Silane Safety/Lessons Learned and Accident Prevention Eugene Ngai, Air Products and Chemicals Dr. Vasilis Fthenakis, Brookhaven National Laboratory Eugene Y. Ngai Dir. Of ER and Disposal Technology Eugene has a BS in Chemical Engineering and an MS in Environmental Engineering, all from New Jersey Institute of Technology. He has over 30 years of Specialty Gas Experience in Production, Laboratory, R&D, Engineering, Safety positions at Matheson, Exxon Research, Solkatronic Chemicals and Scientific Gas Products. Had increasing management responsibilities during his career and held an Executive Management position as Vice President of Corporate Development and Technology for Solkatronic Chemicals for 10 years prior to the Air Products acquisition in 1999. He had responsibility for EHS, Engineering, Information Technology, Research and Development, and Quality. Most recently he was Director of Compound Semiconductor Technology in the Electronics Division and is now Director of ER and Disposal Technology in the Product Safety Group. He is active in a number of industry associations, Compressed Gas Association (CGA), Asia Industrial Gas Association (AIGA), National Fire Protection Association (NFPA) and the Semiconductor Environmental Health and Safety Association (SESHA) He also developed and manages the Emergency Response Equipment and Training group since 1990. He is the Course Director for a 3 day Specialty Gas Emergency Response course, which has trained over 4000 customers, government agencies and employees since 1990. He has trained over 750 Firefighters in Compressed Gas Safety and Emergency Response. He has taught at a number of Fire Academies worldwide, including New York and Singapore He has made numerous presentations worldwide on Emergency Response, Product Safety, Gas Technology and Environment over the last 20 years. He has 4 US patents for Gas Safety Devices and 2 pending for new Purification Technology Silane Safety 2 IEEE Conference 2008 Dr. Vasilis Fthenakis Vasilis Fthenakis is a senior chemical engineer and the head of the National Photovoltaic Research Center at Brookhaven National Laboratory www.pv.bnl.gov. He is also a professor of earth and environmental engineering at Columbia University where he founded and directs the Center for Life Cycle Analysis. www.clca.columbia.edu Fthenakis has authored a book on Prevention and Control of Accidental Releases of Hazardous Gases and about 200 papers on energy-related safety and environmental topics. He serves in several expert panels, two journal editorial boards, and frequently consults the PV and chemical industries. Silane Safety 3 IEEE Conference 2008 Gas Cabinet Testing, May 2006 Color is 0.033 sec/frame Black/White is 0.002 sec/frame Flames for 0.010-0.012 sec Silane Safety 4 IEEE Conference 2008 Silane Gas Cabinet Release Test z High pressure Silane was vented into the gas cabinet through a ¼” tube. z The cabinet was ventilated at 300 cfm. z Silane was released without ignition, mixing with air in the cabinet. z The metastable mass was ignited by an abrupt shutoff of Silane flow. z The ignition was at the valve outlet z Reaction is a rapid deflagration z Obstructions will increase mixing forming a larger steady state metastable mass z It can be dangerous to approach a silane leak that is not burning, especially if there is any confinement Silane Safety 5 IEEE Conference 2008 Taiwan, Silane Explosion, Nov. 23, 2005 During a cylinder change Silane was released from a full cylinder unignited. The metastable mixture ignited, fatally injuring the operator and rupturing the cabinet. Other silane and Ammonia cylinders in the gas room also started to release their contents Silane Safety 6 IEEE Conference 2008 Silane Safety Seminars z APCI Spearheaded worldwide effort to improve the industry understanding of silane through a series of silane safety seminars. z APCI led the effort to organize the first Silane Safety seminar in Asia in Taiwan z Presentations or seminars on silane have been conducted or are planned for all regions of the world z Links with major trade shows has resulted in outstanding attendance Silane Safety 7 IEEE Conference 2008 Silane Safety 8 IEEE Conference 2008 Introduction z Silane has been involved in a number of severe incidents over the last 40 years of use. This presentation will review key incidents and how Silane behaved in the incident. While Silane is pyrophoric gas with a wide flammable range, releases into the air may not always ignite immediately or sometimes not at all. Understanding this behavior can help improve safety in the design and operation of systems as well as improve the response procedure to an incident. z As reported by numerous studies (FM Global, Intel, Hazards Research, etc) conducted on Silane ignition of Silane is influenced