Silane gas safety

Silane accumulated below the bottle cap on silane bottles can cause a "popper" when removing the bottle cap. Always take care, use PPE including fire-proof gloves and closthes, and hearing protection when handling silane gas bottles. Photo: Dow Corning.

Our work on new ways to produce high-value silicon products at IFE is dependent on the gas monosilane. Monosilane, which we normally just call silane, is a gas consisting of molecules of one silicon atom and four hydrogen atoms. It is easy to purify and easily converts back to solid silicon, releasing its hydrogen atoms as gas. Because of this it is heavily used as an intermediate step in silicon purification, and in production of electronics components as e.g. flat screen TVs and advanced integrated circuits.

One of the main issues with silane is safety. The gas holds a lot of chemical energy and reacts violently with air if released through a leak, or if any other mistake is done. Therefore, focus on safe operation and the right maintenance procedures are crucial.

Some facts regarding silane safety:

• There have been several fatal silane incidents since the use of silane started in the 1960’s and 1970’s.
• Silane is pyrophoric: It can catch fire by itself when released to air (autoignition).
• Pyrophoric gases are somehow less dangerous than gases which are only flammable, because a fire generally gauses less damage than an explosion.
• Even though pyrophoric, silane will not always ignite when released. Especially when released at high pressure, it is often observed that there is no auto-ignition.
• If auto-ignition does not take place when released, often the gas actually auto-ignites when the flow from the high pressure reservoir is shut off.
• The most dangerous conditions occur under delayed ignition, especially if the gas release is confined or semi-confined, so that an explosive gas mixture can build up.
• If all precautions are taken, the chances of a serious incident are, luckily, minimal.
• It is not the amount of silane that determines the risk, any amount of silane represents a potential explosion and fire hazard.
• Another risk with silane, especially with using gases with two or more silicon atoms (disilane and higher order silanes) is the formation of “popping gels”. These can form in the exhaust handling systems, in the vacuum pumps or gas abatement systems, and are highly reactive solids that might “pop” or explode very violently upon any physical agitation.
• All handling of silane gas systems and silane based reactor systems should take place using proper personal protection equipment (PPE).

If you are interested in learning more about silane gas safety, do not hesitate to contact our group at IFE. I also recommend Eugene Ngai from Chemically Speaking, who has been working with silane safety and emergency response for over more than 40 years. See also EIGA's Code of Practice for Silane.