unpressurized
/ˌʌnˈpreʃəraɪzd/(亦作 -ised)
adjective
1- (of a gas or its container) not having raised pressure that is produced or maintained artificially（煤气, 气瓶）未增压的。
1.1
- (of an aircraft cabin) not having normal atmospheric pressure maintained at a high altitude（机舱）高空中未保持正常气压的。