A similar question was asked on the SEMI Safety Grapevine. My answer with some edits for this situation is as follows The worldwide guidance document on gas mixture flammability is ISO 10156 "Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets" 3rd edition, 2010. The recent update to CGA P-23 was based on the more current data from ISO 10156 This is referenced in NFPA 55 Compressed Gases 22.214.171.124 Flammability of Gas Mixtures. For gas mixtures other than those containing ammonia and nonflammable gases, flammability of gas mixtures shall be classified in accordance with CGAP-23, Standard for Categorizing Gas Mixtures Containing Flammable and Nonflammable Components; or by physical testing in accordance with the requirements of ASTM E 681, Standard Test Method for Concentration Limits of Flammability of Chemicals (Vapors and Gases), or ISO 10156, Gases and gas mixtures - Determination of fire potential and oxidizing ability for the selection of cylinder valve outlets. Under the global harmonization effort DOT, OSHA and EPA will adopt ISO10156 to classify flammable gas mixtures The heat capacity of the gas that it is mixed with will influence the LEL, in most cases it will increase the concentration. In 10156, the flammable gas is tested mixed with Nitrogen, the lowest concentration that will burn is called the Tci value while the lowest concentration of the pure gas in air that will burn is the Li. In the case of hydrogen the Tci is 5.5% while the Li is 4%. The Tci changes as the balance gas changes. If H2 is mixed with N2, it will not be flammable until it reaches 5.5%. As indicated, P-23 data is primarily based on the Bureau of Mines testing and method which dates to the 1950's. This apparatus used a small diameter open tube which conducts heat from a flame quicker therefore the data will be higher than the more current ISO 10156 test which uses a larger diameter open tube. The ASTM test is a closed sphere. There are also differences in the definition of LFL based on the test. H2 mixed with N2 using 4 different test methods yielded results of 5.4 - 5.7% Hope this helps Eugene Ngai Chemically Speaking LLC www.chemicallyspeakingllc.com -----Original Message----- From: Ken Kretchman [mailto:ken_kretchman**At_Symbol_Here**ncsu.edu] Sent: Friday, September 23, 2011 9:00 AM To: DCHAS-L Discussion List Cc: Eugene_Ngai**At_Symbol_Here**comcast.net Subject: Re: [DCHAS-L] 4% hydrogen mixture While I have been long operating with the understanding that this mixture is well below a flammable concentration, based on company testing and other data also from long ago, I am copying Eugene Ngai of Chemically Speaking who has a great deal of experience with gas suppliers and CGA with extends over many years... thanks Ken >>> "Jeskie, Kimberly B."
9/23/2011 8:14 AM >>> Long story short, the reason I ask this question is that we have a long standing debate with our research community who feel strongly that they have chosen the 4% mixture because it gives them the reducing environment they need while limiting the hazard, that's why they use it. The DOT classification is based on P-32 and the building codes (which is where the debate starts) generally site DOT as the go to place for deciding how to class materials for the quantities allowed inside buildings. That's where we keep coming up against a logistics nightmare. No one can agree on how to account for this mixture and most everyone agrees that using the full volume of a 4 % mixture just doesn't make common sense. One of our Fire Protection Engineers has suggested that the sources of information we use to make these decisions may be dated and an analysis may be the ticket to put this issue to bed. The P-23 pamphlet references Bureau of Mines Bulletin 503-1952 and much of the 503 date is based on simple, ad hoc tests on an apparatus dating back to the 1920s. Some of the data is based on earlier work dating back to the 1870s and 1880s. DOT references and accepts ASTM E-681 to classify flammability of gases. So...we're debating on whether or not to test the mixture under this newer standard, and it sure would be great if it has already been done. Kim Kimberly Begley Jeskie, MPH-OSHM Operations Manager Physical Sciences Directorate Oak Ridge National Laboratory (865) 574-4945 -----Original Message----- From: DCHAS-L Discussion List [mailto:DCHAS-L**At_Symbol_Here**list.uvm.edu] On Behalf Of Todd Perkins Sent: Thursday, September 22, 2011 7:05 PM To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU Subject: Re: [DCHAS-L] 4% hydrogen mixture Do you mean test the mixture for flammability per CGA publication P-23? My understanding is that the data is based on experimental observation as well as calculation. I've never had reason to question the data. Have you observed something different? Todd Perkins Regional Safet Director Airgas Mid America Thanks, Todd - Sent from my mobile phone On Sep 22, 2011 11:41 AM, Jeskie, Kimberly B. <jeskiekb**At_Symbol_Here**ORNL.GOV> wrote: Has anyone actually tested a 4% hydrogen/ 96% argon mixture using ASTM E-681, as opposed to just taking the P-23 data or the Bureau of Mines Bulletin 503-1952 at face value? Kim Kimberly Begley Jeskie, MPH-OSHMOperations ManagerPhysical Sciences DirectorateOak Ridge National Laboratory(865) 574-4945
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