(a) Allowable concentration. The gas distributed by each company shall contain no quantity of hydrogen sulfide greater than that permitted by subdivision (b) of this section.
(b) Equipment and testing procedure.
(1) Each company shall provide each of its testing stations required by section 229.50 of this Part with equipment for the qualitative determination of the hydrogen sulfide content of gas fully complying with the provisions of this Part. In each instance of evidence of or doubt or difference of opinion regarding the presence of hydrogen sulfide in the distributed gas, or where directed by this commission, the company shall provide said testing stations with equipment for the quantitative determination of the hydrogen sulfide content of gas fully complying and maintained in full compliance with the provisions of paragraphs 65 through 87 of the relevant effective code of the American Petroleum Institute, the presently effective code being entitled "Recommended Practice for Measuring, Sampling, and Testing Natural Gas (RP 50A, Third Edition)" (the presently effective code hereinafter referred to as APIRP 50 A).
(2) Each company shall make all of the determinations of the hydrogen sulfide content of the distributed gas required by subdivision (c) of this section in full compliance with the following procedure and record the results thereof:
A strip of white filter paper moistened with a fresh solution containing five percent by weight of lead acetate shall be exposed to the distributed gas for one minute in a previously purged apparatus, fully complying and maintained in full compliance with the form recommended therefor by the second edition of Circular 48 of the National Bureau of Standards entitled "Standard Methods of Gas Testing" (hereinafter referred to as NBS C 48), through which the gas flows at a rate of approximately five cubic feet per hour. The gas shall not directly impinge upon the test strip during the test. At the end of the stated time, the test strip thus exposed shall be compared with a second test strip similarly prepared but not exposed to the gas. If the exposed strip is ascertained to be not noticeably darker than the comparison strip, the gas shall be considered to be free of hydrogen sulfide. If the exposed strip is ascertained to be noticeably darker than the comparison strip or if there is any doubt or difference of opinion regarding the color of the exposed strip, the gas shall be quantitatively tested for hydrogen sulfide in full compliance with the provisions of APIRP 50 A.
(c) Required tests. Each company shall make and record the results of one daily test of the hydrogen sulfide content of the distributed gas on each of not less than five days per calendar week at each of its testing stations required by subdivisions (a) through (d) of section 229.50 of this Part, except that, where there is evidence of the presence of hydrogen sulfide in said gas, three such tests shall be made daily at intervals of not less than three hours until said tests indicate the continued absence of hydrogen sulfide in the gas for a period of at least one week. At a testing station testing distributed gas obtained from a company's standby source, said company need not make a test of the hydrogen sulfide content of said gas during any day that the gas is obtained from said standby source for a total of less than one hour.