Number of small (flash) fire cases occurred while offloading road tankers to underground storage tanks of petrol stations. Most of the cases occurred while changing decanting hose to other storage tanks. Can someone please advice regarding possible causes and regarding statistics of similar occurrences in other organizations?

Metal/metal/tarmac sparks is one cause but I expect all tankers have non-spark metal parts? Static is another possible cause. As Ron says industrial tankers off-loading flammable resins and solvents use earth straps to avoid build up of static in the pipe. Static can also arise from a driver's clothing, I don't have data on tanker drivers but there are CCTV videos that I've seen in fire training from petrol/gas station/garages where flash fires have occurred, not always with serious outcomes. The most frequent occurrences are in USA where people commonly put the spout in their petrol cap/input and switch the delivery to 'automatic'. They then sit in their car for two minutes. When they get out there's sometimes enough static from the clothes/seat fabrics that when they immediately go to the gas spout there is a static spark when they get close to metal. That scenario may ccur with tanker deliveries if the driver gets in and out of his cab during fuel flow and gets near to metal at the delivery point.