Understanding Carbon Dioxide

Carbon dioxide is a naturally occurring gas that people exhale when they breathe. Indoors, rising CO₂ levels are used as an indicator of ventilation adequacy. Elevated CO₂ levels do not indicate an immediate life-threatening emergency, but they confirm inadequate ventilation, which can negatively impact learning, comfort, and well-being.

RSU 16 Classroom and Spaces CO₂ Alert Protocol (click here)

Timeline of RSU 16 HVAC and Indoor Air Quality Efforts

May 2023: $5M HVAC Referendum failed at the polls.
December 2023: Engineering firm estimates $7.4M to fix all three elementary schools; The Board did not move forward with a proposed $10.2M Master Lease.
October 2024: RSU 16 notified no elementary HVAC projects are eligible for Department of Education School Revolving Renovation Funds (SRRF).
August 2025: Major Capital School Construction funding applications submitted for ESS, MCS, PCS. Only top 2 projects funded. MCS was 40th, ESS was 56th and PCS was 84th
October 2025: SRRF applications submitted for Indoor Air Quality projects for ESS, PCS, PRHS/WMS. Project award notification happens by Feb 1.
January 2026: Board approved a Tax-Exempt Lease Purchase for HVAC improvements in Minot, totaling $2,819,767. SRRF awards RSU 16 $6 million (58% of the $6 million will be forgiven) with additional projects costs of $3.1 million to total of $9.1 million in upgrades to ESS, PCS and PRHS/WMS.
February 3, 2026: Board Update (click here)
February 2026 Update: Our plan to install CO₂ monitors in every elementary classroom has not progressed as smoothly as anticipated. We placed an order for 261 units through Amazon on January 9, but deliveries arrived only in small, inconsistent batches. We eventually received enough to equip MCS, and those monitors were installed the week before vacation. With the exception of one detector—whose calibration we are currently questioning—all readings have been within safe limits.
In an effort to speed up delivery, we attempted to purchase the remaining units directly from the manufacturer. While they were unable to ship to us, they did assist in prompting Amazon to send the rest of the order. To move the process forward, we were required to cancel the original order and place a new one. Although the remaining detectors were expected by February 23rd , as of March 3rd, we have received less than half of the reordered units. Minot has now been fully outfitted with detectors. Daily readings show that overall levels remain within acceptable limits, though a few rooms do experience elevated—but not dangerous—levels. These particular spaces lack direct access to outdoor ventilation, and we are developing a mechanical ventilation solution to address that challenge. Monitors were deployed to the middle school during the first week of March, with Elm Street following shortly after.

March 24, 2026

Following the public forum hosted by the School Board in January, there has been increased attention and concern regarding carbon dioxide (CO₂) levels in our school buildings. Carbon dioxide (CO₂) should not be confused with carbon monoxide. CO₂ is a naturally occurring gas that people exhale as part of normal breathing. It is commonly used as an indicator of ventilation and air circulation, not as a measure of toxins or dangerous gases.

The CO₂ readings referenced publicly stem from random testing in a few classrooms in each building conducted last January, as part of our preparation for applications to the School Revolving Renovation Fund (SRRF), which requires detailed environmental and mechanical evaluations. Mechanical Services did our testing and presented a graph of the worst day of CO₂ testing to the Board to send in with our SRRF application. These results were described as concerning but not dangerous.

Following is a picture of the PCS graph of one classroom on its worst day. As you can see CO₂ steadily rises when students come into the classroom to about 2,000 ppm, CO₂ sharply decreases (probably students were out of the classroom) to 1,400 ppm and then steadily rises to its peak at 1:35PM before coming back down. It is important to note these fluctuations, as there seems to be a belief that the room is always at its highest.

Once the data became public, many families understandably raised questions about what these numbers meant for students and staff. In response, the district contacted multiple regulatory and professional agencies, including: Department of Health and Human Services (DHHS), Department of Education (DOE), Department of Environmental Protection (DEP), Department of Labor (DOL), Maine Indoor Air Quality, Members of the Legislature.

