{"operation":"document","citation":"08-0214","title":"DuPont Global Logistics — Hazardous Materials Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2008-11-19","effective_on":null,"summary":"08-0214 response to DuPont Global Logistics concerning 173.124.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-08-0214.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-08-0214.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-08-0214","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/2008/080214.pdf","body":"<<<PAGE 1>>>\n\nU.S. Department\nof Transportation\nPipeline and Hazardous Materials\nSafety Administration\n1200 New Jersey Ave., SE\nWashington, DC 20590\nMr. Kevin Greene\nHazardous Materials Distribution Consultant\nDuPont Global Logistics\n12650 Highway 43 North\nAxis, AL 36505\nRef. No. 08-02 14\nDear Mr. Greene:\nThis responds to your letter dated August 22,2008 regarding classification of Division 4.2\nself heating substances under the Hazardous Materials Regulations (HMR; 49 Parts 171 -\n180). Specifically you asked for our concurrence concerning the technical merit of an\nalternative to the testing method described in the UN Manual of Tests and Criteria, 4th\nrevised edition (UN Manual). The specific requirements you address are contained in section\n33.3 of the UN Manual and are implemented through the provisions of 5 173.124 of the\nHMR.\nThe UN Manual describes a Division 4.2 self-heating material as a material that, when in\ncontact with air and without an energy supply, is liable to self-heat. A material of this type\nexhibits spontaneous ignition or experiences dangerous self heating described by a 60 OC rise\nin temperature over the oven temperature within 24 hours. The UN Manual specifies that\nsubstances with a temperature of spontaneous combustion higher than 50 \"C for a volume of\n27 m3 should not be assigned to Division 4.2.\nThe method described in the UN Manual requires testing of samples in 25 mm and 100 mm\ncubes at discrete temperatures to establish whether a material meets the definition of a\nDivision 4.2 self heating material and to determine the packing group. Your alternative\nmethod utilizes a simplified self heating-model based on Frank-Karnenetskii ignition theory\nto extrapolate from experimentally obtained, small scale data the spontaneous ignition\ntemperature of a given substance at a 27 m3 mass.\n\n<<<PAGE 2>>>\n\nWe have reviewed the information provided with your letter and we agree that the alternative\ntest method you propose will accurately establish the self-ignition temperature of a solid\nmaterial of a given mass consistent with the guidance provided in the UN Manual.\nI hope this satisfies your inquiry. If we can be of further assistance, please contact us.\nSincerely,\n/\nSusan Gorsky\nActing chief, Standards Development\nOffice of Hazardous Materials Standards\n\n<<<PAGE 3>>>\n\nDuPont Global Logistics 2 / I\n12650 Hidway 43\nAxis, ~ l a b a m a 36505\nDuPont Global Logistics\nAugust 22,2008\nMr. Edward T. Mazzullo\nDirector, Office of Hazardous Materials Standards\nU.S. DOTIPHMSA (PHH-10)\n1200 New Jersey Avenue, SE East Bldg., 2nd Floor\nWashington, DC 20590-0001\nDear Mr. MazzuIIo:\nSubiecf: Request concurrence that extrapolated small-scale data may be used to establish whether a solid material\nshould be classified as a Division 4.2 self-heating substance, defmed as having a critical temperature of 50' C or\nless for a 27 m3 cubic mass.\nStatement of Issue\n49 CFR 173.124@)(2) specifies that criteria found in Test Method N.4, Section 33.3.1.6 of the United Nations\nRecommendations on the Transport qfDan~erous Goods, Manual o f Tests and Criteria, 4' revised edition, be\nused to determine whether a solid-phase substance should be classified as a Division 4.2 self-heating hazard.\nHowever, this test method may not always result in a correct classification. It is suggested that in many such\nsituations the application of self-ignition theory coupled with isothermal oven tests may be more appropriate to\nclassify a substance as self-heating, which in the context of the UNRecornmendations means that a test substance\nexhibits a self-ignition temperature of 50' C or less for a 27 m3 mass.