professionals [29], project managers [30], workers [31], accident victims [32] in the construction industry or by analysing accidents [33]. A number of factors have identified a number such as historical, economical, psychological, procedural, organisational, environmental and technical factors [28]. Statistical methods have been used in most analyses, but recently data mining techniques, including Bayesian networks, decision rules, classification trees and support vector machines, have modelled accident data and identified factors underlying accidents [34,35]. In more detail the most important risk factors influencing safety performance in the construction industry are the following [2]: poor work and organisation, company size, lack

O.N. Aneziris et al. / Reliability Engineering and System Safety 105 (2012) 36–46

of coordination, economic and time pressure, poor communications, poor involvement of workers in safety matter, constantly changing worksite, inadequate training, bad equipment selection, use or inspection and poor safety awareness. Best practices in the construction section have been selected from various sources, such as safety design manuals, checklists, interviews and various publications addressing the design phase of construction projects [36]. Designing for construction safety is a factor, which may reduce hazards at work and improve safety and health of construction workers, since it has been demonstrated that 42% of fatal accidents may be linked to the design of construction safety [37,38]. Finally, policy may also contribute to occupational safety and accident prevention. It has been claimed that the European Directive 92/57/EEC, of implementing safety and health requirements at temporary or mobile construction sites, has decreased the number of accidents by 10% in many European countries, within the period 1996–2004 [39]. Recently a new tendency has emerged trying to quantify occupational risk and by doing so to strengthen the basis for occupational risk management. In addition to the identification of causes of accidents in the workplace, this new approach is striving to quantify the extent to which various working-environment-shaping factors are present in the workplaces and combine them with workers’ exposure to hazards to arrive at quantified assessments of risk. Two semi-quantitative risk assessment methods for occupational risk assessment consists of [40,41] (a) risk matrices with two dimensions, the frequency of occurrence and the severity of consequences with semi quantified scales; (b) the proportional riskassessment technique or the so called ‘‘RSPE’’ method based on the function R¼SPE, where R is the risk, S is the severity of accident occurrence, P the frequency of the accident and its consequences and E the frequency of employee exposure to hazard. The scales of RSPE method are arbitrarily chosen and formed on a qualitative basis. A number of attempts to a more systematic and consistent approach to quantitative occupational risk assessment have appeared in the literature. A model has been developed to predict the frequency of occupational accidents in offshore oil and gas industry, based on direct, corporate and external factors [42]. Quantified risk for various occupational groups in Sweden based on the number of accidents and relevant exposure has been calculated [43]. A Construction Safety Analysis method has been proposed for assessing risk for construction activities, based on information provided via interviews among construction superintendents and safety experts, for hazard identification, probability and severity assessment of loss of control events [44]. A method has been proposed for risk assessment of several trades in the construction industry, based on estimating the overall frequency and severity from historical data of accidents in Hong Kong and their consequences regarding injuries, days lost and compensation cost [45]. Fuzzy methods have been used for risk assessment of occupational accidents in a steel company [46], at construction sites [47] and workplaces [48]. Artificial neural networks and a fuzzy inference system have been proposed to assess occupational injury risk indexes and predict number of injuries [49]. Finally an exposure–damage approach for occupational risk quantification in workplaces involving dangerous substances is proposed in [40]. The Ministry of Social Affairs and Employment in the Netherlands developed Workgroup Occupational Risk Model (WORM) project, a large scale project during 2003–2008 to improve the level of safety at workplace, by introducing quantitative occupational risk. This project had four major parts: assembly and analysis of accident and exposure data, generalisation of these data into a logical risk model, deriving improvement measures and their costs and developing an optimizer that supports cost effective risk reduction strategies, as described in [50–52]. The

37

results of WORM are presented in [53] and its main achievements are (a) construction of logic models (bowties), which allow for the quantitative assessment of risk of 63 activities of workers, such as fall from ladders, scaffolds, roofs [54,55], hit by falling objects [56], etc., built on the detailed analysis of 12500 accident reports in the Netherlands extracted from the Occupational Accident Database GISAI (Gemeenschappelijk Informatie Systeem Arbeidsinspectie), and data concerning the exposure of the Dutch population to various hazards, as reported in [57] and (b) the development of the probabilistic occupational risk model (ORCA), which performs risk calculation of workers performing various tasks and exposed to several hazards. The objective of this paper is to demonstrate the features and capabilities of the WORM occupational risk model through the application on a specific site, located in Greece. Occupational risk is performed for the construction of a one storage building with total surface 1100 m2 and serves for recreational activities of patients of a hospital. This paper is organised as follows. After the introduction of Section 1, Section 2 presents the methodology of occupational risk, Section 3 a short description of the building construction project and Section 4 presents data collection for the occupational risk analysis. Section 5 presents the job positions of all workers, Section 6 the occupational risk quantification results and finally Section 7 presents the conclusions of this analysis.

2. Occupational risk In the framework of the WORM project a model for the quantification of occupational risk has been developed. According to this model occupational risk in a company is calculated by assessing the hazards the workers in this company are exposed to, the duration of the exposure and the integration of the risk to all hazards and all workers. A tree-like structure is used to develop the composite model of ORM as depicted in Fig. 1. The top level of the tree corresponds to the entity under analysis. The second level provides the type of ‘‘Company-position’’ corresponding to a specific type of job along with the number of people in each position type. There are i ¼1,2,y,n company positions each occupied by E1,y,En employees, respectively. The third level of the tree describes for each position-type the activities required to perform the corresponding job along with

Fig. 1. Composite occupational risk model structure.

