GLOSSARY OF TERMS AND ACRONYMS A B C D E F G H I J K L M N O P Q R S T U V W X Y Z H Hazard Ranking System (HRS) The Hazard Ranking System (HRS) is the principal tool EPA uses to place waste sites on the National Priorities List (NPL). It is a numerically based screening system that uses information from initial, limited investigations-the preliminary assessment and the site inspection-to assess the relative potential of sites posing a threat to human health or the environment. Hazardous Substance Research Centers (HSRC) The Hazardous Substance Research Centers (HSRC) oversees basic and applied research, technology transfer and training involving problems relating to hazardous substance management. These activities are conducted regionally by five multi-university centers, which focus on different aspects of hazardous substance management.