Electrostatic ignition hazards with plastic pipes at petrol stations

Occasional electrostatic ignitions have been associated with the use of buried, non-conductive (insulating), plastic fuel pipes at petrol stations. The incidents are rare and normally involve only minor flash fires but there is scope for escalation and it is prudent to prevent them.This paper analyses the electrostatic processes associated with the use of non-conductive plastic pipes at petrol stations to establish what ignition mechanisms are plausible. To do this it considers details of the reported incidents alongside the results of published voltage measurements, observations of the typical spread of streaming currents recorded in gasoline handling and theoretical estimates of the voltages on non-conductive pipes. The analysis suggests that the greatest risk is posed by incendive sparks from unbonded conductors but that incendive brush discharges from insulating pipe surfaces are also possible. In all cases the charging mechanism was by fuel flow. Careful earthing of all conductive items would eliminate incendive sparks from unbonded conductors but the hazard from incendive brush discharges would remain. By using plastic pipes with earthed conductive or dissipative inner linings the hazards from both incendive sparks and brush discharges arising from liquid flow charging can be prevented. Hazards arising from charging mechanisms other than liquid flow can be controlled by applying suitable operational procedures whenever flammable atmospheres might be present.

► Occasional flash fires occur with non-conductive plastic pipes at petrol stations.
► Ignition is by sparks from conductors or brush discharges from insulating surfaces.
► All ignitions are associated with fuel flow.
► Measurement and calculation both show that fuel flow generates high voltage.
► Fuel flow cannot produce high voltage with earthed, conductive plastic pipes.