Page 365 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

151340 Risk Management
HSE risk criteria for land-use planning The individual risk ory bodies and those implied by regulations and design
criteria are based on the concept of a “dangerous dose,” rather practices. Some excerpts from those studies are examined
than risks of death. The criteria for a housing development of 10 here.
houses (25 people) are In examining existing criteria, previous studies, failure rates,
and safety factors for limit state design criteria, preliminary
Substantial risk (HSE advises against) 1 0-5 per year work performed for Canadian pipeline regulations established
Negligible risk (HSE does not object) 10“ per year some suggested “target failure probabilities” for pipeline
design [95]. These suggestions and conclusions include the fol-
For developments with individual risk between these limits, lowing:
HSE advises against the development. For a development of 30
houses (75 people), per year is taken as the “substantial Human life safety considerations govern the cases
risk” level. For highly vulnerable or very large facilities, a crite- of gas and highly volatile liquid (HVL) pipelines and
rion of 3 x per year is used. lead to a target failure probability of per kilo-
The criterion of per year for a dangerous dose corre- meter per year for such pipelines. This corresponds
sponds to an average risk of fatality of about 3 x lo4 per year, 1 0“ to a societal life risk of less than loT7 per person per
per year therefore translates to a fatality risk of 3 x 1 0-7 per year. year.
A widely referenced HSE risk criteria chart is a modified FN Environmental damage potential governs the case of low
curve shown in Figure 15.3. vapor pressure liquids and also leads to a target fail-
ure probability of per kilometer per year for these
Studies pipelines.
Sour gas pipelines near populated areas should have a target
Many studies have been performed that examined exist- failure probability set an order of magnitude lower than that
ing criteria-criteria established both directly by regulat- for other gas pipelines.

‘
Unacceptable Risk cannot be justified
region except in extraordinary
circumstances

ALARP region Tolerable only if risk reduction
(risk is undertaken is impracticable or if its cost
only if a benefit is is grossly disproportionate to
desired) the improvement gained

Tolerable if cost of reduction
would exceed the improvement

Broadly acceptable Necessary to maintain
region (no need for assurance that risk
detailed working to remains at this level
demonstrate ALARP)

Negligible risk
Figure 15.3 Framework for risk criteria.