UFC 3-460-03
21 JANUARY 2003
9.2.4.4. The movement of contaminants (e.g., rust, mill-scale water, air) during stable settling in
storage tanks ionizes the contaminants to produce a static charge. These charges build up around
triggering points (gauging and sampling devices, floats, and swing pipes) and, if not discharged
through the fuel to the wall of the grounded tank, sparks can occur in the vapor space above the
fuel. Petroleum products are poor conductors of electricity and bleed off static charges slowly;
therefore, contaminants ionized during the fuel transfer to the tank hasten the build-up of static
charges within the tank and increase the possibility of electrical sparks.
9.2.4.5. Particles of vapor suspended in air can become ionized and create a difference of potential
with the liquid fuel. The normal relative humidity of the atmosphere (moisture in the air) provides
a path to dissipate the static charge safely; however, in dry areas, particularly at low temperatures,
the rate of discharge is slow and a dangerous accumulation of static electricity can build up.
9.2.4.6. Personnel and clothing (wool, rayon, and synthetic materials) accumulate static electricity
from normal body movement. These charges can be discharged through clothing, skin, or tools
and equipment as they come in contact with components of the fuel system.
9.2.4.7. Aircraft or service equipment may become electrostatically charged due to atmospheric
inductive coupling. In this case, the base weather service notifies the maintenance officer of
impending hazardous conditions, such as lightning storms within 8 kilometers (5 miles), so that
fuel handling operations, maintenance and repair activities, and tank cleaning operations will be
temporarily stopped.
9.3. Preventing Static Electricity. It is not possible to completely eliminate static electricity. Use the
following precautions to reduce the magnitude of charge and therefore the possibility of sparks:
9.3.1. Connect a static bonding wire between two components before making or breaking a
connection and before working on flanged connections insulated from one another by nonmetallic
insulating materials. When vehicles or aircraft are grounded, attach grounding wires to the vehicle or
aircraft before bonding to the grounding rod. This is especially important for operations involving
fuel transfers (fueling, defueling, loading, and unloading).
9.3.2. Avoid surface agitation by limiting the initial fill rate into a fuel storage tank to less than
0.91 meter (3 feet) per second. Maintain this flow rate until the floating roof or pan is afloat and the
fill pipe is completely submerged, or until the fill pipe is completely submerged in all other tanks.
NOTE: Wait thirty minutes after loading or unloading an aboveground fuel tank before allowing
anyone on it.
9.3.3. Personnel will ground themselves to the tank by making firm contact between the tank and
back of the bare hand or by holding a coin in the bare hand before opening access covers or
inspection holes. Also, ground sampling devices to the tank before opening the sampling well.
9.4. Relaxation (Release) of Electrostatic Energy. Fuels are poor conductors. Static dissipater
additive (SDA) is added to JP-8 to improve conductivity. JP-5 lacks an additive, so designs rely on time
delays to dissipate the charge (i.e., certain refueling equipment has relaxation tanks to delay movement
and relax electrostatic charges).
9.4.1. Fuel components, such as hydrocarbons and chemicals, permit a flow of electrons. When
there is electrostatically charged fuel in a tank or pipe, the mutual repulsion of like charges in the fuel
and their attraction to the opposite charge on the tank or pipe causes a current flow (i.e., positive ions
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