Joy 2007.

Methods	ITS
Participants	Coal mines Workplace measurements n = 142,735 USA Whole mining branch
Interventions	Introduction of new legislation in 1999 becoming effective in 2000: primacy of engineering and administrative controls, establishment of an Action Level of 85 dB(A), hearing conservation programme enrolment starting from 85 dB(A), introduction of statutory hearing loss of 25 dB average over 2, 3 and 4 kHz in either ear
Outcomes	Median of measurements of compliance with PEL, which includes all sound pressure levels from 90 dB(A) to 140 dB(A) with a doubling rate of 5 dB as an 8‐hour TWA
Notes	Outcomes for general noise levels and underground noise levels respectively: 1987: 61 and 65.8 dB, 1988: 55 and 65 dB, 1989: 62 and 63 dB, 1990: 63 and 65.4 dB, 1991: 59 and 69.4 dB, 1992: 54.2 and 73.4 dB, 1993: 63 and 74.9 dB, 1994: 67 and 76 dB, 1995: 58.9 and 68 dB, 1996: 60 and 69.3 dB, 1997: 56.5 and 73 dB, 1998: 48.8 and 74 dB, 1999: 57.1 and 78.2 dB, 2000: 31 and 63 dB, 2001: 23 and 54 dB, 2002: 22 and 50 dB, 2003: 20 and 52 dB, 2004: 20 and 50 dB