Vacuum - airless space inside the limited areas of the asteroid. It is not a gas, on the contrary, a vacuum is its absence. It has zero heat capacity and thermal conductivity , so the cooling of something with it is impossible. Attaching such an area to the colony is not dangerous, but the vacuum is quickly filled with other gases, which can lead to a strong vacuum in the surrounding cells. Duplicants behave in it the same as in unsuitable for breathing gases.
Vacuum does not conduct heat, which means that interlayers from vacuum can be used as a replacement for heat-insulating tiles , in cases when it is necessary to limit the distribution of hot or cold temperatures .
It is possible to create a vacuum - you need to put the gas pump in a sealed room and turn it on. Gradually, it will pump out all the gases and create a vacuum.
You can also create a vacuum with the help of mechanical locks , if you place three locks in a row, and then open the central one with the help of automation. This is also done by filling an area with tiles then removing them all without having any gases get in, best done using an airlock.