The New Smell of “Clean” – Skytron Ultraviolet Disinfection Robots and Odor

The use of Skytron’s ultraviolet room disinfection robots will result in a distinct odor that has been described as similar to that created by tanning beds or the smell of a furnace when it is started for the first time in the fall. It is very easy to be aware of the unique odor, although it can be more difficult to describe it. It is perfectly safe to enter treated areas immediately after the disinfection treatment has stopped. Air samples in a treatment area have been collected and subjected to a detailed analysis by an accredited lab and found to be safe. The UV robots emit zero ozone. There is no known respiratory irritant resulting from exposure to the odor that is associated with this important “no-touch” room disinfection technology. Use of the highly germicidal UVC light (UV irradiation in the “C” band) creates much safer environments for patients and staff by inactivating dangerous pathogens that may be remaining on surfaces after standard room cleaning procedures. Although not the robot’s primary design function, Skytron’s IPT family of robots will also disinfect the air in the treatment area due to the very high output of UVC energy. Users who are familiar with UVC disinfection technology associate the odor as the smell of “clean” as it is clear physical evidence that a robust amount of germicidal UV energy has been applied to the treatment area. If one does not detect this unique odor after a disinfection treatment please contact your Skytron representative as this may be an indication of poor disinfection performance.

The root cause of the odor is the interaction of UVC light with the airborne dust, which is present at all times in the vast majority of occupied buildings like homes, office buildings, and hospitals. A major component of this dust is a protein called keratin or a keratin variant, both of which contain a significant amount of sulphur. When high energy UVC light contacts keratin molecules it breaks their chemical bonds exposing smaller molecules called mercaptans. Humans can detect mercaptan concentration levels as low as 1 part per billion (ppb). In an environment with airborne dust of only 100 μg/m3, the UVC disinfection process by Skytron robots results in a concentration of mercaptans of about 2 ppb, which is twice the smell detection threshold level of humans, and thus very perceptible. According to OSHA and the CSST in Quebec (Commission de la Santé et de la Sécurité du Travail du Québec), the safe level for an 8 hour exposure to mercaptans is 500 ppb. Consequently, the concentration level after UVC disinfection is negligible and poses no threat to human health.1 

Those who are highly sensitive to the lingering odor are advised to minimize exposure. Suggestions include:

 Turn on the bathroom fan and leave it on before, during and after the disinfection process.

 Do not enter the room immediately upon completion of the process. Wait until the room ventilation has had time to remove the odor.

(Many patient rooms average six air changes per hour in which case the odor should be nearly or totally dissipated in 10 minutes).

1 - Brais Ph.D., P.Eng. and Benoit Despatis P.Eng., Root Cause of the Odor Generated by Germicidal UV Disinfection with Mobile Units, ASHRAE, May 1, 2014.