Frequently Asked Questions (UVC)

Answered by UVC Experts at Planled

Dr. Nardell Answers:

The Effectiveness and Safety of Upper Room GUV

How effective is upper room germicidal UV (GUV)?

The short wavelength ultraviolet light (UVC) used indoors for disinfecting air is different from the longer wavelength in sunlight (UVA and UVB) – it is both more effective in disinfecting air and surfaces and safer for human exposure because UVC penetrates human tissues (eyes, skin) much less than UVA and UVB.

In a TB hospital in South Africa my own studies have shown that upper room UVC reduced the infectiousness of room air for tuberculosis (TB) by 80%.  Another TB study in Peru showed a similar near 80% effectiveness. In the South Africa hospital that protection was equivalent to ventilating the hospital ward with 24 room air changes per hour (ACH). That is an extraordinary amount of equivalent ventilation.

How do we equate UV air disinfection with ventilation? 


One room ACH is when a volume of air equal to the volume of the room enters and leaves the room in one hour.  If the air is well-mixed, 1 ACH removes 63% of room air contaminants, including airborne bacteria or viruses. Another ACH (2 ACH) removes 63% of what air contaminant is left, or a total of 86% reduction. That is true only if no additional airborne bacteria or viruses are being added to the room.

If infectious room occupants continue to generate viruses, for example, higher levels of ventilation (or equivalent UV air disinfection) are needed for effective protection of occupants.  CDC recommends 6 – 12 ACH in high-risk hospital settings. Homes and schools without mechanical ventilation, for example, often have less than 1 ACH if the windows are closed – through passive air infiltration. Adding only 3 or 4 ACH can greatly reduce transmission under non-hospital conditions. While higher levels of ventilation (6-12 ACH) or equivalent ventilation from UV (EqACH) afford greater protection, each additional ACH adds smaller and smaller increments in protection at greater and greater cost – especially if outdoor air must be cooled or heated.

Is SARS-CoV-2 (Covid 19 virus) susceptible to GUV? What about the Delta variant?

Tests of airborne seasonal coronaviruses in the laboratory show that this type of virus is about as susceptible to short wavelength UV as airborne TB tested in the same way.  The 80% protection achieved by upper room in preventing airborne transmission from real patients was produced with a UV dose that resulted in an average of about 4 – 6 µW/cm2 in the treated room air.  Since susceptibility to UV is similar, the protection against any coronavirus should be very similar to what we found with TB with similar UV dosage.  Therefore, half the UV dose used in the TB hospital that produced the equivalent of 24 ACH, that is EqACH – that is, 2 to 3 µW/cm2 – is expected to produce air disinfection equivalent to at least 8 – 12 EqACH.

UV susceptibility of microorganisms is predicted by its DNA or RNA structure. Bacteria and viruses vary in UV susceptibility, but viruses or bacteria have the same UV susceptivity regardless of drug susceptibility or strain mutations. TB with drug susceptibility mutations remain fully UV susceptible. Likewise, viral mutations resulting from viral replication in human hosts impact their ability to infect, replicate, and transmit, but are highly unlikely to change its basic RNA structure or susceptibility to UV. The emergence of Delta variant increases the need for air disinfection to prevent transmission, but it is highly unlikely impact UV air disinfection effectiveness.

How does upper room UV air distinction compare with other technologies?

Mechanical ventilation in buildings is designed for occupant comfort, not airborne infection control – unless specifically designed for that purpose, for example, in hospitals and clinics. If other public buildings require higher levels of airborne infection control, additional engineering approaches are needed.

Air filtration. For economy, most buildings recirculate a portion of ventilation rather than heating and cooling outside air. This still accomplishes the comfort goal by diluting odors, and allowing recirculated air to be heated, cooled, and dehumidified.  Air filters in return ducts are normally not designed to remove airborne pathogens, but MERV 13 and HEPA filters do, making recirculated air equivalent to outside air for airborne infection control.  For SARS-CoV-2, however, there are few if any reports of viral transmission through ventilation systems – probably due to dilution and the fragility of the virus. Air filtration is unlikely to reduce the risk of Covid-19 in schools, for example. Moreover, for occupants sharing air in a room with an infectious Covid-19 patient, it is little comfort to know that the air will be disinfected only after it leaves the room.  Effective Covid-19 prevention requires air disinfection in the room where the transmission risk is present.

