Plant layout refers to the arrangement of physical facilities such as machinery, equipment, furniture within the factory building in such a manner so as to have quickest flow of material at the lowest cost and with the least amount of handling in processing the product from the receipt of material to the shipment of the finished product.
Plant layout is often a compromise between a number of factors, including safety aspects such as
- The geographical limitations of the site.
- The distances for transfer of materials between plant and storage units to reduce costs and risks.
- Interaction with existing or planned facilities on site such as existing roadways, drainage and utilities routings.
- The spaces for plant operability and maintainability.
- The hazardous and flammable material storages.
- Emergency services and escape routes for on-site personnel.
- The need to provide acceptable working conditions for operators.
- Preventing and/or mitigating the escalation of adjacent events (domino effect).
- Ensure that safety within on-site and off-site occupied buildings is maintained.
- Controlling the access of unauthorized personnel.
Significance of Layout Safety Review
Hazard assessment of site layout is critical to minimise consequences of loss of containment and chances of escalation. The Domino effect may be by fire, explosion or toxic gas cloud causing loss of control of operations in another location. The Layout Safety Review will broadly follow the guidance of API 521.
The most important factors of plant layout as far as safety aspects are concerned are those to,
- Prevent, limit and/or mitigate escalation of adjacent events (domino);
- Ensure safety within on-site occupied buildings;
- Control access of unauthorized personnel;
- Facilitate access for emergency services.
Why layout safety review
Plant layout and organization are important functions which influence all aspects of work and sequence to health, safety, and productivity. The design of Plant layouts is often arbitrarily carried out without a full evaluation of all the relevant factors. The organizational framework within which many projects are carried out also leaves much to be desired with lack of adequate structures and facilities for managing safety.
This is despite the fact that there is major scope for preventing, or minimizing, the effects of many accidents through appropriate plant layout design and organization. The layout safety review examines the need for safety to be integrated into layout and organization by considering all the internal and external factors
In determining plant layout the following is taken into account
- Inherent safety
- Domino effects
- Toxic gas releases
- Positioning of occupied buildings
- Aggregation / trapping of flammable vapours
- Segregation of incompatible substances (particularly in warehouses / storage areas)
The figure shows the layout of the 540 MWe PHWR Station (Tarapur Atomic Power Station (TAPS)-3&4). Most plant systems, including all systems important to safety are unitised to enable independence of each unit. Some of the systems like the spent fuel storage bay, fire water system and compressed air system provided in the station are shared.