What Kind of Explosion?
It seems to me that there are two possible types of explosion to be considered. One is an explosion powered by combustion of some material and that combustion aided by the presence of a great deal of oxygen. The other is a purely mechanical type of explosion where the tank came apart mechanically. Given that there seems to be no evidence of fire showing in the pictures available to us, are we not dealing with a mechanical, rather than chemical, explosion? If it was a mechanical explosion, what precipitated it? Was it a weakness in the tank caused by either a manufacturing fault, improper installation, maintenance, or corrosion? Or, was it precipitated by some other action such as "explosion" of some of the cargo?
Commenting on a previous post which speculated as to why the O2 bottles are restrained, it should be obvious why all parts of the airplane are restrained.