under fault conditions the voltage on the earth rod could be lethal
I don't quite understand this. The voltage on the rod will be earth potential. Anyone touching it will be stood right next to it. Surely there can't be enough of a potential gradient over 1ft, and the impedance of a metal rod is effectively zero.
It would of course depend on size of earth rod but if you with a fault connect the earth rod to line then the earth rod and ground right next to it will be at Line voltage. As you move away from the rod the ground will have a gradient and by time you are 50 meters away it will be at neutral potential or there about.
The steepness of the voltage gradient will depend on ground resistance and how wet. If the ground is a very bad conductor the gradient will be gradual but at some point one will reach a point where any animal without shoes could be killed. Dog or Cat and dogs have been killed due to faults under the pavement.
With a boat for example the resistance is more known and a boat in a canal with an earth fault would kill anyone swimming by it. However in the sea because the sea is a better conductor you need to touch the boat before you will be killed.
Two things should protect us. The first is driving in a long stake and covering the top so without a tool no one can touch it. The second is the RCD should trip removing the fault to earth. However we should not rely on a RCD and not guarding the metal work from being touched would be silly.
If the rod is of a very low ohm reading. One I fitted for a Radio Ham was 0.3 ohms being 4 rods each 2.4 meters long and connected together with bear copper strip at 1 foot deep then touching it will not be any real danger. However I have needed to sink 5 rods and more each at 1.2M long to get an 8 ohm reading and earth rods used with a house are often reading 60 odd ohms. Where the water, gas, and other metal work is also bonded the resistance is likely a lot lower but just the rod on it's own it can be accepted at 200 ohm and at that sort of resistance voltages could be high.
Resistance area (for an earth electrode only). The surface area of ground (around an earth electrode) on which a significant voltage gradient may exist.
Simultaneously accessible parts. Conductors or conductive parts which can be touched simultaneously by a person or, in locations specifically intended for them. by livestock.
NOTE: Simultaneously accessible parts may be: live parts. exposed-conductive-parts, extraneous-conductive-parts, protective conductors or earth electrodes.