Saturday, September 19, 2020

Indoor Air Dynamics Management (ADM) For Reducing Transmission of Covid-19

The current pandemic of Covid-19 is spread significantly by inhaling droplets from infected people who are within two metres or less. Outdoor transmission is rare: most droplet transmission happens indoors where there is little movement of the air mass.

This paper looks at ways in which this indoor transmission may be reduced, both in the clinical setting and in public spaces.

At the time of writing (September 2020) the pandemic is showing signs of a second wave at a time when Governments are very strongly motivated to get the economy moving again.  Infection control demands less interaction between people, but re-opening the economy demands more interaction.

ADM technology presents a major opportunity to help resolve these conflicting demands.

First, the core proposal is set out for clinical settings, then for auditoriums, and finally for places where people are moving about freely. Detailed considerations are set out in the second section of this paper.

This is a generic document. Other documents focused on hospitals, bus, train, auditoriums and clubs are available.


1.       Preventing transmission from Covid-19 cases in hospitals and nursing homes

People in hospitals and nursing homes who are known to be infected with Covid-19 are breathing out and coughing out droplets containing the virus Sars-CoV-2 (which causes the disease Covid-19) constantly and in large amounts, especially in the first week since symptoms began. The air in their vicinity and in their room will contain a considerable quantity of virus. Their bed coverings and the floor within a couple of metres will also be hosting significant amounts of virus. These clouds and  deposits of virus present a threat to anyone visiting or attending the patient.

Patients in hospital who are on CPAP or respirators do not cause this problem as their air is contained  in a closed circuit.

Patients undergoing procedures such as medical investigations also present a threat of infection to their attendants given that they may be asymptomatic carriers. Masks mitigate this risk to some extent, but the risk is still there.

This source of potential infection from asymptomatic carriers and/or Covid-19 patients who are not on respirators or closed circuit CPAP will be reduced significantly if the oxygen mask that they are using were to be adapted with a tube that will withdraw their exhaled breath from the room.

Each individual’s exhaled air tube will be connected to a manifold, and the total air removed from all patients in a hospital or nursing home would be passed through a unit that will apply effective sterilisation by chemical means (e.g. sodium hypochlorite mist), physical means (e.g. ultraviolet light or heat) , or a combination of both, before venting to the atmosphere.

Many modern hospitals have a centralised vacuum cleaning system that might well serve as a starting point for the air extraction ducts.

Heat exchangers should be added to minimise heat loss from the establishment in colder months.

In a refinement, the mask may be designed so that oxygen is supplied when the patients are in the inspiratory stage of their respiratory cycle and cut off when the patients are in the expiratory stage of their respiratory cycle. Conversely the exhaust air duct will open with the expiratory phase of the respiratory cycle and close when they are in the inspiratory phase of the respiratory cycle.

This alternate flow may be produced by simple valves fitted at the opening of the tubes in the mask, (See Fig 1), or by an electrically driven rotating valve fixed to the air lines (design available from author).

In a further refinement, for patients with severely compromised respiration, electrically actuated valves could be provided which would be controlled by information from sensors sited on the patient’s chest which would allow synchronised delivery and extraction of gases. The patient would receive useful assistance in respiration from this arrangement.

This positive technology which will substantially remove the virus from the hospital environment means that hospital acquired infections, whether by other patients or by front-line staff, would be greatly reduced. It would remove a great deal of stress from front line staff.


2.       Preventing transmission in auditoriums

Cinemas, music venues and theatres are adversely affected by the pandemic, since their capacity is severely restricted by the need for a safe 1 or 2 metre gap between customers. The same consideration applies to public transport.

ADM technology can allow these places and services to return safely to full capacity.

In places where people sit in rows of fixed seating, as in theatres and cinemas, each seating place will be provided with a double tube, one bringing in filtered and purified air, and one withdrawing exhaled air. The clients will each own their personal face mask (which will be available in the foyer) that will fit to the tube, and on breathing in they will receive filtered air, and on breathing out their breath will be drawn away to be sterilised  (see 1. above) before it is vented.

In a refinement of the system, the masks may be provided with valves that open the supply tube when the user breathes in, and opens the exhaust tube when the user breathes out.

As an addition to this system, exhaust air from the whole site can tested for presence of Sars-Cov-2. If the virus is found in the total exhaust, it may be made possible to sample air from specific parts of the room, and break down the testing to smaller and smaller sections until the row is (or rows are) identified that contains the person who is (or persons who are) the source of the virus.

In the case of places such as a conference or a lecture theatre, the people from that row can be called out and tested individually.

