A deep sea diver may hurt his ear drum during diving because of

A deep sea diver may hurt their eardrum due to high water pressure, a condition medically known as middle ear barotrauma [2]. As a diver descends, the ambient hydrostatic pressure increases by 1 atmosphere for every 10 meters of depth. This increasing external pressure creates a pressure differential across the eardrum (tympanic membrane) [1]. If the diver fails to equalize the pressure in the middle ear space with the external environment, the eardrum is pushed inward, leading to pain, fluid accumulation, or rupture [1]. While atmospheric pressure exists at the surface, the primary force acting on a diver underwater is the weight of the water column [2]. Lack of oxygen (hypoxia) is a separate risk associated with breathing gas mixtures or breath-holding but does not directly cause mechanical eardrum injury. Therefore, the mechanical stress from high water pressure is the direct cause of eardrum damage.

Sources

1. [1] https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/scuba-diving-decompression-illness-and-other-dive-related-injuries.html
2. [2] https://www.ncbi.nlm.nih.gov/books/NBK499851/