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TITLE:The ignition hazards of static electricity associated with vacuum
tankers in tank cleaning operations.
Mike O’Brien.
Product Manager at Newson Gale.
DATE: 20th March 2013.
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30 years in static control for hazardous locations
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Static Electricity – the Basics
Combination and separation of protons and
electrons occurs at the nuclear level.
Generation and accumulation of static electricity
not visible to the naked eye.
Sparks resulting from discharges of static
electricity can ignite combustible atmospheres.
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“Tribo-electric charging”
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Hose wall Product (e.g. Toluene)
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Potential
Difference
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Potential
Difference
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Potential spark energy = 0.5CV2
Potential spark energy at 15 KV = 450 mJ
Typical spark discharge territory
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450 mJ
Potential
Difference
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“Earth”
Layers of resistance
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• “a designated, proven ground source is preferred” (5.4 Grounding and Bonding).
• “before starting transfer operations, vacuum trucks should be grounded
directly to earth or bonded to another object that is inherently grounded such
as a large storage tank or underground piping” (5.4.2 Grounding).
• “this system should provide an electrical contact resistance of less than 10
ohms between the truck and a grounded structure” (5.4 Grounding and Bonding).
• “to assure proper bonding, the continuity should be verified with an ohmmeter
following connection and prior to operation ” (5.4.1.1 Bonding).
API RP 2219: “Safe Operation of Vacuum Trucks in
Petroleum Service” (2005).
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10 ohms or less
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“Secondary Grounding Points”
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“Temporary Grounding Points”
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Static Electricity on Hoses
Wire helix isolated
from end fitting
Summary:
• Try to ensure that the truck is connected to an object that is at
earth potential.
• Don’t assume the structure is earthed just because it is
indicated as such or someone says it is.
• Try to ensure the truck has a connection that is continuously
monitored for the duration of the operation.
• Wherever possible, a break in the connection to earth should
trigger the shutdown of the transfer operation – interlocks are an
option.
• A grounded truck will ensure hoses do not accumulate static
electricity, PROVIDED they are conductive and in good working
order, therefore regularly test the condition of hoses.
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