For Tibet in particular, the major concern we have is less for the safety of the diplomats who travel there, but the surveillance they're under when they do. In Tibet, and I think the ambassador would attest to this, it's very difficult to break away from your handlers and the constant surveillance you might have.
I would note, as mentioned in my opening remarks, that you're not required to have permits for travel to Tibetan areas outside of Tibet, in places such as Sichuan province or Qinghai province. We've noted that, historically, when diplomats do travel there, they are indeed under surveillance and followed when they're there.