{"operation":"document","citation":"07-0012","title":"HMT Associates — Hazardous Materials Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"2007-02-23","effective_on":null,"summary":"07-0012 response to HMT Associates concerning 173.136.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-07-0012.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-07-0012.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-07-0012","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/2007/070012.pdf","body":"<<<PAGE 1>>>\n\nof T-ansportation\nU.S. Department\nFEB 2 3 2007\n400 Seventh Street, S.W.\nWashington, D.C. 20590\nMaterials Safety Administration\nPipeline and Hazardous\nMr. E. A. Altemos\nRef. No. 07-0012\nHMT Associates\n603 King St., Suite 300\nAlexandria, VA 22314-3105\nDear Mr. Altemos:\nThis is in response to your letter requesting clarification of the applicability of the Hazardous\nMaterials Regulations (HMR; 49 CFR Parts 171-180) to gas sensors containing a small amoun\nf a Class 8 (corrosive) material. You ask whether these articles are regulated under the HMR\nAccording to your letter, the sensors contain two electrodes separated by a thin layer of\nelectrolyte and connected by a low resistance external current. The electrolyte is contained\nwithin a matting to prevent the flow of liquid. The sensor produces a current from a chemical\nreaction on contact with the gas it is designed to detect. The current is proportional to the\nconcentration of the gas the sensor is designed to detect and can be measured across a load\nresistor in the external circuit. Gas diffusing into the sensor causes oxidation or reduction, which\ngenerates a low current that flows through the external circuit. You state that the electrolytes\nvary in the sensors; however, the Class 8 (corrosive) material (phosphoric or sulphuric acid)\nnever exceeds 1 milliliter and if the sensors are punctured, no corrosive liquid will flow from the\ndevices. You also state that there is no energy in the sensors when being transported and no risk\nof heat generation or sparking.\nIt is our determination that the hazardous material contained in the gas sensors, as described in\nyour letter, with no more than 1 milliliter of Class 8 (corrosive) material\n(phosphoric or sulphuric acid, is not transported in a quantity or form that poses a risk to\nhealth and safety or property during transportation. Therefore, the gas sensors are not subject to\nregulation under the HMR.\nI hope this information is helpful. If you have additional questions, please contact this office.\nSincerely,\nHattie L. Mitchell\nChief, Regulatory Review and Reinvention\nOffice of Hazardous Materials Standards\n173-136 6)\n070012\n\n<<<PAGE 2>>>\n\nMCIntyre\n$173136 (b)\nHMT ASSOCIATES, L.L.C.\nDefinitions\n603 KING ST.\n07-0012\nALEXANDRIA, VA 22314-3105\nSUITE 300\nE.A. ALTEMOS\n703-549-0727\nPATRICIA A. QUINN\nFACSIMILE: 703-549-0728\n(703) 549-0727, Ext. 11\nWRITER'S JIRECT DIAL NUMBER\nJanuary 17, 2007\nMr. Edward T. Mazzullo\nDirector, Office of Hazardous\nMaterials Standards (PHH-10)\nPipeline and Hazardous Materials\nSafety Administration\nDepartment of Transportation\nWashington, D.C. 20590-0001\nDear Mr. Mazzullo:\nPursuant to the provisions of 49 CFR 173.136(b), this is to request a determination that an\narticle containing a small amount of a Class 8 (corrosive) material is not subject to the requirements\nof the Hazardous Materials Regulations (\"HMR\", 49 CFR Parts 171-180) since in that quantity and\nform the corrosive material presents no hazard to health and safety or property in transportation.\nThe articles for which this determination is requested are gas sensors that operate on an\nelectrochemical principle. The sensors are used in a variety of applications to sense the presence of\nvarious gases at low concentrations in order to provide warning of the presence of the gas. The\nsensors are disk-shaped, typically with a diameter of approximately one inch, and a height of\napproximately 5/8 inch. Two or three metal pins extend an additional approximately 3/16 inch from\nthe bottom of the sensor to make electrical contact when the sensor is installed in an amplifier in the\ngas detector warning system.