Room air cleaners (portable and permanently installed) use filters, UV, ions, and other technologies often remove nearly 100% of airborne viruses and bacteria that pass through them. That is NOT a measure of their effectiveness, however. Their limitation is airflow – that is, moving all of the room air volume through the device enough times (EqACH) without recapturing just processed air (short-circuiting), and without excessive blower noise and drafts. Theoretically, portable air cleaners can produce 4 – 8 EqACH, but in fact, they are often sized to produce 1-2 EqACH on the low, quiet setting. My residential building purchased 4 large, industrial air cleaners for the gym, designed to produce 6 EqACH on the high setting. They are fine for the gym, but noisy and drafty. They would not be acceptable in a school or place of worship due to excessive noise.

Ion generators, in duct and in room. There are few independent reports of effective air disinfection using ions generated in ducts, room air cleaners, or directly into rooms. One such study against human-generated TB aerosol and using infection as an endpoint showed about 60% efficacy compared directly with upper room GUV which showed about 70% efficacy. However, while the commercial GUV fixtures disinfected air in the patient rooms, the large prototype ionizer treated exhaust air and resulted in deposition of air pollutants on the walls. Generation of ozone and unanticipated chemical reactions are additional concerns with room ionizers. In room air cleaners, ionizers suffer from similar flow limitations. Additional clinical trials are needed to determine the safety and efficacy of ions generated both in the room and in-duct.

Is upper room GUV safe?

Germicidal UV (222, 254, 265-275 nm wavelengths) is highly germicidal for all airborne viruses and bacteria and designed to be perfectly safe for room occupants within well-established exposure limits. This apparent contradiction is due to the limiting penetration of UVC into human tissues compared to airborne infectious aerosol. In contrast, UVA and UVB in sunlight are  much less germicidal but much more penetrating into human tissue and are a major cause of skin cancer and cataracts. Four hours of peak sunlight exposure in summer results in a damaging UVA and UVB dose of about 240 µW/cm2 to the skin, whereas the 8-hr exposure limit for 254 nm UVC is only 6.0 µW/cm2. That is, maximum permitted exposure to less penetrating germicidal UV in rooms is a tiny fraction of everyday casual exposure to more dangerous UVA and UVB in sunlight. Because exposed skin cells are continually being replaced, there are no long-term effects of GUV. Based on all available evidence, a renowned UV and skin cancer expert calculated that it would take 300 years continuous exposure to germicidal UV to cause skin cancer at the levels allowed in the lower room! The Illumination Engineering Society (IES) official position is simply that germicidal UV is not carcinogenic when applied under current exposure limits.

But there are a few less serious risks from upper room UV that need to be considered.  The cornea of the eye has no protective outer layer of epidermis. Room occupants can get transient eye irritations if upper room UV fixture installations are not properly designed and tested before being used. More common, but still rare, workers can be overexposed when they climb up on ladders and look directly into fixtures without first having turned the upper room GUV system off. Hours later they can experience acute eye inflammation like overexposure to intense sunlight reflected from snow or water. Like the skin, corneal cells are constantly being replaced, so there are no long-term effects of UV-induced eye irritation. Current official exposure limits are designed specifically to prevent UV-induced eye irritation. Unlike UVA and UVB, UVC does not penetrate the eye to cause cataracts.

Finally, the official safety limits to UVC assume 8-hours constant exposure, which is almost never the case. Clothing completely blocks upper room UVC. Movement in rooms, the protective shape of the brow of the head, and eyelids normally protect eyes from exposure close to the theoretical 8-hour exposure safety limit. In a human monitoring study of nurses, patients, and other works, no subject received more that 1/3 of the exposure limit. In a large study of workers and guests in US homeless shelters, solicited complaints of eye or skin irritation were no different with and without upper room GUV. Upper room GUV is an extremely safe technology. Still, policies and procedures need to be in place to prevent accidental overexposures to cleaners and others working in the upper room.

Dr. Steel Answers:

General Questions

What is UVC light?

