We often receive tasks to calculate lightning protection system for a gas control unit (GCU). According to RD 34.21.122-87, GCU is classified as Category II in terms of lightning protection and must be protected from direct lightning strikes, its secondary effects and external high voltages through on-ground (above-ground) metal utilities. Protection zone B is selected in line with item 2 of Table 1 of RD 34.21.122-87 and expected lightning strikes per year. According to item 2.6 of RD 34.21.122-87, if buildings and structures have direct gas exhaust ducts and respiratory pipe for free discharge of gases, vapors, and aerosols with explosive concentrations to the atmosphere, the lightning arrester protection zone should include the space over the pipe ends limited by a hemisphere having a radius of 5 m. For exhaust gas ducts and respiratory pipes equipped with hoods or stand pipes, the lightning arrester protection zone should include the space above the pipe end limited by a cylinder with height H and radius R for gases lighter than air with the excess pressure inside the installation being above 25.25 kPa, H = 5 m, R = 5 m.
You can read our article Design of Lightning Protection and Grounding System for Closed Stationary Gas Control Unit for more details.
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