0:04

Welcome to tex Stuff, a production of

0:06

I Heart Radios How Stuff Works. Hey

0:12

there, and welcome to tex Stuff. I'm

0:14

your host, Jonathan Strickland. I'm an executive

0:17

producer with I Heart Radio and a love of

0:19

all things tech. And you know, recently

0:21

guys that did episodes about how matches

0:23

work and how lighters work and talked

0:26

about how chemists and physicists

0:28

and inventors were able

0:30

to make it easier than ever to light a fire.

0:33

So I thought it's really only fitting if I do an

0:35

episode about smoke detectors

0:37

and smoke alarms and and other types

0:40

of fire alarms to talk

0:42

about their history and how they work.

0:45

Now, clearly, smoke detectors

0:47

are incredibly important because

0:49

we all know fires can be life threatening.

0:52

They can spread quickly, they can cut off

0:54

potential escape routes for the people who

0:56

are caught in the way. So early warning

0:59

systems that can alert us to danger

1:01

before it becomes a mortal danger

1:03

are fantastic inventions. And

1:06

there are a couple of inventions I want to talk about

1:08

before we actually get to smoke detectors.

1:11

I'm sure that doesn't come as a surprise to any of

1:13

you who have listened to tech stuff episodes

1:16

before, I always like to set the ground. Well,

1:18

the first one that I want to talk about is the

1:20

portable electric fire alarm,

1:23

as in a fire alarm that works on electricity,

1:26

not a fire alarm that detects electric

1:28

fires. Francis Robbins Upton,

1:31

who was a physicist who was a partner and

1:33

general manager of the Edison lamp

1:35

works, you know as in Thomas Edison,

1:38

developed this particular invention back

1:40

in eight Now. According

1:43

to the patent, the design would

1:45

sound an alarm after detecting

1:47

that the temperature had risen

1:49

above some predetermined limit,

1:52

so if it got too hot, this

1:54

thing would go off. And the way

1:56

this would work was really clever. You

1:58

can actually learn exactly how it was supposed

2:01

to work based on the patent that

2:03

Upton got on this particular invention.

2:06

So the way it

2:09

works is that the there are a pair of

2:11

electrical contacts and

2:13

if they are in in contact with each other,

2:15

if they touch each other, it completes a

2:17

circuit. But normally there's

2:19

a gap between them. An electricity

2:21

can't pass between the two that it

2:24

can't cross that gap, so

2:26

it's normally in the off position. However,

2:29

one of those two electrical contacts

2:32

is mounted on a fixed

2:34

arm and the other is on an arm that's

2:36

attached to a coil of bimetallic

2:40

material. Now, I mentioned

2:42

bimetallic strips in the episode

2:44

about lighters, and it's something you find

2:46

in a lot of different technologies

2:48

that depend upon changes in temperature

2:52

as a variable, like thermostats

2:54

have bimetallic strips in them. And

2:57

essentially what it is is a strip of metal

2:59

that insists of two different

3:02

metals. And think of it as like a metal

3:04

sandwich, a top side and a bottom side,

3:07

and one metal is the top side, the

3:09

other metal is the bottom side, and each

3:11

metal has slightly different properties,

3:14

and one of those properties is how quickly

3:16

they expand when they're heated

3:19

up. You know, we know that metal expands

3:21

as it gets warmer. While using a bimetallic

3:23

strip, you have one side that will expand

3:26

faster than the other side,

3:28

and when that happens, it causes the strip

3:30

to curl, so it deforms

3:33

as it gets warmer, one side

3:36

is expanding faster than the other

3:38

and you get this curled metal as

3:41

a result. So with Upton's proposed

3:43

invention in the patent, this

3:45

coil of bimetallic material

3:48

would act as sort of an actuator. As

3:50

it would get warm, it would expand

3:53

and this in turn would create a pushing

3:55

force on the arm

3:57

with the electrical contact on it that

4:00

then can move toward the other electrical

4:02

contact that's in a fixed position. And

4:04

so once the coil had

4:07

expanded enough, the two contacts would

4:09

touch one another and it would

4:11

complete a circuit. At that

4:13

point, electrical current could actually

4:15

flow from a battery that was connected

4:18

to this device all the way through

4:20

to activate an alarm bell. So

4:23

once the temperature got hot enough the two

4:25

contacts touch, you get a circuit.

4:27

The alarm bell goes off. If it cools down,

4:30

the contacts will slowly separate,

4:32

and eventually they'll separate enough where that

4:34

electrical circuit can't be complete

4:36

anymore. The alarm bell would go off. And

4:39

Upton's invention was, without a doubt,

4:41

a very clever one, and it could

4:44

help save property by sounding

4:46

an alarm before a fire had raged

4:48

completely out of control. But there

4:50

are many dangers with

4:53

fires, and heat is just

4:55

one of them. Another very serious

4:57

danger is smoke, which not only

4:59

a scares your vision, but it also

5:02

can suffocate you as well. So

5:04

while the alarm as design would

5:06

work, it wouldn't necessarily be

5:08

enough to save lives, or

5:11

it might not save enough lives,

5:13

because it would only go into action after the

5:15

temperature had already increased enough

5:18

to make this bimetallic strip expand

5:20

to a sufficient degree, and

5:22

by that time it might already be too late

5:24

for the people in that building. Now,

5:27

as far as I know, Edison's

5:29

company didn't actually produce any of

5:31

these fire alarms, but they did patent

5:33

it. Over in Great Britain, there

5:35

was a fellow named George Andrew Darby

5:37

who patented his own fire alarm,

5:39

also triggered by an increase

5:42

in temperature. But Darby's invention

5:44

did not depend upon bimetallic

5:46

strips. It depended on

5:49

butter for some other material

5:51

that melts at higher temperatures.

