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Two people wearing behind-the-neck earmuffs. Thermal earmuffs are worn for protection from the cold. Because the ears extend from the sides of the head to gather sound waves, they have a high skin surface-area-to-volume ratio, and very little muscle tissue, causing them to be one of the first body parts to become uncomfortably cold as temperatures drop.
Mine Safety and Health Administration (1999; 30 CFR Part 62) [57] provides similar regulations as OSHA (above), but further requires simultaneous use of both earplugs and earmuffs when exposure levels exceed a time-weighted average of 105 dB-A. U.S. Department of Defense (2004; Instruction 6055.12, Hearing Conservation Program, March 5, 2004) [58]
Hearing protector fit-testing is a method that measures the degree of noise reduction obtained from an individual wearing a particular hearing protection device (HPD) - for example, a noise canceling earplug or earmuff. Fit testing is necessary due to the fact that noise attenuation varies across individuals.
The Pennsylvania Manual (PDF). Vol. 116. Harrisburg: Pennsylvania Department of General Services. ISBN 0-8182-0285-8. Archived from the original (PDF) on October 1, 2011. Schehr, Elizabeth, ed. (2005). The Pennsylvania Manual (PDF). Vol. 117. Harrisburg: Pennsylvania Department of General Services. Archived from the original (PDF) on June 28, 2009.
Active ear protection (electronic pass-through hearing protection devices or EPHPs) electronically filter out noises of specific frequencies or decibels while allowing the remaining noise to pass through. [99] A personal attenuation rating can be objectively and subjectively measured by using a hearing protection fit testing system. [101]
Sams Publishing was founded in 1946 by Howard W. Sams, originally producing radio schematics and repair manuals. It was acquired by ITT in 1967. ITT sold its publishing division in 1985 to Macmillan. In 1987, Sams was split into three divisions with the computer book division transferred to what later became Macmillan Computer Publishing.
Most user guides contain both a written guide and associated images. In the case of computer applications, it is usual to include screenshots of the human-machine interface(s), and hardware manuals often include clear, simplified diagrams. The language used is matched to the intended audience, with jargon kept to a minimum or explained thoroughly.
A public address system (or PA system) is an electronic system comprising microphones, amplifiers, loudspeakers, and related equipment. It increases the apparent volume (loudness) of a human voice, musical instrument, or other acoustic sound source or recorded sound or music.