Official guidelines for safe ventilation levels in school are not strong enough and raise the risk of superspreader events, some experts have warned.
All schools across the State are being supplied with carbon-dioxide monitors to measure air quality in a room, allowing staff to quickly identify where ventilation needs to be improved.
Official advice from the Department of Education states that carbon-dioxide concentrations of above 1,400-1,500 parts per million (ppm) are “likely to be indicative of poor ventilation” and require measures such as opening windows or doors.
However, Orla Hegarty, assistant professor at UCD's school of architecture and a former member of the Government's expert group on the role of ventilation in reducing transmission of Covid-19, said this level of carbon dioxide was "unsafe".
“The limit of 1,500ppm was used by the department pre-pandemic as an indication of air quality, but it is not suitable for public health in current conditions,” she said.
“As a guide, outside is around 420ppm. At 800ppm indoors, about 1 per cent of every breath you take is rebreathed air from someone else, so as carbon dioxide rises, the amount of rebreathed air, and therefore risk of infection, increases.”
John Wenger, a professor in physical and environmental chemistry at UCC, said it was widely accepted that a carbon dioxide concentration of 1400-1500 ppm is indicative of poor ventilation or overcrowding, while a value below 800 ppm indicates good ventilation.
“During the pandemic, I recommend that people do whatever they can to keep carbon dioxide levels below 800 ppm. In my view, a concentration of 1,000 ppm is a more appropriate upper limit for CO2 concentration at this point in the pandemic,” Prof Wenger said.
This, he added, was in line with recommendations from the Federation of European Heating, Ventilation and Air Conditioning Association
Anthony Staines, professor of health systems at DCU, agreed that the carbon-dioxide threshold was set too high given the greater transmissibility of the Delta variant of Covid-19.
Prof Staines, who is a member of the zero-Covid Independent Scientific Advocacy Group, said: "1,500ppm is the level where there are risks to operating heavy machinery or, in a classroom setting, where you become drowsy and lose concentration. It is not a level where there is adequate ventilation."
Advice from the department is based on guidelines produced by the Chartered Institute of Building Services Engineers and the Brussels-based Air Infiltration and Ventilation Centre.
Officials say the levels quoted in official advice followed a public health review of safe ventilation levels.
The rollout of carbon-dioxide monitors to all schools , meanwhile, has been delayed until next month after faults were identified in 10,000 devices. Teachers’ unions reacted to the delay with “extreme disappointment”.
The full delivery of about 35,000 carbon-dioxide monitors to all State primary and secondary schools was due to have been completed by early next week.
The National Association of Principals and Deputy Principals said its advice to members was to follow official guidance from the department in relation to the use of the monitors.
"These are a welcome tool in the armoury of schools," said Paul Crone, the association's director. "They will be of use in particular when temperatures drop, but all schools can do is follow the official advice."
On foot of a delay in supplying the monitors, the department has authorised schools to purchase the devices.
Companies that supply carbon-dioxide monitors report that they have had a spike in demand from schools for devices this week.
Stephen McNulty, chief executive of environment analytics company Ambisense, said it was vital that schools had access to information on ventilation over time.
“It will spike up and down. The key is to ensure you don’t have constant exposure to poor ventilation. That’s why schools need to know about the trends in individual classrooms. Ideally, they should have monitors which alert staff in advance of high levels,” he said.