I wonder whether mere tensile strength is sufficient, or whether the shearing action of those shards in motion is a consideration? And do small shards pose less of a risk due to their small mass (like birdshot compared to buckshot)?
Although your suggestion of a sock sounds pretty good, what about versions of the mesh bags used to contain onions and other similar vegetables? (Those might be easier to incorporate into existing designs.)
This is an opportunity for a good discussion on risk, and what drives prudent decision-making. How much of the hazard and the associated uncertainty are realistically transferable between the specific tank that failed, others in its lot, others of the same model, others in the product line, and other product lines of similar manufacture? Or is this strictly a matter of perception being everything—action is being taken, so outsiders will perceive it as the responsible course of action?
I’m curious about what specific factors are driving your decision—not particularly to criticize you, but to discuss the proposition that a drastic response often isn’t a methodologically valid way to approach a spectacular failure.
After all, you (and everyone else) obviously take plenty of risks with the students. It’s our responsibility to try to manage those risks in a sensible way.