How much UV-light exposure time is required to disinfect a laminar flow hood?
"Even at the minimum acceptable irradiance in a biosafety cabinet of 40 W/cm2 (U.S. Department of Health and Human Services et al., 2000), it takes 12.5 minutes to reach 30,000 J/cm2 (1 W= 1 J/sec), which has been listed as germicidal for spore forming organisms by one UV manufacturer (www.uvp.com/pdf/ab-115.pdf)." "Even using the NIH/CDC criterion of the minimum acceptable irradiance in a biosafety cabinet
of 40 W/cm2, it takes 12.5 minutes to reach the 30,000 J/cm2 found to inactivate spore forming organisms. Use of a UV light in excess of an hour or overnight is massive overkill." from: http://www.ehs.ucsb.edu/files/docs/bs/Meechan_and_Wilson_2006.pdf
We typically leave the light on for 10 minutes prior to use, although after reading this, I'll up that to 15 minutes.
In my former lab we did it overnight but then you'll run very quickly through your uv light's life span. Alternatively you can put it on a timer for 30min. Don't know what others do and never tested the actual killing of certain organisms with it
i think 30 minutes enough to kill all bacteria except spore forms
Overnight should be good. If you want to use less time and it's really important that UV kill a particular organism you are working with, I would run the test and see how long it takes. For each sterilization technique I use, paraformaldehyde or gentamicin, I did test to see how long it took to kill my pathogen.
Typically 30 minutes to an hour are used for laminar flow hoods. However, it also depends on how old the bulb is. The older it is the weaker the irradiance of the bulb, which will require a longer effective sterilization time.
Assuming you have already cleaned it to remove any biological material, e.g. normal cleaning wipes or ethanol. Then 20 to 30 mins will be sufficient to ensure complete disinfection.
I'd like to add that this assumes that the UV light is actually able to sufficiently hit the organisms vulnerable to it. For example, if there is either a film or shadowing object, etc, the organisms in the shadowed/protected areas will not be hit with sufficient UV energy. Even a newer bulb/lamp can become fouled and/or occluded by dust or other deposits, etc, reducing its emissions.
The suggestions above to validate the protocol for your particular organisms of concern is a good one, and, to make sure the test samples are taken from nooks and crannies, areas most distal/at the most acute angle from the UV source(s) etc, where the UV is LEAST LIKELY to hit sufficiently.
It's better to limit in 30 min to control the cost. But it also depends on the light intensity.
This is from a Stratalinker manual:
Inactivating contaminating DNA in reaction buffer that may act as
a template in primer extension reactions.9 Up to 100 μl of reaction
buffer in a 500-μl microcentrifuge tube may be treated by laying
the tube on its side in the Stratalinker UV crosslinker (making sure
the buffer does not run into the cap) and irradiating it at 200,000–
300,000 μJ/cm2 (2000-3000 on the LED display). More than one
tube may be irradiated simultaneously.
As all hoods are probably not made the same (they don't emit the same amount of UV energy) it may be best to think in terms of energy exposure and not time. The amount of energy suggested above may be overkill as it is treating a solution, but it's a good starting point. I've also seen reference to using 30k μJ/cm2 to disinfect.
"Even at the minimum acceptable irradiance in a biosafety cabinet of 40 W/cm2 (U.S. Department of Health and Human Services et al., 2000), it takes 12.5 minutes to reach 30,000 J/cm2 (1 W= 1 J/sec), which has been listed as germicidal for spore forming organisms by one UV manufacturer (www.uvp.com/pdf/ab-115.pdf)." "Even using the NIH/CDC criterion of the minimum acceptable irradiance in a biosafety cabinet
of 40 W/cm2, it takes 12.5 minutes to reach the 30,000 J/cm2 found to inactivate spore forming organisms. Use of a UV light in excess of an hour or overnight is massive overkill." from: http://www.ehs.ucsb.edu/files/docs/bs/Meechan_and_Wilson_2006.pdf
We typically leave the light on for 10 minutes prior to use, although after reading this, I'll up that to 15 minutes.
Kathryn,
For anyone else reading this, please note that the Meechan & Wilson work had a baseline of 30,000 *micro* Joules per sq. cm.
The 'mu' symbol didn't survive the cut and paste.
(and it left me thinking that this was a truly unholy light - 30kJ per cm^2 is the intensity of a laser cutter!)
James, I have noticed that there is a tendency to shift uJ/cm^2 and J/m^2 in the literature. Since they do not necessarily include the reference it can become confusing. I believe the DOE information said that 120,000 u (micro)w/cm^2/second was sufficient to inactivate Anthrax spores.
Very good information. Thank you all for commenting and sharing your knowledge and experience.
- Badges
- Science topic
- Similar topics
- Biological Science
- Microbiology