Ultrasonic itself has no radiation. It has good direction, strong penetration, can obtain more concentrated sound energy, and can spread far in water. When using the ultrasound welding machine at ordinary times, you need to wear earplugs, otherwise working for a long time will affect your hearing.

For industrial ultrasonic, such as ultrasonic welding and ultrasonic cleaning, it is also necessary to combine the ultrasonic frequency and sound intensity. In many cases, the exposure time and medium coupling should be considered (for example, if there is water between human and sound source, the sound intensity of ultrasonic will be dangerous). In a word, low-frequency ultrasound (about 20kHz) needs to be protected by earmuffs. Although it is harmless in theory, it sounds disturbing.

At present, there is no exact report that airborne ultrasound can cause hearing damage, but there are some subjective discomfort, such as headache, ear discomfort and so on. Even so, the subharmonics caused by ultrasound can still cause damage to hearing under sufficient sound intensity.

Therefore, the industry has clear standards to limit the intensity of ultrasound. Compared with high-frequency ultrasound, the intensity requirements for low-frequency (about 20kHz) ultrasound are more strict, because some people may still hear the sound of this frequency. At present, the most relaxed standard is revised by the American Government Industrial Health Association in the early 21st century. For 20kHz ultrasound, the maximum allowable sound intensity is 135db, while when exposed for 8 hours, only 94db is allowed. For high-frequency ultrasound, this standard will be relaxed appropriately. If there is liquid coupling between human and sound source, it must be reduced by 30dB in this standard.