Are they employees i.e. working under a contract of employment? Or contracted under a contract for service? i.e. a separate legal & commerical entity. 

Generally the local laws apply so a French person working for a British based Bermudan company in Germany would have to work under German H&S laws, cos they are in Germany. The UK Health and Safety at Work Act does not apply to activities taking place overseas (except oil/gas rigs on the UK continental shelf)

Civil law is more complicated. If the person was to be injured there is the question of how they could be compensated. Ideally it would be written into the contract, saying for example take UK law applies or Bermuda law (if you are unlucky). In France and Germany that are compensation schemes which do not go through courts and are paid for by employer’s contributions. There might an agreement between French and Germany allowing people to claim against their home scheme for injuries in a neighbouring country (this is just guess but it seems likely). They guys you are sending abroad are classed as self-employed so they might not be part of such a scheme ( I am not sure how compo works for self-employed people in Europe) .They could sue in the UK if they could demonstrate that the decision to send them somewhere hazardous was taken in the UK and so that might end up being the venue for a legal action for damages.

I did say this might be complicated; I was wrong this is really complicated!