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the respective frequencies. This means that a particular job is described in terms of a number of activities each one of which is performed a specific number of times over a given period. Thus the ith job position is characterised by Mi activities A(i,1),y, A(i,j),..,A(i,Mi) each performed with annual duration T(i,j), (see Fig. 1). Finally, performance of a specific activity is associated with a number of single hazards (out of the 63 single hazards, such as fall from ladders, scaffolds, roofs, contact with falling object, electricity, etc.) and a corresponding duration of exposure to each and every hazard. Thus activity A(i,j) is associated with hazards h(i,j,1), h(i,j,2),y,h(i,j,m), where m is the total number of hazards of activity A(i,j), as depicted in Fig. 1. Risk is calculated as probability of unwanted consequence (recoverable injury, permanent injury or death) at any time during a base period of time (e.g. 1 year), from the combination of the contributions of jobs, activities and hazards. Risk is calculated in a bottom up method, from hazard to company level, while considering Fig. 1. Therefore first risk of each hazard is calculated by considering the duration of its exposure, then risk for each activity and finally risk for each job. Company risk is estimated by integrating risk of all job positions. All the details on the Occupational Risk model are provided in the WORM reports [53,58], while the basic assumptions of the risk model are the following. A worker in a given period of time undertakes a number of activities, where each activity consists of a number of hazards. Activities are sequential but may be repeated several times during the base period (e.g. 1 year) risk is calculated. The duration of the activity and the exposure to each hazard is estimated by the analyst. When performing a specific activity the worker is exposed to a number of hazards, which can occur simultaneously, specified by the risk analyst, out of the 63 hazards presented in [53]. All 63 hazards have been quantified in the WORM project on the basis of the characteristics of the average Dutch worker, as presented in [50,51,53]. While the worker is exposed to a particular hazard an accident may occur according to a Poisson random process and therefore the accident rate is constant. If an accident occurs at any instant of time during the performance of an activity, then the exposure to the same hazard and to subsequent hazards stops. Thus the probability of an accident during an activity is equal to the probability of an accident due to any of the hazards of this activity. The following model quantifies the probability of an accident of a worker during an activity with duration Tm: A worker can be in one of four states, which are the following: (a) state where no accident has occurred, while the worker performs an activity, (b) state of a recoverable injury of a worker, (c) state of a permanent injury of a worker and (d) state of fatality of a worker. Probabilities per unit of time that an accident with the respective consequence will occur in (t, t þdt), given that no accident has occurred at time t from any of the hazards present during period Tm, are the following: Prf No accident during T m g ¼ P 1,m ¼ exp½Lm T m 

ð1Þ

  L2m ½1expðLm T m Þ Pr Recoverable Injury in T m ¼ P2,m ¼

ð2Þ

  L3m ½1expðLm T m Þ Pr Permanent Injury in T m ¼ P 3,m ¼

ð3Þ

  L4m ½1expðLm T m Þ Pr Fatality in T m ¼ P 4,m ¼

ð4Þ

Lm

Lm

Lm

where Ljm is the consequence specific accident rate for period m (j¼2 for recoverable injury, j ¼3 for permanent injury and j¼4 for fatal injury), Lm is the overall accident rate for period Tm, equal to Lm ¼ L2m þ L3m þ L4m, Tm is the time period.

The consequence specific accident rate of recoverable, permanent or fatal injury for time period m (Ljm) is calculated by considering the accident rates of all hazards that affect the activity and is given by the following equation:

Ljm ¼

K X

ljm dðk,mÞ for j ¼ 2,3,4

ð5Þ

k¼1

where Ljm is the consequence specific accident rate for period m (j ¼2 for recoverable injury, j ¼3 for permanent injury, j ¼4 for fatal injury), ljk is the consequence specific accident rate for each hazard k, l2k for recoverable, l3k for permanent and l4k for fatality injury, K is the total number of hazards present during the mth period d(k,m): function mapping the kth hazard to the mth period as follows: ( 1 if hazard k is present during period m dðk,mÞ ¼ ð6Þ 0 if hazard k is not present during period m If an accident results in a recoverable injury during the performance of an activity, then it is assumed that the worker will continue to work in other subsequent activities during the year and the exposure to the hazards of the remaining activities continues. But, if during an activity an accident occurs resulting to permanent injury or death, then it is assumed that the exposure to the subsequent activities stops. Hazard rates ljk for all 63 hazards presented in Table 1 and for recoverable, permanent and fatality injury have been calculated in the WORM project. Single hazard models are based on the ‘‘bowtie’’ models, which influence diagram models, as presented in [54]. These single hazard influence diagrams consist of a centre event, primary and support barriers and a logic between primary barriers and the centre event, as presented in detail in [54] for fall from ladders, in [55] for fall from height, in [56] for contact with falling object from crane, in [59] for contact with moving object, in [60] for electricity hazard and in [61] for fires. Quantification of these models requires the determination of unconditional probabilities of primary barriers and conditional probabilities of support barriers, given the state of the primary barriers. Unconditional probabilities of support safety blocks and certain primary safety blocks are obtained through surveys focused on the working conditions in the Dutch working population. Conditional probabilities are obtained from the accident sequence probabilities divided by the joint probabilities of those support barrier that influence them. Accident sequence probabilities are obtained from the observed accident statistics, which have occurred in the Netherlands for each hazard during the period 1998–2004 and the assessment of the exposure of the Dutch working population to these hazards. The exposure to these hazards and the estimation of working conditions in the Netherlands was estimated by a series of surveys with questionnaires to the Dutch population, presented in more detail in [57]. The assessed risk rates, based on the average Dutch working conditions, exposure rates and accident statistics produced the Dutch National Average (DNA) risk rates for all 63 hazards presented in Table 1. In the ORM model unconditional probabilities of primary barriers can be quantified according to a series questions answered regarding the specific working conditions of a site, as reported in more detail in [53]. Sample of such questions is presented in Section 6, for the specific construction site. In this case modified risk is calculated, by assuming that conditional probabilities remain the same as in the case of the Dutch National Average risk rates. At a company level the expected number of consequences of a particular type is calculated by multiplying the probability of a particular consequence (e.g. fatality) for a particular job by the number of workers in that job position.

