Page 278 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Leak impact factor 12/255
sonar, and subsea vehicles, but even then, the observation is Spills and dispersion
not equivalent to that for an onshore installation. The uncer-
tainty caused by this situation should be considered in the For the more persistent liquid spills, especially oils, mixing and
assessment. An increased reliance on indirect observation transport phenomena should be considered. Consider these
methods increases the potential for errors at some point in the examples:
process. When the method requires interpretation, uncertainty
is even higher. Heavy oils can submerge and experience overwashing. Such
With these considerations in mind, score this item as phenomena make spill detection and cleanup more difficult.
described on pages 124-125. Shorelines remain in danger because submerged oil can still
migrate. Overwashing tendency and the resultant particle size
and depth of submergence are related to the oil density and
C. Operations (weighting: 35%) the density of the water and the sea energy (wave height) [78].
Because this phase ofpipelining is considered to be “real time,” Once spilled, heavy oil can theoretically increase in density
the possibilities for intervention are somewhat reduced. Error due to evaporation. However, this increase is quite minor
prevention, rather than error detection, is emphasized. Score 1781.
this item as described on pages 125-132. Note the importance Sunlight-induced reactions can occur after initial evapora-
of survey techniques here, especially bottom condition and tion of the volatile components. These reactions include
external pipe condition surveys. Internal inspections are dis- photo-oxidation, photodecomposition, and polymerization.
cussed in the covrosion index material. Other survey techniques The effectiveness of the reactions depends on the type and
are discussed in other parts of the assessment also. composition of the oil as well as the sunlight intensity and
duration. Some photoxidation products and effects can
worsen the spill because toxicity, density, and emulsification
D. Maintenance (weighting: 150/) tendency may increase [78].
As in the basic model, a low score in maintenance should cause Crude oil spilled in a marine environment can form a water-
doubts regarding the adequacy of any safety system that in-oil emulsion that has properties different from the original
relies on equipment operation. Score this item as described on oil. Such emulsions can be persistent and can aggravate spill
page 132. countermeasure techniques. The chemical composition of
the oil is thought to determine the tendency to form emul-
sions [78].
VI. Leak impact factor A table of expected behavior for various spills on water is
The type of product spilled, the distance to sensitive areas, and showninTable 7.19.
the ability to reduce spill damages will usually govern the leak The potential range of a spill can he scored using Table 7. I9
impact for offshore lines. Spills of gases or highly volatile prod- and the material’s properties, or using more qualitative descrip-
ucts offshore should be scored as they are in the onshore risk tions as follows:
assessment model (see Chapter 7). This involves assessment and
numerical scaling of product hazard, relative spill size, disper- High
sion potential, and vulnerable receptors. More minor impacts A highly miscible material has spilled into a fast current.
seen in the offshore environment include the possible impact on Conditions are conducive to quick mixing of the product in
marine life from pipeline noise during operations and the pres- the water and fast transport ofthe mixture away from the spill
ence of the pipeline as a barrier to marine life movements. These site. High-energy water conditions and wind-driven spread-
can be addressed in an evaluation ofreceptor vulnerabilities. ing promote wide dispersal of spilled substance.
Medium
Some mixing is possible under most normal conditions or thor-
Receptors ough mixing is possible under more unusual conditions.
Unlike the onshore counterpart, population density might not Travel of the mixture will occur, but relatively slowly or in a
be a dominant concern for offshore pipeline failures. The U.S. direction away from environmental receptors. Some water
Department of Transportation regulations consider offshore energy is present.
pipelines to be class 1 (rural) areas. Proximity to recreational Low
areas (beaches, fishing areas, etc.), harbors and docks, popular An immiscible material is spilled into stagnant water. The
anchoring areas, ferry boat routes, commercial shipping lanes, spilled material will tend to stay separate from the water.
commercial fishing and crabbing areas, etc., will often replace Movements of spilled material will be very minor. Low-
the onshore measures of population densities, when consider- energy water conditions exist. Spill remains localized and is
ing the potential to impact human receptors. relatively easy to clean up.
In many cases, the most significant impact from an offshore
spill will be the effect on environmentally sensitive areas. Emergency response
Offshore liquid spills pose aunique set ofchallenges. A qualita-
tive scale that can gauge the degree ofdispersion based on wind Adjustments to the leak impact factor can be made when
and current actions and product miscibility can be developed. response activities are seen to reliably reduce the spill conse-
The sensitivity of environmental receptors is discussed in quences by some set threshold-perhaps 50% or more. These
Chapter 7. activities are discussed in the onshore risk assessment model