Originally Posted by
chewing4gum
But why do you still see such earthing straps on the underside of tankers if they offer no protection against antistatic charge?
You are intermixing requirements. Those straps have zero to do with refueling ops or the transfer of any flammable liquid, in general. So even if your fuel truck had those straps there is a separate bonding/grounding system(s) specifically required for the fueling ops. For example, in larger fueling systems a large part of the static charge is created by the fuel being forced through the inline filters. So if the fuel system bonding system fails those straps will not provide a back-up to the bonding system as they are only connected to the chassis.
How do small aircraft that are refueled with canisters do this? I can't imagine that a cable / bonding when refueling is always connected? perhaps forgotten?
The long standing guidance is to use metal canisters equipped with their own bonding cable to the aircraft. And while there are plastic canisters and funnels, etc. that can conduct electricity I've never seen references or guidance for their use. However, you also must keep in mind its takes a specific set of conditions to line up to generate a spark to ignite things. Thankfully most get away with fueling ops on any vehicle or aircraft as those conditions don't normally come into play. But when they do boom. Fueling at night in frigid temps from a pumped barrel system can make for quite a blue light show if your bonding clamp gets accidently knocked off the barrel. There are also a few videos out there of statically ignited fuel/chemical fires.