Some days ago, I was in one of these modern wagons of the new Brussels’ metro heading to the station, standing up near the door when a strange individual entered the place.
I have to say, these days the metro is not the happiest place in the world: think of a fastly moving, silent long and closed oven (30°C average), filled with exotic scents reminding us of the multi-cultural, cosmopolitan nature of Europe’s capital social tissue, for the pleasure of the senses and full of either highly communicative, red-faced, boozed people commenting the latest world cup goal in every possible language (reminding us again of the Brussels multiculturalism for the pleasure of our other senses) and second, half-closed-eyed, opium-dreaming folks in profound introspection.  I would think many of the second class specimens reached this state after being in the first one.

The fact is, I was myself in a vague zen self-contemplating state, waiting to reach my final destination to get out of this unhealthy sauna, when this chap entered and parked himself at my right.

I didn’t really notice him as I was in standby, energy-saving mode.

A station later, however, when my right foot reached an obstacle, I peeked down by reflex just to notice a small black wallet lying on the floor.  As it apparently had slipped out the newly arrived chap, I looked up just to face a strange hairy creature very close to Uncle Itt, a tad taller.

“Scuse me”, I said to him, friendly
(no answer)
“Hey”, I exclaimed, on a 20 db higher pitch
(still no answer)
I then moved my hand in front of his face, though it was difficult to locate the exact position of the eyes behind that solid curtain of hairs, to obtain a rather awkward 15° head twist to the left followed by the same movement the opposite sense.
At this point I was considering to just forget about it, give Itt a friendly kick in the ribs or pull off some of these abundant hair (very tempting) or even recollected some of my old sign-language communication skills when I noticed a rythmical, almost imperceptible shaking of the hairstack.

I glanced attentively at the subject, since it wasn’t quite clear if it was due to parkinson, some mild form of Tourette’s syndrome or just autism.

At this moment, Itt’s hand, just like Napoleon, slipped into his jacket and stayed there some seconds, apparently doing some sort of scratching.

To my surprise, the autist now entered a frantically faster rythmical movement, something like a jump from allegro to scherzo furioso.

And the light was.

So I heartly gave the music lover an elbow kick in the ribs, to which, to my satisfaction, I obtained a quick reaction this time, and saw Itt move apart the left side of the hairstack, freeing his furious left teen eye and
uncover a white cable which he plugged off his left ear.

My right cochlea was assaulted by what I immediately recognized as the latest riffs of Let There Be Rock.  The sound was so powerful, going out of this tiny plug that I just stood there in awe and was only able to point my finger to the black wallet in the floor, to which Itt quickly reached and headed off the wagon at the next stop.

I made a quick estimate.  The volume off this earplug inside the ear would almost certainly be delivering more than 90db.  At this rate, I thought, this guy will be deaf in 15 to 20 years, starting at a high-frequency loss to degenerate to a disabling mild-to-severe loss after 45 years age, with just some years of frequent exposure to
loud music over 80db.

I was furious and apalled at the same time.  As an ex-profoundly deaf person now using a cochlear implant, I know what deafness is about.
I am totally against the proliferation of these super-powerful headphones plugged into the ears used indiscriminately.  I see often people of all ages wearing headphones in public places, but you never know at which volume they’re playing music at.  That reminded me of a Wired article I read long ago.

It is widely known that long exposure to loud noise (over 85db) can cause first tinnitus and progressively, deafness.
The human cochlea contains, in the organ of Corti, a number of sensory cells called hair cells.  There are approximately 10000 “inner hair cells” and 30000 “outer hair cells”.  The hair cells are located in rows along the organ or Corti and are functionally different.  The vibrations transmitted from the stapes to the perilymph, then to the endolymph, will cause the vibration of the hair cells which, in the end, will cause electrical potentials which we perceive as “sounds”.

Long, strong vibrations of the endolymph cause hair cell damage and death.
Think about it. 

More information:

The Cochlea
Noise-induced hearing loss: