Page 195 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

7/172 Leak Impact Factor
ronmental sensitivity and high value areas (HVAs). Scores are researchheaching hospital. By population density, the class
determined based on qualitative descriptions and are to be location is 4 (very high). Cleanup costs for leaked natural gas
added to the population class number. The worst case (highest are expected to be minimal. If a fire or explosion occurs, dam-
number) in each column should govern. When conditions from age could be extensive. Given the unique nature of the struc-
both columns coexist, both scores can be added to the popula- tures nearby and the value of the contents within-specialized
tion class number. equipment, research in progress, records, and files-the evalu-
The extremes of this consequence scale will be intuitively ator feels the surroundings represent a higher value and scores
obvious-the most environmentally sensitive area and the the additional consequences for pipeline operations in this area
highest population class and the highest value areas simultane- as 0.9 on a 0-to 1.0-point scale. He adds the environmental/
ously occurring in the same section would be the highest conse- HVA score to the population class to get 4.9 as the receptor
quence section. The scale midrange, however, might score.
discomfort some people in that a certain amount of environ- Emergency response to a gas leak would not always be quick
mental sensitivity (or value ofthe surroundings) is said to equal enough to reduce potential damages. No spill score adjust-
a certain population increase. In other words, environmental ments are made.
loss and economic loss are being equated to loss of life. In Table
7.22, the highest environmental sensitivity and the greatest
HVA can each change the surroundings score by the equivalent Example 7.8: Extreme consequences
of one population class designation.
Assessment schemes such as the one shown in Table 7.22 are A 24-in. crude oil pipeline traverses a wetlands area and par-
of course very general and contain value judgments that might allels a stream for over a mile within the wetlands. This is a
be controversial. They can, however, be useful screening or Class 1 area (low population). Cleanup of a spill in this
high-level tools in a risk assessment. The following examples freshwater marsh would involve much damage associated
illustrate some general (high-level) consequence scoring for with heavy equipment and long-term remediation activities
various receptors, based onTable 7.22. (temporary roads, establishment of pumping stations, etc.).
Immediately adjacent to the wetlands area, and within one-
Example 7.5: Neutral consequences quarter mile of the pipeline, a small community removes water
from the stream to supplement its groundwater intakes. Noting
A natural gas pipeline traverses an agricultural area ofclass 1 the immediate wetlands threat from any spill, the high cost of
and Class 2 (low and medium) population densities. Soil condi- remediation, and the threat to a community water supply, the
tions are organic clay and sand. Nearby housing and commercial evaluator scores the conditions as 0.8 on a 0-to 1 .O-point scale.
buildings are consistent with most comparable class locations. If the water intake was the community’s only water supply and
There is no known endangered species that could be impacted if endangered species were involved, the evaluator would have
by a leak in this area. A leak of natural gas is lighter than air and scored the situation as 0.85 or 0.9. The receptor score is then 1 +
would have minimal chronic impact as shown by its product 0.8 = 1.8.
hazard score (chronic component) of 2. No environmental or The operator has a very strong environmental program that
high-value receptors are vulnerable from these sections. includes a detailed, well-practiced response plan. Cornpany-
owned equipment and contract equipment are on standby and
can be quickly placed in this area through the use ofa helicopter
Example 7.6: Higher consequences that is also on 24-hour-per-day standby. Trained, equipped per-
sonnel can be at this site within 1 hour. A manned control room
Outside a major metropolitan area, a subdivision of very should be able to detect a significant leak here within a very few
expensive mansions has recently been constructed within 1800 minutes. The evaluator judges that this level of response can
feet of a 6-in., 400-psig fuel oil line. The class location is 2. The indeed reduce spill consequences by 50% (threshold estab-
pipeline is located on a slope above the new houses. The soil is lished for modeling purposes) and, hence, he adjusts the spill
sandy. Groundwater contamination is a possibility, but there are score, effectively reducing the assumed quantity spilled.
no intake locations for community water supplies nearby. Spill
remediation would be higher than normal due to the slope effects,
the highly permeable soil, and the anticipatedproblems with long- Hazard zones
term remediation equipment operating near the residential area.
The housing is judged to be far enough from the pipeline and the Hazard zones are defined to be distances from a pipeline
thermal effects from burning fuel oil are limited enough that the release point at which significant damages could occur to a
immediate impact to that community is a remote possibility. The receptor (see also Chapter 14). Therefore, a hazard zone is usu-
evaluator scores this situation 0.5 on a 0-to 1 .O-point scale, in con- ally a function of how far potential thermal and overpressure
sideration of the topography and the high house values. He adds effects may extend from the release point. Note that when haz-
this to the population class to get 2.5 as the receptor score. ard zone is calculated as a distance from a source such as a
burning liquid pool or vapor cloud centroid that source might
not be at the pipeline failure location. In fact, the source can be
Example 7.7: Extreme consequences some distance from the leak site. Relative hazard zones for a
vapor release are illustrated in Figure 7.8. A hazard zone might
A high-pressure, 30-in. natural gas pipeline is in a corridor also include potential liquid contamination distances for vul-
that runs within 300 ft of a major university including a nerable receptors such as water intakes and sensitive environ-