744 Fuel spillage when refueling?

[kuobin]

Hello everybody:
I have heard several times of Spillage when refueling ,How could this happen?Aren't there auto protection device inside aircraft,said even 744 is very vulnerable too.

[gas path]

Broken vent valve in one of the tanks is a common cause as is a duff refuel valve.
Or in our case a higher than recommended volumetric shutoff figure.

[Intruder]

More-than-normal fuel expansion when going from a cold underground tank on a warm, sunny day -- especially when filling to max fuel!

Not all contingencies can be accounted for in engineering...