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U.S. Department of Transportation U.S. Department of Transportation Icon United States Department of Transportation United States Department of Transportation

Interpretation Response #PI-79-010 ([Memo: Internal])

Below is the interpretation response detail and a list of regulations sections applicable to this response.

Interpretation Response Details

Response Publish Date:

Company Name: Memo: Internal

Individual Name:

Country: US

View the Interpretation Document

Response text:

Interpretation of Section 192.625(e)

Associate Director, OPSR, DMT-30

Chief, Southern Region, DMT-16

This responds to your memorandum of November 7, 1978, in which you ask for interpretations of
four different situations as they relate to the requirements of 49 CFR 192.625(e), "Equipment for
odorization must introduce the odorant without wide variation in the level of odorant."

These four situations are as follows:

  1. Given: A distribution operator having fairly constant seasonal flow rates at the point of
    odorization and possessing manufactured odorization equipment capable of measuring tank
    odorant levels at any time.

    Question: Is it mandatory to measure the volume of odorant passed into the system
    over a reasonable period (say 1 or 2 months) and divide this volume by the amount gas passed
    during the same approximate time period in order to calculate an odorant injection rate such that
    each succeeding rate can be compared to determine "variation?"

    Interpretation: Measuring the change in the odorant tank level and comparing the volume
    change with the corresponding gas sendout volume during similar time periods would be the most
    common method to determine the degree of variation in the level of odorant in the natural gas, but
    other available methods may be used including chemical analysis by use of titrators, or

  2. Given: The same situation as (1) above.

    Question: If item (1) is not mandatory is the following procedure acceptable? Taking
    periodic readings at various points on the gas system utilizing a properly functioning odorometer
    and these readings appear during succeeding time periods at an approximate gas concentration in
    air of 1/5 L.E.L.

    Interpretation: The suggested procedure would not be acceptable because some means of
    determining the odorant injection rate for the gas delivered into the system is mandatory under the
    requirements of §192.625(e). Determining that the concentration of gas in air at the odorization
    level is equal to or less than 1/5 L.E.L. is required by §192.625(f).

  3. Given: A distribution operation with wide fluctuations in gas flow (usually a small
    operator with a seasonal industrial load) having a buried tank without a volume level site gauge.

    Question: If situation in item (1) is mandatory and experience tells us that this
    procedure will usually show "wide variation" (i.e., rate calculation is technically impractical or
    inadequate), what could be done by the operator to meet this requirement?

    Interpretation: On odorizing equipment that is not equipped to measure the injection rate
    or the volume of odorant in the odorizer tanks, the tanks would at least have some means of
    indicating when they are full. An operator can determine the number of pounds of odorant
    required to fill the odorizer tanks and by reading the gas meter determine the quantity of gas used
    since the odorizer was last filled. From this, the pounds of odorant per million cubic feet of gas
    can be determined and compared with other periods. Filling of odorizers and reading of gas
    meters should be often enough to assure continuous odorization of gas delivered and should be
    done, in so far as is practicable, near the times when the system gas load characteristics are
    expected to change. These changes should be readily anticipated by operators having knowledge
    of the customer gas usage characteristics and at seasonal or other weather changes such as
    extreme cold weather.

  4. Given: All situations.
    1. Question: When the rate of odorant injection is measured, what variation would
      be allowed? In other words, if the malodorant manufacturer's suggested injection rate is, for
      example, 0.5#/MMCF, what range is acceptable (not "wide variation")?

    2. Question: If the odorometer procedure under item (2) above is allowed, what
      variation in succeeding readings would be allowed above or below 1/5 L.E.L.?

    1. Interpretation: The term "wide variation" relates to the odorant level necessary to
      assure leak detection. This level would depend upon the characteristics of the odorant being
      used. For instance tertiary-butyl-mercaptan (TBM) which is most commonly used, has a high
      impact on the olfactory system and with an excessively high injection rate will cause excess false
      leak complaints which causes the public to be less concerned when they do smell the odorant.
      Dimethyl sulphide has less impact on the olfactory senses but has a unique characteristic of
      reaching a plateau in its effect on the sense of smell. That is, although the addition of 3/4 to 1
      pound per MMCF may provide adequate odorization an operator would not have an "over
      odorization" problem until the injection is increased to 4 or 5 pounds per MMCF.

    2. Interpretation: The procedure described under item (2) above is not acceptable for
      compliance with §192.625(e). Under the requirements of §192.625(f) any readings of gas in air at
      greater than 1/5 L.E.L. would not be acceptable. No limit is set on the variation of readings so
      long as the gas is detectable at a concentration equal to or less than 1/5 L.E.L.

Cesar De Leon

Regulation Sections

Section Subject
192.625 Odorization of gas