The short answer is - minutes - however, it is a little more complicated than that. The effectiveness of UVC light is based on the variables of time (length of exposure), intensity of the source (how "bright" the "light" is), and distance (how far the source is from the target). In addition, because different pathogens require different levels of UVC to deactivate them, there is not one answer about how long it takes to kill all bacteria, as it also comes down to the way the cell is built for each type of bacteria. The good news is bacteria, and viruses, are very susceptible to UVC energy, especially when compared to a spore former, like C-diff.
Because American Ultraviolet is aware of the complexity of the answer to the length of time needed to "kill bacteria," we take the guess work out of it for our clients by taking into account all of these variables, and delivering a calculated dose of energy directly to the target. Our ARTZ 2.0® unit, for example, allows the user to specify the type of pathogen, and the disinfection zone; while our UVC OR package allows the user to select the length of the disinfection cycle needed to target specific pathogens without having to do the math.
Recent reports suggest that ultraviolet (UV) light can be used on the human body to disinfect against the coronavirus. The International Ultraviolet Association (IUVA) and RadTech North America are educational and advocacy organizations consisting of UV equipment vendors, scientists, engineers, consultants, and members of the medical profession. We would like to inform the public that there are no protocols to advise or to permit the safe use of UV light directly on the human body at the wavelengths and exposures proven to efficiently kill viruses such as SARS-CoV-2. UV light under the conditions known to kill such viruses are also known to cause severe skin burns, skin cancer, and eye damage. We strongly recommend that anyone using UV light to disinfect medical equipment, surfaces, or air in the context of COVID-19, applications that are supported by sound scientific evidence, follow all recommended health and safety precautions and to avoid direct exposure of the body to the UV light.
Additional Information on UV Technology for Disinfection:
The ultraviolet spectrum is a band of electromagnetic radiation at higher energies than visiblelight, split into four major categories: UV-A (400 – 315 nm), UV-B (315 – 280 nm), UV-C (280 – 200 nm), and vacuum-UV (VUV, 100 – 200 nm). UV-A and UV-B are present in sunlight at the earth's surface; these parts of the ultraviolet spectrum are common causes of sunburn and, with longer-term exposure, melanoma. The risks of human exposure to UV-A and UV-B are well known. Solar UV may be used for disinfection purposes; exposures in the order of several hours to days might be effective at treating surfaces and water. Artificial sources of UV-A and UV-B are not commonly used for disinfection. UV-C has been used for disinfection for over a century, with applications in water treatment, air systems, and surfaces. The use of UV-C as a disinfectant is supported by decades of scientific research. UV-C radiation is absorbed by DNA and RNA (the genetic code for all lifeforms), changing its structure. This damage inhibits the ability of the affected cells to reproduce, meaning that they cannot infect and are no longer dangerous. Whereas the UV exposure required to inactivate different microorganisms varies, though there are no known microorganisms that are immune to this treatment and it is regularly used against bacteria, viruses, and protozoa.
In the same way that UV-C can inactivate bacteria and viruses, it can be damaging to human cells too, since our cells also contain DNA. This exposure can cause skin irritation, damage to the cornea, and cell mutations leading to cancer. Exposure to UV-C radiation is regulated globally, with a common agreement on the risk to human health and safe exposure levels. These regulations and standards set limits on allowable exposure, though in all cases it is recommended to avoid UV exposure where possible.
There are three common types of germicidal UVC lamps:
"Cold Cathode" lamps are instant-start, using a large cylindrical cathode instead of a coil filament, so lamps have a long life that is unaffected by frequency of starting.
Germicidal UVC lamps can be used in ceiling fixtures suspended above the people in a room, or within air ducts of re-circulating systems. The first method is called Upper Air Irradiation. The fixtures are shielded on the bottom so that the radiation is directed only up toward the ceiling and out the sides. These upper-air germicidal fixtures are mounted at least 7ft. above the floor so that people will not bump into them or look directly at the lamps.
The second method of air disinfection uses UVC lamps placed inside the ventilation system ducts. If a ceiling is too low for an upper-air irradiation fixture, this type of an in-duct germicidal fixture can be used. Also, because people are not exposed to the UVC radiation, very high levels can be used inside the ducts.
UVC Germicidal Fixtures increase the value of all air conditioning and air-circulating systems by:
Treating air that passes through an HVAC unit with ultraviolet light will reduce, or eliminate, DNA-based airborne contaminants (bacteria, viruses, mold spores, yeast, protozoa), and provide much healthier air to breathe. UVC Germicidal Fixtures are a labor-free solution that will not harm occupants, equipment or furnishings because they produce no ozone or secondary contaminants. For more than 70 years, tens of thousands have been safely installed in hospitals, clinics, processing plants, commercial offices, manufacturing sites and other commercial facilities and multi-and single-family residences around the world.
For HVAC applications, just as with all other UVC sterilization applications, direct exposure to 254nm UVC radiation, given appropriate exposure time, will inactivate the DNA and RNA of microorganisms (such as bacteria, viruses, mold spores, yeast, and protozoa), rendering them "sterile" (unable to reproduce), which, in biological terms, results in a "dead" microorganism.
An acceptable kill rate is determined by the total amount of UVC energy a microorganism "sees." This is a "dosage." Dosage is a product of the intensity of UVC radiation (expressed in microwatts per square centimeter) and exposure time to that radiation. You can find the necessary dosage for most common mold spores in the following table. Mold spores are generally much more difficult to kill than microorganisms and viruses and, thus, require a much higher dosage of ultraviolet light. The values shown under the percentage kill are in microwatts per square centimeter of UVC energy.
|Aspergillius flavis||Yellowish green||60,000||99,000|
|Aspergillius glaucus||Bluish green||44,000||88,000|
|Mucor racemosus A||White gray||17,000||352,000|
|Mucor racemosus B||White gray||17,000||352,000|
When researching UVC Germicidal Fixtures, you may come across several different types of lamp technologies and configurations.
All UVC lamps essentially consist of a quartz envelope containing mercury and other gases and electrodes. When the lamp is struck, the energy between the electrodes excites the mercury into a vapor, which produces C-band ultraviolet energy. Almost all germicidal lamps currently being used in mainstream HVAC applications have been low-pressure lamps; American Ultraviolet recommends using High Output lamps. Following is information about some of the more common UVC lamps:
American Ultraviolet Germicidal Fixtures feature the highest High Output (HO) Lamps, which provide even greater efficiency than lamps other companies offer. And these lamps don't lose as much germicidal energy when temperatures fall within the HVAC system, enabling them to kill more mold and bacteria across a wider temperature and air velocity range than all others.
UVC Germicidal Fixtures from American Ultraviolet also: