250 db sound blast

stoneman · Post by **stoneman** » Mon Oct 08, 2012 4:23 pm

does anyone nerdy here know how much a 250 db blast from a sound cannon will dissipate through seawater. the diablo canyon power plant is planning on emitting underwater blast every 20 seconds for 42 days....the frequency will be 300hz. for instance how loud will it be after traveling 2 miles underwater? or four?

while pge admits that these seismic tests will harm and kill many marine mammals they have yet to discuss what impacts it will have on the ears and lungs of surfers (or more importantly surfer/recording enthusiasts).

i understand this is off topic for a tapeop thread but i am not getting what i need from googling. and i want to get started writing letters....

thanks to anyone that has any idea or a good site to steer me towards.

Bro Shark · Post by **Bro Shark** » Mon Oct 08, 2012 7:40 pm

Well. If you use those surfer earplugs, it oughta provide decent production for your eardrums... and plus, you don't want that "surfer's ear" thing anyway. Drilling and such, youch.

Nick Sevilla · Post by **Nick Sevilla** » Mon Oct 08, 2012 10:10 pm

I guess this is the wrong place to ask, but WTF?
Why in the hell would they do this? For 45 DAYS?!?!?!?
Whoa, this does not sound good at all.

jhharvest · Post by **jhharvest** » Mon Oct 08, 2012 11:43 pm

Anecdotally sound travels really, really well in water. Whales use this to communicate miles away.

Luckily the internet is pretty well equipped to answer these kinds of questions:
http://resource.npl.co.uk/acoustics/tec ... bsorption/

At f=300Hz and T=20?C we are seeing figures of 0.006-0.009 dB / km, i.e. diddly-squat. Basically, sound at those frequencies does not attenuate in sea water.

Sound will still spread leading to amplitude drop of 6dB when distance doubles in a free field. However since the ocean has a bottom and a top (sound is reflected back down) it doesn't spread in 3 dimension but only 2, so actually the drop is more like 4dB (I've rounded it up a bit because, well, just because (actually some of it will escape into atmosphere and some into the ground)).

Let's calculate it like this:
attenuation dB = log(distance) * 4dB
distance = 2 miles ≈ 3km
log(3000m) * 4dB ≈ 46dB

So 2 miles away the sound is still pretty bloody loud. Like 200dB loud. But then the 250dB re 1 μPa SPL is equal to a lightning strike on the surface (http://www.dosits.org/science/soundsint ... monsounds/). However SPL is measured differently under water with the reference pressure set to 1 μPa rather than 20 μPa. Basically sounds are measure ~60dB louder in water than they are in air, so effectively the sound level is 140dB. And then your hearing is less efficient in water, ~35dB difference at 300Hz (http://www.subacoustech.com/research/un ... ring.shtml) so the effective heard SPL is 105dB 2 miles away from the location. Still loud but at least you shouldn't die / go instantly deaf.

(Disclaimer: maths may be completely off - do your own research and confirm with experts.)

stoneman · Post by **stoneman** » Tue Oct 09, 2012 7:48 am

well, doc pro plugs don't seem to block too much sound but i'll be trying that too in the vent they get away with doing this.

your right, nick, this PGE thing is wrong on so many levels. there are a lot of concerned folks but the local papers are mostly printing PGE puff pieces so not much is changing so far.

and thank you to harvest for giving me some idea of how to go about calculating this....math word problems are not my forte'. i'll check out that site right now.

fossiltooth · Post by **fossiltooth** » Tue Oct 09, 2012 8:52 am

What in the hell is the purpose of these tests???? Are they trying to figure out the exact number of whales they can beach by being complete d*ckheads??

Seriously, unless we are being invaded by a space-borne species of obelisk-making super-genius whales from the distant past, ala Star Trek IV, and need to create a sea-life-killing super-weapon, I really don't see the value of this in the slightest.

Sound waves travel faster and farther in water than through the air. For some context, the threshold of pain for human beings is 120dB. A sound wave of 250dB is roughly TEN TRILLION times more powerful than that. (Yes, that's how dB works, for anyone who's forgotten that it's a logarithmic scale.)