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39

Table 1 Hazards and bowties of the WORM project. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63.

Fall from height—placement ladder Fall from height—fixed ladder Fall from height—steps Fall from height—mobile scaffold Fall from height—fixed scaffold Fall from height—(de-)installing scaffold Fall from height—roof Fall from height—floor Fall from height—platform Fall from height—hole in the ground Fall from height—moveable platform Fall from non-moving vehicle Fall from height—working on height unprotected Fall on same level Fall down stairs or ramp Struck by moving vehicle Contact with falling object—cranes, part of cranes or crane loads Contact with falling object—mechanical lifting except cranes Contact with falling object—transportation vehicles Contact with falling object—manual handling Contact with falling object—other Contact flying object—machine or handheld tool Contact flying object—object under pressure or tension Contact flying object—blown by wind Hit by rolling/sliding object or person Contact with object person is carrying or using—hand held tool Contact with object person is carrying or using—not hand held tool Contact with hand held tools operated by self Contact with moving parts of a machine—operating Contact with moving parts of a machine—maintaining Contact with moving parts of a machine—clearing Contact with moving parts of a machine—cleaning Contact with hanging/swinging objects Trapped between/against Moving into an object Buried by bulk mass In or on moving vehicle with loss of control Contact with electricity—wires Contact with electricity—tools Contact with electricity—electrical work Contact with extreme hot or cold surfaces or open flame Release of hazardous substance out of open containment Exposure to hazardous substance without loss of containment Release of a hazardous substance out of closed containment—Adding/removing a substance Release of a hazardous substance out of a closed containment—transport of closed containment Release of a hazardous substance out of a closed containment—closing a containment Release of a hazardous substance out of a closed containment Fire—hot work Fire—working with or being near flammables/ combustibles Fire—fire fighting Victim of human aggression Victim of animal behaviour Exposure to hazardous atmosphere in confined space Exposure to hazardous atmosphere through breathing apparatus Impact by immersion in liquid—working in, on or under Impact by immersion in liquid—working nearby Extreme muscular exertion—handling objects Extreme muscular exertion—moving around Physical explosion Chemical explosion—vapour gas Chemical explosions—dust Chemical explosions—solids Chemical explosions—reactions

3. Brief description of construction project Occupational risk has been performed for the construction of a building consisting a total surface of 1100 m2, presented in Fig. 2 and consisting of 5 connected units. It belongs to a Greek psychiatric hospital and serves as a recreational area for the patients of the hospital. The major construction phases of this project are the following: (a) excavation and foundation, (b) framing, (c) finishing and (d) exterior landscape, presented in Fig. 3.

At the beginning of the excavation phase the site was searched for existing electricity and water networks. The excavation was performed with an excavator but also manually in areas with existing networks. Water discovered in the subsoil during excavation, was removed with a pump. Excavated subsoil was removed and the top soil was replaced for improvement and compacted mechanically with a soil compactor. The foundation and the framing of the building were made of reinforced concrete. Therefore timber beams and column formworks were erected during the framing phase

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4. Data collection

(see Fig. 3), so as to provide the desired shape and size to the concrete. The construction of the timber formworks was performed by trained workers and part of this job was performed while working on scaffolds. Steel bars used as reinforcement in the concrete were transported by trucks and welders had to cut and assemble steel at the required positions. Concrete was transported to the site by trucks and was placed in the timber formworks with the help of concrete pumps. Two concrete vibrators were used for compacting concrete at the required consolidation. Timber formworks were removed after the time required time for drying of the concrete. Risk assessment has been performed for all workers participating at the first two phases: (a) excavation and foundation and (b) framing, according to the WORM methodology, presented in Section 2. Each of these phases has been further subdivided into sub-phases, as are presented in Fig. 3.

