Safety and Reliability
ISSN: 0961-7353 (Print) 2469-4126 (Online) Journal homepage: www.tandfonline.com/journals/tsar20
Louvered jet fire deflector – concept and concept
validation for flame length reduction, flame
deflection and explosion overpressure reduction
Nagoor Monnapillai Ahamed
To cite this article: Nagoor Monnapillai Ahamed (2017) Louvered jet fire deflector
– concept and concept validation for flame length reduction, flame deflection
and explosion overpressure reduction, Safety and Reliability, 37:4, 248-258, DOI:
10.1080/09617353.2018.1490486
To link to this article: https://doi.org/10.1080/09617353.2018.1490486
Published online: 11 Oct 2018.
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SAFETY AND RELIABILITY
2017, VOL. 37, NO. 4, 248–258
https://doi.org/10.1080/09617353.2018.1490486
Louvered jet fire deflector – concept and concept
validation for flame length reduction, flame
deflection and explosion overpressure reduction
Nagoor Monnapillai Ahamed
Albain Group Inc, Dubai, UAE
ABSTRACT
In hydrocarbon processing industries, the standard approach to prevent jet
fire escalation to adjacent facilities is to provide a solid fire wall. However,
a solid firewall impedes the air flow through the plant, decreasing ventilation
and increasing the potential flammable gas cloud size resulting in the
generation of higher explosion overpressures if the gas cloud finds an ignition source. The conflicting impact of solid fire walls in preventing jet fire
escalates but conversely increasing the potential explosion overpressures is a
perennial design issue faced by safety engineers. This paper presents an alternate louvered jet fire deflector design concept; along with the validation
work undertaken to demonstrate the explosion overpressure reduction benefits of the louvered wall application. This louvered jet fire deflector concept
was subsequently engineered, fabricated, tested and has been incorporated
into the plant design. This paper is written to increase the knowledge and
awareness of safety engineers of an alternate option to optimise and balance
the fire and explosion risk management.
Abbreviations: CFD: computational fluid dynamics; FLACS: flame acceleration
simulator; ISO: the international organization for standardization; m: meter;
DAL: design accident load
ARTICLE HISTORY Received 13 February 2018; Accepted 6 June 2018
KEYWORDS Deflector; explosion; fire; firewall; jet fire; Louver; overpressure
Introduction
In hydrocarbon exploration or processing facilities, fire and explosion
events are considered as major accident hazard, and mitigation measures
are provided as a part of a plant wide barrier approach to eliminate or
minimise the escalation potential to adjacent parts of the facilities.
CONTACT Nagoor Monnapillai Ahamed
Nagoor.Monnapillai@albaingroup.com; managoor@yahoo.com
Albain Group Inc., 4106/4107, Level 41, Tower AA1, Mazaya Business Avenue, Jumeirah Lakes Towers,
Dubai, UAE
ß 2018 Safety and Reliability Society
SAFETY AND RELIABILITY
249
After implementing inherently safer design measures and other practical mitigation measures to reduce the frequency of the events; and the extent and
severity of the resultant fire events, one of the recognised industry solution to prevent jet fire impingement of adjacent facilities is to provide a
solid jet fire-rated fire wall of suitable construction and testing to resist a
set duration in mitigating a jet fire impingement. These solid fire walls
provide a physical barrier between the source of fire and the adjacent
section of the facility where escalation events could occur. This standard
approach of providing a solid fire wall solution impedes the air flow
through the plant, thereby decreasing ventilation and increasing the
potential gas cloud size within the plant following a hydrocarbon leak,
which subsequently results in the generation of higher explosion overpressure, should the leak reach an ignition source. The solid fire wall also
provides confinement and additional congestion around the plant which
exacerbates the explosion overpressures generated.
Although the solid fire wall would prevent jet fire escalation to adjacent
facilities, due to the potentially increased overpressures generated, the civil;
structural; piping and piping support design would need to be robust
enough to resist higher design overpressures, as a result of the solid fire
wall, thereby increasing the cost and complexity of the overall plant design.
The conflicting impact of solid fire walls in preventing jet fire escalation but
conversely increasing the explosion overpressures is a perennial design
issue faced by engineers.
Project-specific issues
A project to replace a hydrocarbon gas processing plant was undertaken as
the existing plant was becoming obsolete. Due to limited space availability
within the existing facility footprint, the new plant was proposed to be
located adjacent to the existing plant which it is replacing. The hydrocarbon storage tank farm is located on one side of the new plant, with the
closest storage tank located 60 m from the new plant.
