WEBVTT - How Smoke Detectors Work 0:00:04.240 --> 0:00:07.240 Welcome to tex Stuff, a production of I Heart Radios 0:00:07.320 --> 0:00:14.280 How Stuff Works. Hey there, and welcome to tex Stuff. 0:00:14.320 --> 0:00:17.599 I'm your host, Jonathan Strickland. I'm an executive producer with 0:00:17.680 --> 0:00:19.919 I Heart Radio and a love of all things tech. 0:00:20.560 --> 0:00:22.919 And you know, recently guys that did episodes about how 0:00:23.000 --> 0:00:26.760 matches work and how lighters work and talked about how 0:00:27.040 --> 0:00:31.320 chemists and physicists and inventors were able to make it 0:00:31.360 --> 0:00:33.920 easier than ever to light a fire. So I thought 0:00:34.080 --> 0:00:36.640 it's really only fitting if I do an episode about 0:00:36.760 --> 0:00:40.159 smoke detectors and smoke alarms and and other types of 0:00:40.400 --> 0:00:46.239 fire alarms to talk about their history and how they work. Now, clearly, 0:00:46.680 --> 0:00:51.080 smoke detectors are incredibly important because we all know fires 0:00:51.120 --> 0:00:54.319 can be life threatening. They can spread quickly, they can 0:00:54.360 --> 0:00:57.000 cut off potential escape routes for the people who are 0:00:57.000 --> 0:00:59.880 caught in the way. So early warning systems that can 0:01:00.000 --> 0:01:03.640 alert us to danger before it becomes a mortal danger 0:01:03.760 --> 0:01:07.759 are fantastic inventions. And there are a couple of inventions 0:01:07.760 --> 0:01:10.240 I want to talk about before we actually get to 0:01:10.360 --> 0:01:13.440 smoke detectors. I'm sure that doesn't come as a surprise 0:01:13.480 --> 0:01:15.640 to any of you who have listened to tech stuff 0:01:15.640 --> 0:01:18.720 episodes before, I always like to set the ground. Well, 0:01:18.800 --> 0:01:20.760 the first one that I want to talk about is 0:01:20.760 --> 0:01:24.920 the portable electric fire alarm, as in a fire alarm 0:01:25.000 --> 0:01:28.120 that works on electricity, not a fire alarm that detects 0:01:28.160 --> 0:01:32.440 electric fires. Francis Robbins Upton, who was a physicist who 0:01:32.480 --> 0:01:36.240 was a partner and general manager of the Edison lamp works, 0:01:36.520 --> 0:01:40.520 you know as in Thomas Edison, developed this particular invention 0:01:40.600 --> 0:01:45.080 back in eight Now. According to the patent, the design 0:01:45.120 --> 0:01:49.200 would sound an alarm after detecting that the temperature had 0:01:49.320 --> 0:01:53.920 risen above some predetermined limit, so if it got too hot, 0:01:54.440 --> 0:01:57.280 this thing would go off. And the way this would 0:01:57.320 --> 0:02:00.520 work was really clever. You can actually learn exactly how 0:02:00.520 --> 0:02:03.560 it was supposed to work based on the patent that 0:02:03.920 --> 0:02:08.960 Upton got on this particular invention. So the way it 0:02:09.000 --> 0:02:11.600 works is that the there are a pair of electrical 0:02:11.680 --> 0:02:15.360 contacts and if they are in in contact with each other, 0:02:15.400 --> 0:02:18.400 if they touch each other, it completes a circuit. But 0:02:18.560 --> 0:02:22.400 normally there's a gap between them. An electricity can't pass 0:02:22.520 --> 0:02:26.239 between the two that it can't cross that gap, so 0:02:26.400 --> 0:02:29.839 it's normally in the off position. However, one of those 0:02:29.880 --> 0:02:34.960 two electrical contacts is mounted on a fixed arm and 0:02:35.000 --> 0:02:37.720 the other is on an arm that's attached to a 0:02:37.800 --> 0:02:43.640 coil of bimetallic material. Now, I mentioned bimetallic strips in 0:02:43.680 --> 0:02:46.520 the episode about lighters, and it's something you find in 0:02:46.600 --> 0:02:50.920 a lot of different technologies that depend upon changes in 0:02:51.000 --> 0:02:56.560 temperature as a variable, like thermostats have bimetallic strips in them. 0:02:56.880 --> 0:02:59.320 And essentially what it is is a strip of metal 0:02:59.600 --> 0:03:03.480 that insists of two different metals. And think of it 0:03:03.520 --> 0:03:06.200 as like a metal sandwich, a top side and a 0:03:06.240 --> 0:03:09.760 bottom side, and one metal is the top side, the 0:03:09.840 --> 0:03:12.920 other metal is the