According to the methodology presented in Section 2, data required for risk quantification of workers, operators are the following: (a) definition of job positions, (b) definition of activities for each worker, (c) definition of hazards for each activity and (d) exposure of worker to each hazard. In addition the number of workers in each job position is required in order to assess occupational risk for the whole construction project. Construction projects are dynamic, as reported in [11], and are characterised by many unique factors such as work team rotations, exposure to weather conditions and changes in topography, topology and working conditions throughout the duration of the project. Nevertheless, the construction company of this building had long experience in building projects and was able to provide the job positions, the activities and number of workers in each job position of this project. Hazard assessment for each worker was performed by the first major step of a Job Safety Analysis [62], which is the Hazard Identification. According to this method a specific job or activity is chosen and broken down into sequences of stages and all loss of control events that may occur during work are identified. Such events are fall from height, struck by falling object, contact with electricity, fire, exposure to hazardous atmosphere, etc., as presented in [53]. Hazard assessment was performed by a team consisting of an engineer with long experience building construction, the safety engineer of the construction company and the superintendents of the phases of the construction project. The list of all 63 hazards, presented in Table 1, was provided to the team, which assessed the hazards of the activities and the exposure to these hazards, for each job position, by taking into consideration the various tasks and the environmental conditions. All job positions of the building construction project as well as the hazard assessment are described in the following section.

BUILDING 2

BUILDING 1 ΚΤΙΡΙΟ 1

ΚΤΙΡΙΟ 2

Διερχόμενο δίκτυο καλωδίων

BUILD. ΚΤΙΡΙΟ 5

5

BUILDING 3 ΚΤΙΡΙΟ 3

ΚΤΙΡΙΟ 4 BUILDING 4

5. Job positions This construction project consists of 20 job positions, which are the following: truck driver in excavation and soil compaction,

Fig. 2. Building construction project.

BUILDING CONSTRUCTION

EXCAVATION AND FOUNDATIONS

FRAMING

EXCAVATION (1.1)

INSTALLATION OF CARPENTRY(2.1)

REMOVAL OF WATER (1.2)

INSTALLATION OF REINFORCEMENT (2.2)

COMPACTION OF SOIL (1.3)

FINAL CONCRETE (2.3)

FINISHING

REMOVAL OF CARPENTRY (2.4) Fig. 3. Building construction phases.

EXTERIOR LANDSCAPE

O.N. Aneziris et al. / Reliability Engineering and System Safety 105 (2012) 36–46

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Table 2 Job positions in construction site and occupational risk of the building construction work positions (/year). Worker position

Number of workers

Fatality—modified risk

Permanent injury—modified risk

Recoverable injury—modified risk

Fatality DNAa

Permanent injury DNAa

Recoverable injury DNAa

Crane operator (phase 2.1) Truck driver (phase 1.1) Truck driver (phase 1.3) Driver of concrete mixing truck (phase 2.3) Operator of loader (phase 1.1) Operator of excavator (phase 1.1) Operator of loader (phase 1.2) Operator of excavator (phase 1.2) Operator of compaction equipment (phase 1.3) Crane operator (phase 2.2) Crane operator (phase 2.3) Operator of concrete vibrator (phase 2.3) Operator of concrete pump (phase 2.3) Driver of truck crane (phase 2.4) Worker (phase 1.1) Worker (phase 1.2) Worker (phase 2.1) Worker (phase 2.2) Worker (phase 2.3) Worker (phase 2.4)

1 2 2 1

1.82E-05 2.86E-04 1.84E-04 1.65E-04

1.04E-03 5.01E-03 1.75E-03 1.08E-02

2.73E-04 2.88E-03 1.55E-03 2.39E-03

6.11E-07 1.15E-05 6.33E-06 3.10E-06

4.35E-05 2.09E-04 6.78E-05 3.82E-04

1.17E-05 1.21E-04 5.61E-05 8.36E-05

1

6.71E-04 1.26E-03

7.62E-03 7.95E-03

5.65E-03 6.67E-03

2.70E-05 5.52E-05

3.59E-04 3.75E-04

2.46E-04 2.89E-04

1 1

1.33E-03 1.38E-03

5.70E-03 6.61E-03

5.21E-03 5.90E-03

5.21E-05 7.42E-05

2.78E-04 3.09E-04

2.31E-04 2.66E-04

2

5.58E-04

7.82E-03

5.56E-03

2.10E-05

3.49E-04

2.32E-04

1 1 2

1.82E-05 6.50E-04 6.45E-04

1.04E-03 3.88E-02 2.86E-02

2.73E-04 5.82E-02 4.70E-02

6.11E-07 5.55E-05 5.21E-05

4.35E-05 4.91E-04 4.74E-04

1.17E-05 1.37E-03 1.34E-03

1

3.17E-04

3.16E-03

3.51E-03

1.96E-05

1.56E-04

1.87E-04

1 2 2 10 1 4 1

8.89E-06 1.48E-03 1.28E-03 1.57E-03 1.52E-03 4.62E-04 1.14E-03

5.25E-05 5.41E-03 3.55E-02 4.26E-02 4.81E-02 2.24E-02 3.53E-02

9.44E-05 7.89E-03 4.16E-02 6.79E-02 9.42E-02 3.54E-02 5.72E-02

5.57E-07 6.40E-05 7.36E-05 1.56E-04 1.14E-04 5.47E-05 1.18E-04

2.87E-06 2.95E-04 1.77E-04 9.30E-04 7.38E-04 4.73E-04 7.20E-04

5.05E-06 3.45E-04 2.64E-04 2.45E-03 2.15E-03 1.32E-03 1.93E-03

a

DNA: Dutch National Average risk rate.

