There is a new requirement from the FAA. Any airplane certified after the 28 November has to have a desginated LRBL. It´s one of this security theater things from my point of view. A LRBL is a “least risk bomb location”, a location where a bomb explosion would inflict the least damage to the aircraft. I see some problems in such a location. You have to move the bomb to get it to the LRBL. At first you have to find someone who is brave enough to move around an live explosive device. As we know of several hollywood movies ( ;) ) an explosive device would have an trap fuse, that would trigger the the explosion in the event of moving it around. You should at least keep the existence secret and hidden in the aircrafts operation manual to prevent the addition of such trap fuses to terrorists bombs or the usage of an more potent explosive substance. At the end: It´s the classic ammunition/armour competition. There is always one winner and it´s always the same competitor: The ammunition.The only way to increase the airliner explosive survivability is to keep of the explosives offboard.