airtight chamber
Technical term for a sealed room or chamber designed to prevent air leakage, used in engineering, construction, or scientific contexts.
この実験は気密室内で行われた。
This experiment was conducted in an airtight chamber.
Compound of 気密 (kimitsu, 'airtight') and 室 (shitsu, 'room'). The derivation is straightforward from the kanji components.