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Flu Season Meets School Season: How Smarter Air Quality Keeps Classrooms Healthy

Every fall, classrooms fill with students—and viruses. Discover how smarter air quality strategies like low-resistance filtration, ventilation, and HEPA keep schools healthier, reduce absences, and support better learning outcomes.

Ava Montini

Aug 19, 2025

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The scene every September

Every September, the school bell rings and hallways come alive again. But as backpacks and lunch boxes make their way back into classrooms, another unwelcome guest tends to sneak in too: flu season.


Teachers know it all too well. The cough that spreads from desk to desk, the hand sanitizer bottles running low by mid-morning, the spike in absenteeism that leaves lesson plans hanging. Parents know it when the inevitable call from the school office comes: “Your child has a fever, please come pick them up.”


It’s a cycle we’ve come to accept as part of the school year. But what if healthier air could help change that story?


Why flu season and school season collide

Respiratory viruses (including influenza) spread more readily indoors, where exhaled particles accumulate. That’s not speculative; CDC/NIOSH is unambiguous that better indoor ventilation reduces occupants’ overall exposure to airborne viruses. CDC


We also know influenza isn’t only about big droplets from a sneeze. People exhale infectious virus in fine aerosols during normal breathing and speaking, which can linger and travel within a room. That was demonstrated in a landmark study that detected infectious influenza virus in exhaled breath from symptomatic adults, no cough required. PNASNature


The drier, colder air from the fall and winter cause low humidity, helping influenza survive and transmit more efficiently. Put simply: when we bring students back into dry, tightly sealed buildings, small airborne particles build up and stay infectious longer. That’s the fixable part.


Think of clean classroom air as a budget with three line items:

  1. Dilute what’s in the room (ventilation/outdoor air)

  2. Remove what’s in the room (filtration/air cleaning)

  3. Disable what’s in the room (UVGI where appropriate)

The key is using them together, sized to the space, and tuned to the school day.


What the standards now say and why it matters

Before the pandemic, most schools designed ventilation systems mainly for comfort—things like controlling odours or keeping CO₂ levels down—not for stopping the spread of illness.


That changed with ASHRAE’s new Standard 241, which focuses specifically on infection control. ASHRAE’s Standard 241: Control of Infectious Aerosols changes the target by introducing Equivalent Clean Airflow (ECA)—a flexible, additive way to hit a per-person clean air goal using any combination of ventilation, filtration, and proven air cleaning. That means a classroom can meet its target by mixing outdoor air with high-efficiency filters, HEPA units, and/or UVGI, rather than relying on outdoor air alone. ASHRAE+1


In parallel, CDC/NIOSH and EPA emphasize practical steps for schools: keep systems maintained, upgrade to MERV-13 or better where equipment allows, and supplement with portable HEPA when central systems can’t carry the whole load. CDC+1Environmental Protection Agency


The evidence that this keeps kids in class

  • In a study of 162 California elementary school classrooms, illness-related absences dropped by 1.6% for every extra 1 l/s‑person of ventilation. Increasing ventilation to meet the state standard (7.1 l/s‑person) from the average (4 l/s‑person) could reduce absences by 3.4%, gain $33 million annually in attendance-based funding, while costing just $4 million more in energy.

  • A study across Washington and Idaho found that a 1,000 ppm increase in indoor CO₂ correlated with a 0.5–0.9% drop in average daily attendance, translating into a 10–20% rise in student absences.

  • In controlled environments, each 500 ppm rise in CO₂ resulted in 1.4–1.8% slower response times, along with a 2.1–2.4% lower throughput on cognitive tasks.

  • Harvard’s COGfx study revealed that building occupants in green-certified, well-ventilated environments scored, on average, 101% higher in cognitive tests than those in conventional buildings. 


“Will MERV-13 break my units?” (The energy/airflow reality)

The honest answer: it depends on the filter you pick and your fan capacity. Research on rooftop units shows that moving from MERV-8 to MERV-13/14 can raise cooling-mode energy use by a few percent if the filter adds a lot of resistance, or it can reduce airflow if the fan can’t keep up. That’s why filter selection matters as much as efficiency.


