I’ve been pondering this for a few days and figured this was a good a place to ask since there are so many experts here. Why aren’t there two sets of BOP shears? If a tool joint is say, 1m long, if there was a second set of shears at 1.5 meters, there would be at least one that could close in the event of an emergency. It still wouldn’t account for casing or drill collar but would also add a level of redundancy.