How New Security Measures in Schools Impact Classroom CO₂ Levels and Potentially Increase Pathogen Spread

In recent years, heightened concerns about school safety have prompted many districts to implement enhanced security measures. These include reinforced doors, windows, and restricted access points designed to protect students and staff.

However, while these efforts aim to safeguard against external threats, they have unintentionally introduced challenges to Indoor Air Quality (IAQ), with potential consequences for health and learning outcomes.

The Airflow Challenge

Enhanced security measures (prolonged closing and locking of classroom doors) is limiting the airflow in some classrooms, causing CO₂ levels to rise, reducing air changes per hour. This creates an environment where airborne pathogens can linger, exacerbating the exposure identified during COVID-19, and in some cases counteracting deployed mitigation efforts.

Without sufficient air changes per hour (as recommended by the CDC and ASHRAE), students and teachers alike face prolonged exposure to elevated CO₂ and increased exposure to airborne pathogens.

This is less of a challenge in schools built post COVID-19, but our experience is showing a challenge for schools built prior.

That said, the airflow challenge may not necessarily be a challenge for an entire school. Additions to a facility, the number of students, and how the facility is utilized will have an impact on the overall CO₂ levels within a school.

So How Do You Know If You Have a Problem?

Before preparing to speak to the school board, with 'cap in hand' to request a capital additions to budget, its worth mapping your environment and obtaining a snapshot about what is happening by installing IAQ sensors and making an informed decision as to what is actually required. As I am reminded time and time again in my Health and Safety Career, In God we trust...everyone else bring data!

Insights From IAQ Sensors

At Garstang Group we have installed IAQ sensors at a number of schools and monitor and trend what is occurring with the quality of indoor air.

We couple that with an environmental assessment where problems are identified and make recommendations to sustainably reduce exposure.

The introduction of IAQ sensors in schools has provided valuable data on the quality of indoor air, measuring factors like CO₂, Particulate Matter, Relative Humidity, Temperature, Volatile Organic Compounds, Ozone, Formaldehyde to name a few.

Trends from monitored classrooms have resulted in questions about what is happening in these spaces and why?

The data above shows one classroom in a school we are currently monitoring. You can see how the CO₂ levels rapidly increase from ambient levels as students arrive and are sequestered for learning. In this graph the CO₂ levels reached a peak of 1900 ppm in the afternoon making learning an uphill challenge.

CO₂ and Cognitive Performance

Research shows that high CO₂ levels significantly impact cognition and health.

For example, research from Joe Allen et all, shows concentrations above 950 ppm can impair cognitive functions, particularly for complex tasks.

Many classrooms we monitor frequently exceed these levels, underscoring a need for monitoring and action. The graph above shows a 28-day period in one classroom where CO₂ was frequently over 950 ppm.

‍What is the safe level of CO₂ for Indoor Air?

The level of CO₂ considered harmful or impactful is a matter of a small debate and finding an answer to aim for can be confusing. Various standards exist globally to guide CO₂ levels for indoor air, three of the main standards are detailed below.

A summary of these standards provides an indicative value of concern starting at a level >1000 ppm.

USA - ASHRAE 62-2201 - CO₂ levels should no higher than 700 ppm above outside ambient. So if the outside is 400 ppm, the inside should not exceed 1100 ppm.

EUROPE - EN13779 - Categorizes CO₂ into: High Quality <400 ppm, Medium Quality 400-600 ppm, Moderate Quality 600-1000 ppm, Low Quality >1000 ppm.

AUSTRALIA & NEW ZEALAND - NZS4303 - 1000 ppm

‍Addressing the Pathogen Risk

Elevated CO₂ levels often signal reduced air dilution, which increases the risk of airborne pathogen transmission. In crowded classrooms, this can lead to higher rates of absenteeism and diminished learning outcomes due to fatigue and illness. COVID-19 by way of example can remain suspended in an air column for 9 hours or more.

Solutions for Better IAQ in Schools

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Schools need balanced solutions to address safety and air quality. Some pragmatic options to consider:

IAQ Monitoring:

Use IAQ sensors to monitor your Indoor Air Quality in the School, investigate high readings.

Administrative Measures:

Limit classroom occupancy or rotate spaces when air quality deteriorates.

Adjust schedules to prioritize complex learning tasks in the morning when CO₂ levels are lower.

Encourage opening windows (above ground floor), when environmentally feasible, to enhance ventilation.

‍Engineering Controls:

Install demand-controlled ventilation systems.

Add natural ventilation options like operable skylights or ventilated doors.

Upgrade HVAC design.

Pathogen Specific Reduction:

Install E-Disinfection Systems into the ductwork.

Install E-Disinfection Systems into the classroom (portable devices with ASHRAE 241 certification).

A Call to Action

Many schools have struggled with indoor air quality before enhanced security measures, and this additional measure is exacerbating an already existing problem.

While student safety is paramount, environmental health and safety issues associated with indoor air pose a more complex challenge.

Schools must balance physical safety measures with indoor air health, finding solutions that protect students from external threats and indoor health risks.