Radiation in a room.
Radiation is an environmental hazard that completely fills rooms on a derelict, damaging drones and certain other entities over time.
Radiation will fill a room after about 8-10 seconds when an airlock is opened without the docking bay attached, or when a room is hit by asteroids or the Cannon upgrade. Following a timer, there is also a chance for a pipe to burst somewhere on board, filling the room with radiation without also filling it with vacuum. The chances for this to happen early rise with the age of the derelict.
When a pipe is about to burst, the player is first alerted by a loud, metallic groaning sound around 10 seconds before the pipe bursts. In a drone view this sound is audible slightly earlier than it is in the schematic view. When the pipe does burst, the player is alerted of it by an alarm bell noise, and is informed of which room has been irradiated via the console. Unlike asteroid strikes, pipe bursts can only happen in rooms that are on the Schematic View.
When radiation first appears in a room, the player is notified that radiation is filling the room. One minute later, the player is alerted that the room is now completely filled with radiation. In the schematic view, newly irradiated rooms will be filled with flashing, red, diagonal lines, while fully irradiated rooms are filled with solid, dark red, diagonal lines.
Drones will take 2 HP of damage per second in a newly irradiated room, and 5 HP of damage per second in a fully irradiated room.
Radiation will also deal damage to security drones, swarms and dogs at the same rate as drones. You can try to lead them into irradiated rooms to destroy them. Leapers and slime are not affected by radiation.
If there are any open doors in an irradiated room, the adjoining rooms will also be progressively irradiated, and an alarm bell noise can be heard for each new room that fills with radiation.
Radiation can never disperse from a room, you can only clear a room of radiation using the Decontaminate upgrade. You can, however, negate the effects of radiation on your drones by equipping them with a Shield upgrade.
If the rooms on both sides of a door are irradiated, the door will also count as irradiated, doing 2 points of damage per second to anything crossing it (In the case of Airlocks, having no room on the other side counts as an irradiated room). This radiation can never be removed, even with the Decontaminate upgrade.
If playing safe is your style, it's advised that upon hearing the metal groaning noise, close any available doors, herd all of your drones back into your docking ship as quickly as possible, and shut the airlock.