With inputs from Mr Ashish Rakheja (AEON Integrated Building Design Consultants) and Dr K K Kalra (former CEO NABH)

Why we are talking about AC as a concern

From January 26 to February 10, 2020, an outbreak of 2019 novel coronavirus disease in an air-conditioned restaurant in Guangzhou, China, involved 3 family clusters. The airflow direction was consistent with droplet transmission. In order to prevent the spread of the virus in restaurants, it was recommended that the distance between tables should be increased and ventilation to be improved.

The size of a coronavirus particle is in the range of 80-160 nanometres. It is transferred through infected microscopic airborne particles and contaminated aerosol droplets. Droplets and small particles of a wide range of diameters are generated during coughing and sneezing. The air-conditioning system can escalate the spread of the particles in case it is not designed or operated properly. 

 What are the lessons learnt from Diamond Princess Ship

 Researchers at Purdue University in the US investigated the air conditioning systems on the Diamond Princess Cruise ship. This 3,700-passenger cruise was placed on lockdown off the coast of Yokohama after a passenger got off in Hong Kong and tested positive for the novel virus.

A Centers for Disease Control and Prevention (CDC) report stated that 46.5% of the passengers on board the cruise ship had infections at the time of testing. Additionally, traces of the virus were identified on several surfaces in cabins of both symptomatic and asymptomatic passengers up to 17 days after cabins were vacated.

 What is special about cruise ship air conditioning systems

 They are not designed to filter out particles as small as the coronavirus. As a result, the disease can rapidly circulate to other cabins.

It’s standard for the air conditioning systems of cruise ships to mix outside air with inside air to save energy. However, these systems do not filter out particles smaller than 5,000 nanometres. If the coronavirus is about the same size as SARS, i.e., 120 nanometres in diameter, then the air conditioning system would be transfering the virus to every cabin.

 A cruise air conditioning system is like a hotel air conditioning system. The major risk of transmission is in the public areas of cruise ship where the guests are in close contact in a common conditioned space. 

 What about airplanes 

On an airplane, the risk is primarily due to close contact between the passengers while seated and due to touching surfaces like seats, handles, doors, luggage, etc. The air-conditioning is less of a challenge as modern aircrafts are better equipped.

What is droplet

Carries particle size of > 5 micron

What happens if the humidity is high

It will absorb moisture, become heavier and settle on the floor or surfaces quickly.

As per REHVA and ISHRAE guidelines, relative humidity greater than 80% and above tends to neutralize the COVID-19 virus.

 What will happen if the temperature is high

Once settled on the surface which is hotter, the moisture will get dried out exposing the virus to heat and its death.

A report published by Chinese researchers has found SARS-CoV-2 to be highly stable on surfaces for 14 days at 4°C; one day at 37°C and 30 minutes at 56°C. Higher indoor temperatures are therefore advisable.

 What happens if the atmosphere is cold

The droplet on the surface may persist longer.

At colder temperatures, small droplet nuclei or residue are formed from droplets in the air which are usually within milliseconds. They shrink due to the process of evaporation and desiccation in low humidity. These small droplets can be carried to a longer distance through airflow generated by AC systems.

What about home air conditioners

Home AC units may not pose any additional risk of infection during the lockdown period when there is no outside contact. 

The virus does not stay suspended in the air for a very long time. Therefore, air conditioners do not seem to be a threat, given that it is in your own house where no one is infected. 

Home air conditioners are therefore safe if inside occupants are non-infected. It is recommended to keep windows slightly open or introduce a fresh air source to ensure dilution of pollutants.

What about split ACS and central ACs

Coronavirus can spread within centrally air conditioned spaces such as shopping malls and some modern apartments, more so if an infected person is occupying such spaces.

 Also, in places like centrally air-conditioned shopping centers, etc., that have a lot of people at the same time, the virus can get recycled in the air for a short span of time.

 Split AC and Central AC operation in larger buildings run the risk of propagating transmission of virus. However, the risk can be minimized with higher ventilation rate, superior filtration and UV treatment of air.

But virus is not airborne

In AC atmosphere, the surface to human transmission will be more than person to person transmission. 

The virus is not airborne. When a person sneezes, a thick spray is created — that is when a virus is in the air. However, it does not float in the air. Instead, it settles on surfaces and can persist there for a long time.

If people go to a centrally air-conditioned mall during a pandemic, their risk of getting exposed to the coronavirus directly from an infected person is increased than getting it from the recycled AC air.