PLANT WORKERS Twenty jobs in all phases

TRUCK DRIVER

INSTALLATION OF MACHINE

EXCAVATOR OPERATOR

CONSTRUCTION OF RAMP

…

WORKER FOR REMOVAL OF CARPENTRY

EXCAVATION

Fig. 4. Occupational risk model for the tunnel construction project, containing activities of the excavator operator.

driver of concrete mixing truck, crane driver of timber transportation, operator of loader in excavation and water removal sub-phases, operator of excavator in excavation and water removal sub phases, workers in excavation, removal of water, erection of formworks, placement of reinforcement, final concrete and removal of carpentry, operator of compaction equipment, crane operators for installation of carpentry, reinforcement and final concrete, operator of concrete pump operator and operator of concrete vibrator. A number of various workers may perform the same job, as for example there are two truck drives for removing exactor soil. Table 2 presents the number of workers, who participated in each job position. In total fourteen workers participated during the first phase of excavation and foundation and twenty-four in the second phase of framework. According to the occupational risk methodology presented in Section 2, total risk is subdivided into the risk of these 20 job positions, as presented in Fig. 4. The first layer of subdivision in Fig. 4 concerns twenty job positions for all major construction phases of the project. The next subdivision of risk concerns the activities of each job position, as presented for the excavator operator in Fig. 4. His activities are installation of the machine, construction of a ramp and excavation in order to create slopes at

the site. The last subdivision of risk concerns the hazards associated with each activity, presented and discussed for each job position as follows.

5.1. Excavation and foundation. (phase 1) This phase has been divided into three sub phases as presented in Fig. 3, which are excavation, removal of water from the site and compaction of soil. Four job positions participate in the first subphase, which are the operator of the excavator, the loader, the truck driver and various other workers (a) Excavator operator (phase 1.1): He is responsible for the operation of the excavator machine. His activities are installation of the machine, construction of a ramp, excavation in order to discover existing electricity and water networks, but also creation of slopes on the site. Table 3 presents the activities of the operator, the associated hazards and their exposure. Hazards associated with the installation of the machine are struck by moving vehicle, contact with moving parts of machine while operating, and in or on moving vehicle with loss of control. An additional hazard exists during the construction of a ramp, which is buried by bulk mass. Finally during the excavation phase, there are two additional hazards owing to existing networks: (a) hazards contact with electricity, owing to existing high voltage cables and (b) impact by immersion in liquid, owing to possible pools of water. (b) Excavator operator (phase 1.2): He is exposed to similar hazards as the excavator operator in phase 1.1 and additionally to contact by falling objects transferred by vehicles. (c) Operator of loader (phase 1.1): He operates the loader in order to remove the excavated material. During the movement and operation of the loader he is exposed to the following hazards: struck by moving vehicle, in or on moving vehicle with loss of control, contact with moving parts of machines

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Table 3 Activities and associated hazards of excavator operator.

(d)

(e)

(f)

(g)

(h)

during their operating, trapped between and buried by bulk mass. Operator of loader (phase 1.2): There is one loader operator who works in the phase of water removal. He is exposed to similar hazards as the loader operator of phase 1.1 and in addition to contact with electricity and impact by immersion in liquid, while working nearby. Truck drivers of phases 1.1, 1.3: There are two drivers for trucks containing excavated material from the site and another two for trucks providing new clean soil to the area. These drivers are exposed to the following hazards: struck by moving vehicle, contact with moving parts of machine, in or on moving vehicle with loss of control. Workers (phase 1.1): There are two workers who participate in the following activities: excavation with care in order to find existing networks and excavation for slope creation at the site. They are exposed to the following hazards: struck by moving vehicle, contact with falling object from vehicle or load, trapped between, buried by bulk mass, in or on moving vehicle with loss of control, contact with electricity owing to wires and impact by immersion in liquid—working nearby. Workers (phase 1.2): There are two workers who participate in water removal. They are exposed to the same hazards as workers in excavation phase and in addition to contact to electricity and contact with handheld tool. Operator of compaction equipment: There are two operators operating the compactor of the soil. They are exposed to the following hazards: struck by moving vehicle, contact by falling object from vehicle, contact by moving parts of machine during operating, trapped between, buried by bulk mass and in or on moving vehicle with loss of control.

(k)

(l)

(m)

(n)

(o)

(p)

(q) 5.2. Framing (phase 2) (i) Workers (phase 2.1): There are ten workers erecting timber formworks. Part of this job is to construct scaffolds and work on them. Workers are exposed to the following hazards: fall from height while working on ladder, on scaffold, on fixed platform or while installing scaffolds, contact with falling objects, contact object carried or used by other person—not handheld tool, contact by handheld tool by self, contact by hanging or swinging objects and extreme muscular exertion while handling objects. (j) Workers (phase 2.2): There is one worker installing reinforcement. His job includes welding and cutting metal beams with a gas cutter or other cutting machine. He is exposed to the following hazards: fall from height while working on fixed scaffold or platform, contact by falling object transported by crane, contact by object carried or used by other person,

