Here are a series of scenarios that can help you set up a temporary, at home isolation and help mitigate risks of transmission to other family members.

A woman in darkness does a video call with an eldery man at her home as a curtain flutters in the backgroundImage for representation
Coronavirus Coronavirus Monday, April 19, 2021 - 12:24

With rising infection numbers in India, we are currently faced with the dual challenge of a lag in testing and reporting and a lack of beds. This means that many families are being faced with the unfortunate reality of having someone in their household show symptoms or have had a suspected exposure. It may take days to confirm an infection. Once confirmed, the person with COVID-19 may have to be cared for at home for the duration of their illness or until a bed becomes available. This creates a challenge not only in terms of providing adequate care to the sick person, but also ensuring that other members of the household do not get infected in the process. However, with some preparation and understanding of the modes of transmission involved, we can work towards home isolation and care scenarios where we can minimize risks of transmission.

COVID-19, like any respiratory infection, may be transmitted by one of these three routes:  

>Airborne transmission - via aerosols, i.e particles of saliva or respiratory fluid from an infected individual that are suspended in air and then inhaled by a susceptible person

>Close contact and droplet transmission - via large respiratory droplets that are expelled from an infected individual when coughing, sneezing and talking, which can end up in the eyes, mouth or nose of a susceptible person nearby or by personal contact (like shaking hands) with an infected person 

>Surfaces or Fomite transmission - an indirect mode of transmission, from the sick individual’s hand to a surface and from that surface onto a susceptible person

So far we have been wearing masks, practising safe distancing and cleaning and disinfecting surfaces to keep ourselves safe. But these only address close contact (or droplet) and surface transmission. Airborne transmission continues to be poorly understood by the public and thus presents the biggest risk. It is this route that we have to be acutely aware of when considering home isolation of a possibly infected or coronavirus positive family member. Once you are aware of this mode, you can easily take steps to minimise it. 

So what is Airborne or Aerosol transmission?

There is now a large body of scientific evidence that tiny particles, called aerosols, which are emitted by an infected person while breathing, talking, shouting, singing, or even breathing, are a significant mode of viral spread. These aerosols are small enough that they can stay aloft for minutes to hours and can be carried large distances by air currents. In indoor spaces, these aerosols remain suspended in the air. And if the ventilation in that space is poor, they become increasingly concentrated as time passes which increases the risk of infection. Therefore, any susceptible individuals sharing this same air can become infected by breathing in these virus laden aerosols. 

So what can you do?

You can think of the coronavirus laden aerosols that are being exhaled by an infected person as the smoke that a smoker would exhale. If you had to live with a smoker, what would you do? You would create a limited smoking area, and you would try to get more fresh air inside and get the smoke out! A very similar concept applies here. Of the air you or any other susceptible person in your family is breathing in, you want to minimise the fraction that was exhaled by the infectious person to minimise risk. 

So first and foremost, when occupying a home with persons quarantined (healthy people living with a suspected or infected person(s)) wear proper personal protective equipment. Masks limit the amount of aerosols that an infected person emits into the air and are your first line of defence against breathing them in. Therefore, both infectious persons and susceptible persons should be wearing masks. N95 masks are preferable and the most effective. KN94 and FFP2 masks (without valves) are an acceptable substitute but may not be available. In that case, 3 ply surgical masks (with ties instead of ear loops) can be preferred. Otherwise, consider double masking with a surgical mask and a well fitting 3-layer cotton mask over it.

Next, we have compiled a series of scenarios that can help you set up a temporary, at home isolation and help mitigate risks of transmission to other family members. 

In these scenarios, we would be resorting to “jugaad” to ensure the room in which the patient is isolating has a negative pressure. What this means is we try to keep the isolation room at a slightly lower pressure than the rest of the house. Since air always moves from higher to lower pressure, this can ensure a directional flow of air. From the rest of the home, clean air (without virus laden particles) can enter the isolation room, diluting the virus laden particles inside that space. This helps mitigate risks to the caregiver(s) when they have to enter the isolation room. Air from the isolation room will be unlikely to move against the pressure gradient and enter the other parts of your home. In addition to keeping the isolation room at a negative pressure, other areas of the house may be kept at a “positive pressure”, especially, say, the bedroom of an elderly family member. For getting a positive pressure in a room, one of the easiest solutions is to have a table fan or pedestal fan bring air in via a door or window that opens to the outdoors. 

