*Article* **Risk Assessment for Musculoskeletal Disorders in Forestry: A Comparison between RULA and REBA in the Manual Feeding of a Wood-Chipper**

**Margherita Micheletti Cremasco 1, Ambra Giustetto 1, Federica Caffaro 2, Andrea Colantoni 3, Eugenio Cavallo 2,\* and Stefano Grigolato <sup>4</sup>**


Received: 10 December 2018; Accepted: 27 February 2019; Published: 5 March 2019

**Abstract:** The analysis of the postural attitude of workers during the interaction with workstation's elements and working environment is essential in the evaluation and prevention of biomechanical overload risk in workplaces. RULA (Rapid Upper Limb Assessment) and REBA (Rapid Entire Body Assessment) are the two easiest methods for postural risk assessment in the workplace. Few studies investigated postural risk in forestry sector with regard to human–machine interaction, in particular manually fed wood-chippers. The aim of this study was to evaluate the postures assumed by an operator during the manual feeding of a wood-chipper, and to compare RULA and REBA, in order to identify the more effective and appropriate method for the assessment of the risk of biomechanical postural overload. The results pointed out several postural issues of the upper limbs, and showed that RULA is a more precautionary method to protect operator's health during the targeted tasks. Implications to improve the human–wood-chipper interaction are discussed.

**Keywords:** ergonomics; forestry; postural risk assessment; RULA; REBA; wood-chipper

### **1. Introduction**

The analysis of the postural attitude of the worker during the interaction with workstation's elements and working environment is essential in the evaluation and prevention of biomechanical overload risks in workplaces [1]. Awkward working postures may decrease the workers' concentration and increase accidents frequency and biomechanical overload [2–6], giving rise to musculoskeletal disorders in the different body regions involved, as at the main limb joints level and the vertebral column [7].

Some standards [8–10] dealing with the biomechanical overload caused by incongruous static and dynamic postures have been developed to define the risk assessment methods to evaluate postural load referable to activity and workstation characteristics and to human–machine interaction. They are referenced in international [11] and national [12] legislations aimed at protecting workers' health and safety.

RULA (Rapid Upper Limb Assessment) [13] and REBA (Rapid Entire Body Assessment) [14] are two easy methods for occupational postural risk assessment. Indeed, previous studies [15,16] showed that observational methods are considered effective in the assessment of biomechanical work-related overload, having the advantage of being more versatile and less expensive in terms of time and resources required compared to objective laboratory measures. Both RULA and REBA allow to obtain a numerical index that represents the quantitative value of the risk at which the worker is exposed during the targeted work activity and to derive the priority level of intervention and the actions needed. The RULA method is suggested for the identification of postural disorders of the upper limbs, of the neck and of the back in relation to the muscular action and external loads applied to the body. The REBA method is applied to identify postural disorders of the whole body, in relation to the muscular action, to the external loads applied to the body and to the type of grip. They are referenced in the international standard for occupational risk assessment [9] and cited among the selected tools for Work-related Musculoskeletal Disorders (WMSDs) prevention according to International Ergonomics Association (IEA) and World Health Organization (WHO) [17]. These methods are also widely applied in several working contexts, mainly industrial work activities (secondary sector) and those producing services and goods (tertiary sector), characterized by a precise standardization of tasks, geometries, gestures and relative execution frequencies that allow a systematic and controlled forecasting and quantification of the biomechanical overload risk. Furthermore, the two methods have been combined and compared to assess postural risk in industry [18–20], construction [21], supermarkets [22], hospital and dental sector [23], work with video terminals [24], waste collection activity [25], for firefighters and emergency medical technicians [26], and artisans [27–29] and sawmill activities [30].