In the case of a theatre, people from the row that is showing infection can be notified in the interval of the performance that one of them is carrying the virus, and if individual testing is available, each person in the row can be tested during the interval.


3.       Offices

ADM technology can be applied to office workstations in various straightforward ways that are laid out in detail in a separate document available on request.


4.       Public transport

Some bus companies have introduced simple ventilation to their buses. This is better than having no ventilation, but it has drawbacks since horizontal movement of air from a person who is putting out Sars-CpV-2 particles is known to be able to cause spread. ADM technology can be easily applied to buses and trains. Details will be posted here soon.

5.       Dance halls, public houses, and crowded spaces

In some situations, it is impractical to wear masks that deliver to, and remove air from, each individual. Places like dance halls, pubs, clubs, locations where people are required to queue, and places where social distancing is impractical, are areas where the risk of viral transmission is high.

In these situations, the aim should be to create vertical air dynamics. Purified air can be introduced at a level of about 1 metre from the floor. These would be delivered from vents fitted to the wall, by pillars and under tables. Air would be extracted from funnels placed a little above head height, collected, and sterilised (as in 1. above) before venting. This arrangement will mean that exhaled droplets and aerosols are drawn upwards and away from other people. Transmission is still possible with this arrangement, but the degree of transmission will be significantly reduced.

In an alternative embodiment, vertical air dynamics air may be supplied from overhead vents and removed by designed floor tiles.

Sampling of exhaust air may be carried out as described in section 2 above, and if viral load of exhaust air passes a set threshold, the crowd can be notified so that those who do not wish to run the risk of infection can leave. If the viral load exceeds a higher set threshold, the event will be terminated.

It should be noted that air quality in many clubs is already in need of improvement regardless of the pandemic, due to sweat, body odour, perfume, body heat,  low levels of oxygen and high levels of CO2, so the uptake of AQ management in clubs may eventually be widespread.




There will be a significant capital cost attached to fitting these air management tubes, fans, filters and sampling activities, but the costs will be recouped from increased revenue arising from higher attendance figures. It is possible that Government may be persuaded to subsidise these technologies in order to suppress the pandemic.

Apparatus will not have to be scrapped when the Covid-19 pandemic is over. Pandemics are arising more and more frequently as shown in this table:

Table 1

HIV/AIDS             ~1940

Ebola                     1976

Sars                        2002

Mers                     2012

Covid-19              2019


It can be seen that the interval between emergence of new infections is decreasing with time, and we can safely infer that new pandemics will occur from time to time, and therefore the demand for air dynamics management equipment will be sustained and increased.


                                Other measures

Air Dynamics Management  must be seen as one component of a systematic response rather than a magic bullet to stop the pandemic. Hand hygiene, social distancing, face coverings, fever scanning, and even tests for anosmia should be continued alongside ADM.



Attention must be given to the problem of noise associated with air management. Tubes will be of  smooth bore rather than corrugated. Valves will be made of soft material, and the points of impact of valves will be designed to avoid noise. Air flow will be laminar, and as slow as is possible compatible with amounts required for respiration.



There is a serious responsibility undertaken in supplying air to hundreds of people. System integrity is vital since leaks in delivery tubes could result in dust or poor-quality air being delivered. Highest quality materials will be used, with levels of volatile organic compounds from the constituent plastics being kept as low as practically achievable, so material selection will be important. Potential breakdown in the system of delivery and exhaust air management must be monitored with regular checks.


                                Indirect positive effects of ADM

As knowledge of the testing aspect of ADM becomes general, people who are suffering symptoms of Covid-19, or who know that they have been in contact with the disease, will be inhibited from going out into crowded places for fear of being identified in public.




There is a strong case, both from a public health and a financial viewpoint, for venues management to consider which form of Air Dynamics Management would be most appropriate for their venue, and to set about installing it. Similarly, there is a strong case for manufacturers of air management equipment to set about designing, producing and marketing such equipment.

ADM delivery system

Figure 1

The author

Dr Richard Lawson MB BS, MRCPsych is a retired general practitioner of medicine, author of Bills of Health (Radcliffe Medical Press 1996, ISBN 1-85775-101-9), poet (In the Key of Blue (ISBN 978-1-78719-545-5), Green politician (Past national co-speaker, Green Party of England and Wales), past elected Local Authority Councillor, and inventor of physical technology (Aerosail, Phoenix bike stand, BrambleHook) and social inventor (Green Wage Subsidy).

The author asserts, and has protected, the intellectual property included in this paper.


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