Fire consequence assessment undertaken by the project using industry
recognised commercially available consequence modelling tool indicated
a jet fire from the new plant could potentially impact on the nearest
hydrocarbon storage tank. In time, this would lead to catastrophic failure of
the tank which would be a major accident escalation scenario. Failure of
one storage tank is most likely to lead to adjacent tanks being impacted as
they are in close proximity to each other.
The standard solution of providing a solid fire wall between the plant
and the storage tanks to prevent jet fire reaching the tanks was initially
considered for implementation. The project undertook an initial coarse
computational fluid dynamics (CFD) explosion analysis which indicated that
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N. MONNAPILLAI AHAMED
the anticipated design overpressures are high for a solid wall solution. The
use of a solid wall would require the civil; structural; piping and piping support to be designed to a higher design overpressure with the associated
increase in the cost and complexity of the new plant. As a result of this
review, the project evaluated alternative solutions which may prevent jet
fire escalation to the storage tank but at the same time reduce the potential design explosion overpressures within the plant.
Functional requirement of measures to prevent jet
fire escalation
The critical functional requirement for any mitigation measure is to prevent
the jet flame from reaching the storage tanks and to retain its own structural integrity for the duration of the fire to prevent any further escalation
within the plant. As the storage tanks are located at a distance from the
plant, any measure employed that reduces the flame length or deflects the
flame away from the tanks would fulfil the escalation prevention function.
Therefore, it was established that the mitigation measures considered
should fulfil the following functionality:
Provide line of sight obstruction between the new plant and storage
tanks to prevent jet flame from directly impinging the tanks.
The line of sight obstruction should be maintained under jet fire conditions for a prescribed duration. This prescribed duration was estimated
as 30 min, based on depressurisation of the largest isolatable section
inventory in the plant. This is to ensure that the structural integrity of
the mitigation measure is maintained for the duration of the fire to
prevent any further escalation within the plant.
Deflection of jet flame away from storage tanks. The angle of deflection
required for the flame to clear the top of the storage tank was estimated to be 45˚ (Figure 1).
Louvered jet fire deflector concept
The project evaluated a concept of a louvered jet fire deflector wall which
would enable air to flow in and out of the plant; and allow the jet flame
to pass through but partially reduce and deflect the jet flame momentum
away from the storage tanks in the event of fire. The ventilation around
the plant is provided through the gaps between the louvers which allow
air to pass through the louvered wall and dilute any gas release prior to
any potential delayed ignition (explosion) event. This louvered jet fire
SAFETY AND RELIABILITY
Louvered Jet
Flame Deflector
Deflected
Flame
Direction
Hydrocarbon
Storage Tank
Plant
Initial Flame
Direction
251
Angle of Flame
Deflection to
o
45 Avoid Tank
Figure 1. Louvered jet flame deflector and storage tank.
deflector wall was perceived to provide the following benefits over a solid
fire wall:
Increased dilution and dispersion of any hydrocarbon gas leak by allowing increased air flow leading to reduced explosion overpressures.
Reducing confinement leading to reduced explosion overpressures
generated within the plant.
Increase in explosion vent path (through louvers) leading to reduced
explosion overpressures within the plant.
Reduction of the effective jet flame length by disrupting the jet fire
momentum direction and magnitude.
Changing the direction of the jet flame towards a preferred safer
direction away from the storage tanks.
Concept validation
The feasibility of designing and fabricating such a louvered jet fire deflector
and the expected size of opening between the louvers that could be
fabricated was discussed with vendors specialising in designing and
manufacturing blast and fire walls. Based on their input, a louvered jet
flame deflector with about 65% open space was considered feasible to
manufacture. The resultant design was taken forward to assess the following perceived benefits through computational fluid dynamics (CFD) analysis
using FLACS software:
Increased ventilation and subsequent dispersion of releases.
Reduced confinement.
Overall reduction in assessed explosion overpressures.
The louvered wall panels were modelled as porous walls within the
FLACS software for the CFD assessment. A comparative review of the CFD
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N. MONNAPILLAI AHAMED
results was undertaken to ascertain the relative benefits between the
following options:
Option 1: Solid wall on the one side of the plant (facing the
storage tanks).
