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Potential impact radius formulae for flammable gases other than natural gas subject to 49 CFR 192 : final report.
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2005-06-01
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Alternative Title:TTO Number 13;Integrity management program delivery order DTRS56-02-D-70036;OPS TTO13 - Potential Impact Radius formulae for flammable gases other than natural gas.;
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Abstract:This report was prepared in accordance with the Statement of Work and proposal submitted in
response to RFP for Technical Task Order Number 13 (TTO 13) entitled “Potential Impact Radius
Formulae for Flammable Gases Other Than Natural Gas.”
A key element of the Gas Integrity Management Rule (49 CFR 192, Subpart O) is the calculation of
the potential impact radius (PIR) of a circle within which the potential failure of a pipeline could
have significant impact on people or property.
The original derivation of the PIR formula referenced in 49 CFR 192 is contained in the Gas
Research Institute (GRI) report by C-FER Technologies (C-FER), “A Model for Sizing High
Consequence Areas Associated with Natural Gas Pipelines” (Stephens 2000). It must be recognized
that this formula was derived solely on the premise that thermal radiation from a jet/trench fire is the
dominant hazard related to pipe rupture and subsequent ignition. Since natural gas is non-toxic and
significantly lighter than air, this premise is valid.
However, there are certain pipeline operators transporting flammable gases other than natural gas
(e.g. hydrogen) that will be governed by the jet fire hazard, and thus there is a need for derivation of
PIR formulae for use in identifying high consequence areas for these pipelines. While the C-FER
report provides a basis for derivation of such formulae, the dimensionless values for emissivity
factor, release rate decay factor, and efficiency factor used in the original derivation of the PIR
formula have not been validated or optimized for flammable gases other than natural gas.
An introduction to this report is contained in Section 1, while Section 2 presents the more detailed
background on the reasoning and assumptions used in the development of the PIR formulae
presented in this report.
Section 3 documents the process utilized in identifying the various products that are known or
reasonably assumed to be currently transported by pipelines in the US. Four products were chosen
for PIR formula development: ethylene, hydrogen, rich natural gas and synthesis gas (syngas).
Section 4 comprises the majority of the report and describes the actual PIR formula development in
a logical progression. At each step, the underlying formulae are given with the required variables
presented and explained. This section concludes with a generalized methodology for use in
determining the PIR for flammable gas mixtures. The PIR formula for natural gas referenced in 49
CFR 192 is also presented to allow the reader to compare the results of this study with the earlier
work.
Section 5 describes the efforts conducted to validate the PIR formulae. These efforts were essentially
fruitless due to the lack of actual incident data for the products of interest. Section 6 presents a
commentary on the usage of constants for selected model factors that are in fact variables and would
be treated as such if a more rigorous modeling approach were to be employed. Section 7 summarizes
the results of the PIR formula development process. Finally, Section 8 presents a list of reference
documents cited throughout the report.
The information included in the report that was entirely compiled by C-FER Technologies is
contained in Appendix A.
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