RISK MANAGEMENT
SO IS THERE A ROLE FOR QRA IN THE WIND ENERGY INDUSTRY?
LET’S CONSIDER THREE SPECIFIC HAZARDS:
1 Turbine blade failure and subsequent ‘throw’.
For the vast majority of wind turbines, sited in remote/rural locations, the consequences of such an event are relatively low. Here, simple deterministic principles (e.g. compliance with design standards) will be adequate to demonstrate this risk to be tolerable and properly managed. However, if we consider a turbine sited close to a large gas storage facility, the story is very different. Whilst a highly unlikely event, a ‘thrown’ blade could strike a vessel resulting in a loss of containment leading to a gas release. Were this to be ignited it could lead to an explosion resulting in multiple fatalities. Clearly a QRA is appropriate here which would consider a range of factors as illustrated in Figure 1. However this need is not driven by issues specific to wind energy but rather the nature of the adjacent facility. It is inconceivable that such a major hazard facility will not already have a QRA as part of an overall Facility ‘Safety Case’ and so the bulk of work is already done for you. A full QRA is therefore unlikely to be necessary. A more simple comparison of the probability of a blade strike against other existing known hazards with similar effects may be all that is needed to assess whether this new risk is tolerable.
2 Personnel transfer on/off an Offshore Wind Turbine. This is widely recognised as one of the more significant risks of offshore wind operations. Whilst a relatively simple hazard which could be assessed via deterministic means, a precedent has been set for the use of QRA for personnel transfers in the offshore oil and gas industry. With such a precedent comes considerable historical and predictive data on the likelihood and consequence of this hazard. As a result, a simple personnel transfer frequency calculation allied to existing, appropriate data, may be all that is necessary to assess this hazard via quantitative means.
3 Offshore Wind Farm Ship Collision Study.
Depending on the location of an offshore wind turbine, it may be necessary [unless the risk can be discounted via qualitative means] to perform a detailed ship collision study. Such a QRA will quantify the risk of a ship colliding with a wind turbine. In so doing it will need to quantify the likelihood of a ship impacting a turbine considering both passing and visiting vessels via ‘powered’ and ‘drifting’ collisions, whilst taking account of protective measures in place such as sea charts [provided turbines marked], radar visibility and facilities for monitoring and warning vessels in the vicinity. In terms of consequences, the QRA will need to consider damage to the turbine as well as the vessel itself. The evaluation of impact damage is likely to be complex and require considerable structural engineering and marine experience to develop a correlation between collision speed/energy and damage. A breached oil tanker is likely to cause significant environmental harm. Whilst this hazard clearly does not exist within the wind farm, if inappropriately sited, a wind turbine could contribute to the release of this hazard, hence the associated risk must be considered as part of the wind farm safety justification. Such ship collision QRAs are a standard element of any offshore oil and gas facility ‘Safety Case’, so existing precedents exist for risk tolerability which can be tailored to suit this specific application to determine whether the quantified risk is acceptable.
Whilst these are only three very specific, anecdotal examples, they do indicate that there is a role for QRA in the wind energy industry. However this is certainly not a black and white issue. These examples clearly highlight that the nature and scope of any QRA will vary hugely based on a range of factors including; nature of the hazard and its development, available information, existing precedents, stakeholder expectations, but perhaps more crucially, what role the QRA is to play within the overall safety justification strategy. This must be fully understood before embarking on any QRA.
Gareth Ellor
Risktec Solutions Ltd
www.risktec.co.uk
www.windenergynetwork.co.uk
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