Hi Jack
I Jack I have only seen the after effects of a few blown batteries and they have blown the top off the battery box and spread Lead and acid outside the confines (but dont take my word for it see the injuries caused by battery box shrapnel in the military link below)
Yes the optima's have a blow off Valve which releases explosive gases, blow that off into another container (the battery box!) hence they can explode just like any other battery.
If like in the original battery a plate buckles which causes ignition, an AGM contains the same explosive mix (see last quote below)
as to battery box safety here is a quote from a military site, relating the injuries to a soldier who had a battery box and the vehicle seat between him and the explosion.
His arm and hand were resting on the passenger seat when the
battery box exploded. ... The explosion was caused by arcing of the battery cables
from here
https://safety.army.mil/pages/lessonsle ... ttery.html
Do you still think a flimsy plastic box will save you?
Here is another quote highley relevant to the original bomb
The most probable cause of internal battery explosions are from a combination of low electrolyte levels below the plates in the battery, a low resistance bridge is formed between or across the top of the plates, and a build up of hydrogen gas in the cell. The low resistive bridge is called "treeing" between the positive and negative plates. When current flows in the battery, a spark occurs and ignites the residual gas in one or more of the cells. A second possible cause is a manufacturing defect in the weld of one of the plate connecting straps causing a spark igniting the residual gas. Another source of internal battery explosions are caused from direct electrical shorts across the battery's terminals. The battery rapidly over heats form the high current and can explode.
The largest number of internal battery explosions occur in hot climates due to the loss of water while starting the engine. Most internal battery explosions could have been prevented if the plates were always covered with electrolyte.