Tips for using a CO2 meter correctly in the classroom

Knowing where to place the meter in class or waiting the exact amount of time for the device to offer a correct reading are some of the tips offered by a guide created by the University of Zaragoza and the CSIC.

Although almost a year has passed since the start of the pandemic, the truth is that health measures to prevent its spread are still very present in the lives of all citizens. In educational centers, ventilation in classrooms continues to be essential to avoid contagion, an action to which complements can also be added to renew the air, such as HEPA filters, or to analyze its quality, such as CO2 meters.

In the case of CO2 meters, in addition to taking into account the carbon dioxide concentration levels that should not be exceeded in a classroom (no more than 700 ppm -parts per million-), other important aspects must also be considered. at the time of use. 'Natural ventilation in classrooms. I already have the CO2 analyzer... now what?, prepared by the Research Laboratory in Fluiddynamics and Combustion Technologies (LIFTEC) of the University of Zaragoza and the Higher Center for Scientific Research (CSIC), highlights some important issues and advice about the use of a CO2 meter in class.

I have a CO2 meter… now what?: three tips for the classroom

Some of the technical characteristics of CO2 meters make it easier to read and interpret the data, such as, for example, the data sample in real time or that they have NDIR (Non Dispersive Infrared Detector) technology, a non-dispersive infrared sensor. which is used as a gas detector. 

However, we must also take into account other aspects that the guide from the University of Zaragoza and the CSIC highlights, such as the place where the meter is placed, its calibration or the stabilization of the reading.

• Placing the meter in the classroom. The guide recommends placing it away from doors, windows and also people. If the meter is portable, it is recommended to place it in the central area of ​​the classroom, at a height of between 1,2 and 2 meters high. To do this, it can be placed on a tripod or a table, leaving at least one meter of distance from the student closest to the device. If the device is to be installed in the classroom permanently (such as on a wall or ceiling), in addition to looking for the furthest position from doors, windows and people, it should be in a place in the classroom that is considered the worst ventilated. .

• The calibration. Many analyzers already have this default function, since this action serves to correctly measure the level of CO2 in the environment (which is not the same outdoors as indoors). The guide emphasizes calibration as a fundamental aspect before starting to use it for the first time, in addition to verifying that said calibration is maintained. To do this, you must expose the device to outside air and activate the calibration function.

• Reading stabilization. The guide highlights the importance of waiting a short period of time to have reliable reading data on the concentration of carbon dioxide in the classroom. To do this, they recommend doing this exercise:

• Calibrate the meter and write down the outdoor reading (which is usually 400 ppm). 
• Place the analyzer in a place (it could be the classroom) and reach levels of at least 700 ppm.
• Take it outside again and wait for it to drop to a level that is 20 ppm higher than the first data obtained (if outside the first time it gave 400, wait for it to reach 420 ppm). The minutes it takes to drop to that level is the time you have to wait to get a reliable reading of CO2 levels in class.

This activity can serve as a reference for the first times the meter is used, since it involves knowing the time it takes to provide reliable data, an issue that also depends on the model being used. On the other hand, it is essential not to spend a lot of time next to the meter, since it can detect the CO2 that the person is exhaling at that moment and show an erroneous data. 

In addition to these tips, it is also important to create sheets for data collection, as they can be very useful if, for example, you are collecting data in the classroom and suddenly a gust of wind picks up. At that time, the CO2 level will drop due to the renewal of the air in the classroom and this must also be noted. These templates, in Word o PDF, can serve as a guide for this.