The Department of Education is to supply tens of thousands of carbon dioxide monitors to schools to help prevent the spread of Covid-19.

In a move that is being welcomed by teacher trade unions, the department is to provide portable monitors to all primary and secondary schools.

Primary schools will receive between one and 20 devices each, depending on their size, while second-level schools will receive up to 35 monitors each.

Carbon dioxide monitors measure the freshness of the air in a room and can indicate when ventilation needs to be improved by opening a window or doors in order to prevent the buildup of respiratory aerosols.

They typically cost between €80-€100 when bought individually.

The department said the devices will be in schools by September.

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UCD Assistant Professor of Architecture Orla Hegarty has called it a "very welcome development that is in line with best practice for reducing the risk of Covid transmission in schools".

Ms Hegarty, who has been advocating the use of carbon dioxide monitors for this purpose, said it would also enable schools to avoid over ventilation and to manage energy bills better.

The department has also issued new ventilation guidance to schools.

It said the over-arching approach for schools should be to have windows open as fully as possible when classrooms are not in use, and partially open when classrooms are in use.

It advises that keeping internal doors into classrooms open may assist with increasing air movement and ventilation.

The department said the deployment of carbon dioxide monitors can supplement and enhance these measures and can provide a useful general indication that areas/rooms may not be adequately ventilated.

Teacher unions, such as the INTO, had called on the Department of Education to supply the devices to schools.

The General Secretary of the Teachers Union Of ireland Michael Gillespie said the union had called for the measure as far back as last October.

He said the challenges posed by Covid-19 had "put into sharp focus the unsuitability of many school buildings and other facilities for modern teaching and learning".

"In this regard, significant additional spending on education to bring us in line with international averages will be required in the coming years."