OK, now I understand the source of the confusion. Washington state is one four states that run their own mandatory workers comp program that covers workers injured in the course of employment. The same entity the Washington State Department of Labor & Industries (L&I), runs both the workers comp insurance program and the OSHA-compliant WISHA worker safety program.
I am not familiar with the details of the L&I workers comp insurance program, but a quick search suggests that you can buy into it as a self-employed solo worker. If so, then at least you would have some coverage for injuries suffered while working as a solo commercial diver. But if you wanted liability coverage for stuff like damage to a vessel you were working on or if someone tripped over a piece of your equipment, you'd still have to try to get it in the private market. Such coverage is unlikely to be available, at least at a reasonable price, for solo commercial diving operations.
I am not familiar with the details of the L&I workers comp insurance program, but a quick search suggests that you can buy into it as a self-employed solo worker. If so, then at least you would have some coverage for injuries suffered while working as a solo commercial diver. But if you wanted liability coverage for stuff like damage to a vessel you were working on or if someone tripped over a piece of your equipment, you'd still have to try to get it in the private market. Such coverage is unlikely to be available, at least at a reasonable price, for solo commercial diving operations.