1 00:00:02,040 --> 00:00:10,039 Speaker 1: Welcome to brain stuff from how stuff works. Hey, I'm 2 00:00:10,119 --> 00:00:13,600 Speaker 1: Christian Sager and this is brain stuff. If you're standing 3 00:00:13,640 --> 00:00:16,480 Speaker 1: next to a jet during takeoff, your ear drums will 4 00:00:16,520 --> 00:00:19,520 Speaker 1: probably burst. Same thing happens when you fire a twelve 5 00:00:19,560 --> 00:00:22,720 Speaker 1: gage shotgun right next to your ear. When we're exposed 6 00:00:22,720 --> 00:00:26,880 Speaker 1: to exceptionally loud noises, something called the stereocilia in our 7 00:00:26,920 --> 00:00:31,200 Speaker 1: ears gets damaged. This causes our ears to mistakenly send 8 00:00:31,280 --> 00:00:36,760 Speaker 1: signals to our auditory nerve cells. The resulting ghostly reverberations 9 00:00:36,800 --> 00:00:39,839 Speaker 1: are what we call ringing ear. Many of you have 10 00:00:39,960 --> 00:00:43,879 Speaker 1: probably experienced this, possibly from going to a really loud concert. 11 00:00:44,280 --> 00:00:47,600 Speaker 1: The technical term for it is tenitus, and it's usually 12 00:00:47,640 --> 00:00:51,400 Speaker 1: temporary unless you repeatedly damage your ears with loud noises. 13 00:00:51,960 --> 00:00:55,400 Speaker 1: Then it develops into chronic tenitis, where you hear that 14 00:00:55,520 --> 00:00:58,960 Speaker 1: dull ringing for the rest of your life. And that's 15 00:00:59,080 --> 00:01:01,920 Speaker 1: nothing compared what really loud noise can do to you. 16 00:01:02,480 --> 00:01:07,319 Speaker 1: Noise hates you, and noise can kill you. See. Sound 17 00:01:07,319 --> 00:01:11,080 Speaker 1: travels in waves that enter our ear canals. These waves 18 00:01:11,160 --> 00:01:14,000 Speaker 1: make our ear drums vibrate, and if they're too strong, 19 00:01:14,280 --> 00:01:17,160 Speaker 1: they can snap the hair cells inside. And if these 20 00:01:17,160 --> 00:01:20,880 Speaker 1: hair cells die they can never grow back. To avoid this, 21 00:01:21,080 --> 00:01:24,560 Speaker 1: we use units called decibels to measure the power of sound. 22 00:01:25,000 --> 00:01:28,160 Speaker 1: Anything below eighty five decibels is thought to be safe. 23 00:01:28,480 --> 00:01:31,640 Speaker 1: At a hundred and fifty decibels, your ear drums burst 24 00:01:32,000 --> 00:01:34,759 Speaker 1: like with the jet or the shotgun, and at two 25 00:01:34,920 --> 00:01:39,039 Speaker 1: hundred decibels, your lungs will rupture and likely kill you. 26 00:01:39,600 --> 00:01:42,800 Speaker 1: That's right. The threshold for death by sound is somewhere 27 00:01:42,840 --> 00:01:46,560 Speaker 1: between a hundred and eighty five and two hundred decibels. 28 00:01:47,040 --> 00:01:50,160 Speaker 1: What happens is the sound causes an air embolism within 29 00:01:50,240 --> 00:01:52,680 Speaker 1: your lungs that can travel to your heart and kill 30 00:01:52,760 --> 00:01:56,040 Speaker 1: you dead. That is, if your lungs don't burst first 31 00:01:56,080 --> 00:01:59,720 Speaker 1: from the increased air pressure caused by acoustic energy. This 32 00:01:59,760 --> 00:02:03,000 Speaker 1: is how happened during wars, when high energy impulse noise 33 00:02:03,040 --> 00:02:08,160 Speaker 1: from explosions causes