Answer to Question #11622 Submitted to "Ask the Experts"

A few days ago, I was performing a colorimetric (MTT) assay in my lab hood. Accidentally, I did not turn off the germicidal lamp (which produces ultraviolet [UV]-C light at a wavelength of 254 nanometers [nm]) in the hood, and I worked for about 25 minutes with the lamp on. I was wearing latex gloves, and my hands and arms were completely covered by my lab coat and my winter coat. My face, however, was uncovered, although I was wearing my glasses. There was hood glass between the lamp and me, and the distance between my face and the lamp was as is usual in normal airflow hoods.

This happened four days before I wrote this post. After this overexposure, so far I have not seen any symptoms like burns on my cornea or erythema. I am really scared as to what awaits me after 6–12 months, however, as they say this can lead to skin cancer.

I would be really grateful if anyone could suggest what I should do and what fate awaits me in the next year or two.

I suggest we take solace from the Hitchhikers Guide to the Galaxy: "Don't panic." Exposure to UV radiation is a radiation exposure one should take seriously and can have negative effects to the body. Fortunately, it is one of the easiest radiation exposures to mitigate. From the description of the controls you had in place (skin covered with gloves and lab coat, glass sash down, etc.), I see no exposure to be concerned about.

In addition, the intensity of UV exposure does drop off with distance. I have measured the exposure levels on the user side of hood sashes and reflections from countertops. At the standard distance one would be in front of the hood, I have not found exposure levels above threshold limit values (TLVs). So while your concern is good and the germicidal lamp should have had a mechanism to indicate it was on, you should not be concerned about any effects in the future from this exposure.

Ken Barat, CLSO