At colder temperatures and low RH conditions, small droplet nuclei or residue are formed from droplets in the air that shrink owing to evaporation and desiccation in low humidity. These small droplets are carried to a longer distance through airflow generated by AC systems.

What about split ACs in a house, if I must use it

For a split AC system, open the window slightly to let the outdoor air enter room. 

Home air conditioners are safe if inside occupants are non-infected. It is recommended to keep windows slightly open or introduce a fresh air source to ensure dilution of pollutants.

What about window AC, if I must use it

For window AC system, it will help to increase the outdoor airflow rate, if possible. If not, open the window slightly so that more outside air can enter.

Window air conditioners are safe if inside occupants are non-infected. It is recommended to keep windows slightly open or introduce a fresh air source to ensure dilution of pollutants.

What about central AC, if I cannot avoid

If central air conditioning system is used, the virus could be transmitted to all the spaces that it conditions if return air is used. For central air conditioning systems, it is recommended to use 100 per cent outside air.

Central AC operation in larger buildings run the risk of propagating transmission of virus. However, the risk can be minimized with higher ventilation rate, superior filtration and UV treatment of air.

What are the Federation of European Heating, Ventilation and Air Conditioning Associations (REHVA) guidelines 

REHVA recommends that buildings should switch on ventilation systems round the clock, or at least prolong the operation of ventilation systems as much as possible.

It has been recommended that ventilation rates should be switched to low power when there are no people inside so that virus particles are removed out of the building. Exhaust ventilation systems of toilets should be kept on all through the day. 

Buildings that lack mechanical ventilation systems should have windows kept open for at least 15 minutes before somebody enters, more so if it was previously occupied by others.

 Such places should not have windows in toilets open as it will facilitate contaminated airflow from the toilet to rooms.

 What are the CDC guidelines

 Increase ventilation by opening windows or adjusting air conditioning

 What about Car AC

Keep windows open when possible, increase ventilation and regularly disinfect surfaces

 What about planes with newer facilities

The International Air Transport Association has stated that aircraft air conditioning systems have high-energy particulate air (HEPA) filters that are able to screen more than 99.9 percent of airborne threats, including microbes and viruses.

Furthermore, the air is refreshed every two to three minutes in the newest planes with about 50 percent of it entering from outside.

The risk of contracting a virus on an aircraft is therefore lower than the risk from daily activities such as going to the office.

 Airlines have also upgraded aircraft cleaning procedures in order to deal with surfaces that can potentially transmit the coronavirus.

 What about airport lounges and counters

 They tend to carry the same risk as the Diamond Princess cruise ship or AC malls, with a High risk of surface to human transmission. 

 The airport lounges and counters are provided with central air conditioning which run the risk of propagating transmission of virus. However, the risk can be minimized with higher ventilation rate, superior filtration and UV treatment of air.

What about centrally AC hospitals

They have the biggest risk as they, in addition, carry the risk of aerosol production in most procedures.

 The COVID-19 isolation rooms must be run at negative temperatures and exhaust air from these rooms must be treated before being let out in the vicinity. However, the risk from walk-in COVID infected patients is high. The heat recovery wheels, if installed, must be disabled.

Will HEPA filters work

 Air purifiers with HEPA filtration can effectively capture particles the size of, and even smaller than, the virus that causes COVID-19.

So, it seems that HEPA filters will work. The CDC states that the virus is mainly transmitted by person-to-person contact. However, increasing amount of evidence points that it may also be transmitted through the air. If that is the case, HEPA filters will capture airborne coronaviruses.

The COVID-19 causing virus is about 0.125 micron (125 nanometres) in diameter. It is squarely within the particle-size range that HEPA filters can capture with extraordinary efficiency: 0.01 micron (10 nanometres) and above. 

Many people have incorrectly stated that HEPA filters don’t filter below 0.3 micron and therefore could not capture airborne coronaviruses. A NASA study of HEPA filtration explained why HEPA filters are most efficient, almost 100 percent at 0.01 micron, when it comes to capturing ultrafine particles below the 0.3-micron HEPA test standard.

 HEPA filters are efficient in minimizing the spread of airborne virus. However, the air change rate should be minimum 12 ACPH for increasing its effectiveness.

 The room air purifiers also contain HEPA filters. However, only a small air quantity passes through filter and hence their effectiveness is severely limited. 

Will the virus remain alive in the filter

It’s not certain.

The filters run the risk of live virus and should be serviced in Personnel Protection Gears. 

If someone in your household is sick with COVID-19 what to do

 Running an air purifier in their quarantine room may help protect other family members or caregivers. The same goes for healthcare workers who are self-quarantining when they come home.