bottom side, and each metal has 0:03:12.919 --> 0:03:16.359 slightly different properties, and one of those properties is how 0:03:16.480 --> 0:03:19.960 quickly they expand when they're heated up. You know, we 0:03:20.040 --> 0:03:22.880 know that metal expands as it gets warmer. While using 0:03:22.880 --> 0:03:25.959 a bimetallic strip, you have one side that will expand 0:03:26.080 --> 0:03:29.680 faster than the other side, and when that happens, it 0:03:29.720 --> 0:03:34.240 causes the strip to curl, so it deforms as it 0:03:34.280 --> 0:03:38.200 gets warmer, one side is expanding faster than the other 0:03:38.720 --> 0:03:42.000 and you get this curled metal as a result. So 0:03:42.080 --> 0:03:46.600 with Upton's proposed invention in the patent, this coil of 0:03:46.640 --> 0:03:50.520 bimetallic material would act as sort of an actuator. As 0:03:50.520 --> 0:03:53.840 it would get warm, it would expand and this in 0:03:53.880 --> 0:03:57.800 turn would create a pushing force on the arm with 0:03:57.960 --> 0:04:01.280 the electrical contact on it that then can move toward 0:04:01.480 --> 0:04:04.840 the other electrical contact that's in a fixed position. And 0:04:04.920 --> 0:04:09.080 so once the coil had expanded enough, the two contacts 0:04:09.080 --> 0:04:12.760 would touch one another and it would complete a circuit. 0:04:13.200 --> 0:04:16.800 At that point, electrical current could actually flow from a 0:04:16.839 --> 0:04:20.000 battery that was connected to this device all the way 0:04:20.040 --> 0:04:24.000 through to activate an alarm bell. So once the temperature 0:04:24.040 --> 0:04:27.400 got hot enough the two contacts touch, you get a circuit. 0:04:27.760 --> 0:04:30.120 The alarm bell goes off. If it cools down, the 0:04:30.160 --> 0:04:34.560 contacts will slowly separate, and eventually they'll separate enough where 0:04:34.560 --> 0:04:38.120 that electrical circuit can't be complete anymore. The alarm bell 0:04:38.160 --> 0:04:41.640 would go off. And Upton's invention was, without a doubt, 0:04:41.760 --> 0:04:45.479 a very clever one, and it could help save property 0:04:45.680 --> 0:04:48.839 by sounding an alarm before a fire had raged completely 0:04:48.839 --> 0:04:53.599 out of control. But there are many dangers with fires, 0:04:53.880 --> 0:04:57.480 and heat is just one of them. Another very serious 0:04:57.560 --> 0:05:00.960 danger is smoke, which not only a scares your vision, 0:05:01.360 --> 0:05:04.720 but it also can suffocate you as well. So while 0:05:04.720 --> 0:05:08.800 the alarm as design would work, it wouldn't necessarily be 0:05:08.960 --> 0:05:13.560 enough to save lives, or it might not save enough lives, 0:05:13.600 --> 0:05:16.120 because it would only go into action after the temperature 0:05:16.160 --> 0:05:20.200 had already increased enough to make this bimetallic strip expand 0:05:20.200 --> 0:05:23.720 to a sufficient degree, and by that time it might 0:05:23.760 --> 0:05:27.080 already be too late for the people in that building. Now, 0:05:27.080 --> 0:05:30.640 as far as I know, Edison's company didn't actually produce 0:05:30.800 --> 0:05:33.400 any of these fire alarms, but they did patent it. 0:05:33.960 --> 0:05:36.640 Over in Great Britain, there was a fellow named George 0:05:36.680 --> 0:05:40.799 Andrew Darby who patented his own fire alarm, also triggered 0:05:40.880 --> 0:05:44.719 by an increase in temperature. But Darby's invention did not 0:05:45.000 --> 0:05:50.840 depend upon bimetallic strips. It depended on butter for some 0:05:50.880 --> 0:05:55.880 other material that melts at higher temperatures. Say what, all right, 0:05:56.000 --> 0:06:00.120 So imagine you've got a see saw like contraption, a 0:06:00.240 --> 0:06:03.039 lever in other words, and the heavy end of the 0:06:03.120 --> 0:06:07.680 lever uh is up in the air actually because you 0:06:07.720 --> 0:06:10.320 have a weight on the opposite end of that lever. 