Nearly 85 percent of classrooms across the country don't have their own carbon dioxide monitors, potentially increasing the risk of students catching Covid-19.
High levels of carbon dioxide in a space can indicate poor ventilation and an environment where aerosol particles from people's breath can linger, increasing infection risk if someone in the room is sick.
RNZ's 'Whose Breath Are You Breathing?' project tested carbon dioxide levels in a typical intermediate school classroom and revealed that on a cold day when windows were shut, CO2 levels inside reached 1373 parts per million.
To combat Covid-19, the Ministry of Education has told teachers to open doors and windows when CO2 levels go over 800ppm and to briefly vacate the room if the level is over 1251ppm.
"Ideally, every classroom should have a carbon dioxide monitor," University of Otago Department of Public Health senior research fellow Julie Bennett said.
Bennett said although it is "fantastic" the ministry has set guidelines, few classrooms have a CO2 monitor permanently in place so they can take action on increasing levels.
"It's very difficult to know when the CO2 is building up until the levels become very high - when you can feel that the room is really stuffy and that people are becoming sleepy. Often at that point, they've gone way above 800 parts per million," Bennett said.
The Ministry of Education says 1000 rooms have built-in monitors and it has supplied 5400 CO2 monitors to schools but there are approximately 42,000 teaching spaces in New Zealand. This equates to about one portable monitor shared between eight classes.
Ministry head of property Sam Fowler said the portable monitors helped schools assess ventilation in different spaces.
"Typically, the methods employed to manage ventilation and CO2 levels in one learning space will be applicable in similar teaching spaces."
Another 8000 rooms are expected to receive indoor environmental monitors, which monitor CO2, over the next year.
He did not respond to a question asking why the ministry had not supplied CO2 monitors for all rooms.
Central Otago parent Andrew Dickinson took matters into his own hands and bought several monitors for his children's school.
In his son's class, which was a new building, the monitor meant teachers and students could easily manage air quality when the monitor's LED display alerted them.
"You could see immediately the impact. The CO2 will hit the orange level, and they'll open a window and it will drop immediately."
Managing CO2 in his daughter's classroom, housed in an older building, was more of a challenge.
"It regularly gets up to 1200 or higher and they're fighting it all morning. So all morning, they are trying to keep the room warm enough and get enough ventilation in order to drop the CO2 down."
Dickson shared the data with the Ministry of Education, and the school was sent air purifiers for the older classrooms. These can help remove virus particles from the air and are especially useful if schools cannot ventilate classrooms adequately by opening doors and windows.
Fowler said the ministry has so far sent 8250 air purifiers to schools nationwide.
"More air cleaners are available to schools that require them, which the ministry will provide at no cost, to help address ventilation challenges. Schools and other education sector entities are also able to purchase additional CO2 monitors and air cleaners at a discounted rate directly from the ministry's suppliers."
As well as CO2 monitors in all rooms and air purifiers where needed, both Bennett and University of Otago epidemiologist Amanda Kvalsvig would like to see mask mandates reintroduced.
"New Zealand schools need a Vaccines Plus approach, using layered protections because no single measure can protect 100 percent," Kvalsvig said. "The situation is now urgent. A couple of protections could be stepped up tomorrow, including wearing masks and staying home when unwell."
The Vaccines Plus approach was outlined in an open letter signed by more than 150 doctors and scientists, who sent it to government officials in April. The suggestions included a continuation of masking in schools over winter and for the ministry to provide CO2 monitors and air filtration units to all classrooms.