Ventilation: ‘Crack open a window and a door – it doesn’t have to be Baltic’

Ireland goes into the winter badly prepared to make effective use of ventilation to combat the threat posed by Covid-19, according to a Government-appointed expert.

Last March, the expert group on the role of ventilation in reducing transmission of Covid-19 warned that steps needed to be taken immediately to plan and prepare for next autumn and winter.

However, its chair, Prof John Wenger of University College Cork, says "this just wasn't done".

“It was mostly talk and the delivery wasn’t there. There was some level of response but mainly in the form of recommendations. It hasn’t gone much farther than that.”

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While CO2 monitors have been distributed to schools in an effort to monitor air quality, Wenger says their rollout wasn’t well communicated and greater levels of support for teachers are required.

With the Government struggling to keep society open in the face of rising cases, there is a growing focus on the role of ventilation in helping to curb transmission – and frustration among scientists over the lack of investment in the area.

‘Absolutely scandalous’

"We know good ventilation is absolutely vital in helping to make indoor spaces safe," says virologist Prof Gerald Barry of Trinity College Dublin. "Yet to hear a nightclub owner say in recent days he doesn't know how to optimise his system is absolutely scandalous. It's a massive reflection on the communications on this issue, and the strategy from above."

One possible reason ventilation has played a Cinderella role goes back to the earliest days of the pandemic, when it was assumed droplet transmission was the main route of transmission of the virus in the air. This thinking also explained the initial reluctance of officials to countenance mask-wearing.

“Back then, we were pleading with people to recognise airborne transmission of the virus,” Wenger recalls. “The science had been misinterpreted, and a narrative created around the role of coughs and sneezes in spreading particles.

“But most respiratory diseases are spread through breathing and talking, when we breathe in and out very small particles, especially in poorly ventilated places. And the longer you spend in this more infected air that you’re breathing in, the more you are exposed to infection.”

Barry explains: “There’s a threshold of concentration above which you become infected. A few particles won’t matter. If you have good ventilation and distance you are unlikely to reach that threshold.”

Most respiratory particles are less than 5 microns in diameter, compared to 70 microns for something you can see like a grain of sand. “When you’re down to one-tenth of the size of a grain of sand, the particle doesn’t fall out of the air. It can stay in the air for minutes,” Wenger explains.

Specks of potentially allergy-inducing pollen can be up to 50 microns in diameter, he points out, “yet everyone accepts they are airborne”.

Speaking at this week's National Public Health Emergency Team briefing, Prof Philip Nolan restated the official emphasis on transmission occurring through "droplets and aerosols".

While ventilation is important “the risk of infection is much higher close up to the person but diminishes with time and is diluted in the volume of the room”. A train passenger is probably not at much of a risk from an infected person sitting 5-6 metres away, he said.

Virus particles

Scientists cannot measure the level of virus particles in the air so they use concentrations of carbon dioxide, which all of us breathe out, as a proxy.

Typically, the CO2 concentration outdoors is about 400 parts per million (ppm). With good ventilation, levels ranging from 800-1,000ppm are achievable indoors, Wenger says.

A level of 800ppm indicates that 1 per cent cent of the air in the space has been breathed out by someone else; a concentration of 1,200ppm means 2 per cent of the air has been breathed out, and so on.

In winter it becomes harder to strike the right balance between a person's thermal comfort and the need for clean air

Ventilation systems need to deliver about 10 litres of fresh air per second per person in order to provide clean air, but this figure can vary as there are many variables – the size and shape of the room, the number of people in it, etc.

“Every space is different. There’s a spectrum of different buildings, and ventilation systems and activities,” Wenger says.

He contrasts the number of laws that apply to food and water provision in Ireland with the paucity of regulations on air quality.

“The only legislation I could find was that you cannot be exposed to CO2 levels over 5,000ppm – because you could faint.”

At levels over 1,200-1,400ppm, a person’s cognitive function is impaired, so over 1,400ppm is considered the threshold for poor ventilation.

Right balance

Opening a door or window is the obvious first step to improving ventilation, but in winter it becomes harder to strike the right balance between a person’s thermal comfort and the need for clean air.

Schools pose a particular challenge because most rely on natural ventilation alone. This is why the expert group recommended they be supplied with CO2 monitors.

Wenger describes the implementation of that recommendation as imperfect. “I don’t know why every classroom doesn’t have one. There could have been clearer guidelines for teachers; a lot has been left up to teachers and principals, when they have enough on their plate.”

The inflow of air from the outdoors can vary hugely according to weather conditions

The monitors light green at CO2 concentration below 800ppm, indicating good air quality. They turn yellow and amber above that, and red over 1,500ppm. At that level, the room needs to be emptied, he says.

The inflow of air from the outdoors can vary hugely according to weather conditions. On still days, less air flows in, while the temperature difference created by cold days can be beneficial.

Where ventilation is problematic, the use of Hepa filters can act as a stopgap solution while systems are sorted out, Wenger says. This is a plug-in device that removes more than 99 per cent of respiratory particles and typically costs €200-300. Some classrooms might need two filters.

The infection risk faced by homeowners can depend on occupation levels, the number of visitors coming into the house and whether family members are at elevated risk.

“If people are concerned, a Hepa filter is a good buy. They can be turned on in the background but you need to have natural ventilation too. Crack open a window and a door – it doesn’t have to be Baltic.”

Onus on employers

The partial return to the workplace places an increased onus on employers to deliver clean air to staff. Wenger advises employers to first work through the ventilation checklist in the work safety protocol drawn up by the Health and Safety Authority.

Employers need to ensure their systems are working properly, that they are maximising air supply from outside and minimising the recirculation of air, he says.

They should turn off air recirculation units and use CO2 monitors to check air quality. Special attention should be paid to bathrooms and other small or heavily used rooms that could be potential problem areas.

The “paradigm shift” called for by Wenger might seem costly, but the investment in better ventilation can deliver other benefits as employees and other occupants of indoor space benefit from the sharper focus generated by inhaling cleaner air.