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Why Welsh Gov is wrong to use dangerous disinfection machines in schools

30 Aug 2021 8 minute read
Bethany Powell, left, is helped by Sarah Wheelwright, school age coordinator, with pinning a pattern at the Youth Center April 9, 2020, at Hill Air Force Base, Utah. Children at the center have taken on the task of creating masks for themselves and for care givers at Hill AFB’s Youth and Child Development Centers. (U.S. Air Force photo by Todd Cromar)

Dr Eilir Hughes

The announcement that Welsh Government was going to spend nearly £6 million on technology for schools to reduce the risk of Covid-19 transmission came with joy and alarm in equal measure.

As a proponent of measures to mitigate the risk of airborne transmission of Covid-19, which in large parts has been ignored during the pandemic, I was glad to hear that carbon dioxide (CO2) monitoring was finally going to reach schools in every corner of Wales.

What do I mean by every corner? Well, since the beginning of the year, in partnership with Menter Môn, an enterprise agency that delivers a range of innovative projects, CO2 monitors have been provided to schools, care homes and office spaces that are under the responsibility of Anglesey Council.

This was a breakthrough following months of campaigning alongside materials scientist Dr Huw Waters under the banner of #FreshAirWales.

The campaign was born from an ever-increasing frustration that awareness about airborne spread of the virus wasn’t reaching the ears of the Welsh public. So, over the August bank holiday weekend in 2020, we released a bilingual website ( that explained how the virus transmitted via small airborne particles and how improved ventilation could help to limit spread.

We referred to how CO2 monitors could be employed to help ensure ventilation was adequate. They work on the principle that rising levels of CO2 in the air due to exhalation of breath is a proxy for poor ventilation. If the readings are low, the ventilation is likely to be good. If high, you better open that window quick.

Since middle of December 2020, Welsh Government have acknowledged the benefit of fresh air, stating that: “Letting fresh air indoors can reduce the risk of infection from coronavirus by 70%”. 

The Welsh Health Minister Eluned Morgan was quite right to advise people to spend as much as possible of their August Bank holiday weekend outside, where the risk of transmission is thought to be 20 times less than indoor settings.

Fast forward a year later to the beginning of August 2021, the Scottish First Minister Nicola Sturgeon announced that all schools and day care settings for children in Scotland must have access to CO2 monitors.

A couple of weeks later the UK government announced a £25 million fund to equip all English state schools with CO2 monitors.

My response to this was one of delight, shortly followed with trepidation. Are Welsh school children and teachers going to miss out from the benefits of this technology?

Thankfully, with today’s announcement Wales’ schools colleges and universities will also benefit from £2.58 million to purchase 30,000 monitors. I have no doubt it will prove useful to teachers as they kick off the new school year in a week’s time.

‘Ozone disinfecting machines’

However, addition to the monitors, a greater sum of £3.31 million is being spent on 1800 ‘ozone disinfecting machines’.

Their introduction into the education system’s arsenal to tackle transmission came following feedback to Government from schools expressing increasing difficulties and expense in attempts to meet the current expectation for deep cleaning following outbreaks of Covid-19 infections.

By turning to technology that is more familiar to abattoirs than classrooms, the Welsh Government is willing to use extra cash to make us feel safer, but doesn’t actually achieve much to reduce risk.

So how do ozone cleaners work?

They convert oxygen atoms into ozone which readily reacts with other substances it encounters. Their potential use has been lauded by many who claim that they could be useful as air cleaners the fight against the virus.

The intention is to disinfect teaching environments when not occupied. The researchers at Swansea University who are funded to build these machines state that: “Ozone is potent against Covid-19 virus and due to its gaseous nature, it kills the virus whether be it airborne or adhered to a surface.”

But concerns relating to the apparent weakness of such claims has prompted The United States Environmental Protection Agency (EPA) to publish a report that I cannot help but compare to the marketing of snake oil in 19th century America.


Ozone is considered a toxic substance. The EPA refers to the well-known risk to human health when expose to ozone.

It says: “When inhaled, ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation. Ozone may also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections.”

It is important to note that these machines will not be used when occupied by teachers or learners due to the potential harm to health. But someone will have to operate them, probably an employee of the local authority or university.

Using ozone to disinfect does seems counterintuitive. In an attempt to lower the risk of harm to human health, we are using toxic chemicals when safer alternatives are available.

And suggesting that disinfecting potentially infected air when no one is present to breath it is an insult to our intelligence. Background air exchanges occur overnight and so efforts to sterilise the air is futile come the next morning a contagious individual returns to the class for the day, spends hours in the company of others and in so doing the risk of infection continues.

It’s quite likely the surfaces are disinfected, but the sterility of the room’s coving or skirting poses no reduction to contracting Covid-19.

The UK’s Health and Safety Executive has published guidance on the use of disinfectants such as ozone.

It states that: “Soft furnishings may act as a ‘sink’ for the airborne chemicals and emit them for a period of time after treatment (remove items such as sofas before treatment)

They state that people should not enter rooms being treated by such chemicals. The space in which this technology would be operated in would need to be sealed completely, posing an extra challenge for schools, as well as polluting the outside environment. As any Science teacher would tell you, ground level ozone is no friend to nature.

