Emergency bulkhead

"Emergency bulkheads" were barriers which could be engaged to contain areas on a starship which had suffered heavy damage and had decompressed. This had the effect of isolating the decompressed area from the rest of the ship. 

Before the regular use of force fields on Starfleet vessels to contain hull breaches, emergency bulkheads were standard. The was equipped with emergency bulkheads, which were used extensively during their mission whenever a hull breach occurred. 

Emergency bulkheads were installed in turboshafts and could be initiated to stop a turbolift from falling or to restrict access for unwanted passengers of a turbocar. 

Emergency bulkheads are also installed as a prerequisite for structural damage when a starship encounters a hostile environment or situation.