What does depressurise mean?
Depressurise means to reduce or remove the air or gas pressure inside a sealed environment — a spacecraft module, a submarine compartment, a laboratory vacuum chamber, or, most familiarly, the cabin of a passenger aircraft. Used transitively, engineers may deliberately depressurise a system so that maintenance can proceed safely; used intransitively, the word describes a loss of pressure, as when an aircraft cabin depressurises at altitude and oxygen masks drop from overhead panels. Because sudden decompression poses serious physiological risks, including hypoxia and decompression sickness, the term carries strong associations with emergency procedures and technical precision. It is a formal, largely scientific register word, appearing most often in aviation, diving, aerospace, and industrial contexts rather than everyday conversation. British English spells the verb with an -ise ending, while American English prefers -ize; both forms share identical meaning, pronunciation, and grammatical behaviour, with related nouns depressurisation and depressurization likewise differing only in spelling.
verbTo reduce the air or gas pressure inside a sealed container, vehicle, or space, often deliberately; also, to lose pressure in this way. Commonly used of aircraft cabins and spacecraft.
- (transitive) To reduce the air or gas pressure within a sealed vessel, chamber, or vehicle.
- (intransitive) Of a sealed space such as an aircraft cabin: to undergo a loss of pressure, whether accidentally or intentionally.
"The pilot was forced to descend rapidly after the cabin began to depressurise at 30,000 feet."
"Engineers had to depressurise the reactor containment vessel before carrying out repairs."
"The aircraft depressurised slowly as it climbed above 25,000 feet, triggering the oxygen mask deployment."
At 35,000 feet, an uncommanded cabin depressurisation gives you roughly 15–20 seconds of 'useful consciousness' before blacking out — which is why flight attendants tell you to fit your own oxygen mask first.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of depressurise
Depressurise is formed from the prefix de- ('to reverse or remove') combined with 'pressure', itself derived from Latin pressura and ultimately premere, 'to press'. As a technical coinage, it arose in the twentieth century alongside modern aviation, diving, and pressurised-cabin technology, when controlled manipulation of gas pressure became routine engineering practice. Its cognates include pressurise, compress, and impression, all descendants of the same Latin root. The -ise spelling reflects British convention; the equivalent American form is depressurize.
Related word forms
How depressurise is actually used
The spelling 'depressurise' is standard British English; American usage favours 'depressurize'. The word belongs chiefly to technical, aviation, engineering, and diving registers, and is rarely used figuratively. In aviation contexts the noun form 'depressurisation' is especially frequent when describing emergencies.
Easily confused with depressurise
'Decompress' means to release pressure or to expand after compression (or to relax after stress), while 'depressurise' specifically means to reduce the internal gas pressure of a sealed space.