Indoor Ventilation and COVID-19
Direct and indirect modes of COVID-19 transmission to humans through droplets from coughing or sneezing, close contact and prolonged exposure to the infected person and exposure to the contaminated surfaces has been reported in the literature. Findings of several reviewed articles mentioned the strong possibility of the airborne transmission of SARS-CoV-2 in indoor air settings. Aerosolized transmission in the crowded, confined and poorly ventilated settings have been suggested too.
Environmental factors such as, temperature, humidity, ventilation and filtering systems in the indoor environment could play a significant role in the transmission of the infection.
It is important to adopt engineering solutions, such as upgrading the ventilations system, proper ventilation according to the number of person in the room, establishing the minimum Relative humidity, use of proper filters along with other measures such as hand washing, disinfection of fomites, wearing of masks and uncrowded spacing to minimize the risk of infections. Engineering, behavioural and procedural solutions are required to reduce the risk of transmission.
What strategies can be employed to minimize the transmission in the indoor settings?
Hospitals have a high risk of infection. The protection from infectious diseases is needed not only for the patients but also for the hospital staff and relatives of patients who are taking care of the patients. Environmental control of indoor air and surfaces can limit the spread of SARS-CoV-2. Heating, Ventilation, and Air Conditioning (HVAC) systems, non-pharmacological strategies, are aimed to control temperature and humidity. The article also mentioned some strategies of intervention such as negative air pressure in new isolation units, filtration of exhaust air, cross-contamination and recirculation of airflow, terminals cleaning, leakage tests after absolute filters replacement, and use of air purifiers.
To maximize protection of the population against the airborne spread of SARS-CoV-2 and any other airborne virus-containing small microdroplets, controlling measures should focused on indoor environment from where most of the transmission occurs. There should be appropriate distribution of ventilation (e.g. placement of supply and exhaust vents) to ensures that adequate dilution is achieved where and when needed, avoiding the build-up of viral contamination. The principle behind this is to replace contaminated air with fresh air. Air recirculation should be avoided. The dissemination of virus-laden particles throughout the indoor environment should be avoided. For central air handling units at building level or serving multiple zones, recirculation should be avoided, and the system should operate on 100% outdoor air (OA).
Amid a massive surge in novel coronavirus cases in the country and shortage of beds, oxygen supply in hospitals, and isolation centers, the GoI revised the home isolation rules of mild and asymptomatic Covid-19 patients and stated that 'the patients who were clinically assigned to be mild /asymptomatic are recommended for home isolation'.
But in a densely populated country like India, recommending home isolation for COVID-19 patients isn't a feasible or wise option particularly keeping in mind the overcrowding and indoor air pollution in urban and/or rural communities.
World Health Organization recently came up with a road map to ensure good indoor ventilation in the context of COVID 19. This roadmap aims to define the key questions stakeholders should consider to assess indoor ventilation and the major steps needed to reach recommended ventilation levels or simply improve indoor air quality (IAQ) in order to reduce the risk of the spread of COVID-19. It also includes recommendations on how to assess and measure the different parameters, specifically in health care, non-residential and residential settings whenever a person is under home care or home quarantine.
Referred document available at:
There is a strong and persistent evidence to support the aerial transmission of SARS-CoV-2 virus (1). In order to reduce the spread of disease, CDC recommends multiple mitigation strategies, such as improving the ventilation of buildings along with social distancing, vaccination and other preventive strategies. They discuss various ventilation interventions for differential scenarios along with their cost estimations to reduce the concentration of virus in the air (2).
Ventilation is very important to reduce transmission.