0:06:10.440 --> 0:06:12.520 So it's like a kid sitting on a seesaw that 0:06:12.560 --> 0:06:15.080 doesn't have another kid at the end of it. The 0:06:15.160 --> 0:06:17.440 kid at the end of the seesaw weighs it down 0:06:17.800 --> 0:06:20.359 and the free end of the seesaws up in the 0:06:20.400 --> 0:06:24.560 air well in this case, the fire alarms seesaw. The 0:06:24.839 --> 0:06:27.240 arm that's up in the air has an electrical contact 0:06:27.240 --> 0:06:30.560 point on it, and if the arm of the seesaw 0:06:30.600 --> 0:06:34.679 were to come down, that contact would complete a circuit, 0:06:35.200 --> 0:06:38.800 and thus electricity would be able to run from a 0:06:38.800 --> 0:06:43.719 battery through an alarm, very much like Upton's invention. So 0:06:43.800 --> 0:06:45.840 weighing down the other end of the arm, the thing 0:06:45.880 --> 0:06:48.640 that's actually keeping the electrical contact up in the air 0:06:49.360 --> 0:06:53.039 is a block of butter or fat or wax or 0:06:53.120 --> 0:06:57.080 some other material that can melt at higher temperatures. So 0:06:57.160 --> 0:07:00.720 as the temperature rises, the block begins to melt away, 0:07:01.080 --> 0:07:04.320 and eventually it melts enough so that the weight isn't 0:07:04.320 --> 0:07:06.760 sufficient to keep the other end of the seesaw up 0:07:06.760 --> 0:07:09.560 in the air, and it'll sink down and the contact 0:07:09.640 --> 0:07:12.120 will complete the circuit and the alarm will go off. 0:07:12.640 --> 0:07:16.480 I was amused to find a butter based fire alarm. 0:07:16.600 --> 0:07:18.680 I wasn't surprised that it came out of England, but 0:07:18.760 --> 0:07:20.720 I was amused to find it. I can think of 0:07:20.720 --> 0:07:24.280 a few potential problems with such an arrangement. For example, 0:07:24.600 --> 0:07:28.720 it might start attracting pests that could eat the weight. 0:07:29.320 --> 0:07:32.040 So in those cases you wouldn't actually have a fire alarm, 0:07:32.320 --> 0:07:35.640 but you might have a rat alarm, or it would 0:07:35.680 --> 0:07:40.120 just turn rancid and smell awful. It's still a pretty 0:07:40.120 --> 0:07:42.880 clever approach, but not one that I think you would 0:07:42.880 --> 0:07:46.880 actually want to put in your buildings. But these solutions 0:07:47.240 --> 0:07:50.679 weren't practical for homes or anything like that. As I mentioned, 0:07:50.760 --> 0:07:52.960 they wouldn't really alert you to the presence of smoke, 0:07:53.200 --> 0:07:55.120 which on its own would be enough to be deadly. 0:07:55.600 --> 0:07:58.440 So this was really looked at as more of a 0:07:58.480 --> 0:08:02.560 solution for things like factories facilities, where you've got a 0:08:02.560 --> 0:08:05.800 lot of industrial operations going on, where the risk of 0:08:05.840 --> 0:08:09.000 fire is high and the risk of property loss is 0:08:09.080 --> 0:08:15.160 also high. Smoke detectors also trace their history back to chemists, physicists, 0:08:15.200 --> 0:08:18.040 and inventors, and in fact, you could say that smoke 0:08:18.080 --> 0:08:22.080 detectors were made possible not just through exploratory science, but 0:08:22.200 --> 0:08:26.280 also happy accidents. And will begin with a super smart 0:08:26.520 --> 0:08:30.280 Swiss physicist in the early twentieth century and try saying 0:08:30.320 --> 0:08:35.720 that three times fast super smart Swiss physicist. His name 0:08:36.200 --> 0:08:41.280 was Heinrich Grinaker and Grindeker or grind Acre if you prefer, 0:08:41.679 --> 0:08:46.760 studied a lot of different stuff, including radioactivity. Vilhelm Rindken 0:08:46.800 --> 0:08:51.920 had discovered the existence of X rays in and Grindeker 0:08:52.080 --> 0:08:54.440 devoted a good deal of his work toward getting a 0:08:54.520 --> 0:08:59.000 better understanding of X rays and other forms of radiation, 0:08:59.040 --> 0:09:02.560 and to do that he had to overcome some practical obstacles. 