Once the field data has been collected from the instantaneous noise survey, octave band analysis (if completed), noise dosimetry, and time-motion study, it is time to piece the information together to obtain a picture of the noisy environment and how these measurements compare to MSHA standards.
Instantaneous Noise Survey
This data provides information as to which equipment and areas exceed 115 dBA. Immediate action is required in areas or with equipment exceeding 115 dBA. Immediate noise controls need to be implemented as MSHA standards do not allow for exposure to personnel at this level for any period of time. If controls are not possible or feasible, a variance needs to be filed with MSHA and steps need to be taken for redesign of the area/equipment.
The instantaneous noise survey will also allow for the industrial hygienist/safety professional to establish hazardous noise areas (delineated by signage and often by painted lines on the concrete flooring) to visually identify areas in which any personnel (even passers by) must wear hearing protection. The hazardous noise areas should be established for equipment/areas with noise levels of 85 dBA sustained (i.e., when the equipment is in operation).
Octave Band Analysis
While not required for routine noise monitoring, these measurements are essential for the definition of noise sources in terms of operating frequency or spectrum and for design of noise controls. Equipment operating at noise frequencies of 500 Hz and higher (500 Hz - 16,000 Hz) are believed to have an increased effect on personal hearing loss compared to equipment operating at lower frequencies. Further, certain noise controls are efficient for high or low frequencies, respectively.
TWA8 and % Dose measurements collected from noise dosimetry are compared directly to the MSHA permissible exposure limit of 90 dBA TWA8 (i.e., 100% dose) and the action level 85 dBA TWA8 (i.e., 50% dose). These measurements are the basis for MSHA compliance and dictate the mine operator's responsibilites under the regulation.
This study, while not required by MSHA is certainly helpful to discern what tasks, processes, and equipment contriubte the most to the personal exposure. It allows industrial hygienists and safety professional to provide recommendations on which processes and which equipment should be evaluated for noise controls or adminsitrative controls with respect to measured results.