The contractor is responsible to ensure first aid is provided to their workers.
If the plant only has one worker, the plant is unlikely to require a first aid attendant. Yes, as the owner and de facto prime of the workplace the plant employer has a responsibility to ensure appropriate first aid is provided, but the level of first aid required by the contractor might be different than the level provided by the plant, in which case it is on the contractor to ensure an appropriate assessment is conducted and first aid services provided.