Because situations like ours are relatively uncommon, most agencies were only able to reference the general federal standard indicating that sustained exposure above 5,000 parts per million (ppm) over an eight-hour period is considered hazardous. It is important to note that none of our readings were 5,000 ppm and our highest readings were a peak number, not a sustained 8-hour exposure.

As public attention increased, the Department of Labor provided more specific guidance and recommended the district to use a more conservative benchmark of maintaining CO₂ levels at or below 1,999 ppm. The Department of Labor also recommended interim mitigation strategies such as: Opening or cracking windows when possible, Rotating use of rooms. Improving ventilation wherever feasible. The statement that our readings are 2 to 3 times higher is untrue. The Department of Labor has set 2,000 ppm. Two to three times higher would be 4,000-6,000 ppm. Our readings have not had even a peak reading that high.

The district is going a step further by implementing in-room CO₂ monitoring to better understand ventilation conditions or how much fresh air is in each room.

CO₂ monitors are tools used to understand ventilation effectiveness. They do not measure toxins or carbon monoxide. (RSU 16 has separate carbon monoxide detectors like most homes do)

An alert from a CO₂ monitor does not indicate an emergency or that anyone is in danger. Elevated CO₂ levels usually mean that a space needs more fresh air. This is something that naturally happens when a room is full of people. The good news is that CO₂ levels typically decrease quickly once windows or doors are opened or ventilation systems are engaged.

The district has taken the following operational steps:

The Operations Director has completed an inventory of all instructional and occupied spaces across the district.
CO₂ monitors have been ordered for use in these spaces.
A clear protocol for responding to monitor alerts was developed.
Spreadsheet developed for an assigned employee to chart the level in rooms published to a dashboard on our website.
Staff have been provided guidance on managing classroom conditions to help reduce elevated CO₂ levels

The district has been committed to improving ventilation and heating systems for several years. However, the significant cost of these upgrades has repeatedly exceeded what taxpayers have supported, requiring the district to pursue alternative funding options.

One such option is the School Revolving Renovation Fund (SRRF). The district is pleased to share that it has recently been awarded a significant allocation through this program, which will allow meaningful progress on ventilation improvements in our buildings.

Timeline of RSU 16 HVAC and Indoor Air Quality Efforts

May 2023: $5 million HVAC referendum failed at the polls.
December 2023: Engineering firm estimated $7.4 million to address HVAC needs in all three elementary schools; the Board did not move forward with a proposed $10.2 million Master Lease.
October 2024: RSU 16 notified that no elementary HVAC projects were eligible for Department of Education SRRF funding.
August 2025: Major Capital School Construction applications submitted for ESS, MCS, and PCS. Only the top two projects statewide were funded; MCS ranked 40th, ESS 56th, and PCS 84th.
October 2025: SRRF applications submitted for Indoor Air Quality projects at ESS, PCS, and PRHS/WMS. Award notifications expected by February 1.
January 2026: Board approved a Tax-Exempt Lease Purchase for HVAC improvements in Minot, totaling $2,819,767. SRRF awards RSU 16 $6 million (58% of the $6 million will be forgiven) with additional projects costs of $3.1 million to total of $9.1 million in upgrades to ESS, PCS and PRHS/WMS

The MCS project will have substantial completion this summer. The SRRF projects do need voter approval in June. Payments for these projects would be part of the fiscal year 2028 budget.

Elevated CO₂ levels usually mean that a space needs more fresh air. This is something that naturally happens when a room is full of people, even in your own home or any space occupied by people (and pets). The good news is that CO₂ levels typically decrease quickly once windows or doors are cracked open or ventilation systems are engaged. The data that we have collected shows CO₂ levels below the 2,000 ppm set by the Department of Labor. In discussion with our District Physician, headaches can be caused by other causes, including dehydration, diminished sleep, stress, illness, eye strain, or environmental factors. While CO₂ levels help us understand ventilation needs, the levels measured in our buildings are not considered dangerous or life-threatening.

We want our community to know that the health, safety, and well-being of our students and staff remain our highest priority. While the data has prompted understandable concern, it has also strengthened our commitment to continuous improvement. We are taking thoughtful, informed steps, guided by state agencies and professionals, to monitor conditions, respond appropriately, and invest in long-term solutions.

Understanding Carbon Dioxide (CO₂)