Who is responsible for preparing fieldwork safety documents for trips?

employer will be responsible for preparing the documents.

it depend on the type of the trip itself but mostly Cruise leader Who is responsible for preparing fieldwork safety documents for trips

First I have to explain what does means it the trip. When it means vacation trip. Then oblication of tourist is prepare safety insurance for his trip(s). When it means the trip(S) of manufacturer equipment then the manufacturer is obliged to cover trip of equipment on route by the insurance. With one examption. When in its condition of contract is mention that the customer is paying the insurance. But it is unusual. Zo answer is short. The manufacturer of equipment. 

is responsible for safety officer

The Cruise leader responsible for preparing fieldwork safety documents for trips

usually the trip coordinator, transportation planner or event planner, in the coordination with the HSE Department or in some cases it falls in the responsibility of the HSE admin or officer

Kindly refer to your company procedure about the preparation of fieldwork safety documents for trips.In case you have no procedure about it, it is necessary that the stakeholders/responsible persons/process owners who are affected with that task have to prepare the procedure on it.  Whatever the procedure, then all the affected personnel must know it/have the right to know.