Columbia subject headings:
Chemical plants--Security measures--Government policy--United States.
Chemical terrorism--Government policy--United States.
National security--Law and legislation--United States.
United States. Dept. of Homeland Security--Rules and practice.
Harvard subject headings:
Chemical plants--Security measures--Government policy--United States.
Chemical terrorism--Government policy--United States.
National security--Law and legislation--United States
United States. Department of Homeland Security--Rules and practice.
Princeton subject headings:
Chemical plants--Security measures--Government policy--United States.
Chemical terrorism--Government policy--United States.
National security--Law and legislation--United States.
United States. Department of Homeland Security--Rules and practice.