What does "when worn" mean?

[KevinJ]

Originally Posted by FireHorse

I think that spell should be called Delayed Combustion, and it should be bound to the grenade with an object which, when removed, ends the spell and makes the grenade active. The object could be something simple, like, say… a Pin. And it could be built into the grenade at the time of manufacture…

You could apply a Delayed Combustion spell to any flammable item to make self destructing object. Burn after reading...

Also, a fire (normal or magical) would still do damage in darkness, even if you can't see it. And just because you can't see it doesn't mean that fireball isn't going to hurt.