This International Standard specifies an engineering method for measuring workers' exposure to noise in a working environment and calculating the noise exposure level. This standard describes three different strategies for measurement. This method will be useful where a determination of noise exposure to engineering precision grade is required, for example, for detailed noise exposure studies or epidemiological studies in to the cause of hearing damage or other adverse effects. The measuring process requires observation and analysis of the noise exposure conditions so that the quality of the measurements can be controlled. This International Standard provides methods for estimating the uncertainty of the results. This International Standard is not intended for assessment of masking of oral communication or assessment of infrasound, ultrasound and non-auditory effects of noise. It does not apply to the measurement of the noise exposure of the protected ear when hearing protectors are worn. Results of the measurements performed in accordance with this International Standard may provide useful information when defining priorities for noise control measures.