\nAs mentioned above, the sensors work on an electrochemical principle. The basic operation\nof these devices is as follows. Two electrodes are contained within the sensor - a \"sensing\" electrode\nand a \"counter\" electrode. These electrodes are separated by a thin layer of electrolyte, and are\nconnected by a low resistance external circuit. Gas diffusing into the sensor is reacted at the surface\nof the sensing electrode by oxidation or reduction, causing a current to flow through the external\n\n<<<PAGE 3>>>\n\nHMT ASSOCIATES, L.L.C.\nVir. Edward T. Mazzullo\nJanuary 17, 2007\nPage 2\ncircuit. This current is proportional to the concentration of the gas the sensor is designed to detect,\nand can be measured across a load resistor in the external circuit. The current generated is very low,\nand is never sufficient to pose any safety hazard. Thus, in terms of its construction and operation\nthe sensor similar in some respects to a battery - but rather than storing energy the sensor produces\na small current from chemical reaction on contact with the gas it is intended to detect. Since, unlike\na battery, there is no energy stored within the sensor when transported, the sensors pose no risk of\nheat generation or sparking as would a battery in the event of a short circuit.\nThe electrolyte in the sensor will vary depending on the gas the sensor is designed to detect.\nIn some cases, the electrolyte will be a Class 8 material (phosphoric acid or sulphuric acid).\nHowever, the quantity of corrosive electrolyte in any sensor does not exceed 1 rl. In addition, the\nelectrolyte is always contained within a matting (similar to the \"starved electrolyte\" system in many\nlarge batteries), so there is never any free liquid present. Therefore, if punctured, no corrosive liquid\nwill flow from the sensor. Based on the very small quantity of corrosive liquid in the sensors, and\nbecause there is no free liquid present and liquid will not flow from the device if punctured, the\nsensors are not considered to pose a risk to life, health or property during transport by any mode.\nTherefore, pursuant to the provisions of § 173.136(b) of the HMR, a determination is requested that\nthese sensors are not subject to the requirements of the HMR in transport.\nIt is noted that the requested determination would be fundamentally consistent with certain\nregulatory exceptions currently appearing in the HMR. For example, Special Provision 47 attached\nto the Hazardous Materials Table entry for \"Solids containing flammable liquid, n.o.s.\" (UN 3175),\nexcepts from regulation packets and articles containing up to 10 ml (ten times the quantity of\nhazardous material contained in the sensors for which this determination is sought) of flammable\nliquid in Packing Group II or Ill absorbed onto a solid material, provided there is no free liquid in\nthe packet or article. In addition, electric storage batteries (some of which may be very large and\ncontain relatively large quantities of electrolyte) in which the liquid electrolyte s contained in the\nsame sort of matting as the electrolyte in the sensors for which this determination is sought, have for\nmany years been excepted from regulation provided that there is no free electrolyte contained in the\nbattery and that electrolyte will not flow from the casing if it were ruptured. Any possible risk posed\nin transport by the sensors for which this determination is requested would most certainly not exceed\nthat posed by the packets, articles, and batteries currently excepted from regulation under the\nconditions described above.\n\n<<<PAGE 4>>>\n\nHMT ASSOCIATES, L.L.C.\nMr. Edward T. Mazzullo\nJanuary 17, 2007\nPage 3\nIn conclusion, owing to the very small quantity of hazardous material involved, and because\nthere is no free liquid present and liquid will not flow from the device if punctured, the gas sensors\nconcerned pose no hazard to health and safety or property under normal conditions of transport.\nAccordingly, it is requested that a determination be made pursuant to the provisions of § 173.136(b)\nthat the sensors described above are not subject to the requirements of the HMR in transportation.\nThank you for your consideration in this matter. Please do not hesitate to contact me if you\nhave questions concerning this request, or if you require additional information.\nSincerely,\ncact\nE. A. Altemos\nCC:\nDr. Charles Ke (PHH-21)\nGa: SensorLetter.wpd","truncated":false,"body_characters":8042}