Hygienic Characteristics of the Acoustic Environment in the Mi-8 Helicopter Cabin

Introduction: The Mi-8 helicopter generates high-intensity broadband noises by its turboshaft engines whereas a comprehensive hygienic assessment of the acoustic environment in the helicopter cabin has not been conducted.

The purpose of the study was to assess the acoustic environment in the Mi-8 helicopter cabin.

Materials and methods: Acoustic measurements were carried out on the ground, inside the central cabin of the Mi-8 helicopter in three operating modes of the turboshaft engines: at startup, in the idle mode, and during cruise flight in the “right correction” mode. Measuring microphones were placed during the recording of the signal on a stand at the level of the human ear at six points located next to the reclining seats in the cabin. Acoustic indicators were measured using an SVAN-945A digital sound level meter and a GRAS 40AZ microphone. The collected data were processed in accordance with the requirements of sanitary and epidemiological rules, sanitary standards, and general tactical and technical requirements of the Air Force.

Results: Values of regulated noise indicators at the seats of the Mi-8 helicopter crew, sound pressure levels of the most significant tonal frequencies in its central compartment were measured. To establish the presence of tonal noise, a one-third octave analysis of the recorded acoustic signals was carried out. In the central compartment of the helicopter, the values of the regulated infrasound indices and the general sound pressure level were measured in the entire regulated frequency range. Discussion: It was found that the sound pressure levels in almost all sound octaves and the equivalent sound level in all operating modes of the helicopter engines exceed the permissible exposure limits while in the infrasound region they are within the normal range (except for the frequency of 16 Hz). Thus, the class of working conditions by noise corresponds to hazard class 3.3, and by infrasound – to class 2. According to the sanitary regulations, helicopter crews should use noise suppressors to protect themselves from high noise exposures through air and bone conduction.

Conclusion: The existing risks of developing a noise and infrasound-induced diseases necessitate constant monitoring of working conditions and health of the crews of Mi-8 helicopters.

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