Eardrum Rupture – At What Pressure?

Ruptured eardrums are not uncommon, but when they occur, they are traumatic to the person involved.  However, there seems to be little knowledge among professionals working with the hearing impaired as to the actual pressure levels required to rupture the eardrum (tympanic membrane) even though they know that this can happen.

There are many causes of eardrum rupture.  They include, but are not limited to pressures from: middle ear problems, blasts, constant loud noises, and pressure from deep-water swimming.

A typical overpressure required to guarantee a rupture to an eardrum would be about 100,000 pascals, or 100 kPa, but rupture could occur at lower pressure levels as well.

Brief Anatomical Description of the Eardrum, and Eustachian Tube

A brief anatomical description of the eardrum is warranted in order to describe why an eardrum can rupture.  The eardrum (tympanic membrane) consists of three thin layers, with the outer and inner layers continuous with the tissues of the outer ear canal and the middle ear respectively.  The middle layer is fibrous, containing both radial and concentric features.  The tympanic membrane (TM) provides some protection to the middle and inner ears, but also receives sound vibrations from the outer ear and transmits them to the middle ear.

Biologically, the Eustachian tube must be considered in discussions of eardrum rupture.  This tube has elastic properties and extends from the nasopharynx (back of the throat) to the middle ear cavity.  It is normally closed, but opens to equalize air pressure on both sides of the TM, and also to provide an oxygen supply to the middle ear to help “dry up” some of the mucous that is generated in the middle ear by its mucous membrane lining, the same mucous membrane that lines the oral cavity.

It also allows for drainage of normal and diseased middle ear secretions from the middle ear cavity into the nasopharynx.  It normally dilates during yawning, swallowing, shouting loudly, chewing, etc.  However, when it does not dilate naturally (blocked by an infection, cold, allergy, or scarring), air can no longer enter or leave the middle ear cavity.  As a result, either positive or negative middle ear pressure can result from no pressure equalization or to a buildup of fluids in the middle ear, the latter of which, when great enough, can lead to ruptured and bleeding TMs.

How Much Pressure Needed to Rupture Eardrum?

Because the TM is so thin, it can be ruptured or punctured.  One of the ways in which it can be ruptured from the outside is by excessive pressure occurring so rapidly that the Eustachian tube cannot manage the pressure equalization.

Pressure: Force per unit area applied on a surface in the perpendicular direction.  The pressure equation is:

Pressure is measured in pascals (Pa).  A pascal is equal to a newton per square meter [Pa = N/m²].  To relate this to something most people would understand, this would translate to 0.00014 psi (pounds per square inch), a very small pressure – too small for reasonable use.  As a result, the pascal is used, where 100 pascals equals 0.01 psi – still a very low value, but something that one can somewhat get a handle on, especially if one can relate this to tire pressures.  And, because numbers related to the pressures in pascals become so large, it is convenient to relate the pressures in kPa, where 100 pascals is equal to 0.1 kPa.

The tympanic membrane can actually tolerate fairly high pressures, but do reach a level where the amount of pressure can no longer be tolerated.  The eardrum may rupture at pressures above 35,000 pascals (35 kPa, or 5.08 psi) but is normally at higher levels, closer to 100,000 pascals (100 kPa or 14.5 psi).

Ear Drum Rupture Expectations

Water

• 17 kPa (120 mmHg) in about 1.7 to 5.3 ft. of water¹

Differential Pressure

• 20 kPa (2.9 psi) – overpressure required to produce minor, moderate, and major eardrum ruptures²
• 35 kPa (5.1 psi) – May rupture ^3,4,5
• 35-69 kPa (5.1-10.0 psi) – General rupture expectation range⁶
• 100 kPa (14.5 psi) – Almost all will rupture ^3,5

Injuries from Blast Waves

Caused by exposure to high pressures with very short rise times.  Examples:

• 6.9 kPa – TTS – Could result with an overpressure (1.0 psi)⁴
• 35 kPa – injuries from blast waves to high pressure exposure could occur (5.1 psi)^7,8

Used widely as rupture threshold in blast criteria:

• 100 kPa – psi rupture rate increases to 50% (14.5 kPa)²
• Almost all rupture at 100 kPa (14.5 psi)
  • 50% rupture probability – 6.3 psi
  • 90% rupture probability – 12.2 psi
• 100 kPa – 50% probability – 14.5 psi^4,8
• 103 kPa – median overpressure – 14.9 psi

References:

1. Cameron, Skofronick, Grant. Physics of the Body.  Medical Physics Publishing, 1992, 1996:123.
2. Richmond, D.; Yelverton, J.; Fletcher, E.; Philips, Y.  Physical correlates of eardrum rupture.  Annals of Otology, Rhinology, and Laryngology, Vol. 109, May 1989: 35-41
3. Stewart, C. Blast Injuries: Preparing for the Inevitable.  Emergency Medical Practice. Vol. 8 No. 4, April 2006.
4. Beveridge, A. Forensic Investigation of Explosions.  Boca Raton.  CRC Press, 1998: Page 41
5. Stewart, C. Blast Injuries.  Colorado Springs: Charles Stewart & Associates, 2006: Page 33
6. Fraser, T.M. The Worker at Work: A Textbook Concerned with Men and Women in the Workplace.  CRC Press: 323.
7. Alt, L.; Dorcino, D., and Walker, R.  Medical Consequences of Nuclear Warfare.  Office of the Surgeon General Department of the Army, United States of America, 1989: 7
8. Richmond, D.; Yelverton, J.; Fletcher, E.; Phillips, Y.  Physical correlates of eardrum rupture.  New Mexico: Division of Life Sciences, Los Alamos National Laboratory, 1989: Page 140: 35-41
9. Lee.  Chapter 17.  URS Corporation. Guidance Protocol for School Site Pipeline Risk Analysis.  Austin: URS Corporation, 2007: A-1, Page 237
10. Gesswein, J.; Corrao, P.  The Position of Eardrum Rupture and Hearing Loss in the Scale of Injuries From Nuclear Blast.  Bethesda: Naval Ship research and Development Center, 1972: Page 36

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