Lightning Protection for Vent Valve
Vent valves, also called pressure/vacuum relief valves, limit unwanted vapor emissions by maintaining pressure in storage tanks while allowing for thermal inbreathing and outbreathing. Outbreathing results from the inflow of liquid into a tank and from the vaporization, including flashing of the feed liquid. Outbreathing also results from expansion of vapors and vaporization of the liquid that occurs when a tank absorbs heat. This frequent outbreathing from vent valves creates a hydrocarbon vapor cloud near the vent valves and the top of the tank battery. Vent valves are generally one of the highest objects on a storage battery. They tend to release high-energy streamers under the influence of lightning electromagnetic fields, and the energy of these electrical streamers can be high enough to ignite flammable vapors being released during outbreathing.
In the oil and gas industry, static charge results from contact and separation that takes place in a flowing fluid. The vapor that flows in and out of vent valves is considered a fluid. As a result, once there is a source of electrostatic charge, it will be a source of ignition. Then, if charges accumulate more quickly than they can relax, the charges can produce an incendiary spark.