(r)

contact by handheld tool, contact by hanging or swinging objects, fire owing to hot work and extreme muscular exertion while handling objects Workers (phase 2.3): There are four workers participating in this phase, where concrete is poured into the formworks. Workers are exposed to the following hazards: fall from height (scaffold or fixed platform), contact by object carried or used by other person, contact by handheld tool, contact by hanging or swinging objects and extreme muscular exertion while handling objects. Crane operator (phase 2.2): He participates in installation of the reinforcement, while loading steel beams and is exposed to the following hazards: stuck by moving vehicle, contact by moving parts of machine, in or on moving vehicle with loss of control Crane operator (phase 2.3): He participates in installation of the reinforcement, while loading steel beams and is exposed to the following hazards: fall from height while working on fixed scaffold or platform, contact by object carried or used by other person, contact by handheld tool, contact by hanging or swinging objects and extreme muscular exertion while moving around. Operator of concrete pump (phase 2.3): He is exposed to the following hazards: struck by moving vehicle and in or on moving vehicle with loss of control. Driver of concrete mixing truck (phase 2.3): He is exposed to contact with moving parts of machines during operation or clearing. Operator of concrete vibrator (phase 2.3): He is exposed to the following hazards: fall from height while working on fixed scaffold or platform, contact by object carried or used by other person, contact by handheld tool by self, contact with hanging or swinging objects and extreme muscular exertion. Driver of truck crane transporting timber (phase 2.4): He is exposed to the following hazards: in or on moving vehicle with loss of control and contact with moving parts of machine Workers (phase 2.4): There is one worker removing timber formworks, who is exposed to the following hazards: fall from ladder, fixed scaffold, moveable platform, contact by falling object from crane, contact by object carried or used by other person, contact by handheld tool by self, contact with hanging or swinging objects and extreme muscular exertion.

More details on workers’ hazards and duration of exposure are given in [63].

6. Results Occupational risk assessment has been performed for all job positions with two sets of risk rates for all hazards. The first set of

O.N. Aneziris et al. / Reliability Engineering and System Safety 105 (2012) 36–46

risk rates are the Dutch national average (DNA) risk rates, for fatality, recoverable and permanent injury, as they have been assessed for sixty-three hazards, in the WORM project [53], according to the so called ‘‘bowties’’. The second set of risk rates is based on a modification of the Dutch National Average (DNA) rates, by taking into account the specific working conditions of the construction project, according to the WORM methodology

43

presented briefly in Section 2 and in detail in [53]. Modification of risk rates is based on a series of questionnaires for all hazards, regarding the working conditions of the site, as for example those questions presented in Table 4. The safety manager of the site answered to 470 questions concerning working conditions for existing hazards in building sites, such as falls from ladder, scaffold, fixed platform, contact with falling objects, contact with

Table 4 Sample of questionnaires regarding the working conditions of the building construction project and hazard fall from scaffold while working on a fixed scaffold. Questions

DNA (%)

Site answers (%)

What percentage of the time that you were working on a fixed scaffolding structure, was it not equipped with foot, knee and hip rails, whilst the distance between the outside wall and the scaffolding exceeded 10 cm or was the scaffolding not equipped with chest rails whilst the touch height exceeded 2 metres? What percentage of the time that you were working on a fixed scaffolding structure were the guardrails (foot and other rails) missing? What percentage of the time that you were working on a fixed scaffolding structure was it not inspected by an expert after a storm or adjustments prior to it being put into use? What percentage of the time that you were working on a fixed scaffolding structure was it not anchored according to regulation? What percentage of the time that you were working on a fixed scaffolding structure were the working platforms too narrow or the planks damaged? What percentage of the time that you were working on a fixed scaffolding structure, were the floors messy or not cleaned (for instance, tools were lying on it, it was muddy or oil was present)? What percentage of the time that you were working on a fixed scaffolding structure, was the surface on which the scaffolding was not able to support a load, not horizontal or not level? What percentage of the time that you were working on a fixed scaffolding structure, were the staging boards not blocked up with solid wood so that the scaffolding could have shifted or settled? What percentage of the time that you were working on a fixed scaffolding structure, was no safe access mounted in or on the scaffolding, such as a staircase, an access tower or a passenger lift or did you not use the safe access? What percentage of the time that you were working on a fixed scaffolding structure, did you use a ladder or step ladder placed on the scaffolding to increase the working height? What percentage of the time that you were working on a fixed scaffolding structure, was no inspection or investigation conducted into whether you were physically fit enough to climb the scaffolding? What percentage of the time that you were working on a fixed scaffolding structure, could it have been collided with/hit by lorries or vehicles, cranes or other vehicles or machines? What percentage of the time that you were working on a fixed scaffolding structure, was it not equipped with foot and other rails and did you not have a safety line or harness belt?

