Church services are at high risk for the transmission of COVID-19 because singing, chanting, and talking increase aerosol generation and bring people into close proximity.

A super spreader event at Our Lady of Lebanon church in Harris Park, Sydney, is one of many Covid events involving singing and liturgy that have been studied by scientists. In this incident, 25 congregants, some up to 15m away from a Covid-positive singer, were infected. Sadly, one of them died.

Until vaccines are approved for the under 12s, there are about four million young Australians who will not be vaccinated at all.

Across Australia, governments are planning to reduce restrictions, first to double-vaccinated people and then to the unvaccinated. This does carry a risk. In Singapore, where more than 80 per cent of the total population is vaccinated, significant restrictions have recently been reintroduced because of a surge of cases thought likely to overwhelm the health system. In NSW, the 70 per cent over 16 target translates to 56 per cent of the total population, while 80 per cent translates to 64 per cent of the total population – a long way behind Singapore. Until vaccines are approved for the under 12s, there are about four million young Australians who will not be vaccinated at all.

COVID-19 is a challenging disease. Without vaccination, we have no immunity to it because it is new, or “novel” in medical speak. It is a sudden and acute respiratory illness; people can feel relatively well and then deteriorate and die within a short period because they are unable to breathe.

Australia has done relatively well in this pandemic so far, with fewer than six in 100,000 people dying, compared to the UK or the US where more than 200 in 100,000 people have died.

Good ventilation is an effective way to reduce the risk of COVID-19 infection, in concert with other mitigations, including density and time limits, the use of KN95 masks, the use of air-purifying devices to filter out virus particles, limiting vocalisation and, of course, vaccination. Singing, shouting and talking markedly increase the risk of aerosolisation. A congregation singing together is extremely risky until caseloads are low and vaccination rates are high.

Windows need to be repaired and, while you are at it, make sure the glazing is replaced with safety glass.

Most churches and church halls are naturally ventilated using openable windows. The first priority is to make sure they can be opened. Many aluminium and timber window frames more than 30 years old will have failed at the corners with a common repair being to secure the window shut. These windows need to be repaired and, while you are at it, make sure the glazing is replaced with safety glass. Open the windows for at least an hour or two before indoor activities and leave them open afterwards. Try to use the wind to promote cross-ventilation; doors may play a useful role. Don’t risk doors slamming on people; good ventilation means doors can blow shut.

The next step to alleviate risk is to measure ventilation levels when the building is in use. This can be done with a simple CO2 meter. Humans exhale CO2 at high concentrations and if a room is poorly ventilated, the CO2 level will quickly rise above the background level of outside air, which is about 400 parts per million (ppm). Measuring rooms when they are empty will not give meaningful readings because there is no load.

In a high-volume church, such as Our Lady of Lebanon in Sydney’s Harris Park, a CO2 meter may not give a reliable guide to ventilation. Professional help from an appropriately experienced architect, mechanical engineer, occupational hygienist, or aerosol scientist will be required in these circumstances.

Many different types of CO2 meters are available online at different price points, but the key requirement is that they have an NDIR (Non-Dispersive Infra Red) sensor. More expensive models may be more accurate and more durable, but accuracy is not that important for this application. A serviceable CO2 meter can be obtained for less than $200 and people report satisfactory results from meters costing as little as $80.

It is easy to calibrate a CO2 meter. Outside air is consistently about 400-415 ppm CO2. Take the device outside, put it in the shade, move at least 1.5m away, and allow it to stabilise for about five minutes. If it isn’t reading around 400 ppm, it may need to be calibrated. Read the instructions to find out how this is done. If the device is unable to be calibrated, or it reads incorrectly, readings can be adjusted pro-rata or the device can be returned to the seller as faulty.

Taking a reading in an occupied room requires some planning. Pick a location where the device can be left for five minutes at about 700 to 900mm above the floor level and ensure that people have been in the room for at least 15 minutes. Any location with everyone at least 1.5m away is fine. When five minutes is up, take a reading and possibly a photograph of the meter for record purposes. It’s helpful to have a room identifier and a count of the number of people in the photo, but the camera will probably record the time and date automatically. Then take photos showing the configuration of the openable windows and doors, plus the activity.

Action limits should be applied as below:

1. Below 800 ppm – indicates a low relative risk of infection.
2. Between 800 ppm to 1500 ppm  – indicates a moderate relative risk of infection. Improvements should be made where practicable to increase ventilation.
3. Above 1500 ppm  – indicates a high relative risk of infection. Immediate improvements must be made to increase ventilation or air purifiers must be operational.  If this is not possible, the activity should be relocated.
4. About 600 ppm or below is best practice.

Where ventilation can’t be improved, air purifiers with a HEPA filter that is appropriately sized for the space will be required. As a bonus, they will also assist with smoke from bushfires.

Toilets should be very well ventilated due to possible infection by the faecal-aerosol route, or “toilet plume”. Open all windows and keep any fans on permanently if possible.

Cups of tea and biscuits are probably best enjoyed outdoors because, indoors, the risk of an unmasked group talking in close proximity is high.

Geoff Hanmer is an Adjunct Professor of Architecture at the University of Adelaide, an Honorary Professional Fellow at UTS and is also the Managing Director of ARINA, an architectural consultancy. He is an architect and a writer on construction history.