Remember that this is a quick-fix approach, and it is not a guarantee that you will not be infected. It is not intended to substitute the combined advice from a professional engineer and physician which should be sought out if possible. 

Ideally, for isolation, you should choose a bedroom with window(s) and an attached bathroom. It helps if the bathroom also has an exhaust fan or at least a window. The further such a room is from the common areas in the home, the better. We do, however, cover scenarios other than a bedroom with an attached bathroom. 

To set up such an isolation room, you need some basic equipment like table and pedestal fans, exhaust fans (if not already present). Choose fans with high revolutions per minute and the largest size the space can accommodate without coming in the way.

You can also use a portable HEPA air cleaner to directly filter the virus loaded particles from air. There is a handy calculator for estimating what size of air cleaner you would need. The tool is described for classrooms but will also work for bedrooms as long as you input the relevant dimensions. Do not go for any bells and whistles (like ionizers, plasma, ozone etc.) as these are not proven effective and can cause additional harm. A simple air cleaner with a HEPA grade filter and a high enough clean air delivery rate (CADR) to achieve a minimum of 4-5 air changes an hour is all that is needed. As a quick example, say, your bedroom has a floor area of 200 square feet and a height of 20 feet. That means its volume is 2000 cubic feet or about 56 cubic meters. Check the air cleaner’s specifications for its rated CADR with smoke/tobacco smoke. If this value is 200 cubic meters per hour, the flow rate of clean air provided by this air cleaner gives your bedroom a filtration rate of about 3.6 air changes an hour.

Additionally, a carbon dioxide monitor could be useful to evaluate the ventilation in your isolation room and the rest of your home. A general guide is that levels under 800 parts per million (ppm) are good and could be what you target for. But CO2 monitors can be costly for an individual or one family to buy. You could, however, pool together and purchase one among friends and family or by members of a housing society or office complex and share to do evaluations of their home and intended isolation rooms. If you have a CO2 monitor available, position it close to where the occupant(s) would be in a particular living space to get a suitable reading. Place it at about breathing height but not so close to people that their breath would directly impact the readings.

A simple way to check a decent negative pressure gradient has been achieved inside an isolation room is to stand outside the room, blow out a lit candle and hold the smoky wick near the closed room door and see what direction the smoke goes. It should move into the room. Similarly, you can do the same from inside the room at the room door and the air should move towards the window where air is being exhausted out of. 

In the scenarios explored below, for comfort, you may use the air-conditioner (AC) with window open. Remember that the main aim here is to let more uncontaminated outside air in. This may lead to more electricity consumption however, it reduces risks of infection. In hot-humid parts, you can use the AC while in hot-dry parts, it is advisable to use an air cooler/desert cooler. The cooler helps reduce temperature as well as improve indoor humidity, which in turn is useful for reducing infection risks.  

If you have ceiling fans, you can keep them running as per your comfort needs. But remember that any sort of fan should be only operated in a well ventilated space, that is, where you can get lots of outdoor air inside. If this is not possible, then the only things fans would do is to keep recirculating the room air and that can increase risks.

Lastly, the set-ups described here can be kept operational to minimise exposure within the household. For example, such set-ups could be used to mitigate transmission risks from a working member of the family to an elderly member of the family or an unvaccinated member. The steps suggested are mostly about improving ventilation and air quality. You can take these additional risk mitigation measures of cleaning the air you breathe, without waiting till there is a known infectious case at home. 

Scenario 1. Home-based isolation bedroom with attached bathroom that has an exhaust fan. 

The objective when a bathroom exhaust fan is available is to keep the bedroom under negative pressure relative to the rest of the home. This is done by sealing up the bedroom from the rest of the home by blocking the gap at the bottom of the door (undercut) with a towel, and keeping the bathroom exhaust fan on. Keep the window open so that outside air (free of virus loaded particles) can enter inside. If available, a CO2 monitor may be kept in the room to check that CO2 levels are kept under 800 ppm. Remove airborne particles with the help of a portable air filter if available. An air conditioner may be used to maintain the best acceptable temperature conditions during summer. 


Scenario 2. Home-based isolation bedroom with attached bathroom without an existing exhaust fan

The objective when a bathroom exhaust fan is NOT installed, but it is possible to install a window mounted exhaust fan; keep the bedroom under negative pressure relative to the rest of the home. This is done by sealing up the bedroom from the rest of the home as noted, and installing a window mounted exhaust fan in the bathroom. Alternatively you can also place a table fan of appropriate size in the window with the fan facing outwards (pulling room air into the bathroom and blowing it out the window). If possible, try to reduce the window opening to just the size of the fan (think cardboard cutout taped in place). Other arrangements stay the same as in the previous case.

