HEALTH & SAFETY
THE HIERARCHY OF RISK REDUCTION MEASURES CONTINUES...
The hierarchy of risk reduction measures presented as a staircase helps answer our two earlier questions – it not only shows which types of measure are considered to be “better” than others, but can also be used as a prompt to identify candidate measures.
When attempting to identify risk reduction measures, always start at the bottom of the staircase (try to eliminate the hazard) before moving to the next step. The further up the staircase, the less satisfactory the risk reduction measure. Of course, for any project, one or more of these types of measure may not be applicable, appropriate or available (for example, clearly it is not appropriate to eliminate the tiger from the zoo as this is central to its purpose). The key thing to remember is that this shows that a structured and considered approach has been taken to identifying ways in which the risk could be reduced.
APPLYING THE HIERARCHY Let’s consider the example of a small wind power development involving 6 turbines on a piece of land adjacent to a residential area. A preliminary safety analysis has shown that two of the turbines (T1 and T2) have the potential to affect the residential area in the event of a blade throw incident (turbines T3 to T6 are far enough away that they cannot affect the area).
The preliminary risk calculation shows that the risk presented by turbines T1 and T2 is not tolerable and as such, must be reduced further. Using our staircase shown above, starting from the bottom, the available options may include:
• Eliminate - completely removing turbines T1 and T2 from the development would effectively eliminate the risk and no further action would be required. This may not be practicable due to the economics of the development, i.e. to be economically viable, all 6 turbines are required.
• Substitute - by installing different (smaller) turbines, the blade throw distance may be reduced which could either (a) put the residential area outside of the blade throw range or (b) significantly reduce the risk of a blade strike event. Again, this may not be practicable economically, i.e. a turbine which doesn’t present such a large hazard range, may not generate sufficient power.
• Engineering - it may be possible to design a system which detects the early onset of blade failure (e.g. through vibration monitoring) which would trigger shutdown of the turbine. In this case, the reliability of this system would need to be taken into account in determining the risk reduction that would result if it were to be implemented.
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