Dwight was not talking about an EPO (Emergency Power Off). Rather, he was talking about what some manufacturers call a "maintenance mode." You throw a switch or push a button that is located on the board, but that does not in itself constitute an action that risks an arc flash event. The switch or button enables the instantaneous trip feature of the main breaker, without actually opening the breaker. Under normal operation, the instantaneous trip is disabled, in order to force the main breaker to stay closed longer during a fault event, and allow a downstream breaker to trip first. This is the selective coordination notion that is required in some installations. By enabling the instantaneous trip, a fault will cause the main breaker to trip earlier, and that in turn would reduce the amount of arc flash energy that could be released. So you are taking a risk of losing the main breaker on a minor fault during the short time period that maintenance is being performed on the gear. If you install this "maintenance mode" feature, you can have the arc flash calculation revised, and that will probably reduce the required level of PPE.