Casella CEL Home page in the United Kingdom.

CEL Instruments Home page in the United States.

US Occupational Safety and Hygiene Administration (OSHA) Home page.
OSHA Regulations (Standards CFR-29) 1910-95 Occupational Noise Exposure.

US National Institute for Occupational Safety and Health (NIOSH) Home page.
NIOSH selected topics on Hearing and Noise and related information.

US Environmental Protection Agency (EPA) Home page.
EPA link to Historical collection summary on Noise Abatement and Control subjects.

US Federal Aviation Authority (FAA) Home page.

US American National Standards Institute (ANSI ) standards Home page.
List of ANSI Standards available for purchase.

List of ASTM Standards available for purchase regarding noise or sound topics.

International Electrotechnical Committee (IEC) Home page.
List of IEC documents available for purchase.

International Standards Organization (ISO) Home page.
 

Useful information and background reading Noise Pollution Clearinghouse  (NPC)
a voluntary web site with lots of useful information on all sorts of noise topics.