Hydrocarbon Processing - December 2021 - 51

Environment
and Safety
S. JADEJA and N. HARIS, Fluor, Farnborough, UK;
and A. SELIRIO, Fluor, Philippines
Consequence modeling and risk analysis
for safeguarding against jet fires
Due to their high momentum and erosive nature, sustained
jet fires are one of the most hazardous types of fires that can
threaten the integrity of process facilities. Identifying jet fire
risks and providing adequate protection early in the design
are crucial for mitigating-in the most economical manner-
the consequences of, and the potential for, the escalation of
major accident events, while ensuring compliance with applicable
laws and regulations. Although guidance and methodology
are available for determining protection against pool fires
(e.g., API RP 2218), there is no universally recognized code
or standard that addresses jet fire risks. A case study involving
a propane dehydrogenation (PDH) unit is presented here
to demonstrate the value of consequence modeling and risk
assessments to economically determine an adequate level of
protection against credible jet fire scenarios via a combination
of prevention, control and mitigation measures, as early as in
the definition phase of a project.
Jet fires. Jet fires pose a serious hazard to hydrocarbon processing
facilities, with the potential to escalate into a major
incident. A jet fire occurs when a flammable fluid (such as a
gaseous, flashing liquid or two-phase and pure liquid inventories)
is rapidly released from a pipe or orifice and immediately
ignites. The fire's heat intensity poses a hazard to personnel
and can cause damage to unprotected equipment due to direct
flame impingement. Jet flames also dissipate thermal radiation
away from the flame's visible boundaries and transmit heat energy
that could be dangerous to life and assets.1
In 2007, a jet fire from a pressurized liquefied petroleum gas
(LPG) release at the Valero McKee refinery in Sunray, Texas,
caused very rapid heating and the failure of unprotected structural
steel, resulting in the collapse of a pipe bridge, which greatly
increased the magnitude of the fire. The incident resulted in
injuries to three employees and a contractor, with direct losses
attributed to the fire exceeding $50 MM.2
The U.S. Chemical
Safety and Hazard Investigation Board's investigation of this incident
found that a jet flame (approximately 77 ft) impinged on
a pipe rack that was located outside of the fire scenario envelope
(approximately 50 ft), which considered pool fire risk only.
Current industry practice focuses on analyzing the flame
length, thermal radiation intensity extent of impingement and
duration of potential jet fires, as well as the need for passive fire
protection (PFP), emergency depressurization and other mitigation
options.1
The requirement for projects to drive down
costs often does not support the universal application of jetfire-rated
fireproofing, and, thus, warrants some form of risk
assessment to create practical solutions. A full quantitative risk
assessment (QRA) may yield the optimum recommendation
for jet fire protection; however, the level of detail required for a
QRA is often not available during the early stages of a project,
such as front-end engineering and design (FEED).
Although various industry references3,4,5,6
provide some
form of guidance and background material for consideration,
there is no prescriptive method to address jet fire risk. Previous
work summarized proposed alternatives for conducting
full QRAs and their respective limitations, and provided a
methodology suited for offshore fast-track projects.7
However,
the methodology does not address the lack of industrystandard
data required to conduct frequency analysis for
onshore projects. The goal of this article is to present a methodology
to determine appropriate jet fire protection in FEED
projects by applying a semi-quantitative risk assessment that
involves a combination of consequence modeling and simplified
hazard identification or a coarse QRA, where available.
The methodology is demonstrated with a case study involving
a PDH facility.
Method. A summary of the jet fire risk assessment methodology
applied in this case study is shown in FIG. 1. The risk assessment
is initiated by the available information from the coarse
QRA (e.g., high-risk areas and pre-identified failure scenarios).
In the absence of a coarse QRA, a process hazard analysis-
such as hazard identification (HAZID) or hazard and operability
(HAZOP) studies-or a simplified hazard identification
technique can be applied where process hazards are identified
based on hydrocarbon inventories, operating conditions, and
equipment type and location. This information is validated
by project data-including process flow diagrams, piping and
instrumentation diagrams (P&IDs), and heat and material balance-and
then utilized for consequence analysis (e.g., jet fire
modeling and impact assessment) to propose the recommended
preventive, control and mitigative measures.
Hydrocarbon Processing | DECEMBER 2021 51
Hydrocarbon Processing - December 2021

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