Jack Conway asked about the law that has caused an enclosure to
be placed around the carousel organ at Santa Cruz Beach Boardwalk.
I found that both state and federal laws apply.

The federal law is OSHA's Occupational Noise Exposure Standard,
29 CFR 1910.95, "Occupational noise exposure", which says:

  1910.95(a) : Protection against the effects of noise exposure shall
  be provided when the sound levels exceed those shown in Table G-16
  when measured on the A scale of a standard sound level meter at slow
  response. ...

  1910.95(b)(1) : When employees are subjected to sound exceeding those
  listed in Table G-16, feasible administrative or engineering controls
  shall be utilized.

California's Occupational Safety Hazard Administration (Cal/OSHA) also
sets limits on noise exposure in the workplace:

  California Code of Regulations, Title 8,
  Section 5097. Hearing Conservation Program.
  Subchapter 7. General Industry Safety Orders
  Group 15. Occupational Noise
  Article 105. Control of Noise Exposure

  Para. 5095. General.  (a) Scope and Application. Article 105
  establishes requirements for controlling occupational exposures
  to noise. ...

  Para. 5097. Hearing Conservation Program. (a) General.  The employer
  shall administer a continuing, effective hearing conservation program,
  as described in this section, whenever employee noise exposures equal
  or exceed an 8-hour time-weighted average sound level (TWA) of 85
  decibels measured on the A-scale (slow response) or, equivalently,
  a dose of fifty percent.

Ref.:
http://www.dir.ca.gov/title8/5095.html
http://www.dir.ca.gov/title8/5097.html
http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9735

Robbie Rhodes
Etiwanda, Calif.