[Sources of occupational exposure to ultrasonic noise]

Ultrasonic noise is defined as broadband noise containing high audible and low ultrasonic frequencies (from 10 kHz to 40 kHz). According to the most advanced knowledge, this type of noise exerts adverse effects on the hearing organ and the vestibular system. The aim of the study was to evaluate exposure to ultrasonic noise in occupational settings and to identify its essential sources.

The measurements of ultrasonic noise emitted by selected so called low frequency ultrasonic technological devices as well as grinders, circular saws, planers and processes, such as plasma-arc welding and air-acetylene welding, and others, were performed. The study concerned 233 workplaces, where the operators were supposed to be exposed to ultrasonic noise. The measurements were made under typical conditions of work and with reference to Polish standard PN-ISO 9612:2004.

The sound pressure levels in the 1/3-octave bands from 10 kHz to 25 kHz (sometimes up to 40 kHz) occurring at workplaces exceeded the admissible values for 8-h exposure (maximum admissible intensity (MAI) values for ultrasonic noise) in all investigated cases of ultrasonic lace sewing machines and cutters as well as in 75% of grinders, 59.5% of ultrasonic welders, 42.9% of ultrasonic washers, and 28.6% of saws and planers. Moreover, in the majority (83.3%) of ultrasonic lace sewing machines and in a large part (33.5%) of welders, the recorded sound levels exceeded the admissible values of maximum sound pressure levels (MAI) in 1/3-octave bands.

Our results indicate that ultrasonic welders and lace sewing machines are the major sources of occupational exposure to ultrasonic noise.