Page 364 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Risk Criteria 151339
When the cost and effort ofmitigation measures are not dis- Table 15.3 Acceptable risk thresholds
proportionate to the benefits, the measures should be con-
sidered to be practicable and should be put into effect. When Annual chance offatalrty Criteria
it can be demonstrated that the cost and effort of implemen-
tation substantially outweigh the benefit of the risk reduc- <I ox IO" Insignificant, no action justifiable
tion, then the measures are not considered to be reasonably >I ox 10-4 Unacceptable, action to reduce risk
mandatory
practicable to implement. This demonstration should be 1O4<Risk< IO" Action to reduce nsk may be warrantea
sensitive to uncertainties in the risk estimates and in the but should be justified on a
treatment of aversion to high-fatality accidents. costbenefit hasis
Once all measures have either been implemented (or the
company is committed to implementing them) or demon- Source: Jaques, S., "NEB Risk Analysis Study, Development of Risk
strated to be not reasonably practicable, the risks are ALAW. Estimation Method," National Energy Board of Canada report, April
1992.
HSE considers that following engineering codes and good
safety management practices will in general produce an instal-
lation whose risks are tolerable, but fiuther consideration of In one Canadian NEB study, acceptable risk thresholds for
practicable risk reduction measures is also necessary to show individuals are defined as shown in Table 15.3.
whetherrisksare ALARP [91]. Canadian design guidelines for pipelines state that acciden-
tal loadings occurring less frequently than 1 O4 per year do not
Examples of numerical criteria have to be considered. Impact from machinery onshore and
from vessels, anchors, trawl boards, and dropped objects are
Although some examples can be found specifically for noted as examples of accidental loadings. In a sense, this too is
pipelines, it is also useful to examine numerical acceptable risk a criterion because it implies that from a design standpoint,
criteria established for land-use planning, worker safety, and occurrences (at least the accidental type) less frequent than IO-
other industries. In Table 15.2, Ref. [37] was used to compare annually are not significant enough to be incorporated into a
some governmental risk criteria from various sources. design.

Canada UK. Health Safety Executive
The Major Industrial Accidents Council of Canada has recom- U.K. HSE documents are frequently quoted in risk reports and
mended criteria for land-use planning around hazardous indus- studies. Individual risk of fatality criteria are
tries, based on increased fatality rates, as follows:
Maximum tolerable risk for workers IO-) per year
Residential and institutional 1 x 1 o-6 per year Maximum tolerable risk for the public I o4 per year
Commercial and low-density residential 1 x 1 0-5 per year Broadly acceptable risk per year
Industrial and active open space 1 x I o4 per year.
These criteria were originally published for nuclear power
These criteria apply to new land uses and assume that an active stations, but subsequent documents have indicated that they
emergency plan is in effect. If there is no emergency plan, the should apply to any large industrial plant in any industry
criteriaarereducedbyafactorof IO [91]. [911.
Table 15.2 Examples of individual risk criteria forthe public
Maximum tolerable risk
AuthoriQ Application @er year) Negligible risk Iperyear)
Ministry of Housing, Physical New plants 10-6 Not used
Planning, and Environment
(VROM), The Netherlands
VROM, The Netherlands Existing or combined plants I 0-5 Not used
VROM, The Netherlands Transport 10" Not used
HSE, United Kingdom Existing hazardous industry 10-4 10"
HSE, United Kingdom New nuclear power station 10-5 10-6
Advisory Committee on Dangerous Existing dangerous substances 104 10-6
Substances, United Kingdom transport
HSE, United Kingdom New housing near existing plants 10-5 10-6
Hnng Kong Government New plants I 0-5 Not used
Department of Planning, New plants and housing 1 0-6 Not used
New South Wales
Environmental Protection New plants 10-6 Not used
Authority, Western Australia
Santa Barbara, California, USA New plants I 0-5 I 0-7