This paper addresses the following question: Are the hazardous materials pipeline incidents non-randomly time distributed? Our analysis suggests that they are correlated, which means that a hazardous materials pipeline incident is not independent from the time elapsed since the previous event. That is, our statistical tests suggest that previous accident counts correlate with future counts. But, if we consider incidents with a large severity index (spills and property damage), the phenomenon is unpredictable, since it approaches a Poissonian process (random, independent and uncorrelated). (c) 2008 Elsevier B.V. All Fights reserved.