Bulk loading or unloading Rail Cars with liquids or powdered/loose solid materials can generate large electrostatic charges, and this poses a significant risk in a potentially explosive atmosphere. Although the Rail Car is in contact with (earthed) tracks, many tank cars are equipped with non-conductive bearings and wear pads located between the car itself and the wheel assemblies (trucks). This may lead to an unsafe condition where an unearthed Rail Car accumulates a high static charge. Earth Monitoring/Verification systems may be used to provide an interlock with the filling system to prevent product transfer unless the Rail Car is properly bonded to earth.

NFPA 77 states: “bonding of the tank car body to the fill system piping is necessary to protect against charge accumulation. In addition, because of the possibility of stray currents, loading lines should be bonded to the rails” (77-21.7.8)

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