{"operation":"document","citation":"PI-79-010","title":"Memo: Internal — Pipeline Safety Interpretation","source_type":"guidance","agency":"Pipeline and Hazardous Materials Safety Administration","status":"guidance","official":true,"published_on":"1979-03-23","effective_on":null,"summary":"PI-79-010 response to Memo: Internal concerning 192.625.","machine_formats":{"json":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-79-010.json","markdown":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-79-010.md"},"app_url":"https://regulus.evalyn.ai/document/phmsa-interpretation-pi-79-010","source_url":"https://www.phmsa.dot.gov/sites/phmsa.dot.gov/files/legacy/interpretations/Interpretation%20Files/Pipeline/1979/PI79010.pdf","body":"<<<PAGE 1>>>\n\nInterpretation of Section 192.625(e)\nAssociate Director, OPSR, DMT-30\nChief, Southern Region, DMT-16\nThis responds to your memorandum of November 7, 1978, in which you ask for interpretations of\nfour different situations as they relate to the requirements of 49 CFR 192.625(e), \"Equipment for\nodorization must introduce the odorant without wide variation in the level of odorant.\"\nThese four situations are as follows:\n(1) Given: A distribution operator having fairly constant seasonal flow rates at the point of\nodorization and possessing manufactured odorization equipment capable of measuring tank\nodorant levels at any time.\nQuestion: Is it mandatory to measure the volume of odorant passed into the system\nover a reasonable period (say 1 or 2 months) and divide this volume by the amount gas passed\nduring the same approximate time period in order to calculate an odorant injection rate such that\neach succeeding rate can be compared to determine \"variation?\"\nInterpretation: Measuring the change in the odorant tank level and comparing the volume\nchange with the corresponding gas sendout volume during similar time periods would be the most\ncommon method to determine the degree of variation in the level of odorant in the natural gas, but\nother available methods may be used including chemical analysis by use of titrators, or\nspectrography.\n(2) Given: The same situation as (1) above.\nQuestion: If item (1) is not mandatory is the following procedure acceptable? Taking\nperiodic readings at various points on the gas system utilizing a properly functioning odorometer\nand these readings appear during succeeding time periods at an approximate gas concentration in\nair of 1/5 L.E.L.\nInterpretation: The suggested procedure would not be acceptable because some means of\ndetermining the odorant injection rate for the gas delivered into the system is mandatory under the\nrequirements of §192.625(e). Determining that the concentration of gas in air at the odorization\nlevel is equal to or less than 1/5 L.E.L. is required by §192.625(f).\nGiven: A distribution operation with wide fluctuations in gas flow (usually a small\noperator with a seasonal industrial load) having a buried tank without a volume level site gauge.\nDB\nC:\\WP51\\INTERPRT\\192\\625\\79-03-23\n1\n\n<<<PAGE 2>>>\n\nQuestion: If situation in item (1) is mandatory and experience tells us that this\nprocedure will usually show \"wide variation\" (i.e., rate calculation is technically impractical or\ninadequate), what could be done by the operator to meet this requirement?\nInterpretation: On odorizing equipment that is not equipped to measure the injection rate\nor the volume of odorant in the odorizer tanks, the tanks would at least have some means of\nindicating when they are full. An operator can determine the number of pounds of odorant\nrequired to fill the odorizer tanks and by reading the gas meter determine the quantity of gas used\nsince the odorizer was last filled. From this, the pounds of odorant per million cubic feet of gas\ncan be determined and compared with other periods. Filling of odorizers and reading of gas\nmeters should be often enough to assure continuous odorization of gas delivered and should be\ndone, in so far as is practicable, near the times when the system gas load characteristics are\nexpected to change. These changes should be readily anticipated by operators having knowledge\nof the customer gas usage characteristics and at seasonal or other weather changes such as\nextreme cold weather.\n(4) Given: All situations.\nQuestion: (a) When the rate of odorant injection is measured, what variation would\nbe allowed? In other words, if the malodorant manufacturer's suggested injection rate is, for\nexample, 0.5#/MMCF, what range is acceptable (not \"wide variation\")?\nQuestion: (b) If the odorometer procedure under item (2) above is allowed, what\nvariation in succeeding readings would be allowed above or below 1/5 L.E.L.?\nInterpretation: (a) The term \"wide variation\" relates to the odorant level necessary to\nassure leak detection. This level would depend upon the characteristics of the odorant being\nused. For instance tertiary-butyl-mercaptan (TBM) which is most commonly used, has a high\nimpact on the olfactory system and with an excessively high injection rate will cause excess false\nleak complaints which causes the public to be less concerned when they do smell the odorant.\nDimethyl sulphide has less impact on the olfactory senses but has a unique characteristic of\nreaching a plateau in its effect on the sense of smell. That is, although the addition of 3/4 to 1\npound per MMCF may provide adequate odorization an operator would not have an \"over\nodorization\" problem until the injection is increased to 4 or 5 pounds per MMCF.\nInterpretation: (b) The procedure described under item (2) above is not acceptable for\ncompliance with §192.625(e). Under the requirements of §192.625(f) any readings of gas in air at\ngreater than 1/5 L.E.L. would not be acceptable. No limit is set on the variation of readings so\nlong as the gas is detectable at a concentration equal to or less than 1/5 L.E.L.\nCesar De Leon\nDB\nC:\\WP51\\INTERPRT\\192\\625\\79-03-23\n2","truncated":false,"body_characters":5171}