OSHA requires two people minimum if working on anything over 600V when exposed to live conductors or devices. So maybe that's what you are remembering.
29 CFR 1910.269(1)(1)(i)
You just jumped from utilization rules (Subchapter S) to transmission/distribution rules 1910.269 which may not apply here. Plus you missed the three exceptions that for all intents and purposes all but nullify it. Exceptions where the rule would apply would be things like replacing insulators where a lineman installs an insulator then removed the lashing and physically hoists the cable up then sets it back down on the new insulator while it is energized. The rule essentially requires a ground man. Except for emergency work.
The 70E rule is indirect. It is sort of buried in the training section discussing CPR. It is potentially possible to self administer CPR but in most electrical accident cases the patient is going to be unconscious. Thus you can see the obvious problem. You could of course use a cell phone or radio and talk through it with someone remote that can get there in a couple minutes. That being said 70E and OSHA talks about two different types of energized work. Testing and visual inspection are not subject to the same requirements as say the above case of doing anything that involves manually manipulating energized conductors.
Regardless the cutoff is 50 Volts currently. There is ample evidence that 240/120 is no different. A man in Georgia was documented as a fatality from arc flash in 240 in 2009. Above 150 V the big change is that direct contact is no longer the only way to be shocked and arc flash is present. Above 1000 V voltage creep becomes an issue and “insulated” is no longer sufficient by itself to be considered safe. Above 40 kV gloves aren’t available and the work methods are shifting towards live line bare hands.
