Environmental cleaning and disinfection are important components of a comprehensive strategy to control microbials, especially in cases with immuno-compromised patients. However, studies evaluating the effectiveness of improved cleaning interventions have reported that approximately 5–30% of surfaces1 remain potentially contaminated, due to the inability of existing detergent formulations and disinfectants to disrupt biofilms2. 

Additionally, environmental factors such as surface texture, material composition, and the presence of organic matter can also impact the relationship between UVC (Ultraviolet-C) and contact time. 

For example, surfaces with irregular contours or areas shielded from direct UVC exposure may require longer contact times to ensure thorough disinfection. Cleaning is a complex, multifaceted process, plagued with random variation and the potential for introducing pathogens if cleaning cloths and solutions become contaminated and not correctly used. Numerous studies have demonstrated that current strategies for hospital room disinfection are inadequate, and 50% or more of hospital surfaces may go untouched and uncleaned following disinfection3.

The Limited Effectiveness of UVC Disinfection 

In the last few years, no-touch systems for environmental decontamination are increasingly being considered, but many of these come up short. No-touch UV technology depends on the distance between the lamp and the disinfected surface. The inverse square law states that the doubling of distance between the lamp and the surface being disinfected will quadruple the time required for disinfection.

The relationship between UVC (Ultraviolet-C) radiation and contact time is critical in understanding the effectiveness of UVC disinfection. Contact time refers to the duration for which the target surface, water, or air is exposed to UVC radiation. The longer the contact time, the more exposure microorganisms receive to the UVC light, increasing the likelihood of their inactivation. 

There is often a threshold level of UVC radiation required to achieve microbial inactivation. Below this threshold, the disinfection efficacy may be insufficient to achieve the desired level of microbial reduction, regardless of the contact time. In general, air disinfection systems using UVC radiation are designed to expose airborne microorganisms to UVC light as they pass through the disinfection chamber or encounter UVC-emitting surfaces. The contact time in these systems is typically very short, often measured in fractions of a second to a few seconds. The effectiveness of UVC air disinfection systems relies on achieving a sufficiently high UVC dose within this short contact time to inactivate or destroy the microorganisms.

UVC Air Disinfection for Cannabis HVAC Systems 

Additionally, different microorganisms exhibit varying levels of sensitivity to UVC radiation. Some microorganisms may require higher doses or longer contact times for effective inactivation compared to others. Factors such as microbial species, size, shape, and environmental conditions can influence their susceptibility to UVC disinfection. The UVC contact time required for microbial inactivation in the air depends on several factors, including the type of microorganisms present, their concentration, the airflow rate, and the UVC radiation intensity.

For example, in an HVAC (Heating, Ventilation, and Air Conditioning) system equipped with UVC lamps, the contact time for microorganisms in the air may be on the order of milliseconds to seconds as the air passes by the UVC lamps. The airflow rate, lamp intensity, and distance between the UVC lamps and the air stream are critical factors in determining the required contact time to achieve effective microbial inactivation.

UVC air disinfection systems need to be properly designed and installed to ensure adequate UVC exposure to microorganisms while minimizing the potential for human exposure to UVC radiation. Monitoring the maintenance of these systems is also essential to ensure continued effectiveness in controlling airborne microbial contamination. UV disinfection systems typically require periodic lamp replacement and cleaning to maintain optimal performance.

Damaging Effects of UVC in Cultivation

UVC can damage people and plants. Germicidal ultraviolet light, typically at 254 nm, is effective in this context but, used directly, can be a health hazard to skin and eyes. The germicidal effects of UVC irradiation result in cellular damage by photohydration, photosplitting, photodimerization, and photocrosslinking, thereby inhibiting cellular replication. UV-light disinfection systems must operate in unoccupied rooms. 

Additionally, damage to materials in the room can also be a side effect of UV exposure. High-pressure acrylic material may show degradation for prolonged periods of exposure to light UV (e.g., daily or weekly), therefore it is advised to cover them during the treatment.

