In Sandbox mode, Sappers can create huge amounts of TNT in a short period of time. While this has it's legitimate uses, griefers (http://en.wikipedia.org/wiki/Griefer) can easily use this to destory players and buildings easily in a relatively short period of time.
Solution: 2 server flags
- Friendly Fire for Players
- Buildings Affected by TNT
Personally, for my server, I'd like to turn those both off. I find myself with unhappy people EVERY hour because one sapper destroyed their past hours work in 1 minute.
I created a flag for detonations (exploding tnt) for my Dangerous mod and can reimplement it in the main branch if requested by krispykrem.