McPhail said the HPS should have conducted a public consultation before it started using drones, particularly with marginalized communities.

What’s important about HEPA air filters is they’re incredibly effective at capturing almost every size of particle. They can capture viruses, bacteria, pollen, PM2.5, allergens, and more. HEPA air filters are the most important component of any air purifier.

The answer to this question is the most fascinating thing about HEPA filters. Most of us might start out thinking HEPA filters work like a net, like this.

Most flights in 2022 and January 2023 lasted a few minutes or a few hours, but one flight went on for almost nine hours.

HEPAfilter vacuum

“Something should have been stated in here that these drones, under no circumstances whatsoever, will be used for the purposes of arming them and deploying them as weaponry.”

Audience Relations, CBC P.O. Box 500 Station A Toronto, ON Canada, M5W 1E6

“Saying nothing about it leaves it open,” Schneider said, pointing to how Hamilton police tested a controversial facial recognition software in 2020.

On the other hand, fiberglass air filters are made from glass – that means things like silica, alumina, calcium oxide, boron oxide, magnesium oxide, and sodium oxide.

“HEPA” stands for “high-efficiency particulate air” (filter). It sounds complicated, but HEPA air filters are nothing fancy. They were invented back in the 1940s when scientists were developing the atomic bomb, and they’re just a mat of randomly aligned fibers, made from either glass or synthetic materials. The synthetic material used in the air filter is similar to what’s used in quick-dry T-shirts.

Where those two mechanics intersect is the hardest particle size to capture. That’s because it’s not quite so small for diffusion to work its full strength, and it’s not quite large enough for straining to work its full strength. Call it the “weak spot” of HEPA filters. This dip in the graph is called the most penetrating particle size.

“Yes, there is the argument that we need some kind of effective law enforcement operation. What we also need in a democracy is accountability.”

HEPA filters are high efficiency filters that typically capture over 99.5% of all particulate pollution. They’re made from either plastic (PP+PET) or fiberglass, and can capture things like pollen, viruses, bacteria, mold and PM2.5. Diffusion also means they are highly effective at capturing nanoparticles too.

The training, along with the PIA, also says all flight information and other details about drone use would be available on the HPS’s website. An HPS webpage on drones appeared in late March, after questions from CBC, with basic information about the drone program, but there was nothing about specific flights.

Schneider said police in the U.S. used drones to surveil protests after the high-profile murder of George Floyd, who was killed in May 2020 by Minneapolis police officer Derek Chauvin.

For example, records related to a crash could be kept for over five years. Any records unnecessary for investigations or training will be deleted, according to the PIA.

While the flight logs don’t specify locations or the objective of missions categorized as “other,” police tweets indicate drones were used in a range of events, including:

Smart Air provides empirically backed, no-nonsense purifiers and masks, that remove the same particles as the big companies for a fraction of the cost. Only corporations benefit when clean air is a luxury.

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Through a Freedom of Information request, CBC Hamilton obtained the HPS’s privacy impact assessment (PIA) on drones. The document is needed to show how the technology may impact people’s privacy and ensure the service is in compliance with privacy laws.

Karen Louise Smith, an assistant professor at Brock University in St. Catharines who researches privacy, also said that in the case of a protest near a neighbourhood, she wonders how police could effectively use drones without encroaching on the privacy of bystanders and peering “into their homes.”

When identifying people, Bharaj said, the HPS uses techniques similar to any other digital imagery, like security camera footage.

Hamilton police began using drones in 2021, but the HPS has released little information about their use or the guidelines for operating them.

The flight logs also showed the HPS used drones more in January 2023 than in any other month over the previous year, with eight deployments. Seven of those were categorized as “other.”

Bharaj said the PIA provides exemptions for when the HPS doesn’t need to notify the public. They include “emergent situations” or when notifying people would jeopardize the investigation.

The training that drone operators receive about privacy is one page long, and says police will remove and try to avoid capturing personal information unrelated to the flight’s objective.

Privacy researchers interviewed by CBC Hamilton say the PIA doesn’t address using controversial technology like facial recognition to analyze drone images or arming the drones — which at least one U.S. tech firm has recently explored — and that gap leaves room to explore those possibilities.