5:54

Say what, all right, So imagine

5:57

you've got a see saw like contraption,

6:00

a lever in other words, and the

6:02

heavy end of the lever uh is

6:05

up in the air actually because you

6:07

have a weight on the opposite end

6:09

of that lever. So it's like a kid sitting on a

6:11

seesaw that doesn't have another kid at the end

6:14

of it. The kid at the end of the seesaw

6:16

weighs it down and the free

6:19

end of the seesaws up in the air well

6:21

in this case, the fire alarms

6:23

seesaw. The arm that's up in the air

6:25

has an electrical contact point on it,

6:28

and if the arm of the

6:30

seesaw were to come down, that

6:32

contact would complete a circuit,

6:35

and thus electricity

6:37

would be able to run from a battery through

6:39

an alarm, very much like Upton's

6:42

invention. So weighing down

6:44

the other end of the arm, the thing that's actually keeping

6:46

the electrical contact up in the air is

6:49

a block of butter or fat

6:52

or wax or some other material

6:54

that can melt at higher temperatures.

6:56

So as the temperature rises, the

6:59

block begins to melt away, and

7:01

eventually it melts enough so that

7:03

the weight isn't sufficient to keep the

7:05

other end of the seesaw up in the air, and

7:07

it'll sink down and the contact

7:09

will complete the circuit and the alarm will

7:11

go off. I was amused to

7:14

find a butter based fire

7:16

alarm. I wasn't surprised that it came out of

7:18

England, but I was amused to find it. I

7:20

can think of a few potential problems with such

7:22

an arrangement. For example, it

7:24

might start attracting pests that could

7:27

eat the weight. So

7:29

in those cases you wouldn't actually have a fire alarm,

7:32

but you might have a rat alarm,

7:35

or it would just turn rancid and smell

7:37

awful. It's still a pretty

7:40

clever approach, but not one

7:42

that I think you would actually want to put

7:44

in your buildings. But these

7:46

solutions weren't practical for homes

7:49

or anything like that. As I mentioned, they wouldn't

7:51

really alert you to the presence of smoke, which

7:53

on its own would be enough to be deadly. So

7:56

this was really looked at as

7:58

more of a solution for things like factories

8:01

facilities, where you've got a lot of industrial

8:03

operations going on, where the risk of fire

8:06

is high and the risk of property

8:08

loss is also high. Smoke

8:11

detectors also trace their history

8:13

back to chemists, physicists, and

8:15

inventors, and in fact, you could say

8:17

that smoke detectors were made possible not

8:20

just through exploratory science, but also

8:22

happy accidents. And will begin

8:25

with a super smart Swiss physicist

8:27

in the early twentieth century and try

8:30

saying that three times fast

8:32

super smart Swiss physicist. His

8:35

name was Heinrich Grinaker

8:38

and Grindeker or grind Acre if

8:40

you prefer, studied a lot of

8:42

different stuff, including radioactivity.

8:45

Vilhelm Rindken had discovered the existence

8:48

of X rays in and

8:51

Grindeker devoted a good deal of

8:53

his work toward getting a better understanding

8:56

of X rays and other forms

8:58

of radiation, and to do that he had

9:00

to overcome some practical obstacles.

9:02

For example, he needed a device to

9:04

help measure the intensity of X rays,

9:07

and such a device didn't really exist yet,

9:09

so he got to work inventing one. X

9:12

rays are a type of ionizing

9:14

radiation that means that when they encounter

9:17

molecules or atoms, they

9:19

can ionize them. And an

9:21

ion is a molecule or an

9:23

atom that has a net electrical charge,

9:26

So it's either a positive particle

9:28

or a negative particle. And a positive

9:31

ion is one that has more protons

9:33

than electrons, so you have a net

9:35

positive charge. A negative ion would be the opposite,

9:38

has more electrons than protons and has a

9:40

net negative charge. Now,

9:42

one thing Grineker did was to

9:44

create ions by

9:46

building a grid of wires through

9:49

which he could stream high voltage

9:51

current and you would pass air

9:54

molecules essentially through this grid,

9:56

and the current would strip

9:59

electron off of those

10:01

particles, creating positive ions.

10:04

So the grid was in this chamber

10:06

through which gas could move, and as I

10:08

said, the current would ionize the gas.

10:10

But the other really neat thing he did was he invented

10:13

a voltage multiplier circuit

10:15

because he needed to generate this really

10:18

high voltage around two twenty

10:20

volts actually, and that could take

10:23

incoming alternating current electricity.

10:26

That's the type of electricity

10:28

that power plants typically send

10:30

out because it's easier to send out alternating

10:32

current over long distances than direct current.

10:35

Well, Grindaker's invention

10:37

would bring in alternating current and

10:39

then convert it to direct current and

10:42

run the direct current through a circuit with stuff

10:44

like capacitors and diodes. And the

10:46

whole process is a bit complicated

10:48

to explain, particularly without the

10:50

use of visual aids, and also it goes

10:52

beyond today's topic. But the

10:54

future I will have to talk about voltage multiplying

10:57

circuits more specifically, because

10:59

they are in and in all sorts of technologies, including

11:01

super cool bleeding edge science

11:03

stuff like particle accelerators. But for

11:06

the purposes of this episode, The important thing to remember

11:08

is that it made it possible for Grindeker

11:10

to create an ionization chamber.

11:12

Now, Greennecker's concern was

11:15

radioactivity, and so we're gonna leave

11:17

off his part of the story at this point

11:19

because that was his big contribution,

11:22

was creating a feasible way

11:24

to make an ionization chamber.

11:26

We need to focus more on the folks who actually

11:29

made the first smoke detectors. Uh.

11:31

Maybe I'll do a full episode about Grienneker and

11:33

other early physicists in the future, since

11:36

their work would lead to a deeper understanding of

11:38

atomic physics and by extension,

11:40

quantum physics. But for now, we're going to get back

11:42

to smoke alarms. So that brings

11:44

us to our next Swiss smarty

11:46

pants person, Valter Yeager.

11:49

Now, back in n Yeager

11:51

wasn't setting out to build a smoke

11:53

detector. That wasn't his goal. Instead,

11:56

he had developed a hypothesis. He

11:58

thought that perhaps using a device

12:01

with an ionization chamber like the one

12:03

grind Acre had made, he could build

12:05

a poison gas detector.

