TLM said:
The safest silicone lubricants are those used in vacum applications, they have no volatiles, not cheap though. Most serious silicone greases don't have any petrochemical volatiles because that kind of negates the whole point of using silicone.
TLM
For Hi Vacuum and Ultra Hi Vac, most seals/orings are metal to metal gaskets made of materials like copper compressed between "knife edge" sealing surfaces. Most conventional orings are either Buna, silcone, or Viton and use little or no lubricants. Specific lubricants used in HV and UHV have low vapor pressures to reduce outgassing. Lubricants like Castrol's Braycote 600 run about $600 for a 6 oz. tube though. Crytox, Torr-lube, and others are a bit cheaper but not really needed for normal everyday uses.
O-ring materials vary according to use and chemical compatabilties. Just a quick run down on oring materials. efunda.com has more info on their sites at http://www.efunda.com/designstandards/oring/oring_chemical.cfm?SC=none&SM=Buna-N%20(Nitrile)
Buna-N a nitrile rubber is by far the most common type of seal material in the world.
Viton has become one of the most widely used seal materials in the world because of its excellent chemical resistance and outstanding upper temperature limit.
EP ( EPDM ) offers outstanding resistance to solvents like acetone, alcohols, and MEK. It is not compatible with petroleum oils and greases.
Silicone is commonly used in medical devices and hot air applications. It uses a silicon-oxygen (siloxane) main backbone for excellent thermal stability. Mechanical properties are generally poor so it should not be used in dynamic applications.
There are a few high performance materials such as Kalrez® or Chemrez® that can be made tailored to your individual needs and applications - for a small fee of course.
You need to define your application and environment to recommend an oring and lube. For or day to day use as a certed rescue diver, silicone orings and the silcone based lubes like you find recommended above and purchased in dive shops works for my applications. Other apps may vary.......