\nDiscussion\nBackground\nMany organic solids will oxidize when exposed to air. For a given mass the heat generated from these exothermic\nreactions at low temperatures will most likely be safely dissipated to the environment and very little if any\nincrease in material temperature will occur. However, as the air temperature surrounding the material increases\nthe oxidation reaction rate and attendant rate of heat generation also increase until a point is reached where all the\nheat generated cannot be dissipated and material temperature will begin to equilibrate above that of the\nsurrounding air. As the surrounding air temperature is raised further the oxidation rate will continue to rise until a\ncondition is reached where heat accumulated in the solids reaches a 'point of no return' and the sample exotherms\nto its ignition point. This temperature, referred to as the critical temperature (T,), is highly dependent upon\nreaction kinetics, physical and thermal characteristics of the solid, and surface area-to-volume ratio and geometry\nof the mass. Larger material masses of a given geometry will exhibit lower critical temperatures since they are\n\n<<<PAGE 4>>>\n\nless able to dissipate heat due to their lower surface arealvolume ratio. For the same reason different geometries\nof a given mass of material will show different critical temperatures. It is therefore impossible to speak of a single\n'critical temperature' for a given material since this value will be situation-specific. A simplified self-heating\nmodel based on Frank-Kamenetskii ignition theory was developed by Gray and ~ e e ' and further refined by\n~owes' to deal with this problem and has been widely applied to the evaluation of self-heating hazards in\nindustry. This model assumes that one chemical reaction is responsible for self-heating over the temperature\nrange of interest and that the solids temperature rise above the surrounding air temperature is small in comparison\nto the ratio of activation energy to the universal gas constant. It is also assumed that rate of heat loss is governed\nby heat conduction through the solids as opposed to convective heat transfer rate at the surface (i.e., Biot number\n>30). A good abbreviated description of this method is given by rag and Grossel and zaolsh4. Based on this\nmodel boundary conditions for criticality are defined by the equation:\nIn (G,T;/?) = M + (N/TJ (Equation I )\nwhere:\n6, = Georneby Dependent Constant (2.52for cube)\nT, = Absolute Critical Temperature for Exothemic Runaway\nr, = Characteristic Length (half-length ofa sidefor a cube)\nParameters M and N are defined as:\nWhere:\nEA =Activation Energy\nQ = Heat of Reaction\np = Solids Bulk Density\nA = Pre-exponentialfactor in the Arrhenius reaction rate equation\nR = Universal Gas Constant\nk = Solids ~ e n n a l Conductivity\nPractical application of the model involves fust conducting isothermal tests in a forced convection oven to\ndetermine critical temperature for material housed in open mesh containers of a given geometry (e.g., cubes\nfabricated £corn screen) at different volumes. The experimentally determined critical temperatures are then used\nto construct a plot of reciprocal absolute temperature (IK) vs. In &T:/?). A linear regression on these data\nyields a line of slope N and intercept M. These values may then be used with Equation 1 to determine the critical\ntemperature for other volumes and geometries, or alternatively the critical volume for different geometries at a\ngiven critical temperature.