I have researched authoritative sources of information on noise level guidelines for office environments due to an issue we had after procuring a very high end computing unit that required more cooling than normal and the supplier had installed additional PC fans! I found 3 sources lised below. None of them are above 50dB(A). 1) BS8233:1999 –“Code of practice for sound insulation and noise reduction for buildings” recommends 40-45dB LAeq for private offices and small conference rooms, and 45-50dB LAeq for open-plan offices. 2) “Level of noise data”: Extract from 1995 American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbook, HVAC Applications, Chapter 43, Table 2.Admissible Maximum Levels of Noise:- Office Buildings 25-35 Executive and private offices 25-35 Conference rooms 25 (max) Teleconference rooms 30-40 Open plan offices 40-45 Circulation and public lobbies 40-50 Research, extensive telephone use, speech communication 35-45 Group teaching 25-35 Churches, mosques, synagogues Laboratories (with fume hoods) 45-55 Testing/research, minimal speech communication The values and ranges are based on judgement and experience, not on quantitative evaluations of human reactions. They represent general limits of acceptability for typical building occupancies. Higher or lower values may be appropriate and should be based on a careful analysis of economics, space usage, and user needs. They are not intended to serve by themselves as a basis for a contractual requirement 3) Australian Standard, AS 2107: Acoustics – Recommended Design Sound Levels and Reverberation Times for Building Interiors. For open plan offices the recommended levels are 40-45dB(A) There is interesting information from HP, in the form of “HP PCs and Acoustic Noise- Background information on PC noise, and its effect and measurement” http://www.quietpc.com/download/hp_white_paper.pdf