Our team is regularly asked why some sources* suggest exposure for one minute, three minutes or up to ten minutes when using ultraviolet germicidal irradiation (UVGI) to eliminate viruses on an object, when we recommend a set five minutes, or 300 seconds. This answer is easy and we want to set the record straight once and for all.
The reason for our recommend five minute exposure time is directly related to the use of our BioShift® UV-C Chambers. The two factors that directly influence effectiveness of UV-C radiation are time of exposure and light intensity. This means that if an object is directly exposed to UV-C (254nm) light from 12 inches away for five minutes, it will have killed more viruses than if the same object was exposed to UV-C light from 60 inches away for ten minutes. Together with a nationally-recognized laboratory specializing in antimicrobial, biocidal and virocidal effectiveness, we tested how effective the BioShift® UV-C Chamber is at eliminating the import of a common agricultural virus in real-life conditions.
What the results showed was that UV-C radiation on an object in the BioShift® UV-C Chamber for one minute eliminated 99.99% of the common agricultural virus, while exposure of five minutes eliminated more than 99.999% of the same virus. Although the difference doesn’t appear significant on the surface, the elimination rates are HUGE when your entire facility could be at risk. For example, if there are 1,000,000 pathogens on an object and you expose the object to UV-C radiation in the BioShift® UV-C Chamber for one minute, this leaves 100 pathogens still present on the object. However, if you expose the 1,000,000 pathogens for five minutes, this leaves less than 10 out of the 1,000,000 pathogens on the object and you cannot get more effective than that.
In conclusion, yes, you can expose something to UVGI for one minute, three minutes or up to ten minutes, but time is money and when using the BioShift® UV-C Chamber to achieve optimal sanitation, five minutes is our recommendation as striking a balance between effectiveness and time.
*Dee, Scott & Otake, Satoshi & Deen, John. (2011). An evaluation of ultraviolet light (UV254) as a means to inactivate porcine reproductive and respiratory syndrome virus on common farm surfaces and materials. Veterinary microbiology. 150. 96-9. 10.1016/j.vetmic.2011.01.014.
The intensity of light decreases by the square of the distance, meaning that the BioShift® UV-C Chambers are likely to have 100x more UV-C than used in the evaluation conducted by Dee, Deen and Otake.