12:08

So how did he think he could do this? Well,

12:10

this gets into how smoke detectors actually

12:12

work. So we're going to dive into it. All

12:14

right, So, as I said before, you've got your

12:16

ionized particles. That's a basic

12:18

component of a large number of smoke

12:21

detectors. There's actually a different type of smoke

12:23

detector that doesn't use an ionization

12:25

chamber at all, but i'll cover that later

12:27

in this episode. So, these ionized

12:30

particles are positively charged. They've

12:32

had electrons stripped off of them, so they

12:34

have more protons than electrons. They're

12:36

positively charged. A battery connected

12:39

to two metal plates creates

12:41

a positively charged surface on

12:43

one side and a negatively charged

12:46

surface on the other side. So the

12:48

electrons that are stripped away

12:51

from the molecules will

12:53

then move to the positively charged plate

12:56

and the positive ions are going to move to the negatively

12:59

charged plate. But has opposite charges attract

13:02

this movement of electrons is

13:04

electricity. That's what electricity is. So

13:07

it's not a lot of electrical current, but it's

13:09

consistent. Yeager hypothesized

13:12

that poison gas would interfere

13:15

with that current of electricity,

13:17

and that if you detected a drop in

13:20

current, that would set off the detector,

13:23

and Yeager would say, oh, there's

13:25

poison gas here. So he started testing

13:27

it accept it didn't work. The poison

13:29

gas did not set off the detector. And

13:31

as the story goes, Yeager

13:33

was getting frustrated and stressed

13:35

out and he decided to smoke a cigarette

13:38

and think about the problem. And

13:40

so he lights up the cigarette. He starts puffing

13:42

away, and the next thing he knows is detectors

13:44

going off. Now, the poison gas had

13:46

not interacted with the ions, but

13:48

the smoke did, So what's

13:51

going on. Well, there are particles

13:53

in smoke that can bond to ions,

13:56

neutralizing them, So negatively charged

13:58

particles that can bond with the

14:00

positive ones. And when that happens,

14:03

you get a drop in current between those

14:05

two electric plates I was talking about,

14:08

and that's what sets off the detector. Another

14:10

scientist named Ernst Maine improved

14:13

upon this design by using a cold

14:15

cathode tube. I've talked about

14:17

cathode tubes in the past. Here's a quick

14:20

rundown. It's essentially a device that emits

14:22

electrons. Looks a lot like a lightbulb.

14:25

You've got a a filament

14:28

that's encased inside a vacuum tube,

14:30

and the ideas that you pass an electric current

14:33

through the cathode tubes filament the

14:35

cathode tubes filament heats up due to electrical

14:38

resistance, and as it heats

14:40

up, it starts to emit a stream

14:42

of electrons due to thermionic

14:44

emission. Essentially,

14:47

that electrical resistance means

14:49

that the flow gets impeded. You

14:52

convert some of that energy over into heat.

14:54

The heat itself strips electrons away from

14:56

the tungusten filament inside, and

14:59

then you get your dream. Cold

15:01

cathode tubes work on a different

15:03

principle, though they aren't necessarily

15:05

actually cold. So you've got

15:07

a cathode that's the electrode

15:10

that would emit electrons,

15:13

and on the opposite end of the tube you have

15:15

an anode that's the side that accepts

15:17

electron. So it's the positively charged

15:20

part of this particular

15:22

device. And these are both

15:24

sealed in a tube, and that

15:26

tube also has a gas

15:28

inside of it, and applying a sufficient

15:31

voltage between the cathode and the anode

15:34

a difference in electrical charge.

15:36

If it's sufficient enough, it will cause

15:38

a discharge between the two and the

15:40

gas will act as a carrier for that electrical

15:43

current. So a neon light is an implementation

15:45

of the cold cathode tube technology.

15:49

Malee's objective was to boost

15:51

the signal from the detection circuit

15:54

so that the signal could be strong enough to trigger

15:56

an alarm, so not just that would

15:58

detect a drop in current

16:01

or a change in the electrical current

16:03

across these two plates, but that

16:05

it would also have a strong enough

16:07

signal so it could power allowed

16:10

speaker or activate a

16:12

physical bell. And

16:14

a separate circuit in the smoke detector

16:17

activates upon this change in electrical

16:19

current, sending a signal to the cold cathode

16:21

tube, which acts like an amplifier. It takes

16:24

that incoming signal amplifies

16:26

it enough for it to do some of the useful work

16:28

like powering allowed speaker and

16:31

thus alerting you that there is in

16:33

fact smoke in the area. Now.

16:35

Yeager, being an enterprising sort, partnered

16:38

with Maine to launch a business offering smoke

16:40

detectors in the late nineteen forties. However,

16:42

these detectors weren't terribly practical

16:45

because they required that high voltage

16:48

to operate to to create that ionization

16:50

chamber, and homes were not wired

16:53

for that kind of high voltage, so

16:56

that meant that you couldn't really get

16:59

one for your house. They were mostly used

17:01

again in big industrial settings where

17:03

you could wire things up for that

17:05

kind of power. The solution to

17:07

this problem was already set in motion,

17:10

though at the time it was top secret.

17:13

I'll get to that after this quick

17:15

break. Now,

17:23

while the high voltage smoke detectors

17:25

weren't seen as practical from an implementation

17:28

standpoint for your average homeowner, it

17:30

was undeniable that they were useful,

17:32

and this was particularly highlighted in the

17:35

United States by a tragedy

17:37

that took place on December one, ninety

17:39

eight at the Roman Catholic School of Chicago,

17:42

called Our Lady of the Angels

17:44

School. Now, the origins

17:46

of the fire have never been verified.

