Minecraft – How to toggle TNT off

If by a safe way you mean one where the TNT wouldn't destroy valuable resources, then no.

TNT is somewhat impractical for mining, because only about 30%-ish of the destroyed resources actually drop as items (wiki). So if you don't want to risk destroying diamonds and such, don't use TNT — at least when you're deep enough for the resources to occur.

You entered an incorrect damage value for that 64 stack of gunpowder you spawned for yourself via the op /give command. Its gunpowder by name only, wont work in any crafting as it isnt natural gunpowder.

Go get them the real way, or next time don't use the fourth parameter of /give <name> <itemid> [quantity] [dmg value]