hot zone

Short definition from Wiktionary

Noun

1. 1
   An area to which access is restricted because it is contaminated with radiation or a chemical or biological biohazard.
2. 2
   An area where fighting or hostilities are likely to erupt.
3. 3
   An apparatus for growing crystals at very hot temperatures.
4. 4
   Used other than figuratively or idiomatically: see hot, zone.