Decontamination gas is a security protocol to stop Class-D personnel from escaping and a gameplay element found throughout the facility.
Decontamination gas is commonly found on catwalks and will agitate the player's eyes, causing them to blink at a much faster rate. The blink icon will be outlined red and the bar will deplete faster. To prevent this, the player can wear a gas mask or a hazmat suit to protect their eyes from blinking faster. Decontamination gas appears in gas catwalks, some metal corridors, large testing chambers, and lockrooms.
They can also be found in the beginning of the game- the guards fill the player's cell with it and kill them if they do not exit the cell.
SCP-173 spawns more frequently in locations where the gas appears.
Prolonged exposure to the gas will eventually cause death to the player if they aren't wearing a gas mask.