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  • This episode was made in partnership with Lydall.

  • They're dedicated to creatingcleaner, quieter, and safer world.

  • You can learn more at the link in the description.

  • [♪ INTRO]

  • You probably bump into HEPA filters fairly often.

  • They're the basis of modern  filtration, which is everywhere,

  • from your vacuum to your air purifier.

  • What you might not know is that  they represent a straight line

  • from the Manhattan Project to your living room.

  • This very scientific-sounding  acronym really just stands for

  • High Efficiency Particulate Air filter.

  • I guess HEPAF was less catchy.

  • And they do exactly what it says on the tin.

  • We rely on HEPA filters for keeping  our air clean and breathable.

  • They can handle all sorts of  things suspended in the air,

  • like wildfire smoke, particulate  air pollution, and even viruses.

  • And they were developed to protect  people making the first atomic bombs.

  • It all started back in 1938  when two German scientists  

  • accidentally discovered nuclear fission,

  • the process of splitting uranium atoms  to release a huge amount of energy.

  • The US government was worried the  Germans would use this to their advantage

  • during World War 2, so they launched  their own research into atomic weapons.

  • This classified research became  known as the Manhattan Project,

  • and ultimately resulted in the first  atomic bombs being dropped in 1945,

  • with devastating consequences.

  • But it took years of research and  development with radioactive materials

  • to get to that point, and there waspretty big risk of accidental exposure

  • for scientists, workers, and the general public.

  • Like in the manufacturing facilitieswhere processing the radioactive elements

  • uranium and plutonium could generate  dangerous particles in the air.

  • And that meant the Manhattan  Project had to develop

  • some kind of filter to stop  people from breathing all that in.

  • To do this, the researchers at the Army  Chemical Corps and Naval Research Laboratory

  • actually based their design on the gas masks  worn by German soldiers fighting in the war.

  • These designs had a special kind of paper  inside them, made of cellulose and asbestos.

  • The cellulose is nothing special;

  • it's the main component of most kinds of paper,

  • and was primarily there to give the  filter some structure and support.

  • But the asbestos proved to be surprisingly  effective at filtering out tiny particles,

  • whether they were from smoke, chemical weaponsor processing of radioactive materials.

  • So for the Manhattan Projectthe researchers simply

  • made a bigger version of the gas  mask filter to be used in buildings.

  • This was the precursor to today's HEPA filters.

  • Today, we know that asbestos is a less  than ideal choice for masks or buildings,

  • as it can cause a rare form of cancer.

  • But nobody knew that in the 1940s,

  • and scientists were excited at how  well this asbestos filter worked.

  • See, asbestos is a group of  naturally occurring minerals

  • that are made up of really tiny  fibers, just a few microns across.

  • And when they're added to the cellulose paper,

  • those fibers orient themselves in  all directions to form a fine mesh.

  • When air passes through the filter, it needs to  wind its way around all of these tiny strands,

  • so it's diverted in all  directions as it passes through.

  • And while air is just fine doing that,

  • the tiny particles that are carried  in the air have a tougher time of it.

  • To make sure the filters were as effective  as possible, the Army Chemical Corps

  • hired Nobel laureate and chemist Irving Langmuir

  • to figure out exactly what happened to the  particles on their journey through the filter.

  • Langmuir concluded that while the biggest  particles get caught up in the network of fibers

  • like grains in a sieve, this isn't  actually the main trapping mechanism.

  • Smaller particles have to swerve around  the criss-crossing fibers so much

  • that they eventually collide and stick.

  • And the very smallest kind of particleless than a tenth of a micron across,

  • follows an even more convoluted path.

  • These particles bounce off  the air molecules themselves

  • in what's known as Brownian motion.

  • Sooner or later their jerky random  path may bring them into contact

  • with one of the fibers of the filterwhere, once again, they'll stick.

  • But in between the largest  and smallest particle sizes,

  • none of the trapping  mechanisms work quite as well.

  • Medium particles are too big to  follow zig-zagging Brownian motion,

  • but small enough that they can  dodge the fibers more easily.

  • So Langmuir concluded that to make  the filters as effective as possible,

  • they should be designed to stop  these in-between particle sizes.

  • Langmuir found that the  filters were least effective

  • for a particle size of approximately 0.3 microns,

  • and recommended the Army test their  designs on particles of this size.

  • Anything bigger or smaller would  then be even easier to filter out.

  • As it turns out, this analysis from  80 years ago was remarkably accurate.

  • Today, particles between about 0.1 and 0.3 microns

  • are described as the most  penetrating particle size.

  • The exact size can vary  depending on the conditions,

  • but those tend to be the  hardest to stop with filters.

  • For the same reasons, they're also the ones

  • that will travel deepest into  our lungs if we breathe them in. Which is bad.

  • So the first HEPA filters were designed  to stop these penetrating particles,

  • with big sheets pleated many times, to lengthen  the gauntlet that the particles have to run.

  • In this way, the Manhattan Project  created an important safety innovation

  • with uses far beyond the atomic.

  • After World War 2 ended, the  filtering tech was declassified,

  • and the HEPA filters spread beyond  purely military applications.

  • And they got some improvements along the way.

  • They're smaller now, for startersand there's no more asbestos.

  • Instead, the fibers are made of glassWhich is less hazardous than asbestos.

  • Modern HEPA filters are designed to stop  99.97% of the most penetrating particles,

  • and even more of the particles either  side of that most penetrating threshold.

  • So while they continue to  stop radioactive particles,

  • they also stop tiny liquid dropletspollen, dirt, bacteria, and even viruses.

  • These filters, developed  for the Manhattan project,

  • touched off a boom in industries  from healthcare to electronics.

  • Yes, even your phone was made  with the help of an air filter.

  • Who would have guessed that it would  take a secretive nuclear research project

  • to come up with something that's  keeping us safe every day?

  • Thanks to Lydall for partnering  with us on this episode.

  • They believe that it's what's inside that matters,

  • which is why they're in the business of making  the hidden stuff that helps keep us safe.

  • That's everything from the components of  air filters like I talked about today,

  • to the filtration layers in N95 and surgical masks

  • that have been helping to  protect us from COVID-19.

  • And their team of engineers is always focused  on addressing current and future threats.

  • You can learn more about Lydall, and  their work making filtration material,

  • in the link in the description down below.

  • [♪ OUTRO]

This episode was made in partnership with Lydall.

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Thank the Manhattan Project for Your Air Filter

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    joey joey posted on 2021/05/25
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