<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>blahblahblah</author><text>The situation is analogous to what happens when a CT machine malfunctions.  The basic design of a CT machine has an x-ray source on a rotating ring.  The patient lays down on a table and the table is moved through the center of the ring at constant velocity for the duration of the scan.  
The overall motion of the x-ray source relative to the patient is helical.  If the movement mechanism jams and the table stops moving, the pattern of motion collapses into a circle and the patient receives an excessive radiation dose focused in the region of the body that is in the center of the ring when the table stops.  The received dose is a function of the time until the operator notices the malfunction and stops the scan.&lt;p&gt;With a backscatter x-ray system, the person stays motionless and the x-ray source moves.  If the x-ray source stops moving, the person receives an excessive dose wherever the source happens to be pointing when it gets stuck.  The dose received is, again, a function of how long it takes for the operator to notice the malfunction.&lt;p&gt;With a microwave backscatter system, the radiation used is in the RF range and, therefore, not ionizing.  However, if the microwave source stops moving because of malfunction, a portion of the body experiences higher than normal SAR.  If the SAR is high enough, significant localized heating may occur, causing burns on the person.</text><parent_chain><item><author>yummyfajitas</author><text>&lt;i&gt;(This doesn&apos;t take into account other real issues, like &apos;what if the machine breaks down and we start blasting people with focused beams of radiation&apos;...&lt;/i&gt;&lt;p&gt;What if my flashlight breaks down and I start blasting people with focused beams of laser light? What if my cell phone breaks down and the microwaves melt the brains of everyone within 6 feet of me?&lt;p&gt;I don&apos;t know a great deal about the engineering of MWBS, but I see no reason to believe that your fear is any more likely than mine. Most machines just don&apos;t work that way. Do you have evidence that MWBS is different?</text></item><item><author>ohyes</author><text>edit: s/mwbs/bs/g; per comment below&lt;p&gt;Well, X-rays cause cancer. BS uses X-rays So it is a cancer risk. 
And it is a little more founded than someone randomly saying&apos; this causes cancer&apos;.&lt;p&gt;In terms of risