Date 14-05-2025
Subject: Facility Layout, issues and solutions
1. Relevant Definitions
Facility: Process and utility plants, tanks, buildings, marine structures, pipe racks and roads located
within a site boundary. For example, a refinery, chemical plant, storage terminal, distribution center, or
corporate office.
Siting: The Process of locating a Complex, Facility, Plant or Unit
Plant: A collection of units which normally operate together to produce specific products. A process
plant typically has roads on all sides and all the processing equipment within that are intended to be
shut down during a maintenance turnaround. For example, a Refinery could have various units; Crude
receiving, Crude Distillation, Vacuum Distillation, Cat Cracker, Coker, Hydrocracker, Hydrogen
Generation Unit, Gas plant etc. but this is counted as one process plant. Areas that transfer or store
products or generate utilities to support functions of the plant are not process plants, however they are
part of process area.
Process Unit: A process unit is a collection of Equipment within a Plant focused on a single operation,
arranged to perform a defined function. A process unit enables the execution of a physical, chemical
and/or transport process, or storage of process material, e.g. a crude distillation unit, LPG treatment
unit ,water treatment unit, Hydrocracker unit, tank farm etc.
Process Section: An area / part of a unit within a process unit containing a combination of processing
equipment that is focused on a single operation, like Distillation, Compression, Absorption, Adsorption
etc.
Blocks: Blocks represent distinct major parts of a facility. Examples are process units, utility areas,
occupied and unoccupied structures, etc. across the facility.
Battery Limits - The boundaries of a process area that establish the outer limits for location of
associated with a complete process or a group of integrated processes that must be shut down
together for or isolated in the event of an emergency.
Layout: The relative location of equipment or buildings within a given site.
2.0 Layout Philosophy and steps
Following Layout steps are used:
1 Collect quality and quantity information on of feeds, catalysts, products and additives as well as their
hazards.
2 Evaluate hazard indices of item 1 as above. Compare these indices with standards.
3 Generate initial design, sizing and giving desired elevations of major equipment to develop a
preliminary layout.
4. Consider the various layout practices as given in paras 2.1 through 2.16.
5 Develop an elementary layout. Carry out initial hazard assessment based on Dupont or Mond F&I
index. Consider all relevant codes and standards.
6 Produce plan view and GA of plant based on this data and the suggested spacing and put on CAD.
7 Decide elevation on requirements of process conditions and equipment as well as the cost implications.
8 Produce simple plan and elevation GAs of alternatives without structures and floor levels.
9 Produce more detailed plan GAD based on decision of last stage.
10 Use this drawing (item 9) to consider operation, maintenance, construction, drainage issues etc.
Consider and calculate economic viable options.
11 Consider requirements for buildings critically, carry out BRA. Minimize where possible.
12 Carry out informal design review with civil engineering inputs based on this drawing.
13 Revise design based on review.
14 Carry out hazard assessment .determine the safe separation distances for fire and toxic hazards,
zoning .control room locations. Consider off site effects of releases.
15 Revise design based on hazard assessment.
16 Confirm all pipes and cable routes. Design review with electrical engineer would be helpful.
17 Carry out multi discipline design reviews considering ease and safety of operation, maintenance,
construction, commissioning emergency scenarios, environment impact and future expansion.
18 Reconcile the outputs of design review, hazard assessment taking cost into consideration.
19. If they will not reconcile, iterate in these steps as required to reach reconciliation. Decide on Final
Layout and document it.
2.1 The initial layout is usually based on the processes being positioned relative to one another on the
basis of the process flow diagram (PFD) and inter equipment distances based on some
norms/practices prevailing in the country. To ensure that a site’s physical constraints are understood
alongside those of the process, there is a need to accommodate the needs of plant construction and
operation. Such constraints are illustrated and considered by layout designers using 2D general
arrangement drawings or plot plans, as well as 3D models in new designs.
Process Flow Diagram of a Big Refinery in India
Cautionary Note: The inter unit or inter equipment distances given in some norms / practices are
rough estimates as do not have solid scientific basis (the distance should vary with hazardous
substance release rate, inventory released in a definite time, process conditions and cannot remain
constant as indicated in norm/practice)and should be verified through Consequence Analysis .As per
author’s calculations the inter unit distances given in various practices/norms are grossly
underestimate and need to be checked before use in the Final Layout to prevent serious Major
Accident hazards.
2.2 Layout should consider Internal or External facilities such as water, gas, electricity supplies,
effluent disposal services, and the facilities for transport of people and goods.
2.3 Information on initial conditions on Ground water and air quality are often key concerns with
respect to the natural environment and impacts thereof need to be considered.
2.4 Diagrams of the connectivity between plots from flows of material, utilities, fire and emergencies,
vehicles, and people can be made and the connection strengths estimated for the most important
cases.
2.5 Once the conceptual site layout design is agreed, plots can be spaced. An accepted initial
minimum value in traditional chemical industries is 30 m and for hazardous
refinery/Gas/Petrochemical plants it can be upto 60 m.