15

70

31 19

70 80

16 16

50 50

25

70

20

30

13

60

28

60

24

70

59

80

23

30

27

70

1.00E-02 Fatality risk - site conditions Fatality - Average rates 1.00E-03

1.00E-04

1.00E-05

1.00E-06

wo op r er w ker at or (p or op o w ker ha er f e or (p se at xc ke h 2 o r a r a s .1 op of vat (ph e 2 ) er at lo or as .2 a ( e ) or of wo der pha 1.1 ex rk (p se ) op op op ca er ha 1 er er er va (p se 2. at at a or o to wo tor ha 1. ) r b r of o o o rk (p se )2 co f co om f lo er ha 1. m nc _o a (p se 2) pa r p de ha 1 op ct ete er r ( se 1. er io v at ph 2 ) n ib o r a . at eq ra (p se 4) or ui to ha 1 of pm r ( s .1 co dr e ph e 2 ) iv n w c er re ork nt ( ase .)3 of p t tru e p er ha 2.3 co ( se ) u p c m nc re tru k d p has 1. r te c iv (p e 3) m k d er ha 2.3 ix r i ( p s e ) in ve h 2 g r a s .3 dr cr t ( iv an cr ruc pha e 1 ) er e a k . of op ne (p se 1) tru er _op ha .13 ck ato er se ) cr r ( ato 2.3 an ph r_ ) e as .2 (p e 1 ha 2 s e .2 ) 2. )4

1.00E-07

Fig. 5. Probability of fatality of workers in building construction (/year): phase 1.1 excavation; phase 1.2 removal of water from the site; phase 1.3 compaction of soil; phase 2.1 installation of carpentry; phase 2.2 instalment of reinforcement; phase 2.3 final concrete; phase 2.4 removal of carpentry.

44

O.N. Aneziris et al. / Reliability Engineering and System Safety 105 (2012) 36–46

handheld tools, contact with moving parts of a machine, contact with handheld tools, contact with hanging/swinging objects, extreme muscular exertion, struck by moving vehicle, contact with moving parts of a machine, in or on moving vehicle with loss of control, contact with electricity and extreme muscular exertion. Occupational risk has been calculated for all job positions and is presented in Figs. 5–7 and Table 2. Fig. 5 presents annual risk of fatality, Fig. 6 annual permanent injury and Fig. 7 annual recovery injury of all workers with two sets of hazard risk rates, the DNA and the modified set, according to 470 answers concerning the specific working conditions of the site.

Workers installing timber formworks, in phase 2.1, have the highest fatality probability (1.57  10  3/yr) followed by workers installing reinforcement, in phase 2.2, (1.52  10  3/yr). Workers installing reinforcement have also the highest probability of permanent injury (4.81  10  2/yr) followed by workers installing timber formworks 4.26  10  2/yr. Workers installing reinforcement have also the highest probability of recoverable injury 9.42  10  2/yr followed by workers installing timber formworks 6.79  10  2/yr. High risk rates of workers in framing phases 2.1 and 2.2 can be further analysed in order to obtain the most serious hazards. Fall from height (ladder, scaffold, fixed platform) and contact with falling objects are the most serious hazards to

1.00E-01 1.00E-02

Permanent Injury - site conditions Permanent Injury - average rates

1.00E-03 1.00E-04 1.00E-05

bo

w

or k om w er op _o ork (ph er pe er as at ra (ph e 2 or t of w or ( ase .2) dr o co p iv nc w rke ha 2.1 er re o r (p se ) of te rk h 2. op co vi er as 3) er nc br (p e at r at h 1. or op et of er e m w or ( ase 2) o a co to ix rk ph 2. m r o ing er as 4) pa f e ( ct ex truc pha 2.3 i c o s k op n av (p e ) op era equ ato ha 2.3 er to ipm r ( se ) at r o e ph 2. 3 o op r o f lo nt ase ) er f e ad (ph 1. at xc er a 1) or a ( se of vat pha 1. op or l s 3 o er ad (p e1 ) at er ha .1) or of tru wor (ph se1 co ck ke as .2 nc d r ( e 1 ) re riv ph . te e a 2) tru pu r (p se ck m ha 1.1 dr p (p se ) dr cra c iver ha 1.1 s ) iv ne ra er n (p e2 of ope _op has .3) tru ra er e 1 ck tor ato .3 cr (p _2 ) an ha .1 e se (p ha 2.2 se ) 2. 4)

1.00E-06

Fig. 6. Probability of permanent injury of workers in building construction (/year): phase 1.1 excavation; phase 1.2 removal of water from site; phase 1.3 compaction of soil; phase 2.1 installation of carpentry; phase 2.2 instalment of reinforcement; phase 2.3 final concrete; phase 2.4 removal of carpentry.

1.00E-01

Recoverable Injury - site conditions Recoverable Injury - average rates

1.00E-02 1.00E-03 1.00E-04 1.00E-05

op er at or

w or ke bo om wo r (p _ o rke h a pe r ( s e of ra ph 2. 2 co as t ) nc w or (p e 2 o re r h te k e a . 1) vi r ( se br ph 2 a a .3 w tor s e ) or (p 2 k h .4 op w er ( ase ) or ph er ke a 2 .3 a s op op to r ) r w er er of or (ph e 1 at at ke a . 2) e o r xc or s r o av (p e 2 of co op e f ex ato h as . 3) r m c e pa ato av r (p 1. ct r o ato ha 1) i s f r o op e l er op n e oa d (ph 1. 1 q a at e o r rat uip er ( se ) of o r me p h 1. dr iv co of n as 2 ) er n c loa t (p e 1 of re . d h co te er as 1) nc tru p u (p h e 1 re . te ck mp ase 3) m dri (p 1 i x ve h a .2 in se ) r tru g t r (p h 2. u a ck ck s 3 ) dr ( e iv ph a 1 .1 e dr cra cra r ( s e ) i v ne ne p h 2. er 3 _ a of ope op se ) t ru r a e r 1 . ck tor ato 3) cr (ph r_2 an a s .1 e (p e 2 ha .2 se ) 2. 4)

1.00E-06

Fig. 7. Probability of recoverable injury of workers in building construction (/year): phase 1.1 excavation; phase 1.2 removal of water from the site; phase 1.3 compaction of soil; phase 2.1 installation of carpentry; phase 2.2 instalment of reinforcement; phase 2.3 final concrete; phase 2.4 removal of carpentry.