0:09:02.679 --> 0:09:05.480 For example, he needed a device to help measure the 0:09:05.520 --> 0:09:08.680 intensity of X rays, and such a device didn't really 0:09:08.720 --> 0:09:12.160 exist yet, so he got to work inventing one. X 0:09:12.240 --> 0:09:16.160 rays are a type of ionizing radiation that means that 0:09:16.200 --> 0:09:20.800 when they encounter molecules or atoms, they can ionize them. 0:09:21.120 --> 0:09:23.960 And an ion is a molecule or an atom that 0:09:24.000 --> 0:09:27.599 has a net electrical charge, So it's either a positive 0:09:28.320 --> 0:09:32.120 particle or a negative particle. And a positive ion is 0:09:32.160 --> 0:09:35.520 one that has more protons than electrons, so you have 0:09:35.559 --> 0:09:38.240 a net positive charge. A negative ion would be the opposite, 0:09:38.320 --> 0:09:42.480 has more electrons than protons and has a net negative charge. Now, 0:09:42.480 --> 0:09:47.199 one thing Grineker did was to create ions by building 0:09:47.280 --> 0:09:50.640 a grid of wires through which he could stream high 0:09:50.760 --> 0:09:55.520 voltage current and you would pass air molecules essentially through 0:09:55.600 --> 0:10:01.040 this grid, and the current would strip electron off of 0:10:01.040 --> 0:10:05.520 those particles, creating positive ions. So the grid was in 0:10:05.559 --> 0:10:08.880 this chamber through which gas could move, and as I said, 0:10:08.880 --> 0:10:11.560 the current would ionize the gas. But the other really 0:10:11.600 --> 0:10:15.079 neat thing he did was he invented a voltage multiplier 0:10:15.240 --> 0:10:18.920 circuit because he needed to generate this really high voltage 0:10:19.559 --> 0:10:23.760 around two twenty volts actually, and that could take incoming 0:10:23.800 --> 0:10:28.960 alternating current electricity. That's the type of electricity that power 0:10:29.040 --> 0:10:31.880 plants typically send out because it's easier to send out 0:10:32.000 --> 0:10:37.199 alternating current over long distances than direct current. Well, Grindaker's 0:10:37.200 --> 0:10:40.720 invention would bring in alternating current and then convert it 0:10:40.720 --> 0:10:43.520 to direct current and run the direct current through a 0:10:43.559 --> 0:10:46.640 circuit with stuff like capacitors and diodes. And the whole 0:10:46.640 --> 0:10:50.520 process is a bit complicated to explain, particularly without the 0:10:50.600 --> 0:10:54.200 use of visual aids, and also it goes beyond today's topic. 0:10:54.480 --> 0:10:56.480 But the future I will have to talk about voltage 0:10:56.520 --> 0:11:00.240 multiplying circuits more specifically, because they are in and in 0:11:00.280 --> 0:11:03.959 all sorts of technologies, including super cool bleeding edge science 0:11:03.960 --> 0:11:07.199 stuff like particle accelerators. But for the purposes of this episode, 0:11:07.200 --> 0:11:09.320 The important thing to remember is that it made it 0:11:09.360 --> 0:11:14.160 possible for Grindeker to create an ionization chamber. Now, Greennecker's 0:11:14.280 --> 0:11:18.280 concern was radioactivity, and so we're gonna leave off his 0:11:18.360 --> 0:11:20.760 part of the story at this point because that was 0:11:20.800 --> 0:11:24.800 his big contribution, was creating a feasible way to make 0:11:24.800 --> 0:11:28.040 an ionization chamber. We need to focus more on the 0:11:28.040 --> 0:11:31.640 folks who actually made the first smoke detectors. Uh. Maybe 0:11:31.679 --> 0:11:34.320 I'll do a full episode about Grienneker and other early 0:11:34.400 --> 0:11:36.920 physicists in the future, since their work would lead to 0:11:36.960 --> 0:11:41.160 a deeper understanding of atomic physics and by extension, quantum physics. 0:11:41.160 --> 0:11:43.560 But for now, we're going to get back to smoke alarms. 0:11:43.640 --> 0:11:47.400 So that brings us to our next Swiss smarty pants person, 0:11:47.880 --> 0:11:52.920 Valter Yeager. Now, back in n Yeager wasn't setting out 0:11:52.960 --> 0:11:56.440 to build a smoke detector. That wasn't his goal. Instead, 0:11:56.520 --> 0:12:00.560 he had developed a hypothesis. He thought that perhaps using 0:12:00.559 --> 0:12:03.480 a device with an ionization chamber like the one grind 0:12:03.520 --> 0:12:07.559 Acre had made, he could build a poison gas detector. 