Comparison of properties

1. Fully Conductive Systems - metal piping

• The pipe is manufactured from 100% conductive material (e.g. steel)
• Very high capacitance (C₁) to store a charge
• Small resistance (R₁) to earth
• Dissipation of charge is reliable and immediate

The system is inherently safe against electrostatic hazards because it is naturally self-earthing so the voltage (V) is virtually zero.

2. NON-CONDUCTIVE POLYETHYLENE - UPP
• Pipe manufactured from non-conductive materials (e.g HDPE)
• Very low capacitance (C₂)
• High resistance (R₂) to earth
• The maximum amount of energy that can be stored is limited by the small capacitance

The system is inherently safe because it is non-conductive, so does not need earthing.

3. Conductive Polyethylene - Non-conductive plastic pipe with an inner conductive layer
• Very high capacitance (C₃)
• Resistance (R₃) to earth can be low, but this is wholly subject to the efficiency of the connections at all times within the pipework system
• Lack of dissipation efficiency can result in high amount of static energy being generated and stored

The system is not inherently safe because it has to be artificially earthed and is dependent upon the integrity of the installation. If there is any break in the system, the voltage (V) can potentially be as high as 6kV.

What the independent expert says.
“It is important that all conductive items or surfaces exposed to potential charge generation mechanisms such as the flow of fuel are maintained at or near ground potential*. Sparks from isolated (ungrounded) conductors are generally recognised as being the most dangerous form of electrostatic discharge and are responsible for many industrial ignitions and fires.Very conductive surfaces such as metal and some conductive plastics will easily produce spark discharges if charged and in these cases maintaining permanent grounding is particularly important.”
An extract from research by G L Hearn B.Sc C. Eng M.I.E.E of Wolfson Electrostatics Ltd on the electrical/electrostatic performance of conductive and non-conductive polyethylene fuel pipe.
* Ground potential is zero volts.