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

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