Ignition of petrol vapours during refuelling of cars

In the last few years, one has heard of petrol vapours beomg ignited when cars were filled up at public German petrol stations, and of some cars catching fire as a result of this.

Within the scope of a joint project, together with the Deutsche Wissenschaftliche Gesellschaft für Erdöl, Erdgas und Kohle e.V. (DGMK = German Association for Mineral Oil, Natural Gas and Coal) and in cooperation with the mineral oil and auto industry, the Physikalisch-Technische Bundesanstalt (PTB) investigated the causes for the ignitions and prepared safety recommendations.

These investigations have meanwhile been completed. In most cases, electrostatic charging was found to be the probable cause, the increasing use of materials of high electric insulating power for car parts, tyres and sealing coats on the petrol station pavements having done its share. But the electrostatic charge of persons also is a possible source of ignition.

The investigations further showed that there is no ignition hazard inside the filler neck or inside the tank, as the mixture to be found here will be too fat to cause ignition even if the gas is recirculated as is permitted today.

To avoid electrostatic ignition hazards, it is recommended

• to provide petrol station pavements and pump hoses able to dissipate electrostatic charges and to safely ground the nozzle
• to ground the car body via the nozzle
• to avoid use of insulated metal parts in the area of the emerging petrol vapours
• to use tyres able to dissipate electrostatic charges
• to avoid persons being dangerously charged.

Some of these recommendations are already an integral part of legal regulations, for example, of the technical rules for flammable liquids which ensure that the above-mentioned grounding measures are taken at the petrol stations.

Mobile radiophones with a rated power of 6 watt at most do not constitute an ignition hazard when used outside hazardous areas.

Car and tyre manufacturers have been informed about these recommendations. The results are available as DGMK Research Report 508: "Vermeiden der Entzündung von Ottokraftstoff/Luft-Gemischen beim Betanken von Fahrzeugen an Tankstellen" (Avoiding the Ignition of Petrol/Air Mixtures during Refuelling of Cars at Petrol Stations).