The federal government has designated four classifications for incidents at nuclear power plants. Each classification corresponds to the degree of seriousness of an incident. See: Sirens
Indian Point Energy Center (Safe, Secure, Vital), Emergency Preparedness Glossary, Buchanan, NY, USA 2015. http://www.safesecurevital.com/resources/emergency -preparedness-glossary.html, (Emr PrepNucl - Brit) {902}