OK, so do the particles below that size get through? For the really small particles (less than 0.3 microns), the science gets weirder. These particles that small have so little mass that they actually get bounced around like a pinball when they hit gas molecules (that’s called Brownian Motion). So they move in random zigzag patterns.

They also show the HPS didn’t follow part of its own PIA for two years, by not adding a webpage to its site about the drone program. It did so recently, after receiving questions from CBC Hamilton about its absence.

The Canadian Civil Liberties Association and three privacy experts reviewed the HPS drone PIA. They praised police for doing the assessment, but also said it has gaps.

“It is the police who get to decide when and how a protest turns into a riot and allows the police to respond in ways they see fit,” Schneider said, adding he believes the PIA doesn’t say enough about charter rights.

In 2020, the HPS’s police chief at the time, Eric Girt, told the police services board that the service should get drones to enhance officers’ response to “large-scale events” such as McMaster’s Fake Homecoming, protests and demonstrations at city hall, and Supercrawl, the annual downtown music and arts street festival.

Flight logs obtained by CBC Hamilton show the HPS deployed drones 43 times from January 2022 to the end of January 2023.

On the other hand, filters that exceed the requirements of a ‘HEPA air filter’ and capture more than 99.999% of particles are called ‘ULPA filters’ or ‘ultra-low penetration air filters’.

Particles this size can fit between the gaps in the filter. But they have a problem. They’ll try to follow the air around a HEPA filter fiber, but they are a bit heavy. So some of them don’t move fast enough and thus end up getting stuck. Scientists call this “interception.”

Cleaning HEPA filters with water, vacuuming them, or bashing them isn’t recommended, as it may damage the HEPA filter fibers. Smart Air tested washing HEPA filters in the Smart Air Lab. Learn more about the harms of cleaning your HEPA filter here.

OK, so if HEPA filters were invented in the 1940s, and they’re nothing fancy, then what makes any old filter a HEPA filter? Turns out using the term “HEPA” has a strict set of requirements. In Europe, HEPA filters must remove 99.95% (ISO) of particles. In the US, they must remove 99.97% of particles.

While vastly different events and incidents, they have one thing in common: A drone operated by the Hamilton Police Service (HPS) was buzzing around in the sky above and watching.

It is a priority for CBC to create a website that is accessible to all Canadians including people with visual, hearing, motor and cognitive challenges.

What happens for particles smaller than 10 microns? Let’s look at the next size range down: 0.3 – 1 microns. We’re talking about the size of a bacteria.

And here’s how the three different mechanics work for different particle sizes. Straining and impact capture large particles; interception captures medium particles, and diffusion captures the smallest particles.

Schneider said another detail that isn’t mentioned in the PIA is if there’s a possibility for the drones to be armed with weapons.

That intuition is true for big particles. By “big,” we’re talking typically larger than 10 microns. For comparison, a human hair is about 50 microns wide. So 10 microns is actually quite small.

Last summer, Axon Enterprise, a U.S.-based company formerly known as Taser International, announced it had started developing a drone armed with a Taser as part of a plan to stop mass shootings.

When following the ISO or European rules, filters that capture ≥85% of particles but less than 99.95% are called ‘EPA filters’ or ‘efficient particulate air filters’. These air filters do not meet the filtration requirement to be considered a ‘HEPA air filter’.

That’s Brownian motion and diffusion in action. Diffusion is incredibly effective at capturing nanoparticles. That means HEPA filters are also incredibly effective at capturing nanoparticles too.

But these “large” particles fly into a HEPA filter, they’re too big to get through, so they get stuck. Scientists have a name for that. When particles get stuck between two fibers, they call it “straining.”

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The police service has alerted the public via Twitter about deploying drones at least 17 times since Dec. 12, 2021, according to CBC Hamilton’s tracking of the tweets, despite using drones 43 times in one year.

Hamilton police tweeted how it was using drones to monitor protesters during Trudeau’s visit to the city in late January.

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Of those, 20 drone deployments were listed as collision reconstruction, six were filed under search and rescue, and 17 were filed under “other,” defined as anything besides collision reconstruction, and search and rescue.

The company immediately faced backlash, and three days after announcing its plans, Axon said it was “pausing” the project.

OK, but what does “particles” mean? All particles? A particular size of particles? Turns out HEPAs are tested against the “most penetrating particle size” (MPPS)–more on that in a bit.