Option 2: No wall.
Option 3: Louvered wall modelled with about 65% porosity.
Ventilation analysis
The results of CFD ventilation analysis concluded that
The louvered firewall configuration (when compared with solid wall)
results in better ventilation for the whole plant, for all wind directions assessed.
The highest difference in the level of ventilation is from the direction
of wind on the side obstructed by the solid wall.
The increased ventilation could have a significant (positive) impact on
the leak dispersion and resulting in smaller flammable cloud.
Explosion analysis
Further explosion CFD modelling demonstrated that the ‘no wall’ option
(no confinement) does result in significantly reduced overpressures generated
within the plant when compared with solid wall option, as would be
expected. However, when assessed, the louvered fire wall option does not
increase overpressures significantly above those from the ‘no wall’ option. The
result of the explosion analysis is graphically presented in Figures 2 and 3.
The summary of the CFD explosion analysis are
The no wall and louvered wall options show a significant reduction in
maximum and average overpressures when compared with the solid
fire wall option.
For the louvered wall option, the peak explosion overpressure reduction is significant (60–75%) for larger gas cloud volume while at smaller
gas cloud volumes there is little difference between the three options
as the wall has minimal influence on the volume filled for the
smaller clouds.
For the louvered wall option, the average explosion overpressure
reduction is considerable (27–39%) for larger gas cloud volume, while
at smaller gas cloud volumes, there is little difference between the
three options.
SAFETY AND RELIABILITY
253
Figure 2. Peak overpressure.
Figure 3. Average overpressure.
The reduction in the overpressure values for louvered wall option when
compared with the solid wall option are significant enough to positively impact on the civil, structural and piping design criteria. The solid
wall option will increase the overall cost and complexity of the design.
There is minimal difference in overpressures between the no wall and
the louvered fire wall option which was deemed not significant enough
to impact the design cost and complexity.
Based on the above findings, the project opted for the louvered jet fire
deflector wall design which maximises ventilation and minimises the resultant explosion overpressures. The design, engineering and construction of
the louvered fire wall were undertaken through a specialist vendor.
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N. MONNAPILLAI AHAMED
Fire endurance and flame deflection testing
The functional requirement to provide line of sight obstruction between
the new plant and the storage tank was incorporated in the design. The
functions to maintain line of sight obstruction under jet fire condition for
30-min period and deflection of flame by 45˚ (or more) from horizontal was
tested by undertaking a full-scale jet fire testing of the deflector panel at a
Fire and Explosion testing facility. The test arrangement is presented in
Figures 4 and 5.
The test procedure used is as follows:
The louvered jet fire deflector test panel was positioned at 3 m distance from the flame nozzle. This takes into consideration the flame
stabilisation distance of approximately 1 m and a further 2 m to the
start of the luminous region. This arrangement is based on experience
of the Fire and Explosion testing facility. This distance allows the
behaviour of flame to be better visualised on impingement of the
test panel.
Flame nozzle aimed at the centre of the test panel.
Introduce jet fire flame to the sample panel, gas flow rate is maintained in
accordance with the ISO 22899-1 specification (ISO 22899–1:2007, 2007).
The flame was sustained for a period of no less than 30 minutes;
Following a sufficient cooling down period, a visual inspection was
carried out; and
Success/failure criteria defined, as a minimum, the panel should resist
the jet fire without degenerating or significant distortion of the louvre
blades whilst line of sight obstruction of the louvre blades
being maintained.
Figure 4. Side view of test arrangement.
SAFETY AND RELIABILITY
255
Figure 5. Front view of test arrangement.
The jet flame length reduction in the louvered jet fire deflector panel
was compared with the experimental free field jet flame length. The angle
of deflection due to the louvered fire deflector was also measured to
compare with the minimum 45˚ angle requirement. The observed free field
flame length and the flame length reduction as a result of the jet fire
deflector during the test are presented in Figures 6 and 7, respectively.
The free field jet flame distance extends to approximately 7–8m while the
flame distance through the louvered panel is about 4–4.5m from the point of
flame origin (1–1.5 m beyond the panel). The flame length reduction from
the jet flame deflector is, therefore, about 60% for this test arrangement.
