Aircraft Mechanic Ototoxicity

Aircraft Mechanic Ototoxicity

If you are like me, you have met a lot of older Airframe and/or Powerplant Mechanics and pilots that have hearing issues. You might even be one yourself. It makes a lot of sense. We spend a lot of time in loud shops and then a lot of time around loud engines running.

I can remember a time not too long ago when I was stuffed up in the back of a CRJ200 yelling into a cellphone with both packs running off of the screaming APU, trying to tell the pilot when to activate the dump valves. I still think that that is the loudest single event I have ever been involved with.

            

What does not make sense it how few of us have heard of ototoxicity or know the intricacies of the hearing process. So, what is it?

What if I told you that hearing was at its root, a chemical process? The sound waves travel into the auditory canal and vibrate the ear drum, which in turn transmits the waves into the fluid filled inner ear. Along the walls of the inner ear are little tiny hairs that move with the vibrations, and as they move they open up little pores that allow a chemical to enter the fluid. That causes a chemical reaction that produces an electrical signal. That signal is picked up by the auditory nerve, sent to the brain, and interpreted as sound. That was a lot.

Ototoxicity is a phenomenon where certain chemicals have been found to alter this hearing process. Normal hearing has a damage threshold where the hairs can actually break. Certain aerospace chemicals essentially cause the hairs to be more sensitive to sounds, which can cause the damage threshold to lower. Some of those chemicals are organic solvents, like jet fuel, toluene, styrene, and carbon monoxide. These chemicals can alter the hearing process by being inhaled or absorbed through the skin.

This is all relatively new information. But, what it points to is that people like us, that work with these chemicals, smell jet fuel, and are around high noise areas, are much more susceptible to hearing loss than we ever suspected. It makes even more sense then, why we all know so many that have hearing loss.

The difference to the damage threshold is profound. Normally, damage is negligible under 85 decibels (dB). 85dB is where you can start getting damage during long exposures (6-8 hours continuous). It is about the level of noise from standing near a busy highway or a construction site with heavy equipment moving around. If these solvents are present and you are exposed to them, that damage threshold can be lowered to as low as 60dB! That is the level of normal conversation! The 85dB level becomes the threshold at which exposure for any period cause permanent damage.

The point of all of this is, that we as A&P’s really need to pay better attention to when we are wearing our hearing protection. The fact that just smelling or touching jet fuel can cause us to have more damage from noise is hard to get used to. I try to throw little foamy’s in when I am doing anything with jet fuel. I also am much better about protecting my skin from chemicals and solvents. And whenever I have the opportunity, I tell pilots and mechanics about this phenomenon so that we can collectively make our industry safer. Your hearing does not grow back or heal itself.

More information on Ototoxicity

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