In the U.S., the Occupational Safety and Health Administration requires that SDSs be readily available to all employees for potentially harmful substances handled in the workplace under the Hazard Communication regulation. The SDS is also required to be made available to local fire departments and local and state emergency planning officials under Section 311 of the Emergency Planning and Community Right-to-Know Act. The American Chemical Society defines Chemical Abstracts Service Registry Numbers (CAS numbers) which provide a unique number for each chemical and are also used internationally in SDSs.