0:12:08.000 --> 0:12:10.000 So how did he think he could do this? Well, 0:12:10.000 --> 0:12:12.760 this gets into how smoke detectors actually work. So we're 0:12:12.760 --> 0:12:15.680 going to dive into it. All right, So, as I 0:12:15.720 --> 0:12:18.760 said before, you've got your ionized particles. That's a basic 0:12:18.800 --> 0:12:22.200 component of a large number of smoke detectors. There's actually 0:12:22.240 --> 0:12:25.040 a different type of smoke detector that doesn't use an 0:12:25.040 --> 0:12:28.040 ionization chamber at all, but i'll cover that later in 0:12:28.040 --> 0:12:32.280 this episode. So, these ionized particles are positively charged. They've 0:12:32.280 --> 0:12:34.720 had electrons stripped off of them, so they have more 0:12:34.720 --> 0:12:39.680 protons than electrons. They're positively charged. A battery connected to 0:12:39.760 --> 0:12:43.920 two metal plates creates a positively charged surface on one 0:12:44.000 --> 0:12:47.240 side and a negatively charged surface on the other side. 0:12:47.640 --> 0:12:52.679 So the electrons that are stripped away from the molecules 0:12:53.000 --> 0:12:56.720 will then move to the positively charged plate and the 0:12:56.800 --> 0:12:59.760 positive ions are going to move to the negatively charged plate. 0:12:59.800 --> 0:13:05.280 But has opposite charges attract this movement of electrons is electricity. 0:13:05.320 --> 0:13:08.040 That's what electricity is. So it's not a lot of 0:13:08.080 --> 0:13:13.800 electrical current, but it's consistent. Yeager hypothesized that poison gas 0:13:13.800 --> 0:13:18.280 would interfere with that current of electricity, and that if 0:13:18.280 --> 0:13:21.800 you detected a drop in current, that would set off 0:13:21.840 --> 0:13:26.040 the detector, and Yeager would say, oh, there's poison gas here. 0:13:26.120 --> 0:13:28.840 So he started testing it accept it didn't work. The 0:13:28.840 --> 0:13:31.680 poison gas did not set off the detector. And as 0:13:31.720 --> 0:13:36.000 the story goes, Yeager was getting frustrated and stressed out 0:13:36.120 --> 0:13:38.800 and he decided to smoke a cigarette and think about 0:13:38.840 --> 0:13:41.640 the problem. And so he lights up the cigarette. He 0:13:41.679 --> 0:13:43.680 starts puffing away, and the next thing he knows is 0:13:43.720 --> 0:13:47.240 detectors going off. Now, the poison gas had not interacted 0:13:47.280 --> 0:13:52.280 with the ions, but the smoke did, So what's going on. Well, 0:13:52.320 --> 0:13:55.800 there are particles in smoke that can bond to ions, 0:13:56.040 --> 0:14:00.600 neutralizing them, So negatively charged particles that can bond with 0:14:00.640 --> 0:14:03.800 the positive ones. And when that happens, you get a 0:14:03.880 --> 0:14:07.120 drop in current between those two electric plates I was 0:14:07.160 --> 0:14:10.440 talking about, and that's what sets off the detector. Another 0:14:10.480 --> 0:14:14.760 scientist named Ernst Maine improved upon this design by using 0:14:14.800 --> 0:14:18.560 a cold cathode tube. I've talked about cathode tubes in 0:14:18.559 --> 0:14:21.840 the past. Here's a quick rundown. It's essentially a device 0:14:21.920 --> 0:14:25.360 that emits electrons. Looks a lot like a lightbulb. You've 0:14:25.400 --> 0:14:30.480 got a a filament that's encased inside a vacuum tube, 0:14:30.720 --> 0:14:33.400 and the ideas that you pass an electric current through 0:14:33.440 --> 0:14:37.200 the cathode tubes filament the cathode tubes filament heats up 0:14:37.280 --> 0:14:40.640 due to electrical resistance, and as it heats up, it 0:14:40.720 --> 0:14:46.840 starts to emit a stream of electrons due to thermionic emission. Essentially, 0:14:47.360 --> 0:14:51.960 that electrical resistance means that the flow gets impeded. You 0:14:52.160 --> 0:14:55.080 convert some of that energy over into heat. The heat 0:14:55.120 --> 0:14:59.120 itself strips electrons away from the tungusten filament inside, and 0:14:59.280 --> 0:15:02.880 then you get your dream. Cold cathode tubes work on 0:15:02.960 --> 0:15:07.360 a different principle, though they aren't necessarily actually cold. So 0:15:07.480 --> 0:15:12.520 you've got a cathode that's the electrode that would emit electrons, 0:15:13.120 --> 0:15:15.200 and on the opposite end of the tube you have 0:15:15.280 --> 0:15:18.880 an anode that's the side that accepts electron. So it's 0:15:18.880 --> 0:15:23.960 the positively charged part of this particular device. And these 0:15:24.000 --> 0:15:27.080 are both sealed in a tube, and that tube also 0:15:27.200 --> 0:15:31.239 has a gas inside of it, and applying a sufficient 0:15:31.360 --> 0:15:34.800 voltage between the cathode