RSPA's hazardous liquid pipeline safety regulations do not apply to steel pipelines that operate at 20 percent or less of specified minimum yield strength (SMYS)..This final rule extends the regulations to three groups of these pipelines: pipelines that transport highly volatile liquids; pipelines or pipeline segments in populated areas, and pipelines or pipeline segments in navigable . waterways. Accidents have shown that regulating these pipelines or pipeline segments would be in the interest of public safety. Moreover, the Pipeline Safety.Act of 1992 provides that DOT may not exclude.hazardous-liquid . . pipelines from regulation based solely on operation at lowinternal stress. The final rle responds to this statutory prohibition and will reduce the risk that hazardous liquid pipelines present to public safety. and the environment.