Whenever the heroes enter a MadScientistLaboratory in an unconventional way, they'll experience slight air draft coming from inside (or the other way around). Same thing happens whenever a science-y {{MacGuffin}} is opened with a slight hiss.

In RealLife, keeping some 1.2 atmospheric pressures inside is part of airtight sealing of laboratories against dust and other dirt from the outside: even if dust manages to find a crack in the sealing, it'll be blown right out by the pressure difference. On the other hand, labs dealing with dangerous micro-organisms (bio-hazard levels 3 and 4) require the lab to maintain a ''negative'' pressure difference to suck [[ScienceIsBad whatever nastiness is developed there]] right back inside. This trope covers both cases.

In fiction, it is mostly used to invoke some DramaticWind appropriate for the occasion.


[[folder:Anime & Manga]]
* Rin experiences the DramaticWind invocation in Aoyama Pharmaceutical lab in the first episode of ''Anime/{{Mnemosyne}}''.

* The telepods in ''TheFly''.
* Used in ''Film/SmallSoldiers'' when the two company executives visit the company that made the titular toys' chips (PlayedForLaughs when the down-to-earth toy maker gets surprised and his CorruptCorporateExecutive friend has to explain "Don't worry, that's meant to happen.").
* When the door to Nicodemus' study opens in ''WesternAnimation/TheSecretOfNIMH'', Mrs. Brisby is met with a blast of wind and a blinding light. Not sure why that would happen, except that [[RuleOfCool it looks cool]].
* Mentioned as a feature of the secret research facility in ''Film/TheAndromedaStrain''.

* This is how the Big Bad Laboratory in Creator/MichaelCrichton's ''Literature/{{Prey}}'' defended itself against [[spoiler:{{Nanomachines}}. They failed.]] Mainly because [[spoiler:the swarms [[BodyHorror took control of the humans]]]]. Is it any wonder it failed?
* The ''Literature/XWingSeries'' of books has the Imperial labs on Coruscant that were developing the Krytos Virus designed this way. In case of a containment leak and someone came in, the air would flow in instead of out, preventing the virus from leaving the building.

[[folder:Live Action TV]]
* The "negative pressure" bit is used in ''Series/{{NCIS}}'' when HQ suffers a ''Y. pestis'' bio-attack.

* The smoking salon on the Hindenburg was kept at positive pressure to prevent any wayward hydrogen atoms from sneaking in. In the end it didn't help but it was a nice idea.