As the threat of measles and other infectious diseases continue making headlines, building and facility managers are searching for ways to reduce the threat posed by contagious airborne pathogens.

Since the 1940s, many hospitals have relied upon Ultraviolet Germicidal (UVGI or UV-C) energy to control airborne infectious diseases. Use waned with the arrival and proliferation of antibiotics.

In the 1990s, demand for the technology returned following a resurgence of drug-resistant infectious microorganisms; as science has not found any microorganism that can withstand the destructive effects of the UV-C 254-nm germicidal wavelength, including superbugs and other antibiotic-resistant germs. In other words, there is no way for microbes to develop a resistance to UV-C, and repeated exposure to the germicidal wavelength renders microbial replication impossible.

One means of deploying UV-C systems against infectious agents is upper-air/room systems, which are designed to kill airborne infectious agents as they rise into the upper region of most any space. Upper-air/room systems are installed in waiting rooms, classrooms, cafeterias, gymnasiums, locker rooms, childcare centers—anywhere infectious agents may exist. Coil-irradiation and air-stream-disinfection systems are installed within HVAC air-handling units and duct runs in all building types. Some applications combine upper-air/room UV-C units to kill airborne microorganisms along with UV-C lamps installed within HVAC systems to provide supplemental airstream kill ratios and irradiate all plenum surfaces.

Typically, wall mounted at a height of seven-feet or above, the UV light fixture employs louvers to direct the radiation upward and outward to create an intense zone of the UV-C wavelength in the upper-air while preventing dosage in the lower (occupied) portion of the room or area. As convection or mechanical air currents lift communicable airborne agents, the pathogens are exposed to the germicidal wavelength and killed. UV-C breaks the bacteria or virus DNA chain rendering it incapable of reproducing.

Dropping infection rates

The current scare over the measles virus, one of the most contagious diseases known to man, is a good case-in-point. Nearly a century ago, Harvard University sanitary engineer, William F. Wells, discovered that germicidal ultraviolet energy killed airborne microorganisms, including measles.

Wells installed UV-C lamps in suburban Philadelphia day schools to combat the spread of measles and compared infection rates. The schools without the germicidal UV-C fixtures saw contamination rates nearly four times greater than those that employed the ultraviolet technology (53.6 percent vs. 13.3 percent).

Around the same time, in 1936, Dr. Deryl Hart experimented with germicidal UV-C to disinfect an operating room at Duke University Hospital. He reported an 11.38 percent reduction in the rate of postoperative infection rates. Throughout the next few decades, UV-C was applied in schools and hospitals across the country, proving its ability to inactivate microorganisms and bacteria.

Compared to germicidal fixtures used in these previous studies, today’s fixtures provide greater UV-C fluence (dosage/output) and coverage, use less power and are less expensive.

How it works

UV light comprises a segment of the electromagnetic spectrum between 100 and 400 nm, corresponding to photon energies from 3 to 124 eV. The ultraviolet segment has four sections, labeled UV-A (400 to 315 nm), UV-B (315 to 280 nm), very high energy and destructive UV-C (280 to 200 nm), and vacuum UV (100 to 200 nm).

FMs are familiar with the harmful effects of UV transmitted by sunlight in the UV-A and UV-B wavelengths, giving rise to UV inhibitors, or blocking agents, which are found in sunglasses and suntan lotions. They are also familiar with products engineered to withstand the effects of UV radiation, such as plastics, paints and rubbers.

However, unlike UV-A and B, the UV-C wavelength has more than twice the electron volt energy (eV) as UV-A, and it is well absorbed (not reflected) by organic substances, adding to its destructiveness. It owes these effects to the biocidal features of ionizing radiation, that is, UV-C does far more damage to molecules in biological systems than can temperature alone.

Sunburn, compared to the sensation of warmth, is one example of that damage. Sunburn is caused by sun striking and killing living cells in the epidermis. The redness and “heat” from a sunburn is merely a byproduct of that destruction, which is reflecting the increased blood flow to remove the dead cells.

Ionization drives UV-C’s power to alter chemical bonds. It carries enough energy to excite doubly bonded molecules into a permanent chemical rearrangement, causing lasting damage to DNA, ultimately killing the cell.

The Centers for Disease Control and Prevention Healthcare Infection Control Practices Advisory Committee finds that ultraviolet energy helps to control disease transmission: “As a supplemental air-cleaning measure, UV-C is effective in reducing the transmission of airborne bacterial and viral infections in hospitals, military housing, and classrooms…”

Efficient effectiveness

The primary objective of upper-air/room UV-C placement is to interrupt the transmission of airborne infectious diseases where people congregate, especially in high-occupancy settings such as schools, childcare centers, airports, cafeterias, homeless shelters and emergency rooms.

All these spaces can be effectively and affordably treated with UV-C. Airborne droplets containing infectious agents can remain viable in a well-ventilated room for as long as six minutes. Operating 24 hours a day, upper-air/room systems inactivate exposed microbes in under a second, and these units have been shown to be effective against airborne viruses and bacteria, including chickenpox, measles, mumps, varicella, TB and cold viruses.

Although germicidal systems have been used for nearly 80 years, their application in infection control settings has waxed and waned. Given the growing desire to prevent the transmission of infectious diseases in facilities ranging from schools, to hospitals to international airports, facility professionals should examine ultraviolet germicidal technologies as one possible safeguard against infectious agents. In particular, upper-air/room UV-C systems combined with systems that irradiate interior surfaces of HVAC air handling units can greatly reduce pathogen concentrations in a highly reliable and cost-effective fashion.