Tinnitus: Infrasound Effects

Infrasound may cause tinnitus or make existing tinnitus worse. Infrasound occurs when the cochlea is shaken repeatedly for long durations. Normally, ears detect a noise vibration and the brain interprets the vibration as sound. However, with infrasound there is no noise stimuli. It is the fluid in the cochlea being moved back and forth due to being shaken repeatedly. A good example is sea sickness. There is no noise but the boat rocking and vibrating causes the fluid in the cochlea to move. The effects are obvious and immediate. Sea sickness is one result of infrasound overexposure. Some people are more sensitive to infrasound than others.

People who drive or ride in tanks, airplanes, buses, trains, or ships for long durations are exposed to infrasound. Over time, infrasound can begin to weaken the cilia (hairlike cells) of the cochlea which causes the brain to generate a sound (e.g. ringing, whooshing, crickets, crackling, thumping, clicking, popping). 

This may explain why hearing protection will not help some people to avoid tinnitus.
Here's an example, hypothetically speaking: A ship's captain or crew member may be wearing proper hearing protection and yet may still experience tinnitus during or immediately after an 18 hour boat ride. The vibration of the ship passing through the water has vibrated the liquid in the cochlea and caused the liquid to pass over the delicate cilia cells and mat some of them down (like blades of grass that have been trampled down) despite the fact that hearing protection was used. If the boat captain or crew  member is running tours everyday then over time the tinnitus cannot only become permanent but louder and more annoying and even debilitating.

The only protection against infrasound overexposure is to stop the activity altogether or reduce the exposure duration by limiting the activity to safe time limits or intervals.