My reading of the rules concerning Fireball and Delayed Blast Fireball in 5e work it out to be something along the lines of "the caster picks a point in space, and when the spell goes off (or after some delay/trigger in the case of Delayed Blast Fireball) suddenly there's magical fire in a 20 ft. radius around that point."
Notwithstanding the pitfalls of questioning the physical properties of magical effects (personally I like systems where everything makes a reasonable amount of sense), I wonder about how this would interact with small, confined spaces. Supposed a Delayed Blast Fireball was placed in a very small metal case, which was subsequently welded/sealed shut. What would happen when the spell is triggered?
I can think of three reasonable options at first:
- We've created a grenade (albeit an extremely unstable one). This requires that force/pressure was generated by the Fireball, which creates implications for other applications.
- The vessel contains the explosion, and since no force or heat was generated (only "magic fire"), the vessel is afterwards unharmed.
- The vessel isn't blown apart (no force), but depending on its makeup might melt from the focused heat of the Fireball, leading perhaps to partial leakage.
Which scenario would apply? Or would something completely different happen?