250dB means instant deafness, possibly death, for any living thing. Eardrums begin to tear quickly at 140db. They pop instantly around 190 dB. Sounds around 200 dB can cause death to humans. Rocketship takeoffs register around 215 dB and Nuclear bombs around 240 dB to 250 dB.

Do you have links to info this test, Stoneman? I can't even begin to imagine how the value of these tests would offset their costs to life and to our environment. Sorry to get all captain planet on this one, but that sh*t is *f*d up.

jhharvest · Post by **jhharvest** » Tue Oct 09, 2012 10:35 am

It's a bit different as the dB scale is actually different for measures under water and over water. These are usually denoted dB re 1?Pa and dB re 20?Pa. Even whale song can measure at 180dB re 1?Pa and obviously the whales are fine with that. This 250dB is similar to the pop guns they use for seismic surveying or some large scale sonar arrays. The SURTASS LFA for example uses 215 dB re 1?Pa (http://www.surtass-lfa-eis.com/FAQ/index.htm).

That said this isn't great and it would be great if we could stop this.

cgarges · Post by **cgarges** » Tue Oct 09, 2012 12:19 pm

Nick Sevilla wrote:I guess this is the wrong place to ask, but WTF?
Why in the hell would they do this? For 45 DAYS?!?!?!?
Whoa, this does not sound good at all.

TOTALLY! What's up with this?

Chris Garges
Charlotte, NC

stoneman · Post by **stoneman** » Tue Oct 09, 2012 3:15 pm

the deal is...Diablo Canyon nuclear plant is at the end of their lease. they want it to be renewed...but they built it on a fault 30 years ago. with the Fukushima disaster so recent, they feel that getting a 3d map of the bottom will show that there are no new faults (this sound cannon technology is also used for oil and gas exploration...if you want to get really cynical about their reasons). obviously, they already know what faults are there and are doing this to get another 30 year lease. if its too dangerous close the f'ing thing. whale watching and fishing on the central coast will never be the same. surfers hearing maybe too...

there is a ton of info about this but its not national news...

one critical piece:
http://www.newtimesslo.com/shredder/828 ... cowardice/

here is our local paper's (pro-PGE) article that they keep running versions of. http://www.sanluisobispo.com/2012/10/06 ... -will.html

stoneman · Post by **stoneman** » Tue Oct 09, 2012 3:19 pm

sea shepherd guys are on this it looks like
http://www.seashepherd.org/news-and-med ... coast-1435

fossiltooth · Post by **fossiltooth** » Tue Oct 09, 2012 9:22 pm

jhharvest wrote:It's a bit different as the dB scale is actually different for measures under water and over water. These are usually denoted dB re 1?Pa and dB re 20?Pa. Even whale song can measure at 180dB re 1?Pa and obviously the whales are fine with that. This 250dB is similar to the pop guns they use for seismic surveying or some large scale sonar arrays. The SURTASS LFA for example uses 215 dB re 1?Pa (http://www.surtass-lfa-eis.com/FAQ/index.htm).

That said this isn't great and it would be great if we could stop this.

I did not know that. Thanks for the added info -- that does make it slightly less terrible.

The FAQ on that website kind of avoids the question of whether those dB levels can cause death underwater. It seems they've established that at the very least, these tests can "cause injury." And they do openly admit that the blasts can "change behavior" which I take as code for "yes, it seems that underwater testing of this kind probably drives aquatic mammals to beach themselves and die."

This FAQ from the Navy, thankfully, mentions that their standard procedures are to detect and deter any large animals withing 2km and to keep tests 12 nautical miles away from areas that are regularly used by swimmers and boaters. That also makes things a bit less terrible.

Still, I think it's pretty safe to assume that these kinds of concessions probably didn't come from people not putting up a stink about it.

Anyway, I'm no hippie, but I'm going to admit that running with: "Hey, lets torment some whales so that we can try and justify having a nuclear reactor above a fault-line!" makes me feel a little less than comfortable.

I am going to go ahead and guess that I'm not alone on that one.

Bro Shark · Post by **Bro Shark** » Wed Oct 10, 2012 12:28 pm

Isn't it the case that sonar waves are super painful to whales, and we've been housing them for decades without knowing it? I remember reading/hearing that in recent years.

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