and the anode a difference in 0:15:34.880 --> 0:15:38.760 electrical charge. If it's sufficient enough, it will cause a 0:15:38.840 --> 0:15:41.720 discharge between the two and the gas will act as 0:15:41.720 --> 0:15:44.720 a carrier for that electrical current. So a neon light 0:15:44.880 --> 0:15:49.560 is an implementation of the cold cathode tube technology. Malee's 0:15:49.600 --> 0:15:53.680 objective was to boost the signal from the detection circuit 0:15:54.120 --> 0:15:56.360 so that the signal could be strong enough to trigger 0:15:56.400 --> 0:15:59.880 an alarm, so not just that would detect a drop 0:16:00.160 --> 0:16:03.680 in current or a change in the electrical current across 0:16:03.720 --> 0:16:06.840 these two plates, but that it would also have a 0:16:06.960 --> 0:16:10.880 strong enough signal so it could power allowed speaker or 0:16:10.920 --> 0:16:16.120 activate a physical bell. And a separate circuit in the 0:16:16.160 --> 0:16:20.480 smoke detector activates upon this change in electrical current, sending 0:16:20.480 --> 0:16:22.920 a signal to the cold cathode tube, which acts like 0:16:22.960 --> 0:16:26.800 an amplifier. It takes that incoming signal amplifies it enough 0:16:26.840 --> 0:16:29.080 for it to do some of the useful work like 0:16:29.720 --> 0:16:33.240 powering allowed speaker and thus alerting you that there is 0:16:33.280 --> 0:16:36.640 in fact smoke in the area. Now. Yeager, being an 0:16:36.720 --> 0:16:40.120 enterprising sort, partnered with Maine to launch a business offering 0:16:40.120 --> 0:16:43.440 smoke detectors in the late nineteen forties. However, these detectors 0:16:43.480 --> 0:16:48.200 weren't terribly practical because they required that high voltage to 0:16:48.360 --> 0:16:52.520 operate to to create that ionization chamber, and homes were 0:16:52.560 --> 0:16:56.960 not wired for that kind of high voltage, so that 0:16:57.360 --> 0:16:59.920 meant that you couldn't really get one for your house. 0:17:00.120 --> 0:17:03.640 They were mostly used again in big industrial settings where 0:17:03.640 --> 0:17:06.439 you could wire things up for that kind of power. 0:17:07.040 --> 0:17:10.119 The solution to this problem was already set in motion, 0:17:10.320 --> 0:17:13.520 though at the time it was top secret. I'll get 0:17:13.520 --> 0:17:23.840 to that after this quick break. Now, while the high 0:17:23.960 --> 0:17:28.240 voltage smoke detectors weren't seen as practical from an implementation 0:17:28.280 --> 0:17:32.080 standpoint for your average homeowner, it was undeniable that they 0:17:32.080 --> 0:17:35.320 were useful, and this was particularly highlighted in the United 0:17:35.359 --> 0:17:38.560 States by a tragedy that took place on December one, 0:17:38.880 --> 0:17:42.600 ninety eight at the Roman Catholic School of Chicago, called 0:17:42.760 --> 0:17:46.800 Our Lady of the Angels School. Now, the origins of 0:17:46.800 --> 0:17:50.280 the fire have never been verified. No one knows exactly 0:17:50.480 --> 0:17:53.960 what started it, but it appeared to begin in the 0:17:54.160 --> 0:17:58.119 stairwell for the school, and the school had limited fire 0:17:58.160 --> 0:18:01.520 prevention measures in place. The school itself was an older 0:18:01.600 --> 0:18:05.720 building in Chicago and had been grandfathered into Chicago's safety 0:18:05.800 --> 0:18:10.120 standards because it had previously met earlier regulations. So when 0:18:10.119 --> 0:18:14.080 the city updated its fire safety regulations, one of the 0:18:14.119 --> 0:18:16.719 policies there was that older buildings that had passed the 0:18:16.800 --> 0:18:22.800 previous ones were considered safe. Students and staff were unaware 0:18:22.880 --> 0:18:25.119 of the danger of the fire until it became a 0:18:25.119 --> 0:18:29.560 critical threat, and more than ninety children died in that tragedy. 