The irony of all this is that, once the ozone gas is released into the space, the environment needs to be made safe again so that no residue is left over by the time teachers and learners return.


Guess what they should use to do this? Yes, ventilation.

Fresh air helps clear the disinfectant after the treatment so long as the ventilation can be controlled from outside of the room. Another challenge for the school’s caretaker!

What is really surprising is that adopting ozone technology seems to go against the Government’s own advisors. In a report titled ‘Air cleaning devices’ the Welsh Government’s technical advisory group (TAG) stated that “devices which use HEPA filters and germicidal ultra-violet light (UV-C) are better than purifiers using other technologies such as oxidation” which ozone is one of them.

So, it seems clear that ozone should have no part to play in attempting to lower the risk of inhalation of the virus. But its existing usage in other environments such as the food industry and health care is focused on surface disinfection.

Yet we should ask, is surface cleaning worth over half of the funds for technological prevention in our educational establishments? Are sterile surfaces going to make a significant difference to the risk of transmission, or could the money be better more wisely?

For some time, the United States’ national health protection agency, known as the Centers for Disease Control and Prevention (CDC) has referred to the possible risk to being infected through contact with contaminated surfaces or objects, known as fomites, as being low.

It states that: “There is little scientific support for routine use of disinfectants in community settings, whether indoor or outdoor, to prevent SARS-CoV-2 transmission from fomites”

It adds that when a confirmed case of covid-19 has been identified within 24hrs, high-touch surfaces should be disinfected, which is well within the current role of the school domestic cleaner.

Instead of rolling out expensive, untried, unnecessary technology that has the potential of being damaging to the environment and dangerous to human health, I’d argue we should place our efforts on interventions that provide the greatest benefit in reducing risk.

This should focus on what we know. Spending time with others outside offers a 20-fold reduction in transmission. If natural ventilation is provided for indoor settings, transmission reduces by up to 70%.

There is no data to suggest that using surface sanitisation equipment will reduce transmission of SARS-CoV-2 in schools. Instead, the substantial government funds should be re-directed towards maximising natural ventilation, and failing this, turn to methods of purifying the air whilst the classrooms and lecture theatres are occupied, such as high-efficiency particulate absorbing filters.

Remember, nothing beats bringing in some sweet fresh air to make indoor settings safer.

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Adam York
Adam York
2 years ago

Jeremy Miles is not fit for purpose(remember let schools do what they want?).If Florence Nightgale could work out a sensible plan for airborne disease why can’t he?

Paul Waldeck
2 years ago

This is one of the best articles I have read since the pandemic began! We make places safe from pathogens and found this ozone decision bewildering- it’s not supported by SAGE, HSE, CDC, WHO let alone any of the medical, scientific or engineering institutions and experts around the globe. Yes, buy British but only if it works and is safe to do so. Use HEPA or Germicidal UV-C as all guidance says as the alternative to “adequate ventilation” (>6 Air Changes per Hour and 10litres/person/second)

Kerry Davies
Kerry Davies
2 years ago
Reply to  Paul Waldeck

The ozone process is widely used in offices, theatres and cinemas where HSE labels it a “low-risk work activity”. Wales has stricter laws on ventilation in schools than England which mandate ventilation by presumed maximum occupancy whether occupied or not while England legislates on occupant numbers. There is no intention to use these machines while spaces are occupied unlike offices which often have low level constant air treatment. HEPA filtration is good as are CO2 monitors but they all bring new problems. Say a teacher in London has an alarm from a monitor which orders more ventilation; does she open… Read more »

2 years ago
Reply to  Paul Waldeck

Germicidal UV-C lamps that produce 185nM light also create ozone.
Ozone is a very powerful oxidizing agent and may damage materials in the room.
Excess Ozone within photocopiers can damage the machinery and corrode circuits.

Kerry Davies
Kerry Davies
2 years ago
Reply to  Erisian

They do indeed produce ozone as does the prescription printer in Dr Eilir’s consulting room but adequate ventilation makes them safe enough. That is why this storm in a teacup is only giving people half the required information.

2 years ago
Reply to  Paul Waldeck

Someone else who doesn’t know what ozone does! Do some research instead of jerking that knee all the time Paul.

2 years ago

How are you so stupid?

Do you know what ozone is? It occurs naturally in the air and helps to purify it! We’re not talking about using high powered ozone generators here, but very low-level ones which are proven to work, and are in fact used routinely in more forward thinking countries such as Japan.

It is VERY worrying that someone who apparently campaigns for clean air has no basic scientific understanding of what ozone is and does!

2 years ago

You know there is ozone in “sweet fresh air” right? If there wasn’t, it would smell absolutely foul and probably contain a lot more pollutants. But hey, don’t let science get in the way of your deluded rant.

Geoff Symonds
2 years ago

The points made in the article are fundamentally correct regarding ozone but we should avoid throwing the baby out with the bathwater – the article does not account for less aggressive methods of deploying the ozone agent, namely in the form of controlled “aqueous ozone mist” which serves to direct the ozone in lower compositions to the actual contact surfaces. The result is more efficient and safer deactivation by reducing the lingering ozone in the ambient space and carefully avoiding danger to human health. An option for schools is the new mobile Sym-Zone system which will shortly be launched in… Read more »

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