49 CFR §195.306

1. (a)Except as provided in paragraphs (b), (c), and (d) of this section, water must be used as the test medium.
2. (b)Except for offshore pipelines, liquid petroleum that does not vaporize rapidly may be used as the test medium if—
   1. (1)The entire pipeline section under test is outside of cities and other populated areas;
   2. (2)Each building within 300 feet (91 meters) of the test section is unoccupied while the test pressure is equal to or greater than a pressure which produces a hoop stress of 50 percent of specified minimum yield strength;
   3. (3)The test section is kept under surveillance by regular patrols during the test; and
   4. (4)Continuous communication is maintained along entire test section.
3. (c)Carbon dioxide pipelines may use inert gas or carbon dioxide as the test medium if—
   1. (1)The entire pipeline section under test is outside of cities and other populated areas;
   2. (2)Each building within 300 feet (91 meters) of the test section is unoccupied while the test pressure is equal to or greater than a pressure that produces a hoop stress of 50 percent of specified minimum yield strength;
   3. (3)The maximum hoop stress during the test does not exceed 80 percent of specified minimum yield strength;
   4. (4)Continuous communication is maintained along entire test section; and
   5. (5)The pipe involved is new pipe having a longitudinal joint factor of 1.00.
4. (d)Air or inert gas may be used as the test medium in low-stress pipelines.