by a variety of environmental and release conditions. z Of interest is the study by Emeleus and Stewart on the upper and lower explosion limits of silane and oxygen. showed that silane and oxygen in a 1 : 2.3 mol ratio at a total pressure of ca. 0.6 bar do not react appreciably even when kept at 70oC for many days. Yet at a slightly higher partial pressure of silane or at a slightly higher temperature an explosion occurred immediately. Silane Safety 9 IEEE Conference 2008 History of Silane Use z The Semiconductor Industry started to use Silane in small quantities in 1968. z During this time there were many small Silane manufacturing processes at a number of gas companies. The manufacturing method was a batch reaction of Trichlorosilane or Silicon Tetrachloride in a molten Lithium Aluminum Hydride salt bath z As a new compound there was a lot of concern with safety. Considerable study on the safe fill density in the early days only 1 kg z During transportation there were numerous fires due to valves vibrating open and no secondary valve outlet seal on the valve Silane Safety 10 IEEE Conference 2008 Silane Release Behavior z The greatest hazard of Silane is its unpredictable behavior when released to the air – No ignition – Immediate Ignition – Delayed Ignition z Silane can easily be released without ignition. FM Global found that Silane did not ignite in 11 out of 12 release tests at 33 psig from 1/8” line. Even at 7.8 psig. For a ¼” line the lowest pressure with no ignition was 70 psig. z Silane when released at high velocities may not immediately ignite z Smaller the diameter of the release tube the lower the pressure at which no ignition would occur Silane Safety 11 IEEE Conference 2008 Silane, Chemical & Physical Properties z Silane is a compressed gas which is pyrophoric z Silicon Tetrahydride, SiH4 z CAS# 7803-62-5 z UN# 2203 z Molecular Weight 32.11 z Compressed Gas which is filled by weight due to high compressibility z Gas Density of 0.083 lb/ft3, 1.33 gm/l @ 70oF (21oC) z Boiling Point, 1 atm. -169.6oF (-112oC) z Freezing Point, 1 atm. -299oF (-184oC) z Critical Temperature 19.90 F (-70C) z Critical Pressure 632 psia (43 atm) z Liquid Density @ 10oF (-12oC) 21.1 lbs/ft3 (338 gm/l) Silane Safety 12 IEEE Conference 2008 Silane ER Information z Silane has a vapor specific density heavier than air. 1.12 z Gas Specific Volume @ 70oF (21oC) 12 ft3/lb (750 cc/gm) z Autoignition -50oC (-58oF) to -100oC (-148oF) Note: Can vary depending on source of data z Flammability (LFL -UFL) 1.37 - 96% In a fire Silane will oxidize to amorphous Silicon Dioxide z Thermal Stability Silane is thermally stable up to 788oF (420oC) z Water Solubility Silane is slightly soluble in water z Odor While Silane has reported to have a repulsive odor, the more common odor reported has been none and the distinctive “Ozone” like odor after combustion z Latent Heat of Vaporization -170oF (-112.5oC) 166.8 btu/lb (388 kJ/kg) at Boiling Point Silane Safety 13 IEEE Conference 2008 Leaking Silane Cylinder Valve z During the early days, numerous incidents were reported of a Silane release when the vaportight outlet cap on a cylinder valve was loosened z The reactions were reported to be a fire, minor “pops” to explosions. The “pops” can occur when a small amount of Silane trapped behind the valve cap or pigtail is released. In a few cases they have been severe enough to cause Handwheel eardrum rupture. Wire z A severe explosion was reported to have occurred in the US in 1977. A piggyback trailer containing 20 cylinders of Silane and 28 drums of antifreeze exploded as the train was moving Outlet at 70 mph. A 5 kg cylinder leaked into the trailer Cap and exploded at some point. The sides and roof of the trailer were blown out. 17 cylinders and 4 drums were thrown out of the trailer. z This and another incident led to improved procedures for inspection, handwheel wiring, gastight outlet caps. Also block and bracing Silane Safety 14 IEEE Conference 2008 Valve Crossport Leakers Silane Safety 15 IEEE Conference 2008 Recent Silane Incidents z In the last 20 years, a number of major incidents have occurred with Silane use. z Release and detonation of gas cabinet z Release and detonation of duct z Release and Fire z Explosion of Cylinder z Reaction of Solid Byproducts z Pressure Relief Device Leak z Aluminum Cylinder rupture Silane Safety 16 IEEE Conference 2008 Some Causes z Connection Leaks z Failure to cap line during maintenance z Check valve failure z Regulator Diaphragm failure z Improper PRD design z Cylinder contamination with Nitrous Oxide z Operator removes wrong cylinder Silane Safety 17 IEEE Conference 2008 SiH4 Leak from Elastomer Gasket z Silane cylinder on standby z DISS connection with PTFE Gasket z PTFE gasket coldflowed and leaked z Fire from leakcheck hole.