Quantifying the physical demands undertaken by offshore wind technicians during a working day and casualty evacuations

1 Introduction

The wind industry is undergoing large-scale commercial development of offshore wind farms [1]. This is resulting in an increased need to employee wind technicians (WTs) to undertake the regular service and maintenance routines performed on the turbines. To ensure that the industry is recruiting and retaining physically capable WTs, there is a need to understand the associated physical demands of a working day as an important initial step in completing a job task analysis [2].

Previous work by this research group [3] included a small-scale job analysis to identify the essential tasks associated with being a WT, using qualitative focus groups and interviews. In this work five essential tasks for WT were identified: transfer from the vessel to the transition piece (i.e., “an external platform, that allows access into the turbine, Fig. 1”); ascent of the internal ladder; manoeuvre through hatches; torque and tensioning; and casualty evacuation [3]. The working day was found to be tide dependent, with departure times to the turbine varying between 0300 and 1500, and with the potential for technicians to be on a vessel transferring, to and from the turbines, for 3 to 4 hours of a 12-hour working day [3].

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Fig. 1

Schematic of an offshore wind turbine. The schematic is not to scale with variations occurring in all aspects across the industry. The model is based on a 3.6 Offshore Turbine [2].

With significant developments in the accuracy of wearable health devices, there is now the opportunity to measure the physical demands of workers using embedded biosensors such as heart rate (HR) and accelerometer sensors [4–8]. In particular, wristband-type wearable health devices, such as smartwatches and fitness trackers, are lightweight, comfortable, affordable, and have great potential for measuring physical demands at the worksite without disrupting ongoing work. One study objectively measured the physical work demands of offshore WTs [4], using accelerometers and HR data, the average physical work was reported for the following activities as a percentage of the working day: sitting (43%), standing (19%), lying (13%) moving (9%), walking (8%) and high intensity physical activities (1%). Only 1 minute was reported to be spent climbing vertical ladders [4], assuming a 9-hour working day including transfer to and from the turbine this accounts for 0.02% of the day. The approximate median (range) reported for percentage heart rate reserve (HRR) and time spent above 60% (HRR) was 35 (18 to 33)% and 6 (3 to 23) mins, respectively. The data collected included the time spent transferring to the turbine, therefore it is of interest to understand what the physical work demands would be without the transfer time included. When measuring physical demands for a job based on HR, it is important to consider factors such as environmental conditions, nutrition, methods for measuring resting heart rates, mental stress, illness, and medications [9]. Alternatively, wearable physical activity monitors, relying solely on movement data, have proven to offer a valid estimation of metabolic equivalents (METs) during military training. The tasks involved in such training differ from the typical human movements for which the algorithms were initially developed [8]. Therefore, the use of movement data could be considered a more suitable measure when assessing the demands placed on WTs over consecutive working days when external factors (e.g. environment, lifestyle etc) are not controlled.

Casualty evacuation has been identified as an “infrequent essential” task (i.e., “a job that may not occur as part of the regular service pattern in WTs, but when the need arises for people to undertake item, they must have the necessary physical capacity”) [3, 10]. These rescues were classified as rescues from: 1) the Hub 2) the tower and 3) the Nacelle (Fig. 1). Rescues can be broken down into five key areas including: 1) Gaining access to the area where the casualty is, 2) Assessing the casualty, 3) Manoeuvring the casualty to enable the rescue 4) Setting up pully systems and manoeuvring the casualty through the turbine, 5) Lowering or lifting the casualty to the extraction point [10]. One of the key differences between casualty evacuation and the other work tasks performed by WTs is the inability to take a rest break when needed, with rescues reported to last ∼45 mins [10]. Due to the infrequent nature of these tasks it is not possible to measure the physical demands on the turbine. Training centres have been set up that allow the WTs to undertake casualty evacuation scenarios and acquire experience using the equipment and techniques to perform this task, whilst gaining the required advanced rescue trained qualification [GWO Advanced Rescue Training Standard V2.1]. Currently there is no literature or, objectively measured data, to help characterise the physical demands of these casualty evacuation scenarios.

The primary aim of this study was to characterise the working day of WTs in the offshore wind industry. The secondary aim was to quantify the physical demands of two simulated rescue scenarios WTs based on their industry standards.

3 Results

The results of this study identified that the majority of the day (69%) is spent undertaking activities of a moderate nature, with 3% working vigorously. Using MET data to provide an approximation of the aerobic demand suggests that WTs would be working daily between 10.5 mL.kg^–1.min^–1 and 20.9 mL.kg^–1.min^–1 and at work intensities≥21 mL.kg^–1.min^–1 for approximately 15 mins. To ensure WTs can complete tasks without becoming exhausted, and be able to go on to do other tasks, work rates should not require an individual to work at their maximum capacity for anything other than very brief periods. For tasks with an aerobic demand this equates to a percentage of maximum aerobic capacity ( V ̇ O_2max). Åstrand and Rodahl [12] suggested that individuals continuously undertaking physical activity for an eight-hour shift should only work at 30% to 40% of their V ̇ O_2max. Doolittle et al. [13] stated a suitable percentage of V ̇ O_2max for electrical transmission line-workers working on pylons is 55% of V ̇ O_2max due to the intermittent nature of the task. This was one of the earliest papers to recommend a higher percentage of V ̇ O_2max than the previously stated 30% to 40%, based on the rationale that the aerobic demand was intermittent through the day and thus individuals should be able to sustain this higher percentage. Using these principles, and the MET data collected from the WTs, it could be suggested that a potential minimum aerobic standard for WTs be set in the range of 35 (10.5 mL.kg^–1.min^–1 /0.3) to 38 mL.kg^–1.min^–1 (20.9 mL.kg^–1.min^–1/0.55).

