Covid-safe ventilation for school buildings

Covid safe vent5

Andrew Lerpiniere, director at Webb Yates Engineers, takes a look at the complex issue of ventilation specification for educational buildings...

While much of the discussion – and indeed guidance – on how indoor ventilation can reduce the risk of transmission of Covid-19 has focussed on the workplace, and particularly offices, the spotlight is now swinging around to schools.

There are some similarities between workplace and schools, with both being more or less controlled environments. But while many offices feature a building manager who has a clear view of who uses the building and when, schools differ in terms of scale and density of occupation.

The experience to those running our schools dealing with issues around ventilation and fresh-air provision will vary hugely. Add to this the fact that teachers are still learning what to do during a pandemic, and one can see where issues of concern might arise.

Last summer some schools began to reopen with limited attendance. This progressed quite quickly to full attendance in September. Yet there was much around how Covid was transmitted that we were still unsure of.

The reopening of schools coincided with publication of new guidance from construction industry body CIBSE. In version three of its Covid-19 Ventilation Guidance, issued 15 July 2020, CIBSE declared: “Evidence continues to suggest that in poorly ventilated indoor spaces airborne aerosols are a possible transmission route and the precautionary advice remains valid.”

The precautionary advice was to, ‘ventilate spaces as much as reasonably possible with outdoor air.’ While simple in theory, in practice this is not always the case.

The issue facing schools and similar organisations, then as now, was how to follow that guidance in a precise way. In a practical sense there is only so much that can be done with any spaces, be it naturally or mechanically ventilated, in order to introduce as much outdoor air as possible. Indeed many have made rather sweeping statements around how best to do is – including the BESA announcing that opening windows is not enough and that mechanical systems are needed as well – when the solution is more complex.

Advocating mechanical solutions at the cost of other methods misses the point, this being that in the vast majority of cases ventilation will need to be achieved right now, and by working with what a school already has in place. Clearly the vast majority of schools will still be naturally ventilated.

Certainly there will be plenty of poorly ventilates classrooms, but this situation will vary from building to building, not least because anti-covid measures need to be assessed in a wider health context.

For example, there will be enormous differences in the air quality implications of opening windows in a rural village school versus a building that sits on a major road in a city centre.

The challenge is that we really don’t know how well or badly ventilated most schools are, and we need to start the process of finding out with some urgency.

Monitoring CO2 levels, as a direct indication of air quality, is one of the simplest ways to measure how well ventilated a classroom is.

Of course some thoughts needs to be given on how this is done; not every classroom in every school needs to be monitors all the time. A standard, scientific approach to gathering data is important, as is an intelligent approach to analysing that information, surely not beyond the wit of today’s generation of school operators.

Schools could use a good quality, but relatively inexpensive, portable CO2 monitor to record CO2 levels in classrooms at the start and the end of the day and over the course of a week or two. This would highlight problem rooms and focus further effort.

As with any school science project, the important thing is to follow a clear process; measure, evaluate, change, re-measure, re-evaluate, record test conditions and work steadily towards an optimised solution. The evaluation should, initially at least, be simply against target CO2 levels.

Changes could be simple, such as opening more windows, or opening windows at the start of the day, and only one change at a time. Other factors will come into play, not least impact on temperature and comfort. But the aim is first to understand how much fresh air is present and then if there are simple measures that can provide the correct amount.

Air-cleaning solutions for spaces that have to be occupied where ventilation rates are low should only be considered as a last resort.

It is possible that there is a fundamental problem with the ventilation of our schools. It could be that limitations on ventilation systems in some school buildings make effective outdoor air provision next to impossible.

However, in the absence of more research, and if we don’t carry out extensive measurement, we will never be sure. Understanding this pressing issue fully makes finding a pragmatic – and cost effective – solution more important then ever.

This article was originally published in the Public Sector Building July issue