Why only 6 ft ? Why 30 min. contact period is fatal ?

Yes, Why only 6 feet distance is safe distance ? Why cannot 5 feet distance from a covid positive case keep you safe ?

Why 30 minutes exposure to such cases is significant ? why not 20 ?

Why an hand shake can be dangerous ?

These are some of the basic questions that we would try to understand today. Why 6 ft distance is safe , why not 5 feet.

( We shall revisit some basics and try to explain them rationally. Welcome to my blog. Thanks and regards.)

Priniples of virus transmission.

Source: 

Covid-19 virus can come only from an infected person. No animal or plant has yet been established as a true reservoir that can give you the virus.

Location: 

Virus clumps are found usually in the throat of an infectious person. Swabs are used to collect a sample from this site for RTPCR testing. ( Rarely other sites may be used.)

The Virion: 

It is a small virus hence nick named as a virion. Each SARS-CoV-2 virion is approximately 50–200 nanometres in diameter. (  ≈0.1 μm in diameter). It has multiple spikes that gives it the appearance of a crown ( Corona)

What happens when a person coughs ?

When an infected person coughs/ sneezes or gives a vigorous exhale, droplets of liquid of various sizes are ejected from his nose and mouth. 

Average size of a cough droplet is taken to be 5 μm in diameter. It depends on the force. When procedures like nebulization, intubation takes place, much smaller particles are generated. It has a different name: Aerosol.

Cough particles bigger than 5 μm are immediately grounded. Droplets of less than 5 μm diameter evaporate before getting grounded. 

Basically each cough droplet is a ballistic missile with a payload of virion clumps of various denominations.

Particle physics calculates that a 5 μm sphere of cough droplet when gets launched from an average height of 6 ft ( our mouth) should carry upto 6 ft distance before getting grounded. ( It’s a 6×6 Isosceles triangle).

( Please check that physics part. That is the basis of of 6 ft distance of safety for the covid infection.)

What about those cough molecules less than 5 μm ? 

They evaporate before getting grounded. If they are carried in the airflow it can be called airborne. Since the viron is already 0.2 μm, a clump usually needs a vehicle size of a 5 μm droplet. Not necessarily always. For calculation purpose, Covid carrying droplets are taken to be 5 μm in diameter.

What happens to the clumps of the virus inside them ?

Those clumps should hang in the thin air for say 30 minutes before  getting adsorbed onto something, a surface or propelled by the air current . One of the destination can be our nose. That is ominous.

How long these suspended virions can float in thin air ?

We don’t know. It’s assumed that before 30 min they get neutralised either by falling on something or getting swept away by air current.

Science is not unanimous in establishing how long these virions can survive in that stage ? 

Studies differ from 30 min to 8 hours.

This is the basis of 30 min contact period.

How does this virion enters inside our system ?

The spike of virion can not enter us through our skin or nail or hair. It requires a mucosa to move.

What is this mucosa ?

We have two basic body cover program – the rough and tough skin that covers us thorougy and the soft moist mucosa. While the skin is our external affairs ministry, Mucosa line all our internal passages like mouth cavity, inside of our nostril and white of eye. They are the life line of our system and are capable of transporting food, oxygen into our system. They also carry the virus inside our system.

What happens then ?

When a virion so launched lands on my neck, nothing should happen to me. It cannot enter my intact skin. So a clump of virions landing on my cheek or even on the tip of my nose are as harmless as a drop of water. Only when my hand knowingly or unknowingly picks up them and help depositing on a mucosa, they start moving towards their target, the human lung cell. 

The lung cells are well covered by a double layer of oily cum fibrous membrane. But they are bound to have secrets doors for oxygen and enzymes to trickle in. These small chinks are protected with special locks like the ACE receptors. The virus has a key called spike protein. It is an exact fit to human lung receptors.

The virions hitch hike on our body’s transport system to a lung cell, then open it up with their spike and get inside.

Inside a human lung cell.

Once inside, the virus simply overtakes the master manufacturing system of the cell. It stops all normal  production of hormones and enzymes required for daily functioning of the cell. Instead the whole production capacity of the cell is used to manufacture million copies of virions under gun point.

Once a thousand daughter viruses crawl out, the lung cell already starved of food bursts open. The daughter viruses go on to infect other lung cells. A Covid Pneumonia sets in. Oxygen exchange stops inside our chest..

When Covid Pneumonia sets in..

At this time if we put our finger inside an oxymeter the O2 saturation falls to 94 and below. Soon the oxygen saturation falls below 80 and patient requires ventilation.

This is an account of covid physiology, simplified for easy understanding. Now some applied part of this knowledge.

Not all exposure to covid patient can infect you. For example, inside a closed environment like a Lift or an air conditioned cabin the viruses are available more concentrated and have more chance to meet their target than in any open spaces. Ventilation protects against the disease.

The chances of getting infected depends upon the 3D of Infection.

• Dose
• Duration of exposure: 30 min and more.
• Distance less than 6 feet.

About dose, no unanimity has been available. 

That some people can behave like super-spreaders suggests that they are releasing a large dose of virions with each bout of  cough. No explanation yet for this phenomena.

For example, if you are traveling in the front seat of an air conditioned car for 2 hours with an infective person in the back seat, you are a sitting duck for the virions.

A stadium full of crowd gathering ( on that fateful football match in Milan, Italy)  increases your risk. So also if you carry on long discussions with a source across a lunch meeting.

Now the 2 F‘s

Face Cover: Any face cover should reduce the chance of such a virus loaded missile getting into our system. It also prevents us from inadvertently touching our mouth and nose.

Fomite is a collective term used to include all contaminated clothes, utensils, furniture, keyboard, mouse, lift button, tacks, papers, pens. Any item used by the patient that can transmit the infection to a healthy person. Fomites are the reason why any family member of a positive person is graded as high risk contact. For fomites hand washing is the best option.

The bottom line is Neither drugs, nor vaccines, only hand washing and face cover are the two weapons that together can save us from this menace.

Thanks for your patient reading.