Waterfall Air Doors Versus Viruses Caught Cross Currents

Here are some ideas on “visualizing” what needs to be done to fix all of these should one would want to fix this.  Building, retail, restaurant, and other design built-environments are as you can already guess not going to be easy.  Rather than start with the structure start with the people going in, staying and leaving. In regard to restaurants and places where people come and sit/stay, one view is to break inside places into three areas (you can add your own) – 1) entrance/access (including fire exit) – 2) seating/movement (staff and customer movement and 3) Kitchen – food preparation and staff access and dressing. Stopping the enemy at the castle wall starts with building a moat and drawbridge.  Today this means stopping any untested access, no jumping the “rope” everyone needs to be checked and double-checking throughout a staff shift as well as having extra testing along with any customer who requests one.   

1) Starting with entry systems multi-security levels for staff, customers, security/medical, maintenance/service and others aside from all kinds of blood, temperature, public/private testing are required.  One approach is to separate human beings versus non-human objects that are touched, used, cleaned, washed and used again, furniture, IT/telecom, bathrooms and other areas.  Starting with an inventory of each category and then building procedures for each, which could be hundreds. 

2) Seating and movement begins with all humans/objects having been certified safe to proceed.  Humans are escorted to their table/room for contact tracing and objects are also escorted to provide tracing of inventory, use, and discard.

3) Kitchen and staff movement is another level of protection and security.  Business leadership takes charge of this area providing tracing, tracking, reporting and responding to all humans including public relations with customers, government and public safety.

In each area certified and continuously tested “air doors” are installed to provide protection.  Air doors use air like waterfalls to separate distinct areas.  With high pressure fresh and filters using ASHRAE standard MERV Minimum Efficiency Reporting Value Level 9-16 for all areas which may reduce  Large virus droplets or droplet transmission are objects larger >5 um (micrometer) (such as a cough) typically traveling up to 50 feet per second to a distance of less than <1 meter (3.2 feet) from emission (mouth) point. (Source: NIH). Small droplets or aerosol transmission are objects smaller than <5 um such as a person breathing, talking or sneezing at 33-100 feet per second that can travel 23-27 feet inside buildings. (Source: JAMA). Remember these are guidelines not absolute values as your building or space can impact them significantly better or much worse. 

Viruses are sub micrometer (one millionth of a meter) which cannot be seen with the naked eye. Viruses are very small 0.02 or 0.04, a coronavirus is reported to be 0.12 micron/micrometer (symbol is μm) or 120 nanometers whereas a human hair is 17-181 though average about 75 um.  Here’s the math again, a virus is about 1.0 um whereas MERV can filter that coming in but when a person coughs/sneezes, shouts it is meaningless unless there is a Level 9-16 MERV filter between each person.  This is where a waterfall “air door” that provides fresh air MERV Level 9-16 filtered high pressure downward air flow to reduce cross current (person-to-person, etc.) virus contamination.   

The term “waterfall” is used to provide a “visualization” as water falls by gravity down to the ground level and can be easily separated such as in entry, table areas, kitchen and restrooms.  To also remind those, that water needs to be drained as fast or faster than it enters the system.  Negative air pressure systems are designed to drain or even “suck” air out of the room or area.  It is key to remember that drains should be located throughout each key area (entry, seating, kitchen-staff).

Waterfall air doors are not a panacea however, controlling horizontal air flow is a must-have in every situation.   

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