In any oil & gas plant or refinery unit there are many hazardous fluids & gases present or generated. These fluids & gases can be flammable or inflammable in nature and can cause fire in the facility destructing the assets, pollution to the environment & fatality to human life.
To prevent fire from happening the facility is to be protected with some fire protection system is provided based on the hazardous nature of the fluids & gases. The normal fire protection system which are generally present in the plant are explained below:
1. Firewater Systems
· Firewater systems shall be in accordance with NFPA 13 “Standard for the Installation of Sprinkler Systems” and the Technical Requirements.
· Risers or vertical pipe 3” NPS and larger shall have a flanged joint or a mechanical coupling at each deck level.
· Changes in pipe size shall be made with a one piece reducing fitting. Reducing bushings, couplings and unions shall not be acceptable.
· A maximum of eight sprinklers may be installed on any single branch line.
· All sprinkler pipe and fittings shall be designed and installed so that the firewater system can be drained completely, including both wet and dry type systems. Branch lines shall include a minimum slope of 1/2” for each 10’-0” of pipe run. Cross and feed mains shall include a minimum slope of 1/4” for each 10’-0” of pipe run.
· Firewater systems shall minimize low point traps to make the system as “self draining” as reasonably possible. Where unavoidable, low point traps shall be provided with drain valves. Drain valves shall also be provided at the ends or remote points in the system. The minimum size for drain valves shall be 1” NPS.
2. Foam Systems
· General
o Foam systems shall be in accordance with NFPA 11 “Low Expansion Foam and Combined Agent Systems” and the Technical Requirements.
o Strainers shall be provided if solids large enough to obstruct openings in foam equipment might be present.
o In fixed systems for exterior tanks, one flanged or union joint shall be provided in each riser to permit hydrostatic testing of the piping systems up to this joint.
o The laterals to each foam chamber on fixed roof tanks shall be separately valved outside the fire area.
· High Back-Pressure Foam Makers
o High back-pressure foam makers shall be positioned on the tank so that an explosion within the tank which blows off the roof or damages the uppermost roof plates would not result in the interruption or reduction of quality of the foam discharge.
o The foam injection system shall be capable of being injected directly into one or more product supply lines already connected to the tank.
o The water line to each high back-pressure foam maker inlet shall be valved separately.
· Flushing and Draining Provisions
o Systems with foam concentrate piping and solution piping that are normally empty shall be designed so that the piping can be flushed with clean water after the system has been in service.
o Foam distribution piping shall be designed so that the system can be drained. The piping shall be sloped toward the drain a minimum of 1/2” for each 10’-0” of pipe run.
3. Carbon Dioxide (CO2) Systems
· Carbon Dioxide (CO2) Systems shall be in accordance with NFPA 12 “CO2 Extinguishing Systems” and the Technical Requirements.
· Flow in piping shall only be split in the horizontal plane.
· A dirt trap consisting of a capped nipple at least 2” long shall be provided at the end of each pipe run. Dirt traps shall be installed as close as possible to the last nozzle in any one pipe leg.
· Pressure relief devices shall be installed in sections of closed piping isolated by valves, unless the valves are designed to prevent entrapment of liquid.
· If pressure operated container valves are installed in a system, a means for venting off any pressure that leaks from the containers shall be provided. The design for venting shall not permit loss of extinguishing agent when the system operates.