17:49

No one knows exactly what started

17:51

it, but it appeared to begin in

17:53

the stairwell for the school,

17:56

and the school had limited fire prevention measures

17:59

in place. The school itself was an older

18:01

building in Chicago and had been grandfathered

18:04

into Chicago's safety standards

18:06

because it had previously met earlier

18:08

regulations. So when the city updated

18:11

its fire safety regulations, one

18:13

of the policies there was that older buildings that

18:15

had passed the previous ones were

18:19

considered safe. Students and

18:21

staff were unaware of the danger

18:23

of the fire until it became a critical threat,

18:26

and more than ninety children died

18:28

in that tragedy. It was a truly horrifying

18:31

event and it illustrated the need to

18:33

develop better fire detection and prevention

18:36

methods. Research in Canada

18:38

and the United States began looking into

18:41

various catastrophic fires

18:43

that had happened over the years, and

18:45

according to doctor Jim Milkey

18:47

of the University of Maryland, these studies

18:50

found evidence suggesting that

18:52

had smoke detectors been available

18:55

at the time, there would have been fewer

18:58

deaths in those catastrophic

19:00

fires. Uh, there were more than three hundred

19:03

of them that they were looking at, and rise

19:06

of heat detectors, which I'll talk about

19:08

in a second, would have decreased the number of fatalities

19:10

less than ten. And

19:13

these were hypotheses, mind you, you there's no way

19:15

of knowing that that in fact would

19:17

actually have been the way it played out. We only

19:20

know what actually happened, not what might have happened.

19:23

But the scholars were pointing out how the cause

19:25

of death wasn't always due to direct exposure

19:27

to fire itself, which rise

19:30

of heat detectors would help you avoid,

19:32

but exposure to smoke, and smoke detectors

19:34

might activate well in advance of

19:37

a rise of heat detector, giving people

19:39

precious time to evacuate a building. So

19:42

that rise of heat detector, that's like

19:44

the kind I was talking about at the top of this

19:46

episode. It's the type that can

19:49

uh monitor increases

19:51

in temperature and at a certain temperature

19:53

they'll activate, they'll sound an alarm,

19:56

but by then it might be too late. So

19:58

the high voltage requirement for smoke detectors

20:00

that ionized air that had an

20:02

ionization chamber was still

20:04

a problem at this point. They made them impractical

20:07

and expensive, particularly for homeowners. It

20:09

was again more common for really big buildings

20:11

like manufacturing plants and factories and that

20:14

kind of thing, and the rise of heat detectors

20:16

like the ones I first described in this episode would also

20:18

be used in those facilities. So the solution

20:20

to this problem of requiring high voltage

20:22

would have its roots in a top secret

20:24

program that had a very different aim seem

20:27

Back in ninety there was a

20:29

guy named Glenn Seaborg who

20:31

had been asked to join the highly classified

20:34

Manhattan Project. Now this was,

20:36

of course, the United States effort

20:39

to find a way to weaponize

20:41

atomic energy to split the atom

20:44

to release an enormous and destructive

20:46

force that could be used as a weapon. Seaborg

20:50

led a team that researched radioactive

20:52

materials as they tried to determine

20:54

which of them would be the most useful

20:56

in a weapon like an atomic bomb.

20:59

They discovered in numerous radioactive

21:01

elements in the process, elements

21:04

that are above ninety two on the elemental

21:06

table. We're all synthetic. They were

21:08

all created in labs, and

21:10

they're very unstable atoms

21:13

now. Among the ones that they worked on was

21:15

one called amerasirium. So

21:17

a Mera sirium is a synthetic

21:21

h element that was produced

21:23

in the lab in a cyclotron

21:25

experiment in Berkeley, California. The

21:28

specific variant that we're interested

21:30

in for this podcast is an isotope

21:32

of a Mera cirium. It's a Mera cirium too forty

21:34

one. And you know I mentioned what ions

21:37

are, but what is an isotope in

21:39

case it's been a while since you've had basic

21:41

science. Because I always have to look these

21:43

up. I'm not trying to shame anybody. I

21:46

I get my stuff mixed up, so I gotta look it

21:48

up. Well. You know, an ion is an atom or

21:50

molecule that has a net electric charge,

21:52

right, the means that either has too many or

21:54

too few electron electrons for it to

21:56

balance out with the protons. That's an

21:58

ion. I aotopes are different.

22:01

You have the the right number

22:03

of protons and electrons, but you

22:05

have different numbers of neutrons between

22:08

two different two or more

22:10

different variants of the same element.

22:13

So amerasirium two forty

22:15

one and a Mera sirium two forty two

22:18

are nearly identical. They have the same

22:20

number of protons and the same number of electrons,

22:22

but a merasirium two forty two has

22:24

one neutron more than

22:26

a Mera cirium too forty one. It changes

22:29

the atomic mass

22:31

of that particular atom, but otherwise

22:33

as the same protons and electrons

22:35

as the other isotopes of that element.

22:39

So a Mera cirium to forty one is

22:41

radioactive, which means it decays

22:44

and gives off radiation. It's

22:46

ionic radiation, so that means

22:48

that the energy that's given off,

22:50

the radiation that's given off is energetic

22:53

enough to strip electrons off of atoms

22:56

or molecules and ionizing them.

22:58

A small amount of amerasium

23:00

to forty one will ionize atoms like oxygen

23:03

and nitrogen just through the natural

23:05

process of radioactive decay.

23:07

So what do I mean by a small amount. I'm

23:09

talking about one five thousand

23:12

of a gram, so a super

23:15

tiny amount of radioactive material.

23:18

Now, smoke detector

23:20

manufacturers did not immediately jump

23:22

on a mera cirium as a replacement for

23:24

a high voltage circuit. That

23:26

would take some time and a lot of study

23:29

before determining that amerasirium was

23:31

pretty safe to use under specific

23:34

parameters. The type of radiation

23:36

gives off is primarily alpha radiation.

23:39

There's alpha, beta, and gamma radiation. I'll

23:41

talk more about that in a subsequent episode.

23:44

But alpha radiation is the emission of

23:46

alpha particles, and an alpha particle

23:49

is essentially the same thing as a helium UH

23:52

nucleus. UH. The nucleus

23:54

of a helium atom includes two

23:56

protons and two neutrons. That's

23:59

an alpha particle two protons and two neutrons.

