Saif,

There is absolutely a hazard of static electricity whilst filling the tanks. I am no expert on the physics but any friction between the tank and the LPG as its delivered will generate a static charge. That coupled with the fact that LPG is highly flammable and explosive would suggest the vessel needs to be earthed. I am sure that the delivery process is a closed system to prevent LPG vapours being released.

I will have to surrender to the other forum users for a more experienced response.

I don't know what the risk is of static starting a fire, but it is normal practice to have an earth point at an LPG loading/unloading facility.

However, there does not seem to be a standard for the earthing points. Some are a simple clip, others use a clamp. Some are switched, which reduces the risk of a spark when making the connection. Some include an indication that an earth has been achieved, and some are interlocked so that you cannot start the transfer until an earth is achieved.

I would add that there are other mechanisms in place to reduce risk including use of conducting hoses. Also, the vehicle may have design features to reduce static build up.

Petrol tankers have tyres designed to avoid static build up, my guess (only that) is that LPG tankers would have the same.
Notable that there are no earthing requirements for discharge points at retail petrol filling stations, although I have seen them at industrial bulk storage sites (highly flammables stored in tanks).

An "Earth" point, if required would presumably have to be an isolated independent earth point to avoid earth-leakage risk arising from PME /TNCS local systems?

Saifakbar, I don't know what jurisdiction you are working under but assume not UK law. I aren't an expert on it, and as Ron has already alluded to, it seems to me that you need to ensure that all parts of the installation are suitably bonded so that there isn't a potential difference created.

Paul Skyrme may have some other suggestions.

I hope this is useful....

my copy of NFPA is 2008, and looking at NFPA59A

10.8 Electrical Grounding and Bonding.
10.8.1* General. Electrical grounding and bonding shall be provided.
10.8.2 Static protection shall not be required where tank cars, tank vehicles, or marine equipment are loaded or unloaded and where both halves of metallic hose couplings or pipe are in contact.
10.8.3* If stray currents can be present or if impressed currents are used on loading and unloading systems (such as for cathodic protection), protective measures to prevent ignition shall be taken.
10.8.4* Lightning protection ground rods shall be provided for tanks supported on nonconductive foundations.