Leave a stationery vehicle unattended without the handbrake / parking brake applied or using some other method to ensure the vehicle remains stationery. Leaving the engine of an unattended, stationery vehicle running may make it subject of simple theft. It may also suddenly move, damaging objects and injuring people around it.
Leave a stationery vehicle unattended with the engine running.
Leave the engine on or start the engine when the fuel-tank cap is off and/or when fuel is being pumped into the vehicle. The engine is a source of sparks, which together with petrol can ignite gas fumes and flames. The exhaust of a running car is also red hot and it can ignite flames. Between shutting the engine and starting to pump, the exhaust will cool significantly thereby significantly reducing the risk of fire.