Static Electricity 2000 Edition

7.11 Gauging and Sampling.
Gauging and sampling opera-
tions, including temperature measurement, can introduce
spark promoters into a storage tank or compartment. It is rec-
ommended that a conductive gauging well for manual sam-
pling and gauging be used. The precautions given in Section
7.11 should be taken where use of a gauging well is not possi-
ble, where the material stored is a nonconductor, or where the
vapor space of the container could be ignitible. Where these
operations are conducted manually, the personnel grounding
recommendations of Section 6.6 should be considered.
7.11.1 Materials.
Gauging and sampling systems should be
either completely conductive or completely nonconductive.
For example, conductive sampling and gauging devices
should be used with a conductive lowering device, such as a
steel tape or cable. Chains are not electrically continuous and
should not be used in flammable atmospheres. Conductive
sampling and gauging devices, including the sampling con-
tainer and lowering device, should be properly bonded to the
tank or compartment. Such bonding should be accomplished
by use of a bonding cable or by maintaining continuous metal-

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STATIC ELECTRICITY
2000 Edition
to-metal contact between the lowering device and the tank
hatch.
Ideally, if nonconductive hand gauging or sampling
devices are used, no waiting period is required after loading or
filling. However, it should be noted that these devices might
not retain the necessary level of nonconductivity due to envi-
ronmental factors such as moisture or contamination. There-
fore, an appropriate waiting period is also recommended
when nonconductive devices are used.
Cord made from synthetic material such as nylon should
not be used due to possible charging if it slips rapidly through
gloved hands. Although natural cellulosic fiber cord can, in
principle, be used, it is found that such cord is frequently com-
posed of a natural synthetic blend, with corresponding charge
generating ability.
7.11.2 Gauging.
Where possible, gauging should be carried
out with automatic gauging systems. These can be used safely
in tanks, provided the gauge floats and similar devices are elec-
trically bonded to the tank shell through a conductive lead-in
tape or conductive guide wires. Free-floating, unbonded floats
can be effective spark promoters and should be avoided. Non-
contact gauging devices, such as radar and ultrasonic gauges,
are also satisfactory, provided electrical continuity is ensured.
Isolated conductive components must be avoided.