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.
A study was conducted to assess the effect of UV(254) on the concentration and viability of PRRSV on surfaces and materials commonly encountered on swine farms. A standard quantity (5 × 10(6)TCID(50), total dose) of a PRRSV modified live vaccine virus was inoculated onto 2 matched sets of surfaces/materials including wood, plastic, latex, rubber, styrofoam, metal, leather, cloth, concrete, cardboard, glass and paper. One set was exposed to UV(254) radiation (treatments) and the other to incandescent light (controls) for a 24h period. During this time, treatments and controls were swabbed at 10 min intervals from 0 to 60 min post-inoculation (PI) and again at 24h PI. The quantity of PRRSV RNA on each item at each sampling time was calculated by RT-PCR and the presence of viable PRRSV in each sample was determined by swine bioassay. A significant reduction (p<0.0001) in the quantity of PRRSV RNA was demonstrated at 24h PI independent of treatment. In addition, a significant reduction (p=0.012) in the number of UV(254)-treated surfaces which harbored viable virus was observed at 60 min (0/12 positive) when compared to control surfaces (5/12 positive). In addition, all UV(254) treated samples collected between 10 and 50 min PI were bioassay negative. These results suggest that UV(254) is an effective means to inactivate PRRSV on commonly encountered farm surfaces and materials and inactivation can be accomplished following 10 min of exposure.
This paper looked at a 10 minute exposure as the lowest exposure tested and found the PRRS was completely inactivated. There was never any exposure less than the ten minutes. In addition, the UV system used in the experiment had only one lamp that was located eight feet away. ONCE® BioShift® UV-C Chambers have multiple lamps at a much closer distance (about 18 -24 inches).
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.