Whilst other studies have identified WTs as a group who experience high physical demands, strains and musculoskeletal disorders as a result of working on a turbine during service campaigns [14–16], this is only one of two studies to have collected physical demand data on a turbine during the working day. The only other study to have investigated the physical requirements of WTs was that of Oestergaard et al. [4]. The data of our study (METs) and that of Oestergaard et al. (% HRR) [4] reported on average MET data between 2.2 to 4.7 for various job task, and % HRR of 22% ranging between approximately 18% and 33% across days [4]. Comparing the MET and % HRR data [16] suggests that the WTs were working at similar intensities during the both studies, with the main differences occurring in the duration spent completing moderate and vigorous activities e.g. ∼4 min per day on vigorous activity [4] compared to ∼15 mins in the present study, corresponding to the transfer from the vessel to the turbine. Climbing speeds during the transfer were reported on average to be 44.5 rungs. min^–1, with the minimum speed observed being 41.6 rungs.min^–1, which is greater than those observed previously [18]. These data confirm that short ladder climbs are both essential and frequently performed tasks.

The data collected during this study and Oestergaard et al. [4] did not include WTs climbing the full height of the turbine. However, this task has been classified as an essential infrequent task during recent job task analysis in which interviews (n = 45) focus groups (n = 14) and a survey (n = 167) were conducted [10]. If a lift cannot be used it is essential that WTs climb the turbine to get to the Nacelle. Subject matter experts reported that the number of times in a year they are likely required to climb the full height of the turbine was approximately three, ranging between none to >10 [10]. The data presented here do not include days involving climbing the full height of the turbine; it is considered crucial to conduct additional research to investigate whether the physical exertion involved in ascending the ladder’s the entire height of the turbine exceeds the reported physical demands reported in this study. Neglecting this activity may lead to underestimating the minimum aerobic threshold required for establishing a physical employment standard.

Collecting data in-situ results in a number of limitations. The activities/diary were completed retrospectively, and so the timings between tasks are not exact. However, based upon the data from the activity monitors, a picture of the day can be established. Additionally, the use of the rating of physical demand scale varied significantly between individuals. Some rated many tasks high (e.g. median rating of 6.5 across tasks during a day) and another rated similar tasks lower (median rating of 4.5 across the day). However, the scoring within each individual relative to each task (rank order) was similar i.e., “ladder climbing and torque/tensioning were consistently rated highest”. The median of each task, relative to other tasks should represent the difficulty of the task as ranked by the WT.

When analysing the physical activity data, it’s important to consider that the activity monitors were worn on the wrist of the WTs. As a result, these monitors only capture large movements of the whole body and do not account for activities that may cause local muscular fatigue. Ladder climbing, which involves extensive arm movements, emerges as the most physically demanding activity. This finding contradicts the perception of the WTs who believed tasks like torque and tensioning to be the most physically demanding. Thus, the data does not accurately reflect the physical demands of tasks such as holding a 20 kg tool, manoeuvring in confined spaces, and working in uncomfortable positions, in which the physical demands are based in the parameters of strength, strength endurance and mobility.

A number of studies have looked at the physical demands of various casualty rescues under different conditions [19–23]. Both rescues in the present study were performed predominately aerobically, eliciting relatively similar cardiac and metabolic demands, which can be considered “low” when compared to the demands reported in other studies [19–23]. This is likely due to the differences observed in the distances needed to be travelled to get to the casualty e.g. climb a mountain [21], walk, swim or paddle out to a casualty [19, 22]. The higher RPE values reported for the Hub rescue are due to the increase in time to complete the rescue and a greater requirement to manoeuvre the casualty in tight spaces. It should be noted that for the rescue down the ladder, the mass to be manoeuvred was the weight of the rescue dummy, whilst the rescue in the Hub included the rescue stretcher. During a casualty rescue down a ladder WTs are required to lift the casualty to release them from the ladder in order to lower them. This lift was performed with the WT using both hands whilst leaning with their back against the tower –this is only possible in smaller turbines i.e., “<6 mW, such as those used at GWO training centres, where the tower wall is close enough”. In larger turbines, WTs may have to change their technique, which may require one hand remaining on a rung whilst performing the lift single handed. Neither rescue elicited higher aerobic demands than those experienced during the working day or prolonged ladder climbing. Although the metabolic demands are lower, the physical demand comes from working in restricted spaces while having to manoeuvring the casualty onto the stretcher and repeatedly hauling a mass through, up or down the turbine.

5 Conclusion

These data can be used to support the job task analysis undertaken for WTs working in the offshore wind industry [3, 10]. It is concluded that the most physically demanding essential tasks of working as a WT in the offshore wind industry are ladder climbing, torque and tensioning, manual handling, working in restricted spaces and casualty evacuation from the Hub.