Say the magic word to enter the inner realms of BFO...
The purpose of the inner air-lock is to shield the sensors behind the lock from the direct influence of rapid atmospheric pressure fluctuations. The inner air-lock was added in 2008/2009 in anticipation of the superconducting gravimeter.
The air-lock has a time constant of approximately four hours, meaning that pressure fluctuations with periods longer than 12 hours reach the instruments essentially unattenuated.
Say the magic word to enter the inner realms of BFO...