Opening your mouth during an explosion is a common, yet seemingly counterintuitive, safety recommendation. This action has a scientific basis in protecting the delicate structures within the ear. Understanding the forces at play during an explosion and the ear’s anatomy reveals why this simple measure can be effective.
The Force of an Explosion
An explosion involves the rapid release of energy, generating a sudden, high-pressure wave that moves outward from the source. This phenomenon creates a blast wave, also known as a shockwave or overpressure wave, which travels through the air at supersonic speeds. This wave is characterized by a swift rise in pressure, followed by a negative pressure phase before returning to normal atmospheric pressure.
The force carried by this blast wave can be substantial, capable of causing significant damage. The intensity of the blast wave and its potential for injury depend on factors including peak pressure, duration of overpressure, and distance from the detonation point. For instance, a blast overpressure of just 5 pounds per square inch (psi) can rupture eardrums in about 1% of individuals, while 45 psi can affect 99% of subjects.
Why Ears Are Vulnerable
The human ear contains a delicate structure called the eardrum, or tympanic membrane, which is highly susceptible to sudden and extreme pressure changes. This thin membrane separates the outer ear from the middle ear and vibrates to transmit sound waves. Its design for subtle sound vibrations makes it fragile when confronted with the immense force of a blast wave.
When a blast wave hits the ear, it creates a rapid and significant pressure differential between the outside of the eardrum and the air within the middle ear. This unequal pressure can cause the eardrum to bulge inward violently. Such a forceful displacement can lead to barotrauma, which is physical damage to body tissues caused by differences in pressure. A ruptured eardrum is a common outcome of blast exposure and can result in hearing loss, ringing in the ears (tinnitus), or dizziness.
How Opening Your Mouth Helps
Opening your mouth during an explosion helps mitigate potential ear damage by allowing for pressure equalization. The middle ear is connected to the back of the throat by a narrow passage called the Eustachian tube. This tube normally remains closed but opens to allow air to enter or leave the middle ear, balancing pressure on both sides of the eardrum.
When an explosion generates a sudden pressure increase, opening the mouth creates an additional pathway for this pressure to enter the body’s air-filled cavities, including the Eustachian tubes. This allows the incoming blast wave to reach the middle ear more readily, helping to equalize the pressure on both the outer and inner surfaces of the eardrum. By doing so, the eardrum is less likely to experience the extreme inward force that can lead to rupture. While this action helps balance the pressure, it does not entirely eliminate the risk of injury, especially from very powerful blasts.
Other Protective Actions
Beyond opening your mouth, several other immediate actions offer protection during an explosion. Seek cover under sturdy objects like tables or desks to shield from flying debris and glass. If no cover is available, drop to the ground and cover your head and neck with your arms. Move away from windows or anything that could shatter.
If indoors, avoid elevators and use stairs for evacuation, as elevators may become inoperable. After the immediate effects subside, evacuate the area and move upwind to avoid toxic fumes. Remaining low to the ground can also help if smoke is present.