Force field

A force field is a device which is often used to stop air from escaping from an area, usually to protect its inhabitants, for various reasons. They are usually transparent in colour, the only evidence of their existance being when an object hits the field.

Uses
The Judoon would use force fields to keep the air in the area, for example when the Royal Hope Hospital was transported from London to the Moon in 2007, a force field surrounded the hospital for a few metres around. Oddly enough, whilst nothing could escape, the Judoon had no trouble entering the field. (DW: Smith and Jones)

Humans developed force fields at some point, and used them to surround their bases on hostile planets when on missions for various reasons, such as on Krop Tor in the year 43K2.1 to find and retrieve the energy source which was keeping the planetoid in orbit around the black hole K37 Gem 5. However, the force field in this case was only used to cover an openable roof, and air could easily escape if a window was destroyed, letting the air escape. (DW: The Impossible Planet / The Satan Pit)