2.6 Operational considerations for Equipment requiring frequent attendance should be reached by the
shortest and most direct routes from the control room, which must itself be in a safe location. Valves
and instrument dials should be at a suitable height so that they can be easily used or read.All plots
may require emergency escape routes and firefighting measures .All of these considerations may
nowadays be reviewed during design by virtual operation of a “walkthrough” 3D computer model of
the plant.
2.7 For maintenance considerations the layout should arrange equipment to facilitate safe
maintenance. For equipment that is to be maintained in situ, space must be left for maintenance staff
and their tools, access to equipment for inspection and repair, lifting gear (to carry parts, fittings, and
possibly maintenance staff), and laying down of new and used parts. Workshop maintenance facilities
should also be installed. A reasonable distance (depending on the degree of hazard) from plant areas
is needed for safe welding unless special precautions are to be taken.
2.8 For safety and emergency considerations the layout of a plot can have a number of important
impacts on plant safety. Layout designers need to make provision for:
2.8.1. Protecting operators from such hazards as tripping, bumping their heads or coming into contact
with hot surfaces
2.8.2. Containing and channeling liquid spillages to safe recovery points, directing vents to safe
locations, and installing adequate ventilation
2.8.3. Allowing vessels and pipework to be completely and safely drained
2.8.4. Reducing pipe and vessel fractures due to vibration, heat stress, and impact
2.8.5. Separating flammable materials from ignition sources and adopting electrical classification
schemes
2.8.6. Protecting plot equipment and adjacent plots from the spread of fire by means of separation,
insulation, and water screens
2.8.7. Planning appropriate firefighting and emergency escape procedures
2.9 Layout of Storage Tanks:
(a) Petroleum storage tanks shall be located in dyked enclosures with roads all around the enclosure.
Aggregate capacity of tanks located in one dyked enclosure shall not exceed following values:
(i) 60,000 cum. for a group of fixed roof tanks.
(ii) 120,000 cum. for a group of floating roof tanks
2.10 Bulk handling facilities:
(a) LPG truck loading/unloading gantry shall be located in a separate block and shall not be grouped
with other petroleum products.
(b) Maximum number of LPG tank truck bays shall be restricted to 8 in one group. The bay should be
designed in such a way that the driver's cabin will be facing the exit direction and shall have no
obstruction.
(c) LPG rail loading/unloading gantry shall be located on a separate rail spur and shall not be grouped
with other petroleum products.
(d) Rail loading/unloading of LPG should be restricted to a maximum of half rake. Full rake loading /
unloading is shall be done on two separate rail gantries having a minimum distance of 50m.
2.11 Truck loading/Rail Loading
2.11.1Tank truck movement inside the installation shall be kept to minimum and for this purpose the
truck loading or unloading facilities should be located at a safe distance near the gate meant for its
movement and should be oriented to provide one-way traffic pattern for entrance and exit. Tank truck
in the gantry shall always be in drive out position for easy escape in case of emergency;
2.11.2 Rail loading or unloading facilities should be located along the boundary of the installation. In
case Tank wagon (TW) unloading facilities are located outside of installation boundary that should
also have a boundary wall as per Government Guidelines;
2.11.3 Drain shall be provided around the TT gantry loading platform area to collect product due to
accidental spill over or leakage and shall be routed to OWS or ETP. The drains shall always be
maintained clean;
2.12 Firefighting
A requirement for good access for firefighting means that plots should be restricted to 100 m X 200 m
with approaches preferably on all four sides, and at least 15 m between plots and/or buildings. An
independent system of mains water supply should be available to fire services from at least two
sources. Firefighting water ring main systems should be arranged to ensure that hydrants cannot be
isolated except at the entrance to the plot area.
2.13 The siting of a control room is determined by the needs of normal operation and by the
requirement for protection during emergencies. The problem therefore reduces to one of placing the
control room as close as possible to the plant consistent with economic protection against explosion
and fire.
2.14 Two truly alternative Escape Routes should be provided as a minimum except in areas of small
fire risk. To allow safe escape, no workspace should be too far from an exit. The appropriate distance
has to be judged for each case according to the height and degree of hazard of the plant. The length
of a dead end on these routes should not exceed 8 m. Emergency assembly points should be
designated for each building or plot. They should be at least 100 m from any hazard, but this distance
should be checked by the Hazard Assessment of Plant Layout. Wind direction should be easily
located by means of a red flag or modern tools.
2.15 The construction phase may affect layout design in complex ways, and it therefore needs to be
given detailed consideration. Nowadays, many projects employ some element of “modular
construction,” in which the object is to complete as much construction and erection work as possible
in the workshop and as little as possible on site
2.16 Thought should be given to likely future expansion of structures, equipment, and pipework, so
that any additions can be erected and tested with the minimum interference to plant operation.
Plot Plan of a Big Refinery in India
For any comment, query or clarification, please contact:
Krishn Kumar Bhatnagar,
Process and Process Safety Consultant,
Noida, India,
kkb1955@hotmail.com,
+919650584384