\nRelevance to United Nations Test Method N.4\nTest Method N.4 as described in the UN ~ecommendations~ requires testing of samples in 25 and 100 nun cubes\nat discrete temperatures to establish whether a substance must be classified as a Division 4.2 self-heating hazard\nand if so to determine the appropriate packing group. Tests are based on the self-heating behavior of charcoal,\nwhich has a critical temperature of 50\" C for a 27 m3 cubic mass. Charcoal has been found to follow the\nsimplified self-heating model described in the previous section (figure 1). Since tests on 27 m3 masses are\nimpractical another point on the self-heating curve, 140\" C at a 1000 cm3 cubic volume, was selected as an\n'equivalent' test. If an initial test on a test substance at this condition proves positive, defined as a temperature\nrise of >60° C at the center of the mass for a 24-hour test period, the self-heating behavior of the sample is\ndetermined to be equivalent to or worse than that of charcoal and the material is classified as Division 4.2. This\ndecision is based on the assumption that the self-heating behavior of the test substance is similar to that of\ncharcoal, which may not always be the case. Figure 2 shows a situation in which a substance which failed the\n\n<<<PAGE 5>>>\n\ninitial test at 140' C in the 1000 cm3 cube was tested in cubes of various sizes to establish a self-heating curve.\nFor this case all of the assumptions of the simplified self-heating model were satisfied and an extrapolated self-\nignition temperature of 57.8\" C was determined for a 27 m3 cubic mass. The difference in the thermal response of\nthe test material from the behavior of charcoal is explained by the much higher activation energy of the test\nsubstance as shown by the higher value of the self-heating curve slope, which is the ratio of activation energy to\nuniversal gas constant (parameter N in Equation 1 above). Based on this analysis the substance should not be\nclassified as Division 4.2 per Section 33.3.1.3.3 oFthe UV Recommendations which states that:\n\" ... Substances with a temperature of spontaneous combustion higher than 50\" Cfor a\nvolume of 27m3 should not be assigned to Division 4.2.\"\nA recent seminar on the UN self-heating protocol presented at the International Group of Experts on the\nExplosion Risks of Unstable Substances (IGUS)~ reached conclusions essentially identical to those discussed in\nthis document.\nIt is proposed that extrapolated small-scale data may be used to establish whether a solid material should be\nclassified as a Division 4.2 self-heating substance, defined as having a critical temperature of 50\" C or less for a\n27 m3 cubic mass. This method is limited to conditions for which the assumptions in the simplified Frank-\nKamanetskii self-heating model are valid. We would appreciate PHMSA/DOTYs concurrence in the technical\nmerit of our approach to Division 4.2 classification and our position that this method is consistent with guidance\nprovided in the UN Recommendations.\nPlease direct technical questions regarding this document to Robert L. Gravel1 and direct PHMSA/DOT's\nfinal response to Kevin M. Greene at the address provided.\nRobe~.t L. Gravel1\nPrincipal Process Sqfeiy Consultant\nE.I. DuPont de Nemours & Co., Inc.\nExplosion Hazard Laborato y\nPhone: (856) 540.2425\nFax:(856) 540.2296\nRobert.L.Gravell@,usa.dupont.com\nKevin M Greene\nHazardous Materials Distribution Consultant\nDuPont Global Logistics\n12650 Highway 43 North\nAxis, Alabama 36505\nPhone: (251)679.5330\nFax: (302) 355.2888\nKevin.M.Greene(ii,usa.du~ont.com\n\n<<<PAGE 6>>>\n\nReferences\n1. 2. 3. 4. 5. Oxidation and Combustion Review, Vol. 2, P . Gray and P. Lee, Elsevier, 1967\nBowes, P.C., Self-Heating: Evaluatinp and Controllina the Hazards, Elsevier Press, Oxford, 1984\nSFPE Handbook ofFire Protection Engineering 3rd edition, NFPA, Quincy, 2002\nGrossel, S.S and Zalosb, R.G., Guidelines for Safe Handling of Powders and Bulk Solids, AIChE Press,\nNew York, 2005\nRecommendations on the Transport ofDanaerous Goods. Manual o f Tests and Criteria, 4\" revised\nedition, United Nations, 2003\n6. Wildner, W., \"Anomalous Self-Heating Behavior: A Serious Gap in the Regularions, \" IGUS-EOS\nMeeting, May 2008\n\n<<<PAGE 7>>>\n\nFigure 1\nCharcoal SeIf-Heating Curve per UN Recommendations\nIv'ole. Based on criflcul lemperulrrres of 140° C und 50' C: for czrhes 0.1 und 1.5 rn\non o s~de, rc.~pectiv~l~~\n\n<<<PAGE 8>>>\n\nCritical Zgntion Data for Test Substarzce vs. Charcoal","truncated":false,"body_characters":11603}