Page 250 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Assigning risk scores 111227
V. Third-party damage index These factors are needed to fully consider the probability of
actual pipe failure from third-party damages, rather than just
In many areas, third-party damage is one of ifnot fhemost com- the probability ofthird-party damage. They are evaluated in the
mon cause of distribution pipeline failure. With the proximity design index (Chapter S), which includes many aspects of
of distribution systems to population centers and the high con- system strength.
gestion of other buried utilities, the exposure to potentially The specific variables and their relative weightings that can
harmful excavation activities is high. Offsetting this to some be used to evaluate third-party damage potential are very simi-
degree is the fact that in these areas, excavators expect to find lar to those detailed in Chapter 3. The suggested weightings are
buried utilities, which may prompt better use of one-call different from those used in Chapter 3 as is shown in Table 1 1.1,
systems or better cooperation with other utility owners and These are discussed in the following paragraphs.
excavators.
It is usually unclear exactly why a high incidence of third- Cover
party damage exists on any system. Possible factors that con-
tribute to the damage incidence rate in urban areas include the Cover for a distribution system often includes pavement materi-
following: als such as concrete and asphalt as well as sub-base materials
such as crushed stone and earth. These are more difficult materi-
Smaller contractors may be ignorant ofpermit processes. als to penetrate and offer more protection for a buried pipeline.
Excavators have no incentive to avoid damaging the lines Additionally, many municipalities control excavations through
when the repair cost (to the damaging party) is smaller than pavements. This control may offer another opportunity to avoid
the avoidance cost. damage to a pipeline buried beneath a roadway, sidewalk, etc.
Use of inaccurate maps and records. Score this item as described beginning on page 46.
Attempts at locating buried utilities by operators are impre-
cise. One-cull systems
A study into possible contributing symptoms can provide One-call systems are usually a very effective means of facilitat-
guidance on how avoidance of incidents is best achieved. In ing communication among affected parties. Score as shown on
general, some factors that define a pipeline’s susceptibility to pages51-53.
third-party damage failure, can be identified grouped and
evaluated in order to better understand the threat. Activiv level
Factors that logically impact any pipeline’s vulnerability
include While a high activity level nearby normally accompanies a dis-
tribution system, this is not always an automatic risk increaser.
Depth and types of cover Sometimes a more sophisticated group of excavators works
Exposure vulnerability (unburied portions of the system) near distribution systems. These excavators have more expen-
0 ROW accessibility ence working around buried utilities, expect to encounter
Accuracy, thoroughness, and timeliness of locating process more buried utilities, and are more likely to ensure that owners
Accuracy of maps and records regarding the system’s physi- are notified of the activity (usually through a one-call system).
cal location and characteristics Nonetheless, it is still more defensible to conservatively
Patrol or other advance reporting of nearby activities. assume that more activity near the line offers more opportunity
for unintentional damage to a pipeline.
Factors that are thought to correlate to potential for damag- Score this item as shown on pages 48-50.
ing activity near the pipeline are thought to be
Aboveground facilities
Potential level of excavation or other threatening activity
nearby Surface facilities are susceptible to unique dangers such as traf-
Presence of other buried utilitics fic impact, loadings, and vandalism. Score this item as
Population density described on pages 50-5 1,
Pending use of the area-development in progress or
planned Table 11 .I Third-party damage index: possible variables and
ROW condition and control weigts
Use of one-call system or other indication of informed exca-
vators Ezriahle IVerght
Traffic (for exposure ofunburied portions).
Cover 20
Given the presence of third-party activity, factors that make One-call systems 10
the pipe less-susceptible to failure from third-party activities Activity level 15
include Aboveground facilities IO
Public educatiodlocating process 20
ROW condition IO
Material type Patrol 1s
Pipe wall thickness and toughness Third-party index total I00
Stress level.