services for payload developers. The laboratory tested purchased sound sources individually and then built them into larger systems, using noise modeling to predict the noise emission output of the complete system. The noise emission of each payload and system had to be test-verified in the anechoic chamber prior to launch. When systems do not meet noise emission standards, they have to be retrofitted for noise control, often in-orbit, which is expensive and time consuming.
For ground-based noise exposure, she continued, NASA’s program is similar to those of many companies in the private sector, where the primary motivation is prevention of noise-induced hearing loss. Managing occupational noise exposure requires a multidisciplinary program that includes noise exposure monitoring, noise control engineering, and audiometric monitoring, to name just a few elements. The NASA program maintains requirements that are more stringent than those of the Occupational Safety and Health Administration (OSHA): NASA has adopted the “85/3” criterion,8 which consists of a maximum noise exposure limit of 85 decibels (dB) using A-frequency weighting averaged over an 8-hour workday, using a 3 dB exchange rate. Anyone exposed to noise above 85 dBA is required to wear personal protective equipment. Every three years, internal NASA site audits check for policy compliance. Many professional associations, including the National Hearing Conservation Association,9 have been promoting similar standards for many years because OSHA’s more liberal noise emission limit of 90 dBA time-weighted average (TWA), using a 5 dB exchange rate, is not considered to be very protective, according to Cooper.
Creating a low-noise workplace goes a step beyond providing personal hearing protection. Reducing noise greatly lowers the risk of hearing loss and the costs associated with noise, including the costs of maintaining a hearing conservation program and of hearing loss claims, in addition to improving communication and concentration by developing a more productive and comfortable work environment (Nelson 2012).
The NASA Buy-Quiet program and its newer sister program Quiet by Design are built around controlling noise emission rather than worker exposure to noise, Cooper explained (Cooper 2010). The purchaser issues a noise specification and the manufacturer is responsible for designing equipment to meet the specification. The standards are subject
8 For more information, see www.hearingconservation.org/displaycommon.cfm?an=1&subarticlenbr=142.