Ultra high vacuum (UHV) is the pressure range characterized by pressures lower than 7.5 x 10^-9 Torr. This regime of pressure is vital to many fields of scientific research, but does not come without safety risks. Most of these come about due to venting of the chambers where the vacuum is held. The two largest safety concerns are explosive compression and electrical arcing. Explosive compression is the rapid venting of a vacuum chamber, which can be dangerous to those in the area. Be careful when opening and closing gates, and always check the pressure of a chamber or load lock before removing windows or cracking them open. If any part of the vacuum system looks damaged, leak check and vent if necessary. When venting a UHV chamber, do not just pull windows off to expose to atmospheric pressure. Though air is an insulator at atmospheric pressure, and at UHV conditions gas molecules are in free molecular flow and cannot carry current, at medium pressures air is a conductor and can cause electrical arcing inside the chamber. Bleed the system with nitrogen gas through the roughing pump when venting the chamber. THis prevents any electrical arcing when venting a UHV chamber.
The other major safety concerns with UHV systems involve ergonomics, noise, and sharps safety. UHV chambers often require repetitive motions, like moving load lock or prep chamber arms, and steps should be taken to ensure that these are at no strain to laboratory workers. In addition, UHV systems require several pumps in series in order to maintain the UHV pressures. These pumps can be loud, especially roughing and turbomolecular pumps. Make sure that the noise they generate are within the safe limit of 85dB. If they are not, take steps to reduce the level of noise within the laboratory with acoustical treatments on the walls and ceilings and providing ear protection. UHV systems require special flanges with knife edges to make secure seals. When handling these flanges, do not touch the knife edge. Always handle flanges on the outside.