The chair of the Expert Group on the Role of Ventilation in Reducing Transmission of Covid-19, Professor John Wenger, has said that Minister for Heath Stephen Donnelly's decision to take advice from other sources on the role that HEPA filters can play in the classroom is "odd".
Asked if he was surprised to hear Mr Donnelly say the expert advice he had received states that there is not a role for these air filters in school, Prof Wenger said: "Our group was appointed specifically to provide advice on ventilation and related measures like filtration."
He told RTÉ's News at One: "We put in our report, and we've been communicating with the senior officials group in Government over the last months, so all of a sudden to take advice from somewhere else, which is different, does seem a bit odd to me."
Mr Wenger - a professor of chemistry at University College Cork - insisted that HEPA filters are "a great interim solution".
"First of all, what we're saying is that ventilation is the primary measure here because this allows the air to be diluted of the virus, so ventilation is a primary measure, but when there is insufficient ventilation, then we need to look at something else.
"Normally we would look to provide a fix for that ventilation, but that can take time and money to install so these portable air clean devices called HEPA filters are a great interim solution.
"You can buy them off the shelf, and you can put them in the room and then remove the virus from the air and they add to the effect that ventilation gives, so they have to remove the virus from the air," Prof Wenger added.
Earlier, an assistant professor at UCD School of Architecture said HEPA filters are highly effective.
Prof Orla Hegarty - a former member of the Expert Group on the Role of Ventilation in Reducing Transmission of Covid-19 - called on the Government to reconsider its stance on using HEPA filters to improve ventilation in some schools amid the ongoing risks posed by Covid-19.
She told RTÉ's Morning Ireland that people are confused by "so many different rules and suggestions" around the measures to keep them safe.
There is a prioritisation on handwashing and cleaning surfaces, she said, adding that this is a "misstep in NPHET" when "almost all transmission is from breathing infected air".
Prof Hegarty said most of that infection happens indoors, and they know these conditions and they can be prevented.
"It is just a matter of policy makers engaging properly with environmental science and letting people who have the expertise inform policy."
She said the areas where children are most at risk, such as those in childcare settings and crowded classrooms, should be targeted first in terms of ventilation.
'Difficult and challenging time' for principals, says IPPN
The Chief Executive of the Irish Primary Principals Network has said it has been a "difficult and challenging time" for principals, but parents have been very supportive of the new mask wearing measure in schools.
Páiric Clerkin said they are always guided by public health and will support that guidance.
"We all have the same objective; we want to keep schools open but we want them to be safe and we want every mitigation measure in place to keep our school communities as safe as possible", Mr Clerkin told RTÉ's Morning Ireland.
Children in third class and up are now required to wear face masks at school, and can be refused entry if they do not.
Minister for Education Norma Foley said primary schools will adopt a "practical approach over the next day or two" when it comes to implementing the new requirement.
Mr Clerkin said the biggest issue for school principals is how they can access public health advice and support in relation to Covid-19 queries.
He said the feedback he is getting from school leaders is that it can take anything up to 24 hours or longer to get an answer from the principal helpline.
"They are finding it impossible to get a follow up from public health in relation to risk assessment other than in special schools and special class situations.
"That is not acceptable if we want to keep our schools open and safe."
Mr Clerkin said he is looking forward to the Department of Education sharing information on FAQs with schools soon, adding that they are working on that at the moment.
He said that schools want "clear consistent concise" information so every school is implementing the same measures.
Schools are hopeful by everyone doing everything possible to ensure their safety they can see an improvement in the situation, he said.