on a more serious note you need one for working with live DC, and working with AC (safe isolation etc). you need a generic one for all power tools (eye protection, ear protection and all that guff).
if you really want to be comprehensive you should also cover exposure to the elements (cold, wet and Sunlight (burns, sun protection etc)). working at height should cover safe use of ladders, towers and scaffold (your scaffolders should be able to supply a copy of theirs).
You should also cover footwear and hand protection.
designated forst aider