lecture-safety-disasters - Cryogenic Safety Ch 11 Flynn...

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1 Cryogenic Safety Ch. 11 Flynn Cryogens are not high on the danger list, but a few rules must be obeyed 1. Be careful 2. It’s cold 3. Don’t breath 4. Work together 5. Know your materials 6. Let the gas go OUTLINE 1. Properties of Cryogens 2. Pressurization of Warming Vessels 3. Dewar Safety Issues 4. Asphyxiation Risks 5. Hydrogen Combustion 6. Tank Fire Dangers 7. Safe Working Distances 8. Hydrogen Gas Evolution Control 9. Thermal Contraction of Materials 10. Material Properties at Low T 11. Metals Effected by Embrittlement 12. Hydrogen Embrittlement Sources boxshadowdwn Recognize cryogenic safety issues in: boxshadowdwn Materials boxshadowdwn Design boxshadowdwn Operation boxshadowdwn Develop safe practices GOALS http:// www.metacafe.com/watch/126294/kid_gets_his_tongue_stuck_on_a_pole / Gas Boiling Point Centigrade Boiling Point Kelvin Volume Expansion to Gas Flammable Toxic Odor Helium-3 -269.9 3.2 757 to 1 No No(a) No Helium-4 -268.9 4.2 757 to 1 No No(a) No Hydrogen -252.7 20.4 851 to 1 Yes No(a) No Deuterium -249.5 23.6 ... Yes Radioac tive No Tritium -248 25.1 ... Yes Radioac tive No Neon -245.9 27.2 1438 to 1 No No(a) No Nitrogen -195.8 77.3 696 to 1 No No(a) No Carbon monoxide -192 81.1 ... Yes Yes No Fluorine -187 86 888 to 1 No Yes Sharp Argon -185.7 87.4 847 to 1 No No(a) No Oxygen -183.0 90.1 860 to 1 No No(a) No Methane -161.4 111.7 578 to 1 Yes No(a) No Krypton -151.8 121.3 700 to 1 No No(a) No Properties of Cryogens Maximum Pressures of Filled Vessel Warming to 300K without Venting Cryogen Maximum Pressure Mpa (psi) Helium 103 (15,000) Hydrogen 172 (25,000) Nitrogen 296 (43,000) Explosion caused by improper venting or accidental rapid warming of evaporating cryogen is the single biggest safety hazard. This is because the cryogenic liquids have a much higher density than their gases at room temperature. Dewar Design to Prevent Over Pressures Care must be taken to allow venting of any volume which might contain liquid cryogen. Support tubes must be vented with either one end open or small holes placed in wall near top. Joins must be designed so that liquid can not be trapped behind, causing rupture on warming. Figure adapted from Safety in Handling of Cryogenic Fluids by F.J. Edeskuty and W, F. Stewart, Plenum, NY (1996) , p. 54
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2 Dewar Pressurization, Venting, and Liquid Extraction 7. Liquid extraction valve has gas trap which prevents constant heat leak from liquid exposed to room temperature. Figure adapted from Safety in Handling of Cryogenic Fluids by F.J. Edeskuty and W, F. Stewart, Plenum, NY (1996) , p. 64 (Not Liquid Helium) The incident described in the following presentation did not involve an Airgas company. Airgas supplied the following 19 slides. Example Mishap: Misuse of salvaged Oxygen Dewar square6 Improper methods for using scrap dewar (cylinder) square6 Unsafe modifications to cylinder design Personnel Involved: square6 Two individuals (ages 42 and 60) found a liquid oxygen cylinder that had been removed from service and left at a scrap metal dealer square6 The individuals were self-employed in scrap metal cutting operations and intended to use the cylinder in their work square6 The individuals had access to a liquid oxygen supplier
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