But even if you live with a healthcare worker or someone sick with COVID-19, instead of buying an air purifier, simply opening up the windows in the home to let in fresh air will help dilute indoor contaminants, including virus particles. 

If increasing the air flow in the room does not seem to be an option, use a high-efficiency particulate air (HEPA) purifier.

What are lessons from 2003, during the SARS outbreak

During the SARS outbreak, the Hong Kong Hospital Authority had recommended that hospitals should use portable air purifiers with HEPA filters to limit transmission to healthcare workers if isolation wards were not available. 

In the U.S., the CDC also recommended the use of HEPA purifiers to help with the reduction of viral concentrations of the SARS virus in the air when properly ventilated hospital rooms weren’t available.

Recent research in the Journal of Infectious Disease and under review at BMC Infectious Diseases suggests that air filtration can limit the risk of transmission of measles and influenza. 

What is CADR

The faster an air purifier can circulate air through the filter, the better its odds of catching virus particles. The pace at which an air purifier cleans the surrounding air can be noted by looking at its CADR (clean air delivery rate) number on the packaging. 

CADR means, in cubic feet per minute, the volume of clean air produced by an air purifier at its highest speed setting. At lower speeds, the rate decreases. The packaging should carry three CADR ratings - one for smoke, dust, and pollen, which represent small, medium, or large particles, respectively. A purifier with a CADR of 250 for smoke reduces smoke particle levels to the same concentration that would be attained by adding 250 cubic feet of clean air each minute. (Smoke particles are similar in size to the smallest virus droplets while larger droplets are closer to the pollen size range.) 

Based on CRs lab tests of air purifiers, look for a model with a CADR over 240, which can perform about five air exchanges per hour in its suggested room size. 

You may not want to run an air purifier on its highest speed setting. Air purifiers can be quite loud, especially at higher speeds, and can disturb a sick person’s sleep. 

Even the most efficient air purifiers can’t prevent some droplets from landing on surfaces, where they can persist for hours or even days. Therefore, to prevent the spread of the virus in your house, you should clean your home and wash your hands frequently, too.

It is desirable that portable air cleaners must be designed to achieve 3-4 air changes per hour. The higher the air changes, the better the efficiency of cleaning. One must be careful when reading the CADR numbers on most commercial products as they will give either the highest number (based on highest fan speed) which will be very noisy or will give the free-flow air handling capacity of the fan motor.

[Consumer Reports]

Where do we keep the air filter

To use a HEPA purifier at home to prevent transmission of the virus to other family members, you can place the unit three feet from the person who is sick with COVID-19. 

Have the air purifier on low speed near the patient rather than farther away on super high speed.

It may not be able to protect people from direct (droplets) and indirect (surface contamination) exposure but can help reduce the indoor concentration of contaminants through the action of dilution.

How long to run the air purifier

You may run it 24 hours a day on the highest setting that won’t disturb the sick person’s sleep. Keep the air purifier separated from anything that can obstruct airflow, such as curtains or furniture, and keep the door closed. When used correctly, the filter can potentially catch floating virus particles before they reach a caregiver in the same room.

What precautions to be taken

It is mandatory to take extra precautions when handling the air purifier and changing the HEPA filter. Early studies have shown that the coronavirus can live on plastic and steel for up to three days. Both the materials are commonly used for making air purifiers,

Don’t touch the air purifier while it’s in use. When changing the filter, put on gloves and a surgical mask, take the air purifier outside, and clean and disinfect the exterior. Remove the filter and dispose of in a sealed bag. If your air purifier has a fabric prefilter, wash it.

What about UV lights in air purifiers

Take these claims with a grain of salt because there isnt enough concrete evidence yet that proves they work in these settings.

UVC irradiation with an exposure time of 15 minutes at irradiation intensity of 4016 μW/Cm2 is required for inactivation of SARS-CoV. This will be difficult to achieve in air purifiers.

What about OTs 

All operation theatres have HEPA filters and are safe.

It is recommended to operate OTs at highest setting of outdoor air intake.

What about AII rooms (Airborne infection isolation)

Airborne infection isolation (AII; previously called negative pressure isolation [NPI]) room is a single-occupancy patient care room with a ventilation system that can generate negative pressure relative to outside the room. It enables air to flow into the room but not out of the room (since air will naturally flow from areas with higher pressure to areas with lower pressure), thus preventing infectious droplets from escaping the room. The doors and windows of AII rooms must be kept closed to maintain negative pressure, and the pressure should be verified on a daily basis.