The angle of actual flame deflection was observed to be more than the
required flame deflection angle, which is primarily due to the configuration
of the louvers. It is observed that loss of momentum is dependent on the
angle of impingement of the flame on the louvers. As would be expected,
the jet flame momentum loss is minimal when the flame impingement
angle is parallel to the surface of the louvers and the momentum loss is
maximised when the flame impingement angle is perpendicular to the
surface of the louvers. This can be seen in Figure 7, where the flame above
the centre line passes through the louvered wall while very little of the
flame below the centre line passes through the louvers.
Conclusions
As a result of the CFD modelling and the physical tests carried out on the
designed and manufactured full scale louvered wall, the following conclusions can be made:
A porous/louvered wall reduces the confinement and gas cloud size
with the associated reduction in explosion overpressure generated
when compared with solid wall.
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N. MONNAPILLAI AHAMED
Figure 6. Free field jet flame profile.
Figure 7. Flame profile through louvered jet flame deflector panel.
The reduction in overpressures is significant at large gas cloud volume
and to lesser extent at smaller gas cloud volume.
The louvered configuration reduces the momentum of the jet fire
leading to reduced flame length after impacting the louvered wall.
The reduction in flame length is dependent on the angle of jet fire
impingement and configuration of the louvers.
Depending on the angle and configuration of the louvers the jet flame
can be deflected at any required angle.
SAFETY AND RELIABILITY
257
Design benefits to project
An explosion exceedance analysis undertaken using a similar process plant
as a basis to compare the changes in the explosion design criteria between
solid and louvered wall indicated that the maximum and mean design
accident load (a 10 4/year frequency of occurrence) for a louvered wall
configuration is reduced by 86% and 60%, respectively, when compared
with solid wall configuration (Table 1). From this, it is evident that a significant (60%) reduction in explosion overpressure can be expected when
using a suitably designed louvered wall instead of solid wall.
From the CFD assessment results, it is noted that there is significant
explosion overpressure reduction benefit in using a louvered fire deflector
wall which leads to design and cost benefits, whilst providing adequate jet
fire escalation mitigation for this application, equivalent to a solid fire wall.
Subsequently exceedance frequency analysis specific for the plant was
completed and this design accident load (DAL) was implemented within
the plant design.
Potential application of the louvered jet fire deflector concept
In onshore hydrocarbon processing facilities, where protecting specific
targets from jet fire event is required, such a louvered jet fire deflector wall
can be considered instead of solid fire walls. The angle and direction of
deflection can be varied to suit the specific site requirement.
The louvered jet fire deflector wall has the potential to be used in
offshore oil and gas platforms where explosion overpressure is high due to
potentially significant levels of congestion which can be exacerbated by the
confinement introduced by a solid fire wall. Depending on the layout of the
platform, a suitably designed louvered fire wall may provide a balanced
solution to fire and explosion escalation scenarios into adjacent modules.
This has the potential to reduce the explosion design criteria and thereby
have a beneficial effect on the platform weight.
This paper is written to increase the knowledge and awareness of safety
engineers of an alternate option to optimise and balance the fire and
explosion risk management and positively influence the overall design of
the facility.
Table 1. Generic comparison of explosion design criteria.
10–4/year Max. overpressure (barg)
Solid wall
4.80
10–4/year Mean overpressure (barg)
Louvered wall
% Reduction
Solid wall
Louvered wall
% Reduction
0.65
86
0.58
0.23
60
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N. MONNAPILLAI AHAMED
Previous publications
1.
2.
“Stress Corrosion Cracking of Nickel Lined Steel Flange in Caustic
Service”, Material Performance (MP), Sep 2005, NACE, USA.
“Review of International Shipping and Port Security (ISPS) Code”,
Euroship, Aug 2006, Co-Author.
Notes on contributor
Nagoor Monnapillai Ahamed, has 28 years of experience in the oil & gas, petrochemical and chemical industries. He has a B.Eng. degree in Mechanical
Engineering, M.Sc in Ecology and Environment, and M.Sc in Safety Engineering,
Reliability, and Risk Management. He is a chartered engineer in the UK and in
India, is a Fellow of Safety and Reliability Society (SaRS) (UK), member of Institution
of Engineers (India); and joint member of Society of Environmental Engineers (SEE)
(UK). He is also an affiliate professor in BSA Crescent University (India). He currently
works for Albain Group Incorporated, as Consultancy Services Director.
References
ISO 22899-1:2007. (2007). Determination of the resistance to jet fires of passive fire protection materials – Part 1: General requirements (1st ed.).