### Question
How is the "tier" defined?


### Answer
The term **tier** is defined in *6 U.S.C. § 621* as follows -

> given the term in section 27.105 of title 6, Code of Federal Regulations, or any successor thereto;

#### Citation:
  - *6 U.S.C. § 621*
  - Heading: **CHAPTER 1-HOMELAND SECURITY ORGANIZATION > SUBCHAPTER XVI-CHEMICAL FACILITY ANTI-TERRORISM STANDARDS**