SARS-CoV-2 viral particles spread between people more readily indoors than outdoors. Indoors, the concentration of viral particles is often higher than outdoors, where even a light wind can rapidly reduce concentrations. (CDC)
Steps suggested by some research papers:
1. Air cleaning and disinfection devices may be beneficial
2. Recirculation of air should be avoided
3. The number of people within the same indoor environment should be decreased.
4. Ventilation rates should be increased by system modifications.
5. Keep windows open.
Other indirect routes of transmission may include coming into contact with called fomites as a result of contagious droplets falling on these surfaces. When someone touches an infected surface and then touches their face (close proximity to mouth, nose, and eyes), the risk of the virus entering the body is significantly increased.
merely social distancing won't work, we need to be cautious for the surfaces too.
we can prevent transmission of virus in indoor.
1.all window and door always stay open.
2.Regular cleaning of house.
3.Clean dust all surface .
4.use exhaust fan if room ventilation is not good.
The significance of indoor transmission of COVID-19 has been recognised globally therefore there is a need to keep a check on indoor safety. Some important factors such as rate of ventilation, air filtration, breathing rate, room dimensions, respiratory activity and use of face mask indoors, and infectiousness of the respiratory aerosols particles and cumulative exposure time of the occupants can play a major role in spreading of COVID-19.
In order to mitigate the spread of COVID-19, controlling the concentration of droplets containing virus in the air exhaled by the occupants, is needed. Therefore, indoor settings need to be checked by taking some strategical measures such as cross ventilation, efficiency of ventilation, avoid crowding up spaces, maintenance of relative humidity, proper heating, ventilating and air conditioning (HVAC) system, interpersonal distance (6 feet / 2 meters), occupancy time (<15 minutes), floor area per person, maximum occupancy (25 people), or minimum ventilation (6 air changes per hour). Recirculation of air should be avoided and try to operate on 100% outdoor air, if possible. Fumigation and disinfection using UV radiation germicidal effects, and with the help of other disinfecting devices prove to be beneficial for cleaning indoor air.
It is interesting to note the latest guidelines from the building and Construction Authority and National Environment Agency and the Health Ministry of Singapore to curb Covid-19 spread in poorly ventilated spaces. The guidelines says that the ventilation system in the offices or residential places should be functioning well and increase the outdoor air intake. The indoor air should be expelled by using exhaust fans and focus on reducing indoor air circulation. Places which don’t have mechanical ventilation facilities should install exhaust fans in the windows to expel the indoor air. Places like dental clinics and hospitals where the chances of virus transmission is at the peak, should use high quality air filters along with other ventilation systems. Last but not least, the ventilation systems in trains and buildings should be disinfected periodically.
Corona viruses are spherical particles between 0.06 micron and 0.14 micron in diameter, averaging about 0.125 micron, measured by electron microscope (Zhu et al, 2020) which are highly infectious and that there is an increased risk of transmission through the air especially in enclosed spaces like crowded, religious places, etc. Considering the SARS-Cov-2 as airborne contagious infection, the smaller droplets from an infected person can travel further inside, thus increasing the risk of infecting others. To minimise the risk of transmission, correct ventilation becomes crucial at household level especially in urban and periurban areas living in highly densed crowded geography. Thus, to prevent and control this transmission, increasing flow rates of fresh outside air and avoiding re-circulation and transfer of air from one room to another are recommended for COVID-safe environments. In view of emerging indigenous technology several air quality treatments promise to banish coronavirus from the buildings including the use of high output UVC light technology, drawing-in air, deactivating these microbes and delivering clean air back into the facility. Indeed there is a need of revised guidelines by MOHFW to mitigate the risk of transmitting this infection.
Indoor spaces continue to be prime COVID hotspots. The reasons for the same are mentioned below:
Initially, when COVID was declared as a pandemic by WHO, they clearly mentioned that it is not air borne. However, three months later they mentioned that it might be airborne in some specific indoor settings. Also, a lot of scientists and researchers all over the world have been arguing about its transmission through air as a very strong possibility especially in poorly ventilated areas.
2. Indoor threat
- Indoor spaces present some serious threat towards spreading of the virus as the virus tends to stay on the surfaces for a very long time. Even when a person doesn’t come in contact with an infected person directly, he/she might have touched the surface which had infected droplets and later touched his face making it possible to infect himself indirectly.
