Mixing it all together
Those two loops will be feeding the engine two gases, hopefully of very different temperatures and very similar pressures. However, while the Cold Loop does most of the coldwork for you, the engine room itself has the equipment to heat up the Hot Loop's pipes. Four furnaces, which you can load with fuel found in the Power Room to the northeast, can heat it for a basic char burn, while the combustion chamber below can provide additional heating. See Powering the Station: The Thermoelectric Engine for more information.
There is no vent. No escape.
The APC for this area is in the room to the north, the Pump Control Room.