RULA and REBA have been adopted a few times in the agricultural [31,32] and forestry sectors [33,34] because the evaluation of the biomechanical overload risk in the primary sector activities is more difficult; due to the large variability of the tasks the operators have to perform, depending on crops, operations (seeding, weeding, pruning, harvesting, etc.), the machinery and tools adopted, the, sometimes extreme, weather conditions they have to be carried out with, and the daily and seasonal exposure, as well as the lack of a strict standardization of the work in general [35,36]. Interaction with machines, tools and environments in agriculture, and particularly in forestry, requires therefore a particular attention in the application of risk assessment methods conceived for other contexts, or the formulation of specific methods that consider the distinctive characteristics of these activities [37].

Kundu and Gaur [38] compared RULA and REBA in a study addressed at investigating how much these techniques were appropriate for evaluating the postures assumed by agricultural workers. They highlighted some shortfalls in using these techniques to study risk factors associated with agricultural field operations and suggested to add some factors as posture duration, field condition, environmental factors and nutritional status to better assess the occupational risks and possible remedies, especially for agricultural work in the fields.

Besides RULA and REBA, other methods have been used to assess the postural risk in manual agricultural activities. For example, Kong et al. [39] compared RULA, REBA, OWAS (Ovako Working Posture Analyzing System [40]) and ALLA (Agricultural Lower Limb Assessment [41]) for various agricultural tasks. They found that ALLA better estimated the risk because it identifies critical issues that the other methods do not analyse and, therefore, it always returns a higher level of risk, compared to the other methods. Ojha and Kwatra [42] combined REBA and VAS (Visual Analog Scale) methods in rice cultivation manual operations. REBA indicated postural load and suggested interesting corrective measures. However, in both studies [39,42], the object of the analysis was a manual activity, while, in developed countries, most of the farming operations require the use of machinery and workers spend many hours in interacting with them, making the investigation of the human–machine interaction more relevant [43].

Among the studies specifically dealing with the human–machine interaction in agriculture, RULA is the most frequently adopted method. Vyavahare and Kallurkar [44] used RULA to assess postures assumed during the interaction with agricultural machines such as maize dehusker-sheller. The study analysed and evaluated the risk of various key postures, such as squat, forward/lateral bending, hands flexion/extension, wrist/spine twisting. Putri et al. [45] used RULA to study the use of thresher machines for threshing rice plants. In the first study, RULA helped to optimize a digital human manikin

posture, resulting in precise risk assessment and better designed and widely accepted products and workplaces, while, in the second study, RULA provided indications to redesign the machine to reduce injuries and musculoskeletal overload caused by the mismatch between the dimensions of the engine and farmers' postures and dimensions.

In the forestry sector, the studies report postural risk evaluation mainly referred to manual tools. Gallo and Mazzetto [34] applied different methods including REBA and OWAS to evaluate the postural risks from the cutting operations with chainsaw, showing their good applicability for the assessment of WMSD in forestry. The comparison between OWAS and REBA showed that REBA has a higher level of detail of assessment because it considers the angles between body segments and extremities as the wrist, the neck, the elbow and the shoulders (parameters that are not considered by OWAS method) for both sides of the body and, furthermore, it assesses the type of handle coupling and the characteristics of the performed activities. REBA results to be suitable for suggesting interventions to be performed to decrease musculoskeletal overload, even though it has not been developed specifically for forestry operations and it presents some weaknesses during the assessment, as the lack of coded postures as the kneeling posture.

Forestry is recognized as a highly hazardous industry [46] and working postures are one of the most investigated risk factors for workers' safety, even though the postural aspects in the human–machine interaction have been under investigated in this sector [47,48]. With regard to machinery, manually fed wood-chippers are one of the most widely used machines in forestry, agricultural, landscaping and urban tree maintenance to reduce the volume of woods for following disposal or re-use in bio-energy production [47]. The attention to this machine is rising because of the significant increasing interest in biomass production as biofuel [49] and because they are often involved in fatal and non-fatal injuries [50]. Data on the occurrence of accidents provide an objective index of the danger of machinery as well as a valid reason for identifying the most critical features of these machines.

