By design, I suspect, ambulance and fire engine (and police, too) sirens are uncomfortable for us to hear. Not because they're loud, though they are (of course), or sudden, which is part of their charm, but because of their strident urgency--their 'you need to make way now!' demand whenever you hear them.
There's never any place on any road wide enough to move the car when I hear a pulsating siren while driving-and if I'm walking, I stop until the vehicle has gone by (though I'm not sure why, exactly. John Lennon, in explaining the rhythm of "I Am the Walrus", helped me realize why that song always frightened me: the verses' meter mimicked the siren pulsations all public safety vehicles in Europe use.) The worst time for sirens, and most stuff (come to think of it) is at night. We have these amazing brains and these very cool thumbs but there were trade offs.
As we evolved, wandered from the Garden or were left here as detritus from an alien picnic on the planet (I'm trying to be inclusive in terms of the Origin of the Species), our ears can't hear what other passengers on this blue marble can, our noses can't detect the nuances that our pets can and our eyes, while in most instances able to appreciate color, don't have the acuity or other properties some other species have.
As a college kid, I got into one of those endless 'what if you lost' loops, usually precipitated by huge quantities of beverage or herb that might have been troubling to law enforcement members--and the issue always seemed to be how would you cope if you could no longer use, in my case, eyesight. Everyone who knew me then, or knows me now, realizes I am not afraid of the dark-I am paralyzed by my fear of it. Darkness is a magnifier and a mask simultaneously.
Want to see me jump? Call me on the phone after nine o'clock at night. Phone calls at night are never good news and the only reason I ever answer, in much the same way as I pull over for the speeding ambulance or fire engine (I'm usually the reason for the police car siren), is to silence them and to pause the horror movie projecting in my head. It makes no difference if my wife and two children are in the house, in my sight, in the well-lit living room. The fresh new hell that awaits is on the other end of the Bakelite fabrication and someone has released the hounds.
This morning, as I stumbled through my ablutions in preparing for work, the siren sounded for a long time, at first faint then growing louder as it came nearer, then softer again as it approached, I assume, Backus Hospital which is a short walk from my house. Despite the early hour, I could clearly see in my mind's eye emergency personnel struggling to keep alive someone, somewhere, who had been swallowed by the darkness each of us has within that so often and so swiftly spills without.