Acceptable Risk

Many land use planning documents throughout the country refer to 'acceptable risk'. However, these documents do not define what acceptable risk is, or for whom the risk has to be acceptable (i.e. the developers, council, future occupants, or the community). This has resulted in developments being approved in areas susceptible to natural hazards, as the applicant or the developer has been willing to accept the risk associated with the development. When land use planning documents make reference to ‘an acceptable level of risk’, it is important that this term is defined as it provides guidance to developers, council, and the community around what this level of risk is, and to whom the risk has to be acceptable.

Acceptable risk is not a static idea – people’s opinions on this can change over time in response to new knowledge or the raised profile of a hazard. What is deemed acceptable is not always evenly distributed across communities or even within different sectors of society. This makes the aggregation of risk preferences through comparative risk assessment often open to challenge, as groups or individuals regard their risk tolerance as poorly expressed in the aggregated figure.

There are a number of differing metrics and perspectives on what constitutes acceptable risk. In any decision-making process it is important to be clear what approach to defining acceptable risk is being used (and to be aware that councils, stakeholders and communities may be basing their responses on differing views of what is acceptable risk).

Possible perspectives on acceptable risk include: (from Hunter & Fewtrell 2001 in Wein et al. 2009)

Currently tolerated Risk that is no worse than the current risk is acceptable
Improvement of current Any decrease in the risk is acceptable
Intolerable probabilistic threshold The probability of a specified loss (below a threshold) is acceptable
Benefit –cost Risk is deemed acceptable relative to the cost of reducing the risk
Public acceptance & political resolution Deliberative approaches determine acceptable risk (beyond what may be quantifiable)

Factors that influence risk acceptability include: (Institute of Risk Research)

  • Voluntariness (the extent to which a person can chose to accept the risk rather than have it imposed on them)
  • Control (the extent to which a person can modify their risk by their own influence)
  • Fairness (whether everyone is equally affected)
  • Familiarity (those risks taken in everyday life are tolerated more than new unfamiliar risks)
  • Memorability (risks associated with major tragedies can have a lower risk acceptability)
  • Dread (we are simply more afraid of some things e.g. shark attacks)
  • Diffusion in space and time (particularly affects perception of natural hazard risk)
  • Morality (whether we can judge a risk or risk taker as being more or less moral – such as intravenous drug use)
  • Process – the way in which a decision about the risk has been made and the trust in the agency responsible has an impact on the acceptability of the risk.

References

Hӧppner2010 - Risk communication and natural hazard
http://caphaz-net.org/outcomes-results/CapHaz-Net_WP5_Risk-Communication2.pdf

Canadian Institute of Risk Research: Risk Management framework: All steps
http://www.irr-neram.ca/pdf_files/primer/communication.pdf

Wein, et al. (2009) Scenario-Based Risk Analysis within an Analytic-Deliberative Framework for Regional Risk Reduction Planning - MODSIM Proceedings, 2007
http://www.mssanz.org.au/MODSIM07/papers/26_s32/Scenario-Based_s32_Wein_.pdf