Powerful sonar can pose risks to divers. Sonar, which stands for Sound Navigation and Ranging, utilizes sound waves to detect objects underwater. The potential for harm depends on specific conditions, including the sonar’s power and proximity to the diver.
How Sonar Works
Sonar systems operate by transmitting sound waves through water to detect objects. Active sonar, the type of concern for divers, sends out acoustic signals, often called “pings,” and listens for reflections or echoes. These systems use a transducer to convert electrical impulses into sound waves, which travel through water. When these sound waves encounter an object, they bounce back, and the transducer receives the returning echo, converting it back into an electrical signal for analysis.
Sound travels significantly faster in water than in air, at approximately 1500 meters per second compared to about 340 meters per second. This difference is due to water’s distinct mechanical properties and higher density. The speed of sound in water is influenced by temperature and pressure, which can affect how far sound waves travel.
Potential Effects on Divers
Powerful sonar can induce several physiological effects on divers, primarily through intense acoustic pressure waves. These waves create rapid pressure fluctuations that can damage tissues, particularly gas-filled organs such as the lungs, ears, and sinuses. This injury is known as barotrauma. High-intensity sonar vibrations can be akin to a shockwave.
Another mechanism of harm is cavitation, which involves the formation and violent collapse of microscopic gas bubbles within the body’s fluids due to pressure changes. The implosion of these bubbles generates high-energy shockwaves and localized heating, capable of damaging cells and tissues. At 200 decibels, these pressure waves can rupture a diver’s lungs, and at 210 decibels, they may cause brain hemorrhaging.
Divers exposed to intense sonar can also experience temporary or permanent hearing loss. The ear is particularly vulnerable to sudden, high pressures. Beyond physical damage, strong underwater vibrations can cause disorientation, dizziness, and nausea, making it difficult for a diver to manage buoyancy or ascend safely. Blurred vision and lightheadedness have also been reported.
Key Factors in Sonar’s Impact
The severity of sonar’s impact on a diver is determined by several variables. Sonar intensity, or power output, is a primary factor; higher power levels generate more destructive pressure waves. Military and research sonar systems typically have much higher power outputs than commercial or recreational sonar. For instance, some U.S. Navy sonar emitters can generate up to 235 decibel pressure waves.
The frequency of the sound waves also plays a role. Low-frequency sonar travels further and can penetrate tissues more deeply, potentially affecting internal organs. High-frequency sonar tends to have more localized, intense effects closer to the source.
Distance from the sonar source is a critical determinant of risk. The intensity of sound waves decreases rapidly with increasing distance from their origin. Even 300 meters away, a powerful sonar can still be very loud.
The duration of exposure to sonar transmissions also impacts the potential for accumulated damage. Longer exposure times, even to moderately intense sonar, can increase the risk of injury. A diver’s depth and position relative to the sonar beam also influence the effects, as being in the direct path of the beam increases risk, and depth can affect pressure on gas-filled spaces.
Assessing the Real Risks
While extremely powerful, close-range sonar could theoretically cause severe injury or death, actual fatalities or grave injuries from sonar are rare for recreational divers. Incidents involving harm typically relate to military or specialized high-power systems. For example, Australian Navy divers sustained minor injuries, including dizziness, headaches, and hearing damage, from a Chinese warship’s active sonar.
More common risks associated with powerful sonar exposure include temporary discomfort, disorientation, and mild barotrauma. The U.S. Navy Diving Manual provides guidelines for safe distances from transmitting sonar, especially for high-powered naval systems. Divers are advised to be aware of known sonar operations, such as military exercises, and maintain safe distances from vessels using powerful sonar. It is also recommended to listen for unusual underwater sounds and immediately suspend diving operations if pain is felt from an active sonar source. Low-power sonar used in commercial and fishing applications poses minimal to no risk to divers.