Over the last 14 weeks or so we have been encouraged to do all sorts of things to avoid contracting the Covid-19 virus. Much of that information is bogus as people share misinformation and conspiracies around the Internet. But...there are guidelines from the CDC and other professionals in the medical and science fields.
Although those guidelines are based in fact I don't remember seeing the reasons why those actions will work to limit your chances of becoming ill. That has sent me on a search to gain a basic knowledge of why we should do those things.
One of the first things I learned was that the Coronavirus is actually a pretty fragile virus. Unlike viruses such as the Norovirus which has a hard protective protein shell, the Coronavirus is protected by a lipid coating...much like a layer of fat around the cell.
Because this protective coating is relatively weak the virus can be defeated using some fairly routine procedures.
Of course, one of the most frequently mentioned techniques is "social distancing". This is because the virus is primarily transmitted in an airborne fashion when people cough or sneeze. We all know about that but the other side of this is that the droplets created by a cough or sneeze add a second layer of protective mucus to the virus that can keep it viable on surfaces where the particles land. The length of time that the virus can live on a surface outside of the human body is still being researched but the fact that it can be deposited on surfaces is why the use of disinfecants is one of the guidelines. But why does that work?
The answer is pretty simple. The chemicals in the disinfectants break down the lipid barrier exposing the virus to the chemicals that can then render the virus "dead". The problem is that not all disinfectants are the same and some are not effective enough at breaking down the lipid barrier. The information about what disinfectants are most effective is available from the EPA and various company websites but the average consumer simply buys what is on the shelf when they can find it. There are some consumer grade disinfectants that have been tested against the virus, and could carry a label stating that fact, but until more research is complete the companies are only allowed to put the statement on their websites...not something the average consumer refers to...but something that your purchasing people should be aware of.
Alcohol and bleach are both very effective at breaking down the lipid barrier so disinfectants that contain strong enough blends of those items will accomplish the mission....if they are allowed sufficient time to work. Studies indicate that the average consumer will do a quick wipe and dry of surfaces but that does not allow time for the disinfectants to work. Wiping or spraying the disinfectant on the surface but then leaving it to dry on its own should provide adequate time and any of your HVAC maintenance technicians who use disinfectants should make sure that they allow adequate time for the process to work.
The other common guideline is to wash your hands with soap for at least 20 seconds. In this case two things are happening to the virus. First is that the soap can break down the lipid barrier if you wash for the appropriate length of time. The second thing that is happening is good old friction. As you scrub your hands you are scrubbing the surfaces of the virus and using friction to strip some of the lipid barrier away. You are also simply separating the virus from the skin and sending it down the drain.
So far these guidelines work at the individual level...what you can do for yourself. The use of disinfectants in a commercial setting will work the same way on the virus but there are obviously many more surfaces to deal with. That leads to the discussion of UV light as a means to "kill" the virus in large areas or as an option in an air handler.
UV light works in a different manner than disinfectants or soap. Viruses have a DNA/RNA that works to infect cells that it comes in contact with. UV light breaks the DNA/RNA pattern of the virus cell so that it does not recognize and attach to the host cell. This sounds like a simple and effective way to treat large spaces...just blast it with UV. However, much like disinfectants, not all UV is created equal.
Anyone who spends much time at the beach has probably heard of UVA and UVB. UVA is the most abundant version of UV light that the sun emits and is of a fairly long wavelength. UVB is a somewhat shorter wavelength light. But there is also UVC which is a very short wavelength light that can penetrate past the layer of human skin and cause some serious intermal problems. The good news is that our ozone layer filters out virtually all UVC (something to think about related to refrigerants but that is for another time).
Because of the different wavelengths it is estimated that it would take roughly seven days of continuous exposure to the sun to modify the virus DNA/RNA. This is obviously too long to be useful in controlling the virus in almost all cases. UVC, on the other hand, is very effective in a short time (seconds) in rendering the virus inert. The challenge is that UVC in its shortest wavelengths is approaching x-ray wavelengths and continuous exposure by humans is dangerous. So in order to "clean" a space with UVC it must be unoccupied...a problem in a crowded hospital ward or many commercial buildings. The other issue with UVC is that due to its short wavelength it also has difficulty penetrating cracks, folds, or crevices in a space. That means that even after a blast of UVC a space will require a second dose of liquid or spray disinfectant in order to eliminate the virus threat.
So...for those involved in cleaning and sanitizing HVAC equipment or the spaces that equipment serves adequate employee training and a basic understanding of how the recommended methods work will help companies implement the best strategies for their situations.
No comments:
Post a Comment