How to check your church’s ventilation to make sure it’s Covid safe

Eternity commissioned building ventilation expert Geoff Hanmer, Assistant Professor of Architecture at the University of Adelaide, to prepare this report on churches. Hanmer contributed to The Conversation website on this topic.

Church services pose a high risk of COVID-19 transmission because singing, chanting, and talking increase aerosol generation and bring people closer together.

A super spread event at Our Lady of Lebanon Church in Harris Park, Sydney, is one of several Covid events involving chanting and liturgy that have been studied by scientists. In this incident, 25 worshipers, some up to 15 meters from a Covid-positive singer, were infected. Unfortunately, one of them died.

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

Across Australia, governments plan to reduce restrictions, first to people who are doubly vaccinated, then to people who are not vaccinated. This carries a risk. In Singapore, where more than 80% of the total population is vaccinated, major restrictions have recently been reintroduced due to a surge of cases that could overwhelm the healthcare system. In New South Wales, the 70% of 16 target translates to 56% of the total population, while 80% translates to 64% of the total population – far behind Singapore. Until vaccines are approved for those under 12, there are around four million young Australians who will not be vaccinated at all.

COVID-19 is a difficult disease. Without vaccination, we have no immunity against it because it is new, or “new” in medical parlance. It is a sudden and acute respiratory illness; people can feel relatively well, then quickly deteriorate and die from being unable to breathe.

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

Good ventilation is an effective way to reduce the risk of COVID-19 infection, in concert with other mitigation measures, including density and time limits, use of KN95 masks, use of air purifying devices to filter virus particles, limit vocalization and, of course, vaccination. Singing, shouting and talking greatly increase the risk of aerosolization. A congregation singing together is extremely risky until case numbers are low and vaccination rates are high.

The windows need to be repaired and while you are there make sure the glazing is replaced with safety glass.

Most churches and parish halls are naturally ventilated using operable windows. The first priority is to make sure they can be opened. Many aluminum and wood window frames over 30 years old will have failed in the corners, a common repair being to secure the window closed. These windows need to be repaired, and while you’re there, make sure the glazing is replaced with safety glass. Open 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 can play a useful role. Don’t risk doors slamming on people; good ventilation means the doors can close.

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

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 assistance from an architect, mechanical engineer, industrial hygienist or aerosol specialist with appropriate experience will be required in these circumstances.

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

It is easy to calibrate a CO2 meter. The outside air constantly contains about 400 to 415 ppm of CO2. Take the device out, put it in the shade, move at least 1.5m away and let it stabilize for about five minutes. If it does not read around 400 ppm, it may need to be calibrated. Read the instructions to find out how. If the device cannot be calibrated or reads incorrectly, the readings may be pro-rated or the device may be returned to the seller as defective.

Taking a reading in a busy room requires some planning. Select a location where the device can be left for five minutes approximately 700-900mm above floor level and ensure that people have been in the room for at least 15 minutes. Any place with everyone at least 1.5m away is fine. When five minutes have elapsed, take a reading and possibly a photograph of the meter for record purposes. It helps to have a room ID 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 windows and doors that open, as well as the activity.

Action limits should be applied as follows:

  1. Below 800 ppm – indicates low relative risk of infection.
  2. Between 800 ppm and 1500 ppm – indicates a moderate relative risk of infection. Improvements should be made where possible 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 moved.
  4. Around 600 ppm or less is best practice.

Where ventilation cannot be improved, air purifiers with an appropriately sized HEPA filter for the space will be needed. As a bonus, they will also help clear the smoke from bushfires.

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

Cups of tea and cookies are probably best enjoyed outdoors as indoors the risk of an unmasked group talking nearby is high.

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

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