0:18:29.560 --> 0:18:33.240 It was a truly horrifying event and it illustrated the 0:18:33.280 --> 0:18:37.880 need to develop better fire detection and prevention methods. Research 0:18:37.920 --> 0:18:41.480 in Canada and the United States began looking into various 0:18:41.840 --> 0:18:46.000 catastrophic fires that had happened over the years, and according 0:18:46.040 --> 0:18:49.800 to doctor Jim Milkey of the University of Maryland, these 0:18:49.800 --> 0:18:55.119 studies found evidence suggesting that had smoke detectors been available 0:18:55.280 --> 0:18:59.440 at the time, there would have been fewer deaths in 0:18:59.480 --> 0:19:03.040 those catastrophic fires. Uh, there were more than three hundred 0:19:03.040 --> 0:19:06.080 of them that they were looking at, and rise of 0:19:06.160 --> 0:19:08.880 heat detectors, which I'll talk about in a second, would 0:19:08.920 --> 0:19:13.400 have decreased the number of fatalities less than ten. And 0:19:13.480 --> 0:19:15.840 these were hypotheses, mind you, you there's no way of 0:19:15.880 --> 0:19:18.600 knowing that that in fact would actually have been the 0:19:18.640 --> 0:19:21.280 way it played out. We only know what actually happened, 0:19:21.320 --> 0:19:24.280 not what might have happened. But the scholars were pointing 0:19:24.280 --> 0:19:26.760 out how the cause of death wasn't always due to 0:19:26.800 --> 0:19:30.960 direct exposure to fire itself, which rise of heat detectors 0:19:30.960 --> 0:19:34.240 would help you avoid, but exposure to smoke, and smoke 0:19:34.280 --> 0:19:37.679 detectors might activate well in advance of a rise of 0:19:37.720 --> 0:19:41.080 heat detector, giving people precious time to evacuate a building. 0:19:41.800 --> 0:19:44.640 So that rise of heat detector, that's like the kind 0:19:44.720 --> 0:19:46.960 I was talking about at the top of this episode. 0:19:47.240 --> 0:19:51.960 It's the type that can uh monitor increases in temperature 0:19:52.080 --> 0:19:56.320 and at a certain temperature they'll activate, they'll sound an alarm, 0:19:56.359 --> 0:19:58.440 but by then it might be too late. So the 0:19:58.520 --> 0:20:02.159 high voltage requirement for smoke detectors that ionized air that 0:20:02.280 --> 0:20:05.840 had an ionization chamber was still a problem at this point. 0:20:05.920 --> 0:20:09.440 They made them impractical and expensive, particularly for homeowners. It 0:20:09.600 --> 0:20:12.400 was again more common for really big buildings like manufacturing 0:20:12.440 --> 0:20:15.320 plants and factories and that kind of thing, and the 0:20:15.440 --> 0:20:17.600 rise of heat detectors like the ones I first described 0:20:17.600 --> 0:20:19.800 in this episode would also be used in those facilities. 0:20:20.040 --> 0:20:22.760 So the solution to this problem of requiring high voltage 0:20:22.880 --> 0:20:25.520 would have its roots in a top secret program that 0:20:25.560 --> 0:20:29.600 had a very different aim seem Back in ninety there 0:20:29.640 --> 0:20:32.399 was a guy named Glenn Seaborg who had been asked 0:20:32.400 --> 0:20:36.679 to join the highly classified Manhattan Project. Now this was, 0:20:36.760 --> 0:20:41.040 of course, the United States effort to find a way 0:20:41.080 --> 0:20:44.719 to weaponize atomic energy to split the atom to release 0:20:44.760 --> 0:20:48.520 an enormous and destructive force that could be used as 0:20:48.520 --> 0:20:52.760 a weapon. Seaborg led a team that researched radioactive materials 0:20:53.080 --> 0:20:55.399 as they tried to determine which of them would be 0:20:55.440 --> 0:20:58.639 the most useful in a weapon like an atomic bomb. 0:20:59.119 --> 0:21:04.240 They discovered in numerous radioactive elements in the process, elements 0:21:04.240 --> 0:21:07.280 that are above ninety two on the elemental table. We're 0:21:07.280 --> 0:21:10.800 all synthetic. They were all created in labs, and they're 0:21:11.240 --> 0:21:14.960 very unstable atoms now. Among the ones that they worked 0:21:14.960 --> 0:21:19.199 on was one called amerasirium. So a Mera sirium is 0:21:19.520 --> 0:21:24.840 a synthetic h element that was produced in the lab 0:21:24.880 --> 0:21:29.000 in a cyclotron experiment in Berkeley, California. The specific variant 0:21:29.160 --> 0:21:32.480 that we're interested in for this podcast is an isotope 0:21:32.520 --> 0:21:35.040 of a Mera cirium. It's a Mera cirium too forty one. 0:21:35.680 --> 0:21:37.639 And you know I mentioned what ions are, but what 0:21:37.840 --> 0:21:40.760 is an isotope in case it's been a while since 