Fuelling
The refuel incident referred to by Rainbow occured in September 2001 and was a 777 at Denver. As stated it was a fuel coupling failure, where the fuel was ignited by the hot exhaust.
As to refueling with passengers on board that is a matter for the airfield licencee.
In the UK taking into account the requirements of CAP 748, and the HSE Explosive atmosphere regulations (DSEAR). Plus of course your own companies risk assessments.
At Heathrow the BAA OSI 35/01 prohibits passengers within 6 meters of any fueling zone ( the vents, refuel pit or refuel vehicle).
Its just over 3 years since fuel vapour ignited at Buncefield and that cost Heathrow operators nearly £250000
Pax are regulaly boarding while fueling is taking place following laid down procedures. As far as I am aware with out any serious incidents.