Aser,
In Europe and under JAR-OPS 3 there are a number of rules that are relevant:
The first is a change to JAR-OPS 3.330 which is being introduced in NPA-38 because of an accident in a single where a passenger drowned because the life-jacket was not donned. Paraphrasing the rule; for operations in PC3 it requires the operator to have a procedure which indicates to the pilot the conditions under which life-jackets are to be worn by all occupants.
The second is JAR-OPS 3.825 which establishes when the life-jackets are to be carried; and the third JAR-OPS 3.837 is for offshore operations to helidecks in a hostile environment which requires all occupants to wear a (constant wear) life-jacket - unless wearing an integrated survival suit which meets the combined function of the suit and the life-jacket.
Under the proposal for changes to ICAO Annex 6, the revised Standard is for life-jackets to be worn by all occupants when engaged in 'offshore operations' - such operations being defined as those in support of oil and gas exploitation and marine pilot transfer.
The reason for these requirements, including the change to JAR-OPS 3 and ICAO Annex 6, is a Risk Assessment which indicates that where exposure to a ditching is greater, wearing of the life-jacket is called for. This is exactly the individual decision making process that Helinut indicates in his post.
Pistongone; if you are not wearing an integrated survival suit, your Captain is probably in breach of the regulations.
Jim