Not all MERV-13 filters are created equal. Traditional pleated designs often create a higher pressure drop, forcing HVAC systems to work harder and sometimes leading to performance issues. But newer filtration technologies (explicitly engineered for low resistance at high efficiency, like Blade Air's Pro Filter,) are changing that equation. By combining advanced media with optimized form factors, these filters deliver MERV-13 (and higher) performance without the heavy airflow penalty.


California’s Title 24 research reinforces this point: Many modern low-pressure MERV-13 options can maintain pressure drops under 0.20 in. w.c., keeping systems within safe operating ranges. That means schools can improve air quality, meet public health guidance, and stay compliant without sacrificing system efficiency or longevity.


When you factor in the bigger picture—fewer student absences, better cognitive performance, and improved overall school operations—the ROI clearly tilts toward upgrading. Healthier air doesn’t just protect occupants; it protects the bottom line.


How this translates into a classroom target (the ECA idea)

ASHRAE 241’s Equivalent Clean Airflow lets you add up all the ways you’re cleaning air—outdoor air, central filtration, HEPA, UVGI—until you reach the per-occupant target for your space type. It’s flexible, measurable, and avoids unrealistic demands for 100% outdoor air in cold snaps. ASHRAE

A practical approach:

  • Estimate your current outdoor air (from design or testing).

  • Add the “clean air” from MERV-13 upgrades (using published efficiencies) and from each HEPA unit’s clean air delivery rate.

  • If the sum doesn’t meet the ECA target, add another portable unit or rethink your filtration strategy. ASHRAE


What about measurement and transparency?


CO₂ for ventilation

Track a few representative rooms across grade levels and building wings. Persistently high readings during class point to areas needing a fix (dampers, schedules, or supplemental air cleaning). Health Canada’s 1000 ppm residential benchmark is a useful anchor for conversations with families and staff. Canada.ca


PM₂.₅ for smoke days

A couple of low-drift sensors at kid-height in hallways or problem rooms can confirm your filtration strategy keeps indoor levels below outdoors during wildfire events. Health Canada and EPA both recommend this principle. Canada.ca


Bottom line

Flu season doesn’t have to mean higher absence rates and strained HVAC systems. The most effective path is a consistent program: keep ventilation tuned, use filters that balance efficiency with low resistance, and supplement with portable HEPA or UVGI where it makes sense.

The Unseen Reach of Wildfire Smoke

  • Writer: Ava Montini
    Ava Montini
  • Feb 12
  • 4 min read

The Smoke We Cannot Escape


Wildfires have long been a force of nature, shaping landscapes and ecosystems for millennia. But in recent years, their intensity and frequency have surged, fueled by rising global temperatures and prolonged drought conditions. The impact of these fires extends far beyond the visible destruction of forests and homes. Their invisible consequence—wildfire smoke—travels thousands of kilometers, infiltrating cities, homes, and even the bodies of people who may never see a flame.


The microscopic particles in wildfire smoke, known as particulate matter (PM), pose one of the greatest health threats from these disasters. They are not just an inconvenience or a temporary blight on air quality; they represent a serious, often underappreciated, global health crisis.


The Anatomy of Wildfire Smoke: What’s in the Air We Breathe?


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At first glance, wildfire smoke appears as a dense, ominous haze, carrying with it the distinct scent of burning vegetation. But within that haze lies a complex mixture of gases and tiny particles, many of which are harmful to human health.


Breaking Down Particulate Matter in Wildfire Smoke

Wildfire smoke contains a range of particles of varying sizes, each with distinct effects on human health:


Coarse Particles (PM10)

Particles with diameters of 10 micrometers or smaller. These can cause throat irritation, coughing, and eye discomfort but are typically trapped by the upper respiratory system.


Fine Particles (PM2.5)

Particles 2.5 micrometers or smaller are the most dangerous because they can bypass the body’s natural defense mechanisms, reaching deep into the lungs and even entering the bloodstream (U.S. Environmental Protection Agency, 2023).


Ultrafine Particles (UFPs)

Smaller than 0.1 micrometers, these are even more hazardous as they can infiltrate cells and potentially damage DNA.


The Dangers of PM2.5 Exposure

PM2.5 is particularly concerning due to its ability to cause severe health complications:

  • Lung Damage: Chronic exposure can cause scarring of lung tissue and decreased lung function, particularly in children and elderly populations.

