A sonic boom is a powerful event that produces startling noise. While often associated with a single loud explosion, it is a continuous physical event generated by objects moving faster than the speed of sound. Direct harm to humans from a sonic boom is rare, but its indirect effects and the physical forces involved warrant understanding.
Understanding Sonic Booms
A sonic boom occurs when an object, typically an aircraft, travels through the air faster than the speed of sound, which is approximately 767 miles per hour at sea level. As the object moves, it continuously generates pressure waves. When it exceeds the speed of sound, these waves coalesce and form shock waves, much like the wake created by a boat in water.
These shock waves form a cone of pressurized air molecules that propagate outward and rearward from the object. The sound heard on the ground is the sudden onset and release of this pressure as the shock wave passes an observer. A sonic boom is a continuous pressure wave that trails the supersonic object, creating a “boom carpet” along its flight path. The intensity and width of this boom carpet depend on factors such as the aircraft’s size, shape, altitude, and atmospheric conditions.
Direct Human Impact
The direct physiological effects of a sonic boom on humans primarily involve startle responses and temporary auditory impacts. A typical sonic boom generated by an aircraft produces a peak overpressure ranging from less than one pound per square foot (psf) to about 10 psf. This pressure change is comparable to what one might experience in an elevator descending a few floors, but it occurs over a much shorter duration. While the sound can be intense, often registering around 110 to 140 decibels (dB), similar to a thunderclap, direct harm from the pressure wave itself is highly improbable.
For context, eardrum rupture typically requires a pressure differential of about 720 psf. Lung damage, a more severe internal injury, would necessitate even higher overpressures, around 2,160 psf. The strongest sonic boom ever recorded, at 144 psf, did not cause injury to the exposed researchers. Such extreme pressure levels are rarely encountered during a typical sonic boom event due to energy dissipation over distance and regulations restricting supersonic flight over populated areas.
Collateral Damage and Indirect Hazards
While direct physical harm from a sonic boom is uncommon, the sudden pressure change can lead to indirect hazards. One notable effect is potential damage to structures. Buildings in good repair are generally unaffected by typical sonic booms below 16 psf, but pressures between 2 and 5 psf can cause minor damage, such as cracked glass or plaster. Repeated exposure to booms can also lead to cumulative stress on building foundations.
The intense noise and pressure can also dislodge objects or cause them to fall from shelves, creating a risk of injury. The startling nature of a sonic boom, comparable to a loud explosion, can lead to a sudden startle response in individuals. This involuntary reaction could, in rare circumstances, result in accidents such as falls, particularly for the elderly. These secondary effects, rather than the direct impact of the pressure wave, represent the primary ways a sonic boom could indirectly contribute to injury.