At first, it is thought the Underground Shelter contains three wards that each house their own Decontamination Room. These rooms are all identical, each possessing multiple shower heads and a typical shower room floor and wall, complete with drains.
However, as revealed later in the game, there is only one Decontamination Room, not three. The players are swapped in and out at different times. Zero puts C-Team in first, then Q-Team, then D-Team, essentially giving an unfair advantage and disadvantage to the teams, since one team could push it without any other team getting a fair chance to press it.
During the events of Zero Time Dilemma, the sole door of the rooms are welded shut and the only other feature in the room is a singular yellow button near the door.
First Come, First Saved
Should all three teams' initial vote be spread evenly (no team receives two votes), Zero II places the three teams into their respective Decontamination Room. There, he tells them that since the votes earlier did not result in any team's deaths, he is giving them a free chance to escape the facility.
The yellow button near the door in their chambers acts as a switch which, when pressed, causes the showers in the other teams' Decontamination Rooms to fill the room with hydrofluoric acid, a corrosive acid that can easily melt through human flesh as well as glass and metal. However, once a team presses the button, all other teams' buttons no longer work, thus, the first team to activate it kills the other two teams and obtains the necessary X-Passes to escape the facility as a result.
In order to get to the Central Elevator Hall, D-Team sets the bomb from Manufacturing next to the Decontamination Room's outer door (which has been welded shut). Zero, seeing through this plan, sets the unconscious Q-Team on the other side of the door and turns on the hydrofluoric acid showers in the Decontamination Room. D-Team finds a protective suit in the prep room, but Sigma says there isn't enough time and that they should run away. Diana is given the choice to run away or stay put.