  • Cardiovascular Issues: PM2.5 has been linked to an increased risk of heart attacks, strokes, and hypertension due to systemic inflammation (American Heart Association, 2022).

  • Neurological Effects: Recent studies suggest that PM2.5 particles may cross the blood-brain barrier, potentially contributing to neurodegenerative diseases such as Alzheimer’s and Parkinson’s (National Institute of Environmental Health Sciences, 2023).

  • Cancer Risk: Many PM2.5 particles contain carcinogenic compounds like benzene and formaldehyde, increasing the likelihood of developing lung and other cancers (National Cancer Institute, 2023).


Toxic Chemical Composition

  • Wildfire smoke contains carbon monoxide, volatile organic compounds (VOCs), benzene, formaldehyde, and other carcinogens (World Health Organization, 2022).

  • The exact composition depends on what is burning—trees, vegetation, homes, and even industrial materials can release different toxins.


Smoke Without Borders: The Far-Reaching Effects of Wildfire Pollution


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It’s a common misconception that wildfire smoke only affects areas directly adjacent to the fire itself. The reality is much more alarming: smoke travels vast distances, often impacting populations thousands of kilometers away.


In 2023, wildfires in Canada sent smoke as far south as Florida and even across the Atlantic to Europe (NASA Earth Observatory, 2023). This isn’t an isolated event—wildfire smoke from California has been detected in New York, and Siberian wildfires have impacted air quality in Alaska.


Why Does Smoke Travel So Far?

Smoke travels vast distances due to atmospheric transport, where large-scale wind patterns, jet streams, and pressure systems carry it far from its source. High-altitude smoke plumes further contribute to this movement, as intense fires generate their own weather patterns, creating pyrocumulonimbus clouds that inject smoke into the stratosphere, allowing it to spread across continents. Unlike localized pollution sources, wildfire smoke lingers in the atmosphere for weeks, gradually dispersing but remaining hazardous over time.


Strategies for Mitigating Wildfire Smoke Exposure


With wildfires becoming more frequent, protecting against smoke exposure is no longer a seasonal concern—it’s a year-round necessity.


Importance of Filtration and Indoor Air Quality

  • HEPA and Advanced Filtration: Using high-efficiency particulate air (HEPA) filters and low-pressure, high-efficiency filtration technologies can effectively remove PM2.5 and harmful gases from indoor environments.

  • HVAC Integration: Homes, schools, and businesses in wildfire-prone areas should consider upgrading HVAC systems to include electromagnetic and carbon filtration, which can significantly reduce the concentration of wildfire pollutants indoors.

  • Portable Air Cleaners: During wildfire events, having standalone air purifiers with activated carbon and HEPA filters can provide localized air quality improvements, especially in homes without central air filtration.

  • Sealing Indoor Spaces: Proper insulation, window sealing, and positive air pressure systems can prevent outdoor smoke from infiltrating indoor spaces, creating a safer breathing environment.


Individual Actions

  • Stay Informed: Monitor air quality indexes (AQI) through resources like AirNow.gov.

  • Limit Outdoor Exposure: On high-smoke days, reduce outdoor activity, especially for children, older adults, and those with respiratory conditions.

  • Wear Protective Masks: N95 or P100 masks filter out fine particles and are significantly more effective than cloth masks.


A Global Challenge Requiring Collective Action

Wildfire smoke is not a localized problem—it is a planetary issue with far-reaching consequences for public health and the environment. As climate change accelerates, wildfires will only grow in scale and intensity, making it crucial to acknowledge the real risks posed by airborne pollutants and take action to protect communities worldwide.


Understanding wildfire smoke’s movement, composition, and health effects is the first step in mitigating its dangers. While technological advances and policy interventions are essential, awareness and individual preparedness remain our best defense. As we move forward, we must rethink how we manage forests, protect air quality, and safeguard human health in an era where wildfires no longer recognize borders.

Explore expert insights, stay up to date with industry events, and gain a deeper understanding of the cutting-edge developments that are revolutionizing the indoor air quality landscape within Blade Air's comprehensive Insights Hub.

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