Scenario 3. Home-based isolation bedroom with attached bathroom without exhaust fan

If a bathroom exhaust fan is NOT installed, and a window mounted fan is not possible; the objective is to keep the bedroom under negative pressure relative to the rest of the home. This is done by sealing up the bedroom from the rest of the home as noted in the figure, and installing a portable fan (table/pedestal fan) between the bedroom and bathroom with the fan blowing into the bathroom. Ideally the bathroom doorway opening should be creatively reduced to the size of the fan only but making it flexible (options include a/c curtain, shower curtain) for the quarantined person to use the washroom. This will aid in pressurising the air in the bathroom to force bedroom air out the bathroom window. Keep this fan on at all times. Other arrangements stay the same as the previous cases. 

Scenario 4. Home-based isolation bedroom with attached bathroom when fans are unavailable

The objective when a bathroom exhaust fan is NOT installed, and a window mounted fan is not possible and fans are not readily available (this approach relies on the wind and is an emergency approach only until a fan can be installed); keep the bedroom under negative pressure relative to the rest of the home. This is done by sealing up the bedroom from the rest of the home as noted, and opening up the bedroom and bathroom windows. Ideally the bedroom window should open into the wind (think sail) and bathroom window against the wind (think blowing across the top of an open bottle). When the wind is blowing it is possible (but not reliable) to use this set up to draw outdoor air into the bedroom and have it pulled out of the bathroom window. Other arrangements stay the same as in the previous case.

Scenario 5. Home-based isolation bedroom WITHOUT attached bathroom.

The objective when an attached bathroom is NOT available is to keep the bedroom under negative pressure relative to the rest of the home. This is done by installing a window mounted exhaust fan or table fan (as in Figure 2) to pull air out of the bedroom and encouraging uncontaminated/filtered air from the home to travel under the door into the bedroom. Creatively reduce the bedroom window opening to just the size of the fan (think cardboard). Keep the exhaust fan on. 

Scenario 6. Home-based isolation bedroom sharing a common bathroom with a non-isolated bedroom. 

The objective is to keep the bedroom under negative pressure (right side) relative to the rest of the home; and the bathroom does not need to be used by the non-quarantined person (left side) (see Figure 7 below). This is done by sealing up the isolated bedroom from the rest of the home as noted, and exhausting with the ceiling exhaust or window mounted exhaust fan (as shown) or table fan in the bathroom. If necessary, creatively reduce the window opening to just the size of the fan (think cardboard). Keep the exhaust fan on. Other arrangements stay the same as in the previous cases.

Scenario 7. Home-based isolation bedroom sharing a common bathroom with a non-isolated bedroom with bathroom access to a non-quarantined person.

The objective is to keep the air from the isolated bedroom from contaminating the rest of the home/apartment/condo. The non-quarantined person should coordinate with the isolated person so that the bathroom is used for as short a period of time as possible. To change over, the quarantined person should vacate the bathroom, close the bathroom door and remain in bed with the bedroom portable filter on. The bathroom exhaust fan should be on all the time. After a few minutes of purging the bathroom air, the non-quarantined person should don personal protective equipment (PPE) and enter the bathroom to disinfect. Use N95 grade masks if available. Seal the bottom of the isolated room door with a towel. Other arrangements stay the same as in the previous cases.

Please note that Scenarios 1,2,3,4,6 and 7 can be used to create an isolation room for an uninfected person or at risk person if others in the household are infected. 

The scenarios and layouts presented in this article are based off Robert Bean’s original blog on the subject available here

Robert Bean is a Registered Engineering Technologist as well as a Professional Licensee in Mechanical Engineering. He is also an American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE)  Distinguished Lecturer and has over four decades of experience with comfort conditioning in buildings.

Asit Kumar Mishra, PhD, is a researcher in the field of indoor climate quality of healthy, low energy buildings with close to a decade of experience in understanding how indoor climate affects performance, comfort, and health.

Aditi Joshi, is caregiver to and shares their home with three at risk seniors and has spent the better part of the last year obsessing about reducing indoor transmission of SARS-CoV-2 and DIYing science based transmission mitigation strategies in their home.  

 

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