Emergency Services

[gman76]

Does anyone know, to the rough dB how loud the emergency services sirens are?

Heard one today that started out of the blue - nearly jumped out of my skin!

I based my thoughts on a 90bB smoke alarm - the siren was a lot louder!

I would guess around 200 - 300dB?

 

[joinerjohn]

I would guess around 200 - 300dB?

Unbelievably way out with your estimate there gman.
If it were 200db, then passers bye would be instantly deafened. At 180db deafness is caused by the death of the receptor cells responsible for hearing

As it is the loudest possible sound is 194db

 

[wotan]

Sirens on British fire appliances, are in the region of 123 decibels,
I think 200 to 300 db would destroy your hearing, or at the very least cause you intense pain.

Wotan

 

[conny]

Probably around the 110-115 range.
Strange thing with noise is that 93 decibels is twice as loud as 90.

90 Decibels used to be the level that you could work in for 8 hours without protection. Believe its now down to about 84. Anything above and you need ear protection and for every 3 decibel rise your exposure time is halved. So 87 decibels would be 4 hours and 90 decibels would now be 2 hours.

Hell of a difference.
I've got it in my old H&S books somewhere.

Just found this;

http://www.nidcd.nih.gov/health/hearing/ruler.asp

 

[wobs]

Probably around the 110-115 range.
Strange thing with noise is that 93 decibels is twice as loud as 90.

90 Decibels used to be the level that you could work in for 8 hours without protection. Believe its now down to about 84. Anything above and you need ear protection and for every 3 decibel rise your exposure time is halved. So 87 decibels would be 4 hours and 90 decibels would now be 2 hours.

Hell of a difference.
I've got it in my old H&S books somewhere.

Just found this;

http://www.nidcd.nih.gov/health/hearing/ruler.asp[/QUOTE]

Close, but the mandatory 8hr exposure limit is 85dB.

As you say, its all about exposure, but I should add that distance makes a big difference. With every doubling of distance, the level halves (in other words, drops by 3dB). This means that the level you are exposed to will vary enormously depending upon the distance you are from the vehicle.

Also, some sirens may have directional influences, so you may hear it more from certain directions.

As a point of reference, the Space Shuttle is about 188dB near the tower, and 120dB at the 3mile mark apparently. We went to the launch site (didn't see a launch owing to it being cancelled, grrrr), and there's a point in between the two pads which has a bunker for a generator to power monitoring equipment, as the noise/vibration has knocked out generators at that point in early launches. If you were at that point during launch, the guide claimed it could kill you due to the noise. Not sure how true that would be though.

The legal limit for instantaneous noise is 140dB.

This study puts it at 115dB:
http://www.ambulancevisibility.com/index.php?p=1_12

One assumes that this would be from 1m from the source, as this is a normal monitoring distance, so one would not normally be exposed to such levels in reality. It shows that a siren must overcome sound proofing in modern cars, and stereos, and air con noises within the car to make them heard.

Edit:
This source gives it at 120dB
http://www.nidcd.nih.gov/health/hearing/ruler.html
Again, remember the issue with distance.

 

[snico]

Sirens on police vehicles are approx 100 - 115 decibels.

 

[joe-90]

Why doesn't the siren phase in over a three second period? There's no need to startle people.

 

[noseall]

...yeah, and has anyone took into consideration the Doppler effect...

 

[conny]

Regardless of the level, how many of you have seen the driver so engrossed in his 'modern-deadbeat-thumping-tuneless music' that he doesn't hear it even when its sitting on his exhaust pipe!

PRATS!!!

(Personally, if I was driving a fire engine I'd run them into a ditch and carry on. )

 

[Nige F]

Probably around the 110-115 range.
Strange thing with noise is that 93 decibels is twice as loud as 90.


http://www.nidcd.nih.gov/health/hearing/ruler.asp[/QUOTE]

.

,
The legal limit for instantaneous noise is 140dB.




.

I`ve broken the law with my flatus then

 

[conny]

Rather the noise than the gas poisoning!

 

[Donkmeister]

In my unenlightened youth I attended a lot of tuning shows, there would always be the SPL (sound pressure level) vans and cars. These are vehicles outfitted with stereo systems that make the Corsas and Clios you see on the streets sound like a mouse sneezing.

The loudest I experienced was a system that was rated at 130dB SPL - no idea if they had it on full but it felt like someone was physically pushing and pulling on my eardrums. So, an ambulance is not as loud as that.

At the same show, a friend leaned against a van demonstrating 154dB (with doors shut, steel bars to stop the windscreen popping out etc) and spontaneously got a nosebleed. They reckoned that inside, the volume was equivalent to someone firing a machinegun with the muzzle sat right next to your ear.

So, for sirens, I would agree with the 120dB figures bandied about above.

Dunno if we have a sound engineer here who can elaborate, but I seem to recall a large part of how loud something sounds is down to the pitch and also bandwidth. I.e. a broadband signal of x decibels sounds quieter than a single note of the same decibels. Plus treble sounds louder than bass.