Safety and isolation transformers
What safety measures can be taken when using a 1:1 isolation transformer in order to avoid electric shock even if someone touches both ends of the secondary?


There's very little you can do if someone might touch both ends of the secondary.


Keep the secondary voltage below about 50 V.
Ensure there's not enough energy present at the secondary to harm a person. For example, by not having any capacitive load on the secondary, and by feeding the primary through a high resistance, so that the secondary voltage will drop when a "low" resistance load is attached. 


The challenge is that a person touching the terminals doesn't look particularly different to the circuit than whatever load you are powering from the secondary. If there's something special about the usual load (for example, it's purely capacitive, or it never draws more than a few nanoamps) then perhaps you could design a useful safety circuit.