Are there OSHA regulations that cover a driver going on top of a tank trailer?
No. The authority to develop such regulations lies within the Department of Transportation. However, OSHA would cover workers going on top of a tank that is not “in transportation.” So, OSHA would have authority over a worker going on top of the tanker in a cleaning rack or repair facility.
However, NIOSH (National Institute of Safety and Health) which governs mining operations does have fall protection requirements. If you are providing tanker service at a NIOSH covered location, their rules would apply.