HEALTH & SAFETY


formulated such an approach in 1988 via their “Tolerability of Risk” [TOR] guidance. It identified a level of risk that was ordinarily accepted by substantial groups of workers in UK industry. This level represented the dividing line between what is just about tolerable to an individual in their working life and is unacceptable for all but exceptional groups [e.g. fisherman and divers]. This value was an individual risk of fatality of 1 in 1000 per annum.


This guidance also identified a maximum level of risk to the general public that society should be prepared to tolerate. This threshold was set an order of magniutude lower at 1 in 10,000 per annum, recognising that the public are unlikely to get direct benefit from exposure to a given industrial risk. This threshold corresponded to the average annual risk of dying in a road traffic accident, hence ensuring that their overall risk exposure could not be significantly increased through any industrial endeavour.


Conversely, the guidance defined a lower bound of tolerability whereby risks lower than this are considered broadly acceptable without further action. This threshold was set at an individual risk of fatality of 1 in 1 million per annum corresponding broadly to the risk of death from naturally occurring events such as lightning, over which we have little or no control. A risk below this threshold will clearly not significantly increase the risk to an individual and hence is considered broadly acceptable.


These thresholds, which have remained unchanged ever since, establish three distinct risk tolerability regions as illustrated in Figure 1. Risks that fall within the middle region are only considered tolerable if all reasonably practicable measures have been taken to reduce risk and that the time, cost, effort and inconvenience of implementing further risk reduction measures are grossly disproportionate to the benefit obtained. This is the basis of the HSE’s principle of “ALARP” [As Low As Reasonably Practicable] which we will explore in more detail in a future issue.


The HSE’s “Reducing Risk, Protecting


Unacceptable region


Risk cannot be jusfied save in extraordinary circumstances


Tolerable only if risk reducon is impraccable or if its cost is


grossly disproporonate to the improvement gained


Tolerable if ALARP


region Risk is taken only if a benefit is required


These criteria are generally accepted internaonally as applicable for


hazardous industries


Tolerable if cost of reducon would exceed the improvement


Broadly acceptable region


Risk generally insignificant. Risk reducon usually not required (unless reasonably praccable)


Workers & Public 10-6 IRPA


IRPA: Individual Risk Per Annum Figure 1: Tolerability Of Risk “Carrot Diagram”


People” document [Reference 1] sets- out the HSE’s current expectations on risk based decision making and is founded on the original TOR guidance.


Care should be taken when using these risk tolerability criteria as the defined thresholds represent an individual’s total risk exposure. For example, a typical hazardous development may contain a number of hazards. The risk from each of these hazards may, in isolation, be shown to be tolerable but when they are summated this may no longer be the case. As such, we must be mindful of considering the total risk picture presented by our activities and judging that totality against these acceptance criteria.


It is important to note that simply assessing the effect on individuals via this approach may not be sufficient in demonstrating a risk to be tolerable. Large scale, emotive incidents raise questions of responsibility for safety and public accountability in a way that accidents to individuals do not. As such, society is likely to be much less tolerant of these. Consideration must therefore be given to wider societal effects and implications. We will touch on this in a future issue although it is unlikely to be a major issue for the Wind Industry as, unlike a nuclear power station or major chemical plant, an incident is unlikely to affect large numbers of people.


Whilst this article has focused on safety www.windenergynetwork.co.uk 23


risks, it is equally appropriate that business, security and environmental risks may be considered for tolerability. There is little benefit in having a process which is demonstrably safe to the workers and public if the risk it poses to the environment or business continuity is intolerable.


Gareth Ellor


Risktec Solutions Ltd www.risktec.co.uk


Workers 10-3 IRPA


Public 10-4 IRPA


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148