Hydrocarbon Processing - December 2021 - 54

Environment and Safety
nal recommendation was that all process equipment holding a
large hydrocarbon inventory within a 40-m radius from Source
Identifying jet fire risks and providing
adequate protection early in the design are
crucial for mitigating the escalation of major
accident events, while ensuring compliance
with applicable laws and regulations.
4 should be provided with suitable protection through a combination
of prevention, control and mitigative measures against
jet fire impingement to minimize the risk of escalation. TABLE 3
provides a summary of the jet fire modeling results.
Case study-Safeguards and protection measures.
Remotely operated shutoff valves (ROSOVs)-also known
as emergency isolation valves (EIVs)-are equipped with
actuators, and are configured to be quickly and reliably operated
from a safe location, such as a well-sited control room.
ROSOVs should be used in facilities where fast and effective
isolation is needed to reduce the impact of major hazardous
releases.12
In this case study, ROSOVs had been applied
in some process sections. However, if the application
of ROSOVs is not accompanied by timely depressuring/deinventory
actions, its effectiveness in fully mitigating the risk
of incident escalation from jet fires is limited, especially for
relatively large, isolated inventories.
An assessment was carried out to determine the provision
of ROSOVs by following guidance from the UK Health and
Safety Executive.13
ROSOVs can provide rapid isolation of
plant items containing hazardous substances in the event of
a failure of the primary containment system-including, but
not limited to, leaks from pipework, flanges, valves and pump
seals. A ROSOV offers risk reduction benefits by allowing the
isolation to be made from a safe distance (such as via a remote
push-button system or from a control building) when combined
with fire and gas detection systems.
Based on the study, it was determined that, because of large
inventory and the physicochemical properties of propane,
the pressure could not be sufficiently reduced, even when the
TABLE 3. Jet fire modeling results summary
Jet fire source
1
2
3
4
5
6
7
Process section
Propylene refrigeration
Product compression
Product compression
Product splitter section
Product splitter section
Deethanizer
Low-temperature section
54 DECEMBER 2021 | HydrocarbonProcessing.com
Maximum flame
length, m
16
12
13
41
19
10
10
Maximum frustum
tip width, m
2.4
1.5
1.8
11.9
2.8
1.4
1.1
Maximum radiation
intensity, kW/m2
173
156
153
261
183
108
125
Full release
duration, min
210
400
360
370
> 1,500
60
60
inventory was blocked off through ROSOVs-therefore, the
application of ROSOVs was determined to be ineffective. For
example, jet fire Source 5 is a candidate for the
addition of ROSOVs, due to its high operating
pressure (19.8 barg) and large flammable liquid
inventory (nearly 228 t). However, as Source 5
encompasses a large pressure vessel and large
pipework (up to a 46-in. nominal size), the provision
of ROSOVs was estimated to reduce the
largest isolatable inventory by less than half of
the initial volume. This translated to a jet fire
release duration of more than 12 hr, which still
posed considerable jet fire risk to the facility.
The application of ROSOVs was still recommended,
although it was concluded that it did not sufficiently
mitigate the risk on its own. Consequently, other combinations
of risk reduction measures were explored.
Risk of credible jet fires and congestion due to modular design
posed a unique challenge from a fire protection perspective.
Therefore, a combination of prevention, control and mitigation
measures were required to adequately address the risk
of jet fire, along with methods for escalation prevention. Taking
into consideration the control hierarchy, a multidiscipline
assessment was carried out to systematically apply protection
measures. Various options were explored to reduce the jet fire
frequency and to bring this risk to an acceptable level where
no additional protection measures would be required. These
measures included the possibility of improving the equipment
design through such measures as using seal-less technology for
pumps, providing increased thickness for process piping, and
reducing the number of flange connections and flange guards.
The fire and gas detection systems were already specified;
therefore, it needed to be ensured that the potential leak
sources were within the coverage of flame detectors, so that
any potential jet fire could be quickly detected and control
measures could be initiated. Additionally, close-circuit television
coverage was provided, so that any jet fire incident
could be rapidly detected and protective measures employed.
While some of the equipment were already specified with
insulation for process reasons, they also required protection
against jet fire impingement.
Active fire protection through a water-spraying deluge system
was explored; however, due to its ineffectiveness against
jet fires, it was decided to upgrade the process insulation to
fireproofing, ensuring that the fireproofing material was suit
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