Static Electricity 2000 Edition

7.6.4 Highway Transport.
As noted in API RP 2003, Protection
Against Ignitions Arising Out of Static, Lightning, and Stray Cur-
rents, tank vehicles normally create no static electricity hazard
during transport, provided they are compartmented or con-
tain baffles. The compartments or baffles minimize sloshing of
the liquid in the tank vehicle, which could result in significant
charge generation. Clear bore (unbaffled) tank vehicles
should not be used for liquids that can generate an ignitible
mixture in the vapor space.
7.6.5 Antistatic Additives.
Charge accumulation can be
reduced by increasing the conductivity of the liquid by adding
a conductivity-enhancing agent (antistatic additive). These
additives are normally added in parts per million concentra-
tions and should be used in accordance with manufacturer
instructions. When antistatic additives are used as a primary
means of minimizing accumulation of static electric charge,
the operator should verify the concentration of the additive at
critical points in the system.
7.7* Vacuum Trucks.
For control of static electricity, hoses
should be conductive or semiconductive. Alternatively, all
conductive components should be bonded and the truck
should be grounded. In no case should plastic dip pipes or
plastic intermediate collection pans or drums be used.
7.8 Railroad Tank Cars.
In general, the precautions for rail-
road tank cars are similar to those for tank vehicles in Section
7.6. The major exception is the larger volume typical of rail-
road tank cars (e.g., greater than 87 m
3
) compared with that
of tank vehicles (e.g., about 50 m
3
). This greater volume allows
greater maximum filling rates to be used, up to a maximum of
(0.8/d) m/sec, where d is the inside diameter of the inlet, in
meters. Many tank cars are equipped with nonconductive
bearings and nonconductive wear pads located between the
car itself and the trucks (wheel assemblies). Consequently,
resistance to ground through the rails might not be low
enough to prevent accumulation of a static electric charge on
the tank car body. Therefore, 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.

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