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CDC Guidelines on Schools Safety: Air Quality

When it comes to safe school reopenings, air quality is key.

The CDC has published guidelines on air quality for schools. But the CDC publishes as much information as they can, without considering how difficult it is to understand. All that information can be overwhelming.

We’ll sum it up neatly…

School safety and air quality

To reopen safely, here’s what the CDC guidelines suggest:

1. Continue wearing masks

2. Get as much outdoor air into rooms as you can

3. Improve HVAC ventilation and filtration as much as you can

4. Use in-room portable HEPA filter air purifiers to scrub the air of aerosols

(Ventilation in Schools and Childcare Programs)

The CDC and industry professionals recommend having an ACH of 6. We will explain what that means and how to achieve it.

CDC: school safety and air quality
Source: CDC

Before we get into it, some terms you’ll need to know are:

ACH: Air Changes per Hour. This refers to how quickly polluted air can be replaced by clean air. As a rule of thumb, the CDC recommends at least 6 ACH for effective mitigation of the spread of COVID-19.

HEPA: High Efficiency Particulate Air. This is used to describe certain extremely fine air filters. HEPA filters will theoretically remove at least 99.97% of aerosols with a size of 0.3 microns (µm).

MERV: Minimum Efficiency Reporting Value. This applies to how effective air filters air at capturing aerosols. The higher the MERV rating on a filter, the smaller the aerosols it will trap.

CADR: Clean Air Delivery Rate. This describes how fast air is purified and returned to a space. The higher the CADR, the higher the ACH. Rhymes with “radar.”

CFM: Cubic Feet per Minute. This refers to how quickly air can be pushed through a filter. To calculate ACH, you can take the CFM, multiply it by 60, and divide by the volume of the room. The CDC also provides a 2/3 rule – take the square footage of the room, and your target CFM should be about 2/3 that.

The primary means by which COVID-19 spreads is by biological aerosols. Every person produces these aerosols by talking, singing, coughing, or even just breathing.

1. Continue wearing face masks

The way to prevent the spread in schools is twofold. Firstly: prevent aerosols that carry the virus from entering the air. Secondly: remove the aerosols from the air by turning over the air as many times as possible.

Face masks are still recommended, as they are the #1 way to stop the spread via biological aerosols. The CDC doesn’t specifically recommend single-use surgical masks for the general public. (Improve the Fit and Filtration of Your Mask to Reduce the Spread of COVID-19)

Cloth masks, with a good fit and no gaps, reduce aerosol release by 50-70%. (Science Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2)

Masks are simple and widely adopted. Students and staff may provide their own.

The next three components have to do with removing aerosols from the air.

2. Get as much outdoor air into rooms as you can

The CDC recommends pulling in as much outdoor air into an indoor space as possible, or as much as possible, holding instruction or events outside. However, opening windows or going outdoors is not always a viable option. Potential obstacles include:

  • Inclement or extreme weather
  • Excessive pollution in the area
  • High pollen count in the atmosphere
  • Too much outside noise

Additionally: opening portals does not always guarantee air exchange. The CDC advises some mechanical means, either by child-safe electric fans or the school’s HVAC system.

3. Improve HVAC ventilation and filtration as much as you can

A typical school HVAC system may provide further help. In addition to ventilation for outdoor air, filtration can be improved to capture aerosols. The CDC recommends installing MERV-13 filters on HVAC systems, but cautions that professional consultation is necessary. (Ventilation in Buildings)

Problems that can arise with incorrect filter installation or usage include:

  • Increased energy costs due to increased difficulty of venting air through thicker filters
  • Disabling demand-controlled ventilation systems eliminates cost-saving technology
  • Longer times to achieve desired temperature or humidity
  • Potential reduction in outdoor air exchange due to reduced airflow
  • If ill-fitted, reduced efficacy of the filter

Please note, too, are only 50% efficient at capturing viral-sized particles from 0.3 micron to 1 micron. (ASHRAE – Filtration/Disinfection) It is not a replacement for HEPA filtration, which will capture 99.97% or better.

Outdoor air ventilation can improve an indoor space’s ACH by 1 or 2. The HVAC system can add another 2 to 3 ACH – provided airflow is sufficiently maintained. But installing a MERV-13 filter can reduce airflow, which reduces ACH.

To get to the recommended 6+ ACH, and capture far more viral-sized aerosols, schools should use portable HEPA filter air purifiers.

4. Use in-room portable HEPA filter air purifiers to scrub the air of aerosols

An in-room HEPA filter air cleaner can push indoor air through a filter to trap aerosols on which viruses can transmit and return the purified air to the room. With a high enough CFM on the air purifier, you can achieve the recommended 6 ACH in classrooms, infirmaries, offices, and other rooms. Again, you’ll need to know the square footage of each room, and the 2/3 rule applies.

Portable air purifiers are a far simpler solution to indoor air quality; you simply plug them in and they begin to work immediately. There is no installation time or cost.

There are already many air purifiers on the market. Some use HEPA filters, others offer other technologies to scrub aerosols from the air. The CDC only recommends HEPA filtration; other emerging technologies cannot be determined to provide sufficient safety in schools. The CDC doesn’t specifically recommend one way or the other; they are simply unknown. Their precise wording is:

“…in the absence of an established body of peer-reviewed evidence showing proven efficacy and safety under as-used conditions, the technologies are still considered by many to be ’emerging.’ As with all emerging technologies, consumers are encouraged to exercise caution and to do their homework.” (Ventilation in Buildings)

Since that is the case, they can be considered a poor use of funds. Air purifier features schools should avoid include:


The CDC guidelines on air quality are designed to ensure maximum safety for schools. Masks, outdoor air, HVAC ventilation and filtration, and indoor portable HEPA filter air purifiers are recommended in their guidelines. Each component is only at max effectiveness with a portable HEPA air purifier unit to hit the recommended 6 air changes per hour.

We strongly recommend getting started today!

About the Vaniman Pure Breeze HEPA Air Purifier

The Vaniman Pure Breeze HEPA Air Purifier is an indoor portable air cleaner designed 20 years ago for the industrial sector. A powerful 735 CFM motor combined with multi-stage HEPA filtration system and advanced sound-dampening technology (keeping it below the average human conversation level) make our unit an ideal selection for most school districts looking to ensure safety during the pandemic, and continue safety and clean air standards for years to come. Our units are reliable, cost effective, easy to maintain, and ship quickly from our facility in Southern California.

Can you use federal funds to get these things?

Yes. Each state has different criteria for school funding use; if you’d like to know how your school or school district can use the federal funds to achieve safe air quality, reach out to Vaniman Manufacturing Co. today to talk with a specialist and get all your questions answered.


Ventilation in Schools and Childcare Programs

Ventilation in Buildings

Improve the Fit and Filtration of Your Mask to Reduce the Spread of COVID-19

Science Brief: Community Use of Cloth Masks to Control the Spread of SARS-CoV-2

ASHRAE – Filtration/Disinfection

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