# Proper Stack Exchange site to ask about: "Power calculation for Covid-19 UV sterilization For 1 meter distance"

What is the proper Stack Exchange site to ask about the following question?

I like to know about the power needs to sterilization one 1x1 Meter surface with 1 meter distance.

I have seen this post and one answer was:

"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.

Which the 30,000j/cm^2 is not correct and must be 30,000 micro J/cm2 like this:

so my calculation shows:

30×10⁻³÷(2×60)=0.00025 w/cm2

which needs to calculate for one 4*pi*1 meter surface for 2 minuets sterilization time, and because of distance effect on light based of this post it must be multiple by 4*pi*100^2 for 1 meter distance to light source (lamp location), which means needs 0.00025×4×3.14×100×100=31.4 W as 2 minute sterilization.

But I have seen this data from this robot:

It takes between 10 and 15 minutes to disinfect a typical room, with the robot spending 1 or 2 minutes in five or six different positions around the room to maximize the number of surfaces that it disinfects. The robot’s UV array emits 20 joules per square meter per second (at 1 meter distance) of 254-nanometer light, which will utterly wreck 99.99 percent of germs in just a few minutes without the robot having to do anything more complicated than just sit there. The process is more consistent than a human cleaning since the robot follows the same path each time, and its autonomy means that human staff can be freed up to do more interesting tasks, like interacting with patients.

and based on this data it use 20 joules per square meter per second which it means use 2000 micro J /cm2:

20÷(100*100)=0.002

which it gives the surface 2×60×20×10⁻⁴ = 0.24 J/cm2 energy, 0.24÷0.03 = 8 time more that 30,000 micro j/cm2!!!

That needs 0.002×4×3.14×100×100 = 251.2 W for 1 meter distance and one time sterilization and if 2 minutes for sterilization it needs, 50 times bigger than my calculation!!!

Finally I don't know what UV lamp power is proper to sterilization from 1 meter distance and (31.4 W or 250 W)?

What do you think about the not correct consideration in this calculation? (I think it must related to different standard of UV standard energy needs to sterilization!!)

Update:

According to this paper:

and this:

I think it is proper to have 2j/cm^2 and 0.02 W/cm^2.

The comments suggest to ask on the physics Stack Exchange site, but I ask here: Is this Stack Exchange site good for asking or do you suggest another Stack Exchange site. Also is there any bio-engineering Stack Exchange site to ask there?

• I expect this question would be closed as off-topic on Physics.SE. Apr 30, 2020 at 0:14
• I am trying to find proper w.s/cm2 and j/cm2 from papers and commercial devises, so 40 mic w.s/ cm2 is come fron first paper which dont fit to the commercial robot with 8 times bigger j/cm2, by my calculations. Apr 30, 2020 at 2:05
• You can use superscript (<sup></sup>) as a higher fidelity version of "^" (short of using MathJax). Apr 30, 2020 at 18:41
• @PM2Ring So what's the conclusion? No SE site for this problem? Or should the problem be broken down into subproblems more suitable for different SE sites? May 1, 2020 at 8:13
• @Ariser Sorry, I'm not familiar enough with all the sites on the network to give a good answer, I just know that it's likely to get closed on Physics, since engineering questions are off-topic there, as are questions that ask to check calculations. It might be ok on Engineering.SE, I don't know. I suppose the OP has found the answer in another place (or has given up), since they appear to have abandoned this question. May 1, 2020 at 8:20