O.N. Aneziris et al. / Reliability Engineering and System Safety 105 (2012) 36–46

workers erecting timber formworks (phase 2.1). Fall from height (scaffold, fixed platform) and fire owing to hot work are the most serious hazards for workers installing reinforcement (phase 2.2). Drivers and crane operators have the lowest fatality, permanent and recoverable injury risk, owing to low exposure to hazards, such as struck by moving vehicle, contact with moving parts of machine, in or on moving vehicle with loss of control. Overall annual risk, for all 38 workers of the project, is equal to 3.48  10  2/yr for fatality risk, 0.85/yr for permanent and 1.27/yr for recoverable risk. Risk of all job positions, in the specific working conditions of this project, is one to two orders of magnitude greater than the Dutch National Average risk, as presented in Table 2. The cause of this increase is the degraded working conditions in the specific site, compared to the average Dutch conditions, justified by the answers to the questions, presented in Table 4. In all answers regarding working conditions while on scaffolds, existence of preventive measures, equipment and inspection were absent much more frequently than in the average Dutch situation. Occupational risk results of this site are in accordance with the overall accident rate of workers in the construction industry in Greece. The accident rate for building trade workers is 41.7 accidents per 1000 workers per year, as it has been reported in [64]. This is translated into 1.58 accidents per year for this specific site with 38 workers. This value is slightly lower than the overall annual risk rate calculated with this methodology and data. In this analysis fall from height (ladder, scaffold and platform) is the most risky job for all workers in the framing phase, followed by contact by falling objects and hot work for the worker installing reinforcement. These results are in accordance with the major causes of accidents in the construction industry as reported in [20,24].

7. Conclusions The occupational risk model evaluates risk on three levels of consequences, recoverable injury, permanent injury and fatality and is based on a set of 63 different hazards such as fall from ladder, scaffold, roof, platform, etc. It permits the quantification of occupational risk of a single job with multiple hazards, of an operating unit and of an entire installation. Occupational risk analysis was performed for a building construction site and risks of fatality, permanent and recoverable injury have been calculated for all job positions and for two major phases of excavation—foundation and framing. Risk prioritisation was achieved by quantifying occupational risk and therefore the most dangerous jobs were identified. Estimation of the exposure to various hazards for each type of work is crucial in this risk assessment model. In this analysis exposure was estimated with collaboration of the safety manager and the industry workers of the plant. Information was collected by visiting the workplace and discussion with workers about their activities. This probabilistic occupational risk model allows the incorporation of measures in order to reduce risk, as already reported in [51,53]. The most important hazards to the workers of this construction project are fall from height (scaffold, platforms), hit by falling objects, struck by vehicles, fire while performing hot work and contact with electricity–hot lines. The Occupational Risk Model contains a database with 347 risk reduction measures, applicable to all 63 hazards presented in Table 1. The collection of measures consists of generic and circumstance specific measures aimed at strengthening organisational, human and technical aspects of barriers. Generic measures include safety training, inspection and maintenance of physical barriers, toolbox meetings, monitoring of safe work practices, daily work meetings for maintenance coordination and positioning of signs and warnings for

45

the dangerous area. Specific risk reducing measures for falls from scaffolds or platforms are the following: use of harness belts, safety nets and guardrails while working on height, platform/scaffold anchorage, safeguard of holes and floor openings, following instructions for scaffold construction, foundations of scaffolds, periodic maintenance and inspection of platforms and scaffolds, clean and tidy working space and qualified personnel. Specific risk reducing measures to protect from falling objects are the following: securely attach objects, which might fall, evenly distribute loads on cranes, use of Personal Protection Equipment and/or nets, periodic maintenance and inspection of lifting equipment and following procedures for stacking and moving objects. Specific risk reducing measures to protect workers from being struck by vehicles are the following: clean up spills in roads, road surface design, separate pedestrian areas from vehicles routes, fit blind spot mirrors, periodic maintenance and inspection of vehicles, lightning and driver’s training. Specific risk reducing measures to protect from fire are the use of fire extinguishers, fireproof clothing, labelling of flammable substances, use of Personal Protective Equipment, use of less combustible substances if possible, cleaning and ignition training. Specific risk reducing measures, which may be used so as to avoid contact with electricity–hot lines, are the following: training for work near high voltage lining and in situations where a vehicle might be subject to voltage, use of Personal Protective Equipment, prevent unauthorised access to areas with high voltage lines, monitoring and procedures for safe working practices. A further detailed analysis can propose the best groups of measures, which reduce risk, by taking into account their cost, as reported in [53]. Extensive additional work is required in order to estimate the additional cost of measures for a construction project and also consider possible delay of the project owing to additional preventive measures. This method of probabilistic quantified occupational risk has a lot of potential for companies and policy. It can be applied in plants or projects where limited experiential information concerning reported accidents and exposure exists. It can also be further applied in other industrial plants and also in construction projects concerning buildings, roads and highways.

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