It is recommended to have at least 6 air exchanges per hour (for construction prior to 2001); for renovations or newer construction, 12 or more exchanges per hour are the standard.

Air should be moved to the outdoors (where the droplet nuclei are diluted in the outdoor air), far removed from any intake vents, people, or animals and in accordance with applicable regulations on environmental discharges. If it is not possible to avoid recirculation to general ventilation, air must be passed through a HEPA filter installed in the exhaust ducts to remove infectious droplets from the air before it reaches general circulation.

Patients should be educated about the purpose of the isolation room and be instructed to cover their nose and mouth when coughing or sneezing, even while in the isolation room. Procedures should be performed in the AII room in order to minimize exposure of others in the hospital to the patient. If the patient must leave the room, he or she should wear a surgical mask. [UpToDate]

Entry of visitors and HCWs should be restricted to minimize transmission.

The AII rooms should be under negative pressure of minimum 2.5Pa (preferably >5 Pa). It is advisable to install differential pressure meters to measure this metric. The desirable supply air quantity is to achieve a minimum of 12 air changes per hour. The position of the extract air in the room shall be just above the head of the patients bed.

What are other points

Timely replacements of HEPA filters, routine maintenance and cleaning of ducts regularly. Separate AHU for each OT & ICUs and other high-risk clinical areas of a hospital.

In old building where common AHU for OTs /ICUs are there and cannot be modified, inlet air has to be separate and common outlet with filtration may be acceptable. Minimum 12 air changes per hr, with 4 fresh air changes.

CMAAO CORONA FACTS and MYTH BUSTER 58

How many healthcare workers have died in US

As on April 9, at least 27 healthcare personnel have died of COVID-19 in the US. The estimate; however, is an underestimation because healthcare personnel (HCP) status was available for just over 49,000 of the 315,000 COVID-19 cases reported to the CDC as of April 9. Of the cases with known HCP status, 9,282 (19%) were healthcare personnel. [Medscape]

What was the profile of the doctors

The median age of around 9,300 HCP with COVID-19 was 42 years, and the majority (55%) were aged 16-44 years; 21% were aged 45-54, 18% were 55-64, and 6% were > 65 years of age.

The oldest group; however, represented 10 of the 27 known HCP deaths, as reported in the Morbidity and Mortality Weekly Report. [Medscape]

How many got it in the healthcare settings

The majority of infected HCP, i.e., about 55%, reported exposure to a COVID-19 patient in the healthcare setting. However, there were known exposures in households and in the community as well, thus highlighting the potential for exposure in multiple settings, particularly as community transmission increases. [Medscape]

How many of them were hospitalized

HCPs with COVID-19 were less likely to be hospitalized (8%-10%) than the overall population (21%-31%), which might point to the younger median age of HCP patients, compared to that of COVID-19 patients overall, as well as prioritization of HCP for testing, which might detect less-severe illness. [Medscape]

What  was the percentage of underlying illnesses in them

The prevalence of underlying illnesses in HCP patients (38%) was the same as all patients with COVID-19. [Medscape]

What was the presentation

About 92% of the HCP patients had fever, cough, or shortness of breath. Two-thirds reported muscle aches, and 65% reported headache, noted the CDC response team. [Medscape]

What are doctors and first responders in US doing to protect the family

1. A firefighter in Boston moved into a Harvard University dorm to protect his wife and two children.
2. An emergency room doctor has sent his wife and four kids to live with her parents, so he wont risk bringing COVID-19 home.
3. There’s one who strips in the garage, throws his clothes right into the washing machine and jumps into the guest bathroom shower before meeting his family.
4. Healthcare workers and first responders worry that they are carrying the virus home on their shoes, in their hair, or on a layer of clothes.
5. The lack of personal protective equipment (PPE), such as masks, gloves, and gowns, is putting healthcare workers lives at risk. But the workers are also quite conscious of the others it puts at risk: their closest family members.
6. Not everyone has free housing, willing in-laws, or a place to change safely before coming in the front door.
7. Ganelle Salmon, a patient information specialist at Beth Israel Deaconess Medical Center in Boston, can do little more than put her clothes into a plastic bag on the porch and hope that she doesnt bring the virus into her apartment. Getting only about 3-4 hours of sleep every night, she hasnt yet understood how to take the time out to go to a laundromat, now that she doesnt feel safe running over to her mothers place to use the washer.

 [Medscape]

Dr KK Aggarwal

President CMAAO, HCFI and Past National President IMA