Steel Tank Lightning Protection
Lightning Protection for Steel Tanks Containing Flammable Vapors, Flammable Gases, and Flammable Liquids that Give Off Flammable Vapors
Operators are notified to reduce the ignition of flammable vapors by minimizing the venting at locations that are at risk of a direct strike or static discharge. Openings where flammable concentrations of vapor or gas escape to the atmosphere must be kept closed and adequately bonded to an effectively grounded lightning protection system. Specifically thief hatch bonding is critical to minimize this risk of ignition.
NFPA considers metallic structures that are electrically continuous; tightly sealed to prevent the escape of liquids, vapors, or gases; and of 3⁄16 in. (4.8 mm) thickness or greater to be inherently self-protecting. At the same time, it also states that "a tank installation on top of a ground insulating membrane shall be grounded through a minimum of two grounding electrodes". For this reason, steel tanks at production and salt water disposal facilities must be furnished with a full lightning protection system.
Lightning protection materials for steel tanks will comprise of air terminals as strike termination devices, ground electrodes, and lightning protection conductor to accomplish effective grounding and bonding and a low resistance pat the conduct lightning current safely to ground.
NFPA 780 further requires that the zone of protection of lightning protection system for structures containing flammable vapors, flammable gases, or liquids that can give off flammable vapors shall be based on a striking distance of 100 ft (30 m) or less. This relates to Lightning Protection Level 1 (LPL 1) or Lightning Protection Level II (LPL 2) based on IEC standard.
Steel Tank lightning and static protection system features:
- Strike termination Air Terminals are placed along the vent lines at a spacing not exceeding 15Ft to meet the requirements of LPL 1 level of protection.
- Air Terminals will be connected with a network of lightning protection main conductors over vent pipes and under the catwalk.
- A minimum of two grounding electrodes must be installed to which the lightning protection main conductors will terminate to. Additional down conductors with grounding electrodes need to be installed as the spacing between grounding electrodes should not exceed 100Ft.
- While the external structures on a steel tank will maintain electrical continuity, the in-tank static neutralization devices must be bonded to the lightning protection main conductor.
- Lightning surge protection device suitable for the hazardous area application must be installed at each of the Tank Level Transmitters to protect the 24VDC and signal lines.