24:01

An alpha particle has good

24:04

ionization power, but

24:06

it also doesn't have a lot of penetrative

24:08

power. It can't go through matter

24:11

very easily. It's a massive

24:14

particle in the grand scheme of things UH

24:16

and moves more slowly than other types

24:18

of radiation. So an alpha

24:21

particle is too weak to pass through a thin

24:23

sheet of paper. It can only go through

24:25

a few centimeters of air before

24:27

it loses energy and can't move

24:30

anymore. So, while embarrass serrium to

24:32

forty one is radioactive, it's

24:34

considered relatively safe in small

24:36

amounts, and if kept in isolation.

24:39

You wouldn't want to come into direct contact

24:41

with the stuff. And you definitely wouldn't

24:44

want to inhale or ingest any emiss

24:46

cerium or get it in

24:48

an open wound because it is carcinogenic.

24:51

But it would have to get past barriers.

24:54

It's not even strong enough to get through the

24:56

skin, but it is strong enough if

24:58

you were to ingest or breathe in some dust,

25:01

it could potentially cause

25:03

cancer. It could certainly increase your risk

25:06

of developing cancer. So

25:08

there is a danger to it. So your typical

25:11

smoke detector actually has some

25:13

radioactive material in it to create the

25:15

ions that flow between two charged

25:17

plates. The ions behave just

25:20

as the ones did with Yeager's high voltage

25:22

device. It's the same source stuff. It's charged

25:25

particles, So smoke particles will

25:27

still interact with them, just as they would with Yeager's

25:29

invention with the high voltage grid,

25:32

and they will still bind and cause a drop

25:35

in current, and that's what triggers the circuit that

25:37

powers the actual alarm. Now,

25:39

it would be nearly two decades

25:41

between the invention of amerasirium

25:44

two forty one and its application

25:47

as an ion generator in a smoke detector.

25:49

The United States Atomic Energy Commission

25:52

would grant a license in nineteen

25:54

sixty three authorizing the use

25:56

of a Merra cirium to forty one in

25:59

smoked at hectors. And the thought was that

26:01

the amount of radioactive material that

26:04

would be so tiny that,

26:07

uh, it would not really stand

26:09

to be a hazard, and it's just a very

26:11

low risk. But there was a very

26:13

real risk of fire

26:16

and smoke. And so when

26:18

you weighed it against each other and said

26:21

the risk of fire is high and the risk

26:23

of something happening because of this very

26:25

tiny amount of radioactive material is low,

26:27

it makes way more sense to air on

26:30

the side of detecting fires.

26:32

So two years later, in a

26:35

guy named Dwayne d Personal

26:38

introduced a battery powered smoke

26:41

detector. This eliminated the need for

26:43

that high voltage circuit, and

26:45

Personal came by this accidentally.

26:47

A lot of inventions really end up being

26:50

created as a consequence of some other unrelated

26:52

effort. So in nineteen sixty three,

26:54

that same year where the Atomic Energy

26:56

Commission granted the license, Personal

26:59

had been working on some tough problems

27:02

with his employees. Not problems

27:04

with his employees, but with his employees. They were

27:06

working on tough problems. Personal was

27:08

in a rough spot, so he had taken out a second mortgage

27:10

on his house to create a company called

27:12

Personal Company and a spinoff company called Satra.

27:15

To all are Sata Troll rather

27:18

Santatoral Corporation in Denver, Colorado.

27:21

Uh I find that name incredibly

27:23

difficult to say properly. In fact, I'm sure I'm

27:25

saying it incorrectly. But anyway, the company's

27:28

main business was selling heating

27:30

and air distribution equipment for commercial

27:32

buildings, so sort of like an HVAC

27:35

company for big, big, big

27:37

buildings. But the products his engineers

27:39

were working on was what he

27:41

called a static neutralizer.

27:44

The idea was he was going to create an ion

27:46

generator, and the idea was that these ions

27:48

would neutralize static electricity

27:51

build up on equipment, and that's

27:53

something that could be a real issue for industrial

27:56

operations and clean rooms and stuff.

27:58

So you need to have a way to new trill eyes

28:00

static build up, or else you can have a discharge

28:02

that could ruin tons of work.

28:05

However, his team had encountered a problem.

28:08

They saw that their ion generator was

28:10

getting clogged up pretty quickly. The ions

28:13

were attracting particles like dust

28:15

and stuff, and as it

28:17

was attracting dust, it was starting

28:19

to make the entire device as a whole

28:21

less effective. An engineer named

28:24

Lyman Blackwell was running tests to

28:26

see what could be done to keep the

28:28

ion generation going. While

28:30

testing the system, they noticed that the

28:32

ion meter they were using to monitor

28:35

performance would occasionally fluctuate, and

28:37

one of the technicians running the equipment

28:40

was a smoker. He was chained

28:42

smoking during the whole testing process. Eventually,

28:45

they figured out that the meter was detecting fluctuations

28:47

in the ion flow whenever

28:50

smoke was getting pulled in through the

28:52

fan on the generator and inserted

28:54

into the ion stream.

28:56

So essentially they were making the same discovery

28:59

that Yeager had aid decades earlier,

29:01

but the big difference was that Purcell's

29:04

ion generator didn't require

29:06

that high voltage to run because it was depending

29:08

on that small amount of ameras serium to forty

29:10

one. So he had the bright idea to

29:13

take this unexpected result and turn

29:15

it into an actual product. Two

29:17

years later, he had the first battery

29:19

operated ionization based smoke

29:21

detector. He called it the Smoke Guard

29:24

seven hundred, but it wasn't quite

29:26

ready for the home market yet because government

29:28

regulations had not yet caught up

29:30

to the technology. We're gonna get into

29:32

that as well, because, as it turns out, it's not enough

29:34

just to make tech that works. You have

29:36

to make tech that works within the boundaries

29:39

of laws and regulations. Meanwhile,

29:42

a pair of inventors named

29:44

Donald Steele and Robert Emerk

29:46

came up with an alternative method for

29:49

detecting smoke with a with

29:51

a device, And this approach wouldn't

29:53

used ionized particles at all, so there's

29:55

no need to create any

29:58

sort of ionization chamber. Instead,

30:00

Steel and m Mark created a smoke

30:03

detector that relied upon light and

30:05

photo detectors. So photo detectors

30:08

those are that's light sensors, rights a

30:10

sensor that detects light. There

30:12

are two basic categories of light sensors.

