Q. Safety considerations in multi-unit plants?
Segregation of process units within large or multi-unit plants is necessary in order to reduce the risk of a fire spreading. This is normally achieved by providing fire breaks of at least 6m (20 ft.) in width approximately every 60m (200 ft.) either by means of access ways or through equipment layout considerations. These roads should preferably surround the unit to provide good fire-fighting access. Fire-fighting access is not normally provided through the unit or under unit pipe racks. Toxic, acidic and dusty equipment within the plant should be separated by grouping items handling similar commodities together often within a curbed area.
Ideal access to most process areas should generally be from upwind and a higher elevation. Secondary access should preferably be from a crosswind direction.
Firewater ring mains with post-indicator isolating valves usually surround the units, and supply hydrants and monitors. Where fixed foam installation is required the foam making tanks are usually located close to the point of application. In some remote locations where water for fire-fighting is scarce, increased spacing between process plant facilities may be required. Other fire protection criteria such as active versus passive methods need to be considered, as space around equipment may need to be reserved for deluge and sprinkler systems.
When equipment handling low flash point media, including flammable gases, is grouped together, its implication on the classification of the hazardous area needs to be considered.