Page 165 - Pipeline Risk Management Manual Ideas, Techniques, and Resources

71142 Leak Impact Factor
and compositions. The pipeline operator will no doubt be Product hazard score
familiar with his products and their properties.
Note that there is a 2-point spread between each RQ classifi- We arrive at a total product hazard score by using this equation:
cation. The evaluator may pick the midpoint between two
RQs if she has special information that makes it difficult to Product hazard score = acute hazard score + chronic hazard score
strictly follow the suggested scoring. Once again, she must be
consistent in her scoring.
6. Leak volume
Notes on toxicity
For purposes here, the terms leak, spill, and release are used
An important part of the degree of consequences, both acute interchangeably and can apply to unintentional episodes of
and chronic, is toxicity. The degree of toxic hazard is usually product escaping from a pipeline system, whether that product
expressed in terms of exposure limits to humans. Exposure is in the form of liquid, gas, or a combination. The total spill
is only an estimate of the more meaningful measure, which quantity is the sum of leak volumes prior to system isolation
is dosage. The dose is the amount of the product that gets (includes detection and reaction times), the leak volume after
into the human body. Health experts have established facility isolation (drain and/or depressure time), and mitigated
dosage limits beyond which permanent damage to humans leak volume (secondary containment). The following para-
may occur. Because the intake (dose) is a quantity that is graphs discuss pipeline spills and suggest ways to model spill
difficult to measure, it is estimated by measuring the opportu- size for a relative risk assessment.
nity for ingesting a given dose. This intake estimate is the Leakedvolume or spill size is a function of leak rate, reaction
exposure. time, and facility capacities. It is a critical determinant of
There are three recognized exposure pathways: inhalation, damage to receptors under the assumption that hazard zone size
ingestion, and dermal contact. Breathing contaminated air, is proportional to spill size. This assumption is a modeling
eating contaminated foods, or coming into skin contact convenience and will not hold precisely true for all scenarios.
with the contaminant can all lead to an increased dose level Some leaks have a negative impact that far exceeds the
within the body. Some of the exposure pathways can extend impacts predicted by a simple proportion to leak rate. For
for long distances, over long periods of time from the point example, in a contamination scenario, a 1 gaVday leak rate
of contaminant release. Plants and animals that absorb the corrected after 100 days is often far worse than a 100 gaVday
contaminant may reach humans only after several levels of leak rate corrected in 1 day, even though the same amount of
the food chain. Groundwater contamination may spread product is spilled in either case. Unknown and complex interac-
over great distances and remain undetected for long periods. tions between small spills, subsurface transport, and ground-
Calculations are performed to estimate dosages for each expo- water contamination, as well as the increased ground transport
sure pathway. opportunity, account for the increased chronic hazard. On the
EPA ingestion route calculations include approximate other hand, from an acute hazard perspective, such as thermal
consumption rates for drinking water, hits and vegetables, radiation, the slower leak is preferable.
beef and dairy products, fish and shellfish, and soil ingestion The overall equation for LIF recommends breaking the spill
(by children). These consumption rates, based on age and sex of and dispersion variables into separate components. This facili-
population affected, are multiplied by the contaminant concen- tates the assessment of possible spill mitigations. For example,
tration and by the exposure duration. This value, divided by the dispersion potential can be affected by secondary containment
body weight and life span, yields the lifetime average ingestion where the released contents are fully contained in a leak recov-
exposure. ery system, or at least limited in their spread by in-station
In a similar calculation, the lifetime average inhalation expo- berms or natural barriers. So, even if the potential volume
sure yields an estimate of the inhalation route exposure. This is released has not changed, risk can be reduced by preventing the
based on studies of movement of gases into and out of the lungs spread of the spill.
(pulmonary ventilation). The calculation includes considera- However, in many of the sample approaches discussed
tions for activity levels, age, and sex. below, it is a modeling convenience to select variables that
The dermal route dose is obtained by estimating the dermal impact both the spill size and dispersion potential and use
exposure and then adjusting for the absorption of the contami- them simultaneously to assess the overall spill scenario.
nant. Included in this determination are estimates of body Therefore, this leak evaluation section is organized into sepa-
surface area (which is, in turn, dependent on age and sex) and rate discussions for leak size, mitigation, and dispersion poten-
typical clothing ofthe exposed population. tial, but the actual scoring examples usually blend the three
In each of these determinations, estimates are made of components.
activity times in outdoor play/work, showering, driving, etc.
Life spans are similarly estimated for the population under Hole size
study.
We are not proposing that all of these parameters be individ- As a critical component of assessing the volume or rate of a
ually estimated for purposes of a risk assessment. The evaluator release, the failure opening size (hole size) through which the
should realize the simplifications he is making, however, in rat- release occurs, must be estimated. A criterion must be estab-
ing spills here. Because we are only concerned with relative lished for choosing a leak rate scenario for a release from a
hazards, accuracy is not lost, but absolute risk determination pipeline. It is reasonable to assume that virtually any size leak
often requires more formal methods. may form in any pipeline. The evaluator could simply choose a