0:21:40.760 --> 0:21:43.520 you've had basic science. Because I always have to look 0:21:43.560 --> 0:21:46.639 these up. I'm not trying to shame anybody. I I 0:21:46.720 --> 0:21:49.080 get my stuff mixed up, so I gotta look it up. Well. 0:21:49.200 --> 0:21:51.320 You know, an ion is an atom or molecule that 0:21:51.359 --> 0:21:53.680 has a net electric charge, right, the means that either 0:21:54.080 --> 0:21:56.800 has too many or too few electron electrons for it 0:21:56.840 --> 0:21:59.840 to balance out with the protons. That's an ion. I 0:22:00.000 --> 0:22:03.240 aotopes are different. You have the the right number of 0:22:03.240 --> 0:22:07.200 protons and electrons, but you have different numbers of neutrons 0:22:07.320 --> 0:22:11.960 between two different two or more different variants of the 0:22:12.080 --> 0:22:16.160 same element. So amerasirium two forty one and a Mera 0:22:16.280 --> 0:22:19.879 sirium two forty two are nearly identical. They have the 0:22:19.920 --> 0:22:22.280 same number of protons and the same number of electrons, 0:22:22.520 --> 0:22:26.280 but a merasirium two forty two has one neutron more 0:22:26.640 --> 0:22:29.560 than a Mera cirium too forty one. It changes the 0:22:29.600 --> 0:22:34.000 atomic mass of that particular atom, but otherwise as the 0:22:34.040 --> 0:22:38.560 same protons and electrons as the other isotopes of that element. 0:22:39.080 --> 0:22:42.760 So a Mera cirium to forty one is radioactive, which 0:22:42.800 --> 0:22:47.919 means it decays and gives off radiation. It's ionic radiation, 0:22:48.080 --> 0:22:51.040 so that means that the energy that's given off, the 0:22:51.280 --> 0:22:55.200 radiation that's given off is energetic enough to strip electrons 0:22:55.280 --> 0:22:59.040 off of atoms or molecules and ionizing them. A small 0:22:59.080 --> 0:23:02.639 amount of amerasium to forty one will ionize atoms like 0:23:02.680 --> 0:23:07.480 oxygen and nitrogen just through the natural process of radioactive decay. 0:23:07.600 --> 0:23:09.880 So what do I mean by a small amount. I'm 0:23:09.920 --> 0:23:14.119 talking about one five thousand of a gram, so a 0:23:14.359 --> 0:23:21.000 super tiny amount of radioactive material. Now, smoke detector manufacturers 0:23:21.040 --> 0:23:23.600 did not immediately jump on a mera cirium as a 0:23:23.600 --> 0:23:27.399 replacement for a high voltage circuit. That would take some 0:23:27.520 --> 0:23:31.200 time and a lot of study before determining that amerasirium 0:23:31.400 --> 0:23:35.560 was pretty safe to use under specific parameters. The type 0:23:35.560 --> 0:23:40.320 of radiation gives off is primarily alpha radiation. There's alpha, beta, 0:23:40.359 --> 0:23:43.040 and gamma radiation. I'll talk more about that in a 0:23:43.080 --> 0:23:47.919 subsequent episode. But alpha radiation is the emission of alpha particles, 0:23:48.160 --> 0:23:50.920 and an alpha particle is essentially the same thing as 0:23:50.920 --> 0:23:55.160 a helium UH nucleus. UH. The nucleus of a helium 0:23:55.200 --> 0:23:59.479 atom includes two protons and two neutrons. That's an alpha 0:23:59.480 --> 0:24:03.560 particle two protons and two neutrons. An alpha particle has 0:24:03.720 --> 0:24:08.000 good ionization power, but it also doesn't have a lot 0:24:08.000 --> 0:24:12.720 of penetrative power. It can't go through matter very easily. 0:24:13.119 --> 0:24:16.000 It's a massive particle in the grand scheme of things 0:24:16.600 --> 0:24:19.600 UH and moves more slowly than other types of radiation. 0:24:20.040 --> 0:24:22.760 So an alpha particle is too weak to pass through 0:24:22.800 --> 0:24:25.480 a thin sheet of paper. It can only go through 0:24:25.520 --> 0:24:29.479 a few centimeters of air before it loses energy and 0:24:29.520 --> 0:24:32.800 can't move anymore. So, while embarrass serrium to forty one 0:24:33.160 --> 0:24:37.640 is radioactive, it's considered relatively safe in small amounts, and 0:24:37.680 --> 0:24:40.880 if kept in isolation. You wouldn't want to come into 0:24:40.920 --> 0:24:44.320 direct contact with the stuff. And you definitely wouldn't want 0:24:44.359 --> 0:24:48.239 to inhale or ingest any emiss cerium or get it 0:24:48.600 --> 0:24:52.080