Questions and Answers

Questions and Answers on Upper-room Germicidal UV to control airborne diseases

How much is the percentage of infections caused by airdrops and how much is by surface contact?

It depends on the pathogen of interest.  Some pathogens, e.g. SARS-CoV-2 is mixed mode both through the air, direct droplet spread and potentially by touching an infected surface.  Other pathogens, e.g. are strictly airborne.

I have a school district I am meeting with today after this. Could you touch on that type of application and any recommendations. Can these units run while students are in the classroom?

Upper room would be main focus in classrooms, gymnasiums, cafeteria, hallways where many people are congregated.  This of course would depend on having the right room height ( a minimum of 8 ft (2.3 m).

Is there any study that shows how much airborne particles can be generated by an individual, a small group, or a large group of people in an enclosed area? If there is a little amount of aerosol that end up in the ceiling area, wouldn't this minimize the effectiveness of upper room UV system, which is probably not cheap? And the study report cited is quite old (e.g. Riley 1976). So I wonder if there are more updated academia/government studies. BTW I'm a Signify employee so you don't have to bring this up. It's just for my learning.

There are studies that artificially try to simulate these types of aerosols.  Aerosols that reside at the ceiling level would not infect people; however, we recommend air-mixing to ensure and efficient lifting of the lower room air to the disinfection zone and then returning the disinfected air to dilute the concentration.

Could you define each term (e.g. GUV, UVGI, etc.)?

Both Germicidal UV and Ultraviolet Germicidal Irradiation are equivalent both are the process of providing UV photons to the microbes in the air (or depending on the application toward surfaces).

Which frequency is 'safe' for human exposure (e.g. I have read that 222nm is safe for human exposure - is this correct)?

All frequency can be used safely by knowledgeable designers and installers when applied according to the Threshold limit value  (TLV) for eye and skin exposure AND based on a time weighted average for occupancy and onsite measurement after installation.

Can I get this lighting in my home?

This type of product in a commercial grade device.  UVC lamps are most often used in air-conditioning ducts for homes to control mold growth in moist or humid climates.

What about material degradation over time in the space?

It is true some materials will have some degradation overtime (e.g. paint) It there is valuable  artwork it should be placed where there would be no direct or reflected UVC or covered by a protective glass or cover (e.g. as seen in museums). 

What is the impact of UV-C on plants in an office? We have many plants in our offices.

It would depend on the sensitivity of the plant. Normally it would be advisable not to have hanging plants in the upper room (other than artificial).  Plants on a desk if tested for UVC exposure would

 

Can this light help against the coronavirus?

Yes, the coronavirus is easily inactivated by exposure to UVC 254 nm.

 

Due to burning of UV-C lamps, the efficiency of disinfection decreases. How to calculate the dosage timing due to lamp radiation depreciation?

Most quality UV-C Hg lamps will maintain their output over a year. By taking baseline measurements of output after installation and with maintenance and monitoring of the output with a radiometer UV-C output can be tested and when the output fall by 30% then the lamp would be changed.

Should you have upper UV system powered on 24/7?

It depends on the occupancy.  For office buildings, e.g., the UV system could be powered off when unoccupied with a timer to turn-on before workers arrive.

What is the average lifetime of a UVC lamp?

Most will last one year before needing to be changed; however, with careful monitoring, cleaning the lamps should last longer.

How efficient is the UV in a closed chamber and placed in an upper room?

It depends on conditions of ventilation and air-mixing.  Laboratory studies have found UV to be very effective depending on these conditions.

What about for UVC lamps? Are they really harmless to human eyes and skin?

When used applied properly and tested before spaces are occupied there is low risk.  Safety for eyes and skin can be tested based on Threshold limit values (TLV) balanced with time weighted average of exposure for occupants.

The dosing criteria, 12mw/m3 and 38mw/m2, is that accepted by ASHARE? Also what about the timing factor?

ASHRAE is drafting its guidance using these dosing criteria are a beginning point of design to be followed by placement with a lighting CAD program adapted for calculating gonioradiometric files of GUV fixtures.  (Unclear what is meant by timing.)

Are UV diodes equally good as mercury lamps or can they be in the right setting?

It would depend on the volume of air to be treated and the efficiency of the UV LEDs. UV LEDs can be used separately and/or in combination with mercury lamps.   

Hello, how does Upper Air compare to Air Purifiers made with Ventilators, HEPA filters and UVC “in a box”?

There is very little information on direct comparison of these technologies. Research in this area is needed.

Do you see big potential for far UV-C applications ?

It depends on when the sources are available with filtering of the excimer lamps or when UV LEDs are available.  It is certainly a source to watch but it is expensive, short life and potential ozone needs to be addressed.

The effectiveness of UV-C, does it have any difference on different type of virus, bacteria, etc.?

Different microbes vary in the dose of UV required for inactivation.  The main point is that given sufficient dosage, all pathogenic microbes can be inactivated with virus being the most susceptible vs. spores and fungi requiring higher levels of UV. For example, SARS-CoV-2, measles and influenza (all easy to inactive), tuberculosis (moderately resistant) and fungi and spores (highly resistant).

Do you have references on training facilities and programs?

There is discussion on creating a training program similar to the summer course conducted at Harvard for many years.  This will require a combined effort to create a sustainable venue which could also provide certification.

By adding UV-C to a space, can you reduce air changes per hour?

UV-C can be added to ventilation for disinfection; however, there is still a need to have proper ventilation to clear odors, CO2, etc for occupant health and comfort.