4.1 Federal regulations (49 CFR Part 192.625) state: “A combustible gas in a distribution line must contain a natural odorant or be odorized so that at a concentration in air of one-fifth of the lower explosive limit, the gas is readily detectable by a person with a normal sense of smell.” These regulations state further that “To assure the proper concentration of odorant with this section, each operator must conduct periodic sampling of combustible gases using an instrument capable of determining the percentage of gas in air at which the odor becomes readily detectable.” Additionally, a number of states have enacted legislation that requires natural gas to be odorized so that it is detectable at concentrations less than one fifth of the lower explosive limit. See Note 1. While regulations do not specify the exact method for determining compliance, it has been documented that compliance testing must be olfactory in nature.4

Note 1: For example, Massachusetts Section 192.625 MFS Standards requires that “... a concentration of fifteen hundredths of one percent gas in the air is readily perceptible to the normal or average olfactory senses of a person...”

4.2 This test method covers procedures to measure the odor level of natural gas by way of olfactory determination. No direct correlation may be ascertained between this test method and those methods available or under development that quantitatively measure the concentration of sulfur compounds in natural gas.

4.3 This test method outlines general procedures to measure the odor detection levels of natural gas. It is the responsibility of persons using this test method to develop and maintain equipment and specific operating procedures to ensure public safety and compliance with all appropriate regulations.

1.1 This test method covers the procedures for determining the threshold detection level, readily detectable level, and odor intensity of natural gas using instruments that dilute and mix the sampled natural gas with air. The mixed gas stream is then sniffed by the operator for the purpose of determining any of these parameters for odorant in a natural gas stream.

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.