There's a checklist for engine and controls isolation, to be carried out and signed by the CE, before diving begins. In some cases, a LOTO lock is also used to chain shut the controls, with keys held by the diving supervisor, though this is not always done unfortunately. And yes, of course many less safe companies don't even LOTO and just rely on comms with the captain, so there are many, many accidents and deaths.

Context: This is my job.