something called blast over pressure. It leaves 34 00:02:08,360 --> 00:02:12,640 Speaker 1: no external injuries, but damages organs like your ears, lungs, 35 00:02:12,720 --> 00:02:17,839 Speaker 1: and gastro intestinal tract. Now, acoustic weapons are actually being developed, 36 00:02:18,040 --> 00:02:21,760 Speaker 1: but usually there for non lethal purposes. There's been talk 37 00:02:21,800 --> 00:02:25,760 Speaker 1: of acoustic bullets to burst ear drums, incapacitate a target, 38 00:02:26,040 --> 00:02:30,080 Speaker 1: or even kill them. Others claim that an infrasound generator 39 00:02:30,160 --> 00:02:34,040 Speaker 1: could also be lethal, but there's been little practical evidence 40 00:02:34,120 --> 00:02:37,960 Speaker 1: of such weapons so far. The closest we've seen is 41 00:02:37,960 --> 00:02:41,680 Speaker 1: a long range acoustic hailing device developed by the l 42 00:02:41,760 --> 00:02:44,960 Speaker 1: Rad Corporation, which can cause hearing damage from up to 43 00:02:45,040 --> 00:02:49,560 Speaker 1: fifty feet or fifteen point two four meters away. Some 44 00:02:49,680 --> 00:02:53,639 Speaker 1: shipping companies have started using these devices as seaborne defense 45 00:02:53,720 --> 00:02:57,799 Speaker 1: against pirates. There is one device, however, that could most 46 00:02:58,240 --> 00:03:01,560 Speaker 1: definitely kill you with sound. It's not a weapon, but 47 00:03:01,639 --> 00:03:05,320 Speaker 1: the European Space Agency has developed a huge air horn 48 00:03:05,400 --> 00:03:09,560 Speaker 1: that they used to test satellites and spacecraft, using nitrogen 49 00:03:09,680 --> 00:03:12,200 Speaker 1: gas to produce sounds up to one hundred and fifty 50 00:03:12,200 --> 00:03:15,519 Speaker 1: four decibels. They blast objects to make sure they can 51 00:03:15,560 --> 00:03:18,960 Speaker 1: withstand the noise of a rocket launching. The e s 52 00:03:19,000 --> 00:03:22,280 Speaker 1: A themselves are so concerned about how lethal this horn 53 00:03:22,440 --> 00:03:26,280 Speaker 1: is they've surrounded it with half meter thick walls made 54 00:03:26,280 --> 00:03:30,800 Speaker 1: of steel reinforced concrete coated with an epoxy resin to 55 00:03:30,880 --> 00:03:35,480 Speaker 1: reflect noise back into its chamber. But Christian, you're asking, 56 00:03:35,560 --> 00:03:38,400 Speaker 1: didn't you just say that the threshold for death is 57 00:03:38,440 --> 00:03:41,760 Speaker 1: between one hundred and eighty five and two hundred decibels. 58 00:03:42,080 --> 00:03:44,800 Speaker 1: It's true I did, but the E s A believe 59 00:03:44,920 --> 00:03:47,839 Speaker 1: that prolonged exposure to the one hundred and fifty four 60 00:03:47,960 --> 00:03:51,560 Speaker 1: decibel horn will kill you as well, probably rupturing your 61 00:03:51,560 --> 00:03:54,960 Speaker 1: ear drums, vibrating your eyeballs, and destroying you from the 62 00:03:55,000 --> 00:03:58,600 Speaker 1: inside out. If you're not dead, you'll probably wish you were. 63 00:04:03,480 --> 00:04:05,760 Speaker 1: Check out the brainstuff channel on YouTube, and for more 64 00:04:05,760 --> 00:04:08,320 Speaker 1: on this and thousands of other topics, visit how stuff 65 00:04:08,320 --> 00:04:22,800 Speaker 1: works dot com.