Page 158 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

Background 71135
Changes in LIF calculations LV =leak volume (relative quantity of the liquid or vapor
release)
Some changes to the leak impact factor (LIF), relative to the D = dispersion (relative range of the leak)
first and second editions of this text, are recommended. The R =receptors (all things that could be damaged).
elements of the LIF have not changed, but the protocol by
which these ingredients are mathematically combined has Because each variable is multiplied by all others. any indi-
been made more transparent and realistic in this discussion. vidual variable can drastically impact the final LIE This better
Additional scoring approaches are also presented. Given the represents real-world situations. For instance. this equation
increasing role of risk evaluations in many regulatory and shows that if any one of the four components is zero. then the
highly scrutinized applications, there is often the need to con- consequence (and the risk) is zero. Therefore, if the product is
sider increasing detail in risk assessment, especially conse- absolutely nonhazardous (including pressurization effects),
quence quantification. There is no universally agreed upon there is no risk. If the leak volume or dispersion is zero, either
method to do this. This edition ofthis book seeks to provide the because there is no leak or because some type of secondary
risk assessor with an understanding of the sometimes complex containment is used then again there is no risk. Similarly, if
underlying concepts and then some ideas on how an optimum there are no receptors (human or environmental or property
risk assessment model can be created. The final complexity and values) to be endangered from a leak. then there is no risk. As
comprehensiveness of the model will be a matter of choice for each component increases, the consequence and overall risks
the designer, in consideration of factors such as intended appli- increase.
cation, required accuracy, and resources that can be applied to The full range of hazard potential from loss of integrity of
the effort. any operating pipeline includes the following:
I. Toxicit?,/asphyxiation~ontact toxicity or exclusion of air
Background from confined spaces.
2. Contamination pollution-acute and chronic damage to
Up to this point, possible pipeline failure initiators have been property, flora, fauna, drinking waters, etc.
assessed. These initiators define what can go wrong. Actions or 3. Mechanical eflects-erosion, washouts, projectiles. etc.,
devices that are designed to prevent these failure initiators have from force of escaping product.
also been considered. These preventions affect the “How likely 4. Firdignition scenarios:
is it?’ follow-up question to “What can go wrong?” a. Fir.eballs-normally caused by boiling liquid, expanding
The last portion of the risk assessment addresses the ques- vapor explosions (BLEVE) episodes in which a vessel,
tion “What are the consequences?” This is answered by esti- usually engulfed in flames, violently explodes, creating a
mating the probabilities of certain damages occurring. The large fireball with the generation of intense radiant heat
consequence factor begins at the point of pipeline failure. The b. Flame jets--occurs when an ignited stream of material
title of this chapter, Leak Impact Factor: emphasizes this. What leaving a pressurized vessel creates a long flame jet with
is the potential impact of a pipeline leak? The answer primarily associated radiant heat hazards and the possibility of a
depends on two pipeline condition factors: (I) the product and direct impingement of flame on nearby receptors
(2) the surroundings. Unfortunately, the interaction between c. Vapor cloudfire--occurs when a cloud encounters an
these two factors can be immensely complex and variable. ignition source and causes the entire cloud to combust as
The possible leak rates, weather conditions, soil types, popula- air and fuel are drawn together in a flash fire situation
tions nearby, etc., are in and of themselves highly variable d. Vapor cloud explosion--occurs when a cloud ignites and
and unpredictable. When the interactions between these and the combustion process leads to detonation of the cloud
the product characteristics are also considered the problem generating blast waves
becomes reasonably solvable only by making assumptions and e. Liquid poolfires-a liquid pool of flammable material
approximations. forms, ignites, and creates radiant heat hazards
The leak impact factor is calculated from an analysis of the
potential product hazard, spill or leak size, release dispersion, Naturally, not all of these hazards accompany all pipeline
and receptor characteristics. Although simplifying assump- operations. The product being transported is the single largest
tions are used enough distinctions are made to ensure that determinant of hazard type. A water pipeline will often have
meaningful risk assessments result. only the hazard of “mechanical effects” (and possibly drown-
The main focus ofthe LIF here is on consequences to public ing). A gasoline pipeline, on the other hand, carries almost all of
health and safety from a pipeline loss of containment integrity. the above hazards.
This includes potential consequences to the environment. Hazard zones, that is, distances from a pipeline release
Additional consequence considerations such as service inter- where a specified level of damage might occur, are more fully
ruption costs can be included as discussed in later chapters. discussed in Chapter 14. Example calculation routines are also
The LlF can be seen as the product of four variables: provided there as well as later in this chapter. Figure 7.8, pre-
sented later in this chapter, illustrates the relative hazard zones
LIF=PH x LV x D xR oftypical flammable pipeline products.
where There is a range of possible outcomes--consequences-
LIF =leak impact factor (higher \slues represent higher conse- associated with most pipeline failures. This range can be seen
quences) as a distribution of possible consequences; from a minor nui-
PH = product hazard (as previously defined) sance leak to a catastrophic event. Point estimates of the more