30:15

The first type are sometimes called photovoltaics.

30:17

These are devices that emit electrons

30:20

when they're exposed to light, So solar

30:22

panels are a type of photovoltaic

30:25

cells, uh they generate

30:28

electricity when exposed to light. The

30:30

other type of light sensor would be the

30:32

photo resistor or photo conductor. These

30:35

sensors have electrical properties that

30:37

change if they are actually exposed

30:40

to light. So, for example, a

30:42

photo resistor has a relatively high

30:44

electrical resistance when it's in the

30:47

dark, so that material resists

30:49

the flow of electricity going through it.

30:52

However, as the material is exposed

30:54

to light, the electrical resistance

30:56

decreases, an electricity can

30:58

pass through it more readily. So if

31:00

you place one of these devices in a circuit and

31:03

you have a voltage detector also

31:05

attached to that circuit, the detector

31:07

will pick up changes in voltage as

31:09

light hits the sensor. Now,

31:13

you could try and build a

31:15

smoke detector that works by having

31:17

a light shining on a photo sensor

31:20

of some sort that's at least partially

31:22

open to the air outside of the detector,

31:25

and if something like smoke were to enter

31:27

that pathway the direct

31:29

detector's events, and it somehow gets

31:32

in between the light and the sensor. Then

31:35

you would have smoke obscuring

31:37

or blocking some of that light, and

31:40

if it were enough, then the alarm would go off.

31:42

But that actually wouldn't be a very sensitive

31:44

smoke detector. It wouldn't work unless

31:46

the smoke was thick enough to really cause an

31:48

issue. It's actually pretty tricky for a

31:51

sensor to detect dips

31:53

in light intensity, and

31:55

by the time it would the smoke might

31:57

be thick enough to already be a major threat to people's

31:59

safety. But there's a clever work around

32:01

to this. So instead of an alarm that

32:04

goes off when a light no longer is

32:06

shining on it, designer

32:08

system where the alarm goes off if the sensor

32:11

detects light. Even a small

32:13

amount of light can create enough

32:16

of a signal for it to send a message

32:18

to start the alarm. So

32:20

in this version, you've got a light that's shining

32:23

down a pathway. So imagine a

32:25

chamber. You've got a light at one end, and

32:29

uh it's open, so that air

32:31

can come into the chamber nine

32:34

at a nine degree angle, like a perpendicular

32:36

angle to this light and tucked away

32:38

just a bit back. You have a little alcove where

32:41

there's a sensor. So under normal conditions,

32:44

the light is going through the chamber, but the

32:46

sensor is tucked in at a right

32:48

angle, so it's not picking up any light.

32:50

The sensor stays in the dark. However,

32:53

if smoke enters the chamber

32:56

that the light is passing through, some of

32:58

that light hits the smoke and starts

33:00

to scatter. And this is the

33:02

same sort of effect you would see if you were driving

33:04

a car on a really foggy day.

33:07

That's why you're not supposed to use the high beams

33:09

on your headlights when you're in the fog. The

33:11

light will hit the fog and scatter. It's

33:14

more likely to make it harder for you to see

33:16

rather than easier. When the smoke

33:18

detector, some of that scattered

33:20

light hits the sensor, which then

33:23

activates a signal to the alarm. And

33:25

that approach allows for far

33:27

more sensitivity In a smoke detector. They

33:30

can go off much faster than

33:32

one that would require the smoke to

33:34

block the light. So a dark

33:36

sensor picking up on light is just more reliable

33:39

than a lit up sensor trying to detect

33:42

a dip in brightness. However,

33:44

it's also not fool proof because vapor

33:46

or dust could cause false

33:48

alarms. Now, during all this innovation,

33:51

changes were starting to happen on regulatory

33:53

levels around the world. And when we come back,

33:56

I'll talk more about how that played out in the

33:58

United States. But first let's take an their

34:00

quick break. All

34:08

right, So now we've got the basic technology

34:10

of smoke detectors understood, let's talk

34:13

about regulations. See, if you're

34:15

going to produce and market something that's

34:17

meant to protect lives, it's

34:19

often the case that a government agency

34:22

or two will take notice and

34:24

they want to make sure that the thing you're

34:26

making does what you claim it does

34:29

it if lives literally hang in

34:31

the balance, it's important. So this is the

34:33

same basic underlying philosophy we

34:36

see an agencies that monitor stuff like

34:38

food processing and pharmaceutical

34:40

development and production. The

34:42

era I'm talking about in the late

34:44

nineteen sixties in the United States was

34:46

a particularly tumultuous time.

34:49

You had the Civil rights movement, you had America's

34:51

involvement in Vietnam, and other

34:53

really politically charged events

34:56

playing out in the US, and

34:58

these were sparks pun in tended

35:00

that ignited civil unrest across

35:03

the entire country, and

35:05

in turn that was testing the limits

35:07

of police forces and fire

35:10

prevention and fire uh

35:13

extinguishing services.

35:15

So this prompted the

35:18

US Congress to re examine policies

35:20

around safety to better protect

35:23

citizens. One thing to come out

35:25

of this was the Fire Research and

35:27

Safety Act, which was signed into law by

35:29

then President Lyndon Johnson.

35:32

The President was citing some figures that suggested

35:34

as many as twelve thousand Americans had

35:37

died in fires in nineteen sixties.

35:39

Six Later estimates adjusted

35:42

that number down significantly to like eight

35:44

thousand, but that's still way too many people.

35:46

The Act called for the creation of a

35:49

twenty person panel to study

35:51

the challenges and make recommendations

35:53

for new safety standards that could

35:55

be carried out at the federal level

35:58

and require any building in

36:00

the US to follow certain

36:02

processes to make sure that they were safe for

36:04

people. And it took a few years for

36:06

all of this to actually coalesce into a report.