- CO2 monitors have been suggested by some scientists for monitoring the air in a closed room, however, not everyone agrees about its effectiveness in recognising the spread of the virus.
3.No set standards
- It is almost impossible to to set a standard ventilation target for an area since it is not known how much ventilation can reduce the infection rates.
- The WHO recommends a minimum ventilation rate of 6–12 air changes — in which the entire volume of air in the room is replaced — per hour to prevent airborne transmission of pathogens in health-care facilities, but a lower rate of air changes for other venues. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) establishes minimum standards for indoor air quality. Recommended targets are as low as 0.35 air changes per hour for homes, 2–3 for offices, 5–6 for schools and 6–12 for hospitals.
4.Incorrect budget allocation
Governments and businesses are spending millions of dollars on disinfecting surfaces instead of using methods to improve indoor air quality.
For reference: //www.nature.com/articles/d41586-021-00810-9
The vast majority of SARS-CoV-2 transmission occurs indoors, most of it from the inhalation of airborne particles that contain the coronavirus.
Few Steps are as follows:
1. The safest indoor space is one that constantly has lots of outside air replacing the stale air inside i.e cross ventilation. In homes, outside air gets in through open windows and doors. Simply put, the more fresh, outside air inside a building, the better. Bringing in this air dilutes any contaminant in a building, whether a virus or a something else, and reduces the exposure of anyone inside.
2. Use of Air cleaners, If you are in a room that can’t get enough outside air for dilution, consider an air cleaner, also commonly called air purifiers. These machines remove particles from the air, usually using a filter made of tightly woven fibers. They can capture particles containing bacteria and viruses and can help reduce disease transmission.
3. Proper interpersonal distance should be maintained between patient and other members of family who are not covid19 positive, 6 feet diatnce should be maintained.
4. Appropriate building engineering controls include sufficient and effective ventilation, possibly enhanced by particle filtration and air disinfection, avoiding air recirculation and avoid overcrowding.
5. wearing 3 layered masks , proper sanitation, frequently handwashing, disinfecting households materials.
Ventilation systems do exactly what they are designed to do. They remove stale air from an inhabited space and replace it with fresh air to make it a comfortable inhabited space.
A covid positive patient can transfer the infection through
air more quickly. Adequate ventilation may not totally eliminate the infection but can help to reduce the transmission.
Air filtration or ventilation with adequate outdoor air ,
followed by ensuring all other safety precaution may surely
Help to eliminate the risk.
Ventilation should depend on number of people present in the indoors environment. If people are many in that indoor environment with limited ventilation then it may cause a havoc and infection may spread quickly. To avoid these, all the necessary Ventilated doors , Windows should be kept open. Air cleaner , filtration should be used
If available. I.e. 100% fresh air should be circulated to avoid transmission and reduce risk of infection.
Understanding and controlling building ventilation can improve the quality of the air we breathe and reduce the risk of indoor health concerns including preventing the virus that causes COVID-19 from spreading indoors. Ensuring proper ventilation with outside air can help reduce the concentration of airborne contaminants, including viruses, indoors. Proper ventilation also reduces surface contamination by removing some virus particles before they can fall out of the air and land on surfaces. However, by itself, increasing ventilation is not enough to protect people from COVID-19. When used along with other best practices recommended by CDC and others, increasing ventilation can be part of a plan to protect people indoors. increasing ventilation during and after cleaning, for example by opening windows or doors, is helpful in reducing exposure to cleaning and disinfection products and byproducts. Increasing ventilation can also reduce risks from particles resuspended during cleaning, including those potentially carrying SARS-CoV-2. Local bathroom or kitchen fans that exhaust air outdoors and remove contaminants directly from the room where the fan is located also increase the outdoor air ventilation rate. Running ACs while keeping windows and doors shut, traps infected air inside the room and increases the risk of transmission from an infected carrier to others. Keep windows and doors ajar while the ACs are running to bring in clean air and dilute virus particles.