National Toxic Substance Incidents Program Case Definition

Incident data are collected about a spill or air release if the incident fits the following definition:

  • an uncontrolled or illegal acute release of any toxic substance. A release is defined as acute if it lasts less than 72 hours. A substance is considered toxic if it can reasonably be expected to cause an adverse human health effect(s) due to its properties or based on scientific literature.

Releases must also meet predetermined quantity criteria based on the substance. For most substances, the inclusion quantity is one gallon or ten pounds. Additional information on the chemical inclusion criteria and the mandatory chemical reporting list is available by contacting program staff.

As the surveillance system transitioned from the Hazardous Substances Emergency Events Surveillance (HSEES) program to NTSIP in 2010, the Agency for Toxic Substances and Disease Registry implemented changes in the case definition. For example, the HSEES program collected data on threatened events (no chemical actually released) if a public health action, such an evacuation or road closure, occurred. NTSIP does not. Also, HSEES did not collect data about any incident that involved only a petroleum product. NTSIP does collect these data if there are public health consequences, such as injuries or evacuations.

The historical HSEES webpage contains reports, fact sheets, brochures and articles published in journals, magazines and newsletters.