36:09

I mean, it was a big task,

36:11

and we also happen to know that

36:14

things in the U. S. Government don't go

36:16

super fast. But in nineteen

36:19

seventy three, the panel released

36:21

a report. The report was titled

36:23

America Burning, which is pretty

36:26

sobering all on its own, and America

36:28

was leading the way in industrial

36:31

nations when it came to per capita deaths

36:33

and property loss due to fire. So

36:37

the argument they were making was that America

36:39

is this incredibly advanced country, Why

36:42

the heck are we losing so much to fire?

36:44

We should be doing better than that, And

36:47

of the deaths were occurring in people's homes.

36:50

The report also contained

36:52

pictures of Person's smoke guard

36:54

detector. He had come

36:57

to overcome challenges

36:59

to make his detector practical and safe, and

37:01

his original design did not have

37:03

a battery. Instead, it was to be hardwired

37:06

into the electrical system of a building. It

37:09

didn't require two twenty volts like

37:11

the earlier smoke detectors of Switzerland

37:13

did, but it still was an expensive

37:15

proposition and it made it an unlikely

37:18

candidate for home adoption because every

37:20

unit would set someone back about a thousand

37:22

dollars at the time, which would be a

37:24

lot more than that today.

37:27

So his team was able to create a version

37:29

that would operate on battery power, which

37:31

was already an engineering triumph, but they need

37:33

to figure out how to make

37:35

this a reliable one, or to

37:37

convince people that it was reliable, because

37:40

batteries, as we all know, eventually

37:42

exhaust themselves. The chemical reactions

37:45

inside a battery are what produces

37:47

electrons, and over time

37:50

you get to a point where there's been enough of the

37:52

chemical reaction going on that you

37:54

don't have the active ingredients necessary

37:56

to sustain that

37:58

that supply of electricity anymore, and

38:01

not the proper voltage anyway. And

38:03

we're talking about something as critical as a smoke detector,

38:05

that's a real problem. So his

38:07

team solved this issue by creating

38:09

circuits that would send a chirping

38:12

alarm to the smoke detector

38:15

if it detected a drop in voltage

38:17

across the primary circuit of the smoke detector.

38:20

So the chirp wouldn't require very much energy

38:22

of itself, and it would be repeated

38:25

until the voltage across the circuit returned

38:27

to the proper level, in other words, until the battery

38:29

was replaced. In addition, Personal

38:32

included a small card in

38:34

the box for the smoke guards seven,

38:37

and customers were meant to take the card

38:39

and then fill out little forms

38:41

on the card with their own information,

38:43

including their address and the date

38:46

that they installed their smoke detector,

38:48

and Personal's company would actually mail out an

38:50

annual reminder to its customers

38:52

saying, hey, it's time for you to replace the battery

38:55

and your smoke detector. In order to keep it operational.

38:58

Personal worked closely with safety

39:00

officials and organizations both to

39:02

improve his smoke detectors and

39:04

make them more useful, and

39:06

also to help shape policy so

39:09

that these detectors would be recognized as

39:11

effective and a good option to help curb

39:13

the problem of fatalities due to fire disasters,

39:16

and the work paid off both for Personal

39:19

and for people in general. He was able to convince

39:21

officials that a battery powered smoke detector

39:24

was effective if it

39:26

had the ability to alert occupants of

39:28

a dying battery. The government actually

39:30

would mandate that the chirping alarm

39:32

sound should last at least

39:35

seven consecutive days in

39:37

an effort to alert homeowners to change

39:39

out a battery. And this was specifically in case

39:41

so I might be out of town when the battery

39:43

starts to give out. They wanted it to

39:46

last long enough so that you would have time to

39:48

get back and find out. Oh gosh, I

39:50

need to switch out the batteries on my smoke detector.

39:52

The government also had to balance out the cost of

39:54

installing fire prevention systems and homes,

39:57

including in newly constructed homes.

40:00

Initially, plans called for both smoke

40:02

detectors and rise of heat detectors.

40:05

However, after numerous studies,

40:08

the government concluded that rise of heat detectors

40:10

weren't really practical if you were looking at

40:12

trying to save lives. They just they just

40:15

weren't good enough to do that, and

40:17

they were really expensive, and that

40:19

smoke detectors were much better

40:22

for the purpose of preventing fatalities.

40:25

And so that meant that they got rid of the rise

40:27

of heat detector requirement,

40:30

and that helped bring the cost down of

40:32

implementing fire protection systems and homes,

40:34

and that in turn increased the likelihood

40:37

that people would actually follow the rules and adopt

40:39

smoke detectors. The regulations

40:42

paved the way for Personal to manufacture,

40:44

market, and sell his smoke detectors to the American

40:46

public, who could be reassured that the devices

40:48

would actually provide a valuable and potentially

40:51

life saving service. He scaled up

40:53

his company to meet demand before eventually

40:55

selling it off in nineteen seventy seven.

40:58

And from everything I've read about him, it sounds

41:00

like he was motivated not only by an entrepreneurial

41:03

spirit, although he certainly had that,

41:05

but also a genuine desire to make his community

41:08

and the world a better place if

41:10

he could, And I think that's pretty cool.

41:13

Since the introduction of the optical and the

41:15

ionization chamber based smoke

41:17

detectors, we've seen some innovations,

41:20

but the basic principles all remain the

41:22

same. There are smoke detectors

41:24

that incorporate both types

41:26

of methodologies, meaning there are smoke detectors

41:29

that have independent systems to detect

41:31

the presence of smoke, and we've

41:33

seen some incorporate other types of text

41:35

such as network connectivity in the form of products

41:38

like the Nest Protect smoke detector,

41:40

and those smoke detectors add a little more

41:43

functionality to the basic kind. They

41:45

work on basically the same principle, but

41:47

they have some more features.

41:50

For example, they can send information

41:52

across a local area network wirelessly,

41:55

and then that network can send an alert to

41:57

you on an app on a smartphone,

42:00

and that could be valuable if, for example, you're away

42:02

from your home. When an alarm goes off to

42:04

give you a notification, you can perhaps

42:08

either call home, or if no one's home, you might

42:10

even call a fire department to go and check on your

42:12

home to make sure that everything is all

42:14

right. And most homes have

42:16

multiple smoke detectors. In fact, you're supposed

42:18

to have one outside of every bedroom,

42:21

for example, as well as maybe one in the kitchen.

