The Circlotron (AKA bridged or balanced) amplifier configuration, as used in the Atmosphere and other amplifiers is not exempt from possibly damaging a speaker when just one rail fuse blows. That many of these amplifiers do not damage speakers when just one fuse blows is not surprising. In fact, the owners manual for one such amplifier asks that one fuse be removed when setting the bias of amplifier with a speaker attached to the output! (One trade show trick that always garners "oohs" and "ahs" from the unknowing is to remove one tube while the amplifier is in use.) This is not a testament to brilliance of the design, but rather an incrimination of trivial idle current used in a supposed Class A amplifier. (Oh no. He touched the audio third rail again; he must be brave or what is more likely, mad. Here is an experiment:

take a true 60 watt Class A amplifier and disable the safety circuitry, hook up your speakers, and remove one power supply rail fuse and see what a true Class A amplifier will do your speakers.)
   Thus iff a serious amount of idle current is used in a Circlotron amplifier, the speaker is at risk. Making the amplifier safer requires that the same condition obtain as in the totem pole arrangement: both output tubes, or banks of tubes, transistors, and MOSFETs must both turn off when just one fuse blows. How? Very easily it turns out. Rather than reference the bias circuitry to ground, reference it to the opposing tube's connection to the blown fuse. Thus when a fuse blow the bias voltage drops on the opposing tube, thereby cutting it off. Once  again, we achieve safety at no cost to performance.