Depends if the wall is for fire segregation or blast protection. I've seen both types - sometimes the choice between fire wall and blast wall is an economic decision based upon factors such as the criticality or capital value of the transformers involved, for example.
Let me add, I haven't seen a transformer break its can when exploding! The last time I remembered, the bolted top plate, housing the HV bushings and the pressure relief device flew off, leaving the secondary porcelain terminals and the damaged core/windings behind. Why does making the walls blast-resistant important?
I am not familiar with the term "blast" wall for transformers as what I have seen before for most of utilities is a "fire" wall. Requirements for that usually comes with oil containment and fire protection (e.g. NFPA 850).
Just to mention, I found somewhere that the TR firewall shall withstand two .44 magnum projectiles....see the link:
In my opinion, the comments in the link article are highly exaggerated. The only item that may blast and damage the nearby transformer is porcelain insulator. I have not seen metal pieces or tank parts flying around during transformer fires or blasts. Today the trend is to go for dry type bushings with silicon rubber housing(RIP- resin impregnated condenser bushing)so that a bushing failure will not cause porcelain blast and initiate a fire. Major transmission utility in India is specifying such RIP bushings up to 1200 kV level in their transformers. Even with porcelain insulator shrapnel, a normal fire wall will dampen the forces so much that the piercing out pieces cannot damage nearby transformer. So a fire wall is sufficient and blast resistant wall may be superfluous.
Thank you all for the input. I have always thought of these walls as fire walls and not blast walls. In the past I have desgined them for conservative wind load. And to me, these walls should be deemed sacrificial with a good chance that the wall may have to be re-built in case of a large fire.