Electromagnetic energy comes from the sun or is produced artificially and can be separated into different categories based on the frequency or wavelength of that energy. We are most familiar with the visible part of the spectrum, which gives us different colors of light. There are other kinds of higher energy that are not visible to the eye, and one of these is Ultraviolet or UV light. Ultraviolet-C light (called UVC) is a short wavelength subset of UV, with a wavelength range of 200-280 nm.

Why is UVC light called germicidal?

Light in the UVC range is able to kill microbes (bacteria, protozoa, molds, fungi, and viruses) because the energy in the form of radiation can enter these organisms and interfere with their ability to make copies of themselves by attacking their DNA or RNA. When used in this way it is referred to as GUVC – or Germicidal Ultraviolet C light. GUVC is safe (when properly used), and very effective at killing microbes in seconds.

What is Upper Room Air GUVC?

In spaces that have a ceiling height greater than 7 feet, GUVC-producing units can be positioned along the walls of that space at a height of 7 feet to constantly disinfect the air in the upper regions of that space by killing all bacteria and viruses. The UVC emitted by the fixtures is angled upwards so that it never comes in contact with people.

How does COVID-19 spread?

The consensus of scientific and medical data is that SARS-CoV-2 spreads through the air in the form of respiratory droplets expelled by coughing, sneezing, talking, or singing. These droplets tend to travel fairly short distances and settle on surfaces where they can be spread by touch. In addition, small-particle aerosols can be exhaled through the normal breathing of infected people. These circulate through the air in a room are after they are exhaled by infected persons, and can linger in the air for hours until they are inhaled by healthy people – leading to dangerous spread.

How then does Upper Room Air GUV address the problem of airborne spread of Coronavirus aerosols?

The continuous operation of GUVC units at a wall height of 7 ft or more creates a “kill zone” of UVC light that extends horizontally through the upper room air layers. As SARS-CoV-2 is exhaled by people in aerosol form, it enters the air in the room and starts to move following a flow pattern. Natural or fan-assisted circulation of room air draws virus aerosols through the Kill Zone, where virus particles are inactivated as they recirculate in that space. This has the effect of disinfecting almost the entire airspace in infected rooms, making them significantly for occupancy.

How do we know this approach works?

Upper room air GUVC has a long history of successful use in greatly reducing the spread of diseases during previous epidemics and pandemics. In the 1940’s it was successfully used to reduce the spread of measles in classrooms along the East Coast of the US. In more recent decades it has been used to kill influenza and tuberculosis in countries around the globe. The current pandemic is driving the development of improvements in the technology that make UVCUE products safer and more cost-effective than ever before.

Is GUVC a substitute for mask-wearing, wiping surfaces with liquid disinfectant, or other preventive measures?

Absolutely not! The safest strategy for protecting people and environments from the risks posed by COVID-19 virus infection is to utilize a multi-modal approach combining preventive measures that reduce the risk of infection with a number of different surface and air treatments. Collectively, such an approach will eliminate most of the major paths by which infection might occur.

About UVCUE:

How many units do we need in a typical room?

Each unit delivers about 8 eACH per 1,000 SF.

How big is a unit?

UVCUE is 17.71″ by 7.87″ (and 5.51″ in depth).

Does UVCUE make noise?

UVCUE is slient and odor-free.

Our Advisors

Working with Experts in the Field

Dr. Edward Nardell

Harvard Medical School

Educational Advisor, Planled

Dr. Bruce Davidson

Washington State University

Medical Advisor, Planled

Dr. Steel

Dr. Doug Steel

Columbia University

Director of Medical Science, Planled

Our Advisors

Working with Experts in the Field

Dr. Edward Nardell

Harvard Medical School
Educational Advisor, Planled

 

Dr. Bruce Davidson

Washington State University
Medical Advisor, Planled

Dr. Steel

 

Dr. Doug Steel

Columbia University
Director of Medical Science, Planled

Our Advisors

Working with Experts in the Field

Dr. Edward Nardell

Harvard Medical School

Educational Advisor, Planled

>> Intro Video

Dr. Bruce Davidson

Washington State University

Medical Advisor, Planled

>> Intro Video

Dr. Doug Steel

Dr. Doug Steel

Columbia University

Director of Medical Science, Planled

>> About Dr. Steel