Indoor greenhouse agriculture farm air ventilator cooling wind flow pipe tube temperature humidity control system for planting

Referencing the paper Unwanted Indoor Air Quality Effects from Using Ultraviolet C Lamps for Disinfection4, “In the atmosphere, the photolyzing ability, i.e. ability to break molecular bonds, of solar UV radiation initializes the majority of the chemistry taking place in the air, (27,28) including the formation of oxidants, e.g. ozone and the gas phase hydroxyl (OH) radical. Both photolysis of, and radical reactions with, volatile gases and compounds emitted from surface materials (29,30) can form new compounds, with different properties concerning e.g. toxicity or volatility. Less volatile compounds can contribute to aerosol formation. These unwanted gas- and particle-phase compounds can have adverse human health effects, (31−33) raising concerns about using UVC radiation from the indoor air quality (IAQ) perspective.”

WillowAir for Cannabis Air Purification 

Compared to the science behind using UV for air disinfection, our own air purification solution, WillowAir, is a more effective solution to air purification without the use of ozone or UV. Willow’s air purification system captures and removes the contaminants in the air with powerful MERV 13 filters, deactivating and killing toxic microbials including Aspergillus. With 5 air changes per hour, the WillowAir system creates a powerful airflow for optimal growing conditions. 
Learn more about WillowAir and how it can be a clean-air solution for your cannabis cultivation and grow room.

REFERENCES

  1. Carling PC, Huang SS. Improving healthcare environmental cleaning and disinfection: current and evolving issues. Infect Control Hosp Epidemiol. 2013 May;34(5):507-13. doi: 10.1086/670222. PMID: 23571368. ↩︎
  2. Vickery K, Deva A, Jacombs A, Allan J, Valente P, Gosbell IB. Presence of biofilm containing viable multiresistant organisms despite terminal cleaning on clinical surfaces in an intensive care unit. J Hosp Infect. 2012 Jan;80(1):52-5. doi: 10.1016/j.jhin.2011.07.007. Epub 2011 Sep 6. PMID: 21899921. ↩︎
  3. Carling PC, Parry MM, Rupp ME, Po JL, Dick B, Von Beheren S; Healthcare Environmental Hygiene Study Group. Improving cleaning of the environment surrounding patients in 36 acute care hospitals. Infect Control Hosp Epidemiol. 2008 Nov;29(11):1035-41. doi: 10.1086/591940. PMID: 18851687. ↩︎
  4. Environ. Sci. Technol. Lett. 2023, 10, 2, 172–178
    Supporting References:
    (27) Madronich, S.; Flocke, S. The role of solar radiation in atmospheric chemistry. In Environmental photochemistry; Springer: 1999; pp 1−26, DOI: 10.1007/978-3-540-69044-3_1.
    (28) Seinfeld, J. H.; Pandis, S. N. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 3rd ed.; Wiley: 2016.
    (29) Kauffman, R. E.; Wolf, J. D. Study of the Degradation of Typical HVAC Materials, Filters, and Components Irradiated by UVC Energy-Part III: Manufactured Components. ASHRAE Trans. 2013, 119, 203.
    (30) Mitxelena-Iribarren, O.; Mondragon, B.; Perez-Lorenzo, E.; Smerdou, C.; Guillen-Grima, F.; Sierra-Garcia, J. E.; RodriguezMerino, F.; Arana, S. Evaluation of the degradation of materials by exposure to germicide UV-C light through colorimetry, tensile strength and surface microstructure analyses. Mater. Today Commun. 2022, 31, 103690.
    (31) Pekkanen, J.; Peters, A.; Hoek, G.; Tiittanen, P.; Brunekreef, B.; de Hartog, J.; Heinrich, J.; Ibald-Mulli, A.; Kreyling, W. G.; Lanki, T.; Timonen, K. L.; Vanninen, E. Particulate air pollution and risk of STsegment depression during repeated submaximal exercise tests among subjects with coronary heart disease – The exposure and risk assessment for fine and ultrafine particles in ambient air (ULTRA) study. Circulation 2002, 106 (8), 933−938.
    (32) Schraufnagel, D. E. The health effects of ultrafine particles. Exp. Mol. Med. 2020, 52 (3), 311−317. ↩︎