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The drone program also uses software to “stitch” images together to create 3D renderings of scenes, similar to Google Street View.

Smart Air is a social enterprise and certified B Corp that offers simple, no-nonsense air purifiers and provides free education to protect people from the harms of air pollution. We are proud to be the only certified B Corp dedicated to fighting air pollution.

The term “HEPA filter” can be confusing. What does HEPA stand for? What is a HEPA filter made from, and what actually makes it a HEPA filter?

The Canadian government adopted rules in 2019 that say drones must stay within a person’s eyesight, unless they get an exemption. The rules have faced some pushback from drone users and police.

“It’s pretty short,” Tusikov, an assistant professor in York University’s criminology department, said of the privacy portion of the training.

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In a March 15 email, Const. Indy Bharaj, media relations officer with the HPS, wrote drones enhance public safety, adding that police and fire services around the world use the technology.

“This ‘other’ category raises some concerns. It could just be anything,” said Natasha Tusikov, a former analyst with Criminal Intelligence Service Canada and researcher with the RCMP. “I’d like to see some greater specificity.”

Police across Canada are increasingly using drones. In Hamilton, there are privacy ‘red flags,’ and new documents reveal when, how and why this aerial technology is used

The technology is increasingly being employed by police services across Canada, including in Charlottetown, Fredericton, Toronto, Ottawa, Vancouver and Winnipeg.

ULPA filter

In early 2022, Const. Krista-Lee Ernst, an HPS media relations officer, said in an email that when the police service used drones at the Grey Cup and the NHL Heritage Classic at Tim Hortons Field in March, it was to have a “bird’s-eye view” of the stadium for when officers have to control traffic at the start and end of the games. Drones were not used to identify people, she added.

HEPA is the international gold standard for filtering particles. Studies have shown the dangers of ionizers as they create air pollution. Because (1) most ionizers are too weak to have an effect, (2) they produce harmful ozone, PM2.5, Harmful VOC Gases, and Formaldehyde (3) they shoot out negative ions which cause particles to stick to surfaces in your home, rather than removing them.

“It all sounds very orderly, and considerate and thought through, but there are red flags,” said Brenda McPhail, CCLA’s director of the privacy, technology and surveillance program.

Rick Smith, Axon’s chief executive officer and founder, said at the time that using “remotely operated non-lethal drones capable of incapacitating an active shooter in less than 60 seconds” would be “a more effective, immediate, humane and ethical option to protect innocent people.”

Since HEPA filters are so great at capturing nanoparticles, it’s reasonable to think they might capture VOCs and gases too. Unfortunately, this is not the case. Since gases are not particles, they move and behave differently in the air. To capture VOCs and gases you’ll need a carbon filter for that.

To see what the randomly aligned mat of fibers looks like, here’s a closeup of the HEPA filter Smart Air makes for The Sqair air purifier, and then alongside it a view at the nano-level with the help of a microscope.

Most of the major air purifier companies use ionizers in their air purifiers, including Xiaomi, Blueair, Levoit, and many more. The reason is that it is a cheap way to get a boost in CADR (metric measuring the effectiveness of air purifiers) as a cheap ionizer can slightly improve the efficiency of the HEPA filter. Unfortunately, much of the time the user is unaware an ionizer is being used and unaware of the possible harmful effects.

She and all the privacy interests interviewed said drones may have a chilling effect on protests and people standing up to the police service because they may feel they’re being watched.

So the larger the particle, the better a HEPA filter filters out the particle? Not so fast! Did you notice the dip in the last graph? That happens because diffusion works really well under about 0.3 microns.

The dip in the graph most commonly occurs around the 0.3 microns mark, which is why people mention 0.3 microns all the time.

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These particles are so small they could easily fit through HEPA filters. But sadly (for their freedom) and happily (for our lungs), they don’t fly in straight lines. Because they fly in zigzag patterns, they end up hitting the fibers and getting stuck. Scientists call that diffusion.

A car crash in rural Hamilton. A search for a missing elderly woman. The 2021 CFL Grey Cup. A protest during a visit from Prime Minister Justin Trudeau.

Christopher Schneider, a sociology professor at Manitoba’s Brandon University whose research examines policing and technology, said introducing drones is a sign of the militarization of policing.