A good design requires safety aspects to be incorporated throughout the project lifecycle-
starting from Front-End-Engineering-Design (FEED) phase and continued in Engineering-
Procurement-Construction (EPC) phase, as this will address risks related to hazard and
operability of the project during its operation. For this purpose, the concept of Layers of
Protection Analysis (LOPA) will be introduced as a rough guide as to how inherent safe
design could play a major part in plant safety.
Ac`ve Fire Protec`on System
Physical Protec`on
Safety Instrumented System
Alarm and human interven`on
Structural integrity
Photo 1: An overall bund configuration,
encompassing several tanks due to a tight layout,
Figure 1: Layers of Protection Analysis
LOPA is based on the concept of using protection layers to mitigate risks, such
as fire and
prohibits
360Ëšaccess to firefighters and hampers
explosion. The LOPA tool is an effective way of analysing the adequacy of these independent
action in fire emergencies.
Figure 1: Layers of Protection Analysis
protection layers. As there is no perfect protection barrier, several layers may be needed to
achieve a risk Tank
that is fire
as low
as reasonably
practicable.
figure
example pool
of fire size and heat radiation towards
hazards
include,
but are The
not above
limited
to, is an limiting
LOPA analysis for bulk flammable storage in the event of tank fire. Tank fire hazards include
adjacent tanks are equally important objectives
tank rupture/collapse, explosion, and boil over.
but are not limited to tank rupture/collapse, explosion, and boil over.
Five independent protection layers (IPLs) besides preventing contamination of land and
are identified, with minimum Probability water courses.
Five independent protection layers (IPLs) are identified, with minimum Probability of Failure
-1
-1
1 shows an example where effective
Failure
Demand
(PFD)
of 1 For
x 10
assigned
for each.
catastrophic Photo
failure,
on Demand of (PFD)
of 1 on
x 10
-5
assigned for each. For catastrophic failure, bunding separating each tank was not in place.
1 x 10 IPL level is required and hence the need to have minimum five IPLs shown in Figure
Due
to the tight configuration layout of the tank
x 10 -5 IPL integrity
level is which
required
and account
hence maintenance
the need and
1. First layer 1
is structural
takes into
risk-based
inspection. The second layer is alarm and human intervention, which accounts for Fire and
to have minimum five IPLs as shown in Figure 1. farm, access was limited for firefighters to
Gas Detection First
System
and is Public
Address
General which
Alarm System.
Third layer
is safety provide cooling by directing water and
effectively
layer
structural
integrity
takes into
instrumented account
system, accounting
for
Shutdown
System.
Forth
layer
is
physical
protection,
maintenance and risk-based inspection. foam to affected areas . The layout also advanced
which accounts
for second
bunding layer
acts as
and layout/spacing
heat between
radiation from one tank to cause fire to
The
is secondary
alarm and containment
human intervention,
tanks. Lastly, active fire protection system makes up the fifth layer of protection. Each layer
which accounts for Fire and Gas Detection System multiple tanks. Below is the recommended bund
provides a layer
protection
in terms
of reducing
accident,
minimising to be put in place:
specification
and of Public
Address
General
Alarm frequency
System. of Third
response time and minimising damage to safeguard life and property.
layer is safety instrumented system, accounting for
Material: Bund floor and walls shall be built of
materials
Shutdown
Forth
layer
is physical
protection,
Specifically, this
articlewill System.
look further
into
physical
protection
and active fire
protection impervious to the contents of any tank
which accounts for bunding which acts as secondary within the bund. It shall be of sufficient strength
system as means of inherent safe design and their associated challenges.
containment and layout/spacing between tanks.
Lastly, active fire protection system makes up the
3 layer provides a layer
fifth layer of protection. Each
of protection in terms of reducing frequency of
accident, minimising response time and minimising
damage to safeguard life and property.
Specifically, this article will look further into
physical protection and active fire protection
system as means of inherent safe design and their
associated challenges.
Physical protection: Bunding system
An effective bunding system for flammable liquid
should be able to contain spillage from a full tank
of liquid within set parameters, like maintaining
a safe distance from adjacent tanks. For risk
management of bulk storage of flammable liquids,
and structural integrity to ensure that it is unlikely
to burst or leak within ordinary use (2). In the
particular case of bulk storage of flammable liquids,
bunds shall have fire resistant structural integrity.
The objective is to retain the integrity of a bunded
area for as long as possible in the event of a fire.
Concrete and clay are inherently fire resistant, but
the risk of a loss of integrity exists due to joints and
penetrations to the bund walls and floors, and the
way these features are sealed (3).
Size: The depth/height of the bund and the
distance of bund wall shall be designed such that a
full tank spill will be contained within the parameter.
Bund capacity should be at least 133% of the net
capacity of the largest tank. If an automatic fire
sprinkler/deluge system is installed in or over
any bunded tank or drum storage compound, the
capacity of the bund should be increased either by
a volume equal to the output from the sprinkler/
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