In the United States, between 1992 and 2002, Struttman [50] reported 31 fatal and 2042 non-fatal accidents involving wood-chippers. The estimated social cost of these fatal accidents were estimated in 2003 to US\$28.5 million; furthermore, an in-depth analysis disclosed that 58% of these fatal accidents involved groundskeepers and machinery operators in the forestry and agricultural sectors [50]. Analyses of the non-fatal accidents showed that 60% of the accidents caused immediate injury or amputation of parts of the upper-body limbs. For 25% of these injuries, the victims were unable to return to work for periods of up to 30 work days [51]. Further studies indicated that more than one-third of these accident victims had less than 11 months of experience in that particular job [50].

In the further period between 2008 and 2018, statistics from the United States Occupational Safety and Health Administration of Department of Labor [52] reported 56 incidents during chipping operations: 64% of the accidents dealt with feeding operations and 36% of them were fatal for the operators. From the same statistics, the accidents not related with feeding operations of wood-chippers had a lower rate, 16%, of fatal accidents.

Accurate statistics about accidents with wood-chippers are not available from most of the European Union countries [53]. Only the French Ministry of Agriculture, Agrifood, and Forestry reported that at least one severe accident related to the use of wood-chippers occurs every year in France and that, in most of the cases, the operators involved were young apprentices [54], one of the category of users for which warnings to eliminate hazardous behaviours when intrinsically safe machine are used, are less effective [55,56].

Based on the literature review, the aim of this study was to identify the more effective and appropriate method between RULA and REBA for the assessment of the risk of biomechanical postural overload, evaluating the postures assumed by an operator during the manual load of a wood-chipper, in a controlled experimental setting. The study further discusses which of the two methods is more precautionary in evaluating postural risk and reports higher risk indices, for the specific activity considered.

For the present study, a small manually fed wood-chipper has been selected since: (1) small-size wood-chippers are widespread among forestry, agricultural and urban green maintenance operators; (2) similar types of wood-chippers are used for occasional and accessory operations to the main activity [47]; (3) often experienced, but not specialized, operators are involved in the wood-chipping operations and this category of operators are known to be the most exposed to safety risks [57]. As a consequence, the manual feeding seems to be critical both in terms of safety and health risks for the operators [58,59].

### **2. Materials and Methods**

#### *2.1. The Wood-Chipper*

The manually fed wood-chippers generally consist of a feeding system, a chipping units based on rotating knives (drum or disc mounted) and on a discharge system. Alternative solutions for the comminution devices are available for production of quality wood chips for fuel [60]. In the case of manually-fed wood-chippers, the operators feed small trees, part of trees and/or branches into the infeed chute by hand with a following risk of biomechanical postural overload, which is typical of manually-loaded wood machines [61].

The study was carried out with a manually fed wood-chipper model Tirex, made available by the manufacturer Peruzzo (Peruzzo Srl, Curtarolo, Italy). The machine was connected to the rear three-point hitch of a 55 kW tractor and was powered by the rear Power Take-Off (PTO) (Figure 1). The feeding system consists of a feeding hopper with an infeed chute above 600 mm from the ground level and with a width of 1200 mm at the external edge. The feeding system consists of two horizontal rollers electro-hydraulically controlled by a load-limiting mechanism and located at the end of the infeed chute at a distance of 1200 mm from the external infeed chute limit, in accordance with EN 13,525:2005 + A2:2009 [62]. The machine is equipped with an electro-hydraulic feed control bar fixed on the bottom and along the two sides of the infeed chute. The chipping unit consists of a flywheel (diameter 620 mm, mm thickness 30 mm) rotating at 1500 rpm and with a torque of about 33 Nm. The flywheel is equipped with four knives (thickness 25 mm and length 200 mm) while an anvil is fixed to the frame of the machine. The manufacturer claims the machine is able to chip wood stems with a diameter up to 180–200 mm.

**Figure 1.** The manually fed wood-chipper used during the test.