42:23

My own home has six of the darned

42:25

things, and there

42:28

could be an issue of figuring out which detector

42:31

is going off, and that could be of vital

42:33

importance. So with connected

42:36

detectors, then you get a notification

42:38

saying detector number three is going

42:40

off, and you know that number three happens

42:43

to be outside the guest room, so

42:45

you would be able to very quickly

42:48

figure out what's going on, as

42:50

opposed to trying to determine which of your

42:52

numerous alarms is going off. It

42:55

also means that if a battery is running out

42:57

and a smoke detector

42:59

is chure ing, or maybe a battery was just a

43:01

bad battery and starts to chirp, you

43:03

get more quickly track down which detector

43:06

is making the chirping noise. This

43:09

really applies to folks like me

43:11

because I live in a townhouse that has

43:13

a few floors, and the center

43:15

of the townhouse is essentially like a chimney.

43:17

There are stairs that go from the bottom

43:19

floor, and the

43:22

stairwells open all the way to the top of

43:24

the town house, so it's

43:27

like an echo chamber inside my house,

43:29

which means when something like a smoke detector starts

43:31

to chirp, I can't easily identify

43:34

whether it's on the floor I'm on the

43:36

floor above me or the floor below me.

43:38

And I have six smoke detectors.

43:41

If it's time to replace the batteries, that's

43:43

one thing, But if it's just that a battery is

43:45

going bad early, then

43:48

I have to figure out which of those detectors is

43:50

making the problem. And exacerbating

43:53

this issue for me is the fact

43:55

that I have a cute little doggie named Timbolt,

43:58

and the chirping smoke detector noise

44:00

causes him intense distress,

44:03

like he starts to shake with fear.

44:06

So I get really

44:08

upset when one of my smoke detectors starts

44:10

to chirp prematurely. There's

44:13

no smoke or anything, it's just giving

44:15

me a chirp alarm, but that's a me

44:17

problem. One other thing that

44:19

a lot of smoke detectors can do these days

44:22

is they can also perform as

44:24

carbon monoxide detectors. So

44:27

carbon monoxide is an odorless

44:29

and colorless gas, so human beings

44:31

can't easily detect it, and it's

44:34

also toxic. It's a byproduct

44:36

from burning carbon based fuels like gasoline,

44:38

heating oil, or natural gas, and

44:41

in confined spaces it

44:43

can be really dangerous stuff, so like

44:45

a garage, for example. And while

44:47

we humans can't really detect carbon

44:49

monoxide with our own senses, there

44:51

are a lot of other ways to see if the stuff

44:54

is around. So carbon monoxide detectors

44:56

can work using one of a few different methods.

44:59

Upon detect action, they basically do the same thing

45:01

as a smoke detector. They send a signal to

45:03

sound an alarm, but the way they detect

45:06

the carbon monoxide can be a little

45:08

different. So there are three

45:10

basic approaches to this uh

45:13

and one you might have what are called

45:15

bio mimetic sensors.

45:17

These sensors mimic, thus

45:20

the name some sort of biological

45:22

functions, such as hemoglobin,

45:25

which interacts with carbon monoxide.

45:27

So These sensors have a gel

45:30

inside of them, and that gel can absorb

45:32

carbon monoxide. As the gel

45:35

does absorb carbon monoxide, the gel

45:37

changes color. You have a separate

45:39

sensor that's monitoring the color

45:42

of the gel, and if the gel

45:44

changes, then the sensor picks

45:47

up on that change and sends a signal to the alarm.

45:49

UH. These sensors can actually be reset.

45:52

The gel will return to its original

45:54

color once it

45:57

it gets rid of that carbon monoxide,

45:59

but it has to be set in an environment that's

46:01

free of carbon monoxide for several hours in order

46:03

to reset. The next type

46:06

is the metal oxide semiconductor

46:08

sensor. This has components to have a

46:10

certain level of electrical resistance, very

46:12

much like the optical smoke detectors I

46:14

talked about earlier. So these components

46:17

react with carbon monoxide in a way that lowers

46:20

the materials electrical resistance, and

46:23

so meters are monitoring a voltage

46:25

across a circuit and if it detects this change

46:28

in voltage, then it

46:30

will send a signal

46:33

to the alarm. And the third type

46:35

of sensor that you could find in a

46:37

carbon monoxide detector is an electrochemical

46:40

sensor. These sensors also detect

46:42

changes an electrical current in the

46:44

presence of carbon monoxide, but they

46:47

have electrodes that are inside

46:49

a chemical solution, so they're actually engulfed

46:52

in a chemical solution around these electrodes,

46:55

and the chemicals in the solution react very

46:57

very quickly in the presence of carbon monox

47:00

eide, and that changes the electrical

47:03

qualities of the the solution,

47:05

which means that you are able to detect

47:08

a change in the circuit very

47:10

very quickly. In fact, this stuff is used

47:13

in professional settings. Uh,

47:15

it's a very sensitive kind of alarm.

47:17

Today, there are a lot of smoke detectors that double as

47:19

carbon monoxide detectors with separate

47:22

components monitoring the environment. And

47:24

that's all smoke detectors work. Uh.

47:26

It's a fascinating journey letting us

47:29

learn a lot about physics, including

47:31

nuclear physics, and we will be

47:33

talking more about nuclear physics in our

47:35

next episode. We'll talk about radiation

47:38

and Geiger counters and

47:40

uh, the discoveries that were made

47:43

that really taught us all about radiation,

47:45

and a lot of those discoveries came at a

47:48

significant human cost. But

47:51

that's an episode for our

47:54

next tech stuff. This

47:56

particular episode is now concluded,

47:59

so if you guys have suggestions for future episodes

48:01

of tech Stuff, reach out to me on social

48:03

media. We are at Facebook and we

48:05

are at Twitter with the handle text stuff

48:08

H s W and I'll talk

48:10

to you again really soon. Text

48:17

Stuff is a production of I Heart Radio's How Stuff

48:19

Works. For more podcasts from my heart

48:21

Radio, visit the i heart Radio app,

48:23

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48:25

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