We know that sonar poses a danger to whales and dolphins, but how do the pulses affect humans under water? Australian naval divers had an unwanted taste of the experience this week after a Chinese destroyer ignored their ship’s diver-down warnings.
Australia’s defence minister and deputy prime minister Richard Marles launched a tirade against the Chinese government, calling the conduct of its People’s Liberation Army-Navy destroyer Ningbo “unsafe and unprofessional”.
The incident occurred on 14 November, while the Royal Australian Navy frigate HMAS Toowoomba was in international waters in Japan’s Exclusive Economic Zone. After conducting operations in support of UN sanctions enforcement, it had been heading for a Japanese port on a scheduled visit.
Fishing-nets then became entangled around the 116m frigate’s propellers, so it stopped to enable divers to remove them. “At all times, HMAS Toowoomba communicated its intention to conduct diving operations on normal maritime channels, and using internationally recognised signals,” stated the minister.
Forced to exit the water
While the diving operations were underway Ningbo, which had been in the vicinity, approached Toowoomba. The frigate’s crew reminded the Chinese vessel that diving was underway and asked that it keep clear.
Ningbo acknowledged receiving Toowoomba’s communications but maintained its approach. Soon afterwards, it was detected operating its hull-mounted sonar “in a manner that posed a risk to the safety of the Australian divers, who were forced to exit the water”.
The divers were medically assessed and found to have sustained minor injuries. This was considered “likely due to being subjected to the sonar pulses from the Chinese destroyer”.
“Defence has for decades undertaken maritime surveillance activities in the region and does so in accordance with international law, exercising the right to freedom of navigation and overflight in international waters and airspace,” stated Marles.
According to the UK’s Diving Medical Advisory Committee, divers exposed to sonar transmissions can suffer from dizziness, hearing damage or other injuries to other sensitive organs, depending on the frequency and intensity of the sound.
“This may include neurological symptoms such as blurred vision, light-headedness, vibratory sensations in hands, arms and legs, and tremors in upper extremities,” it says. “The single most important criterion related to diver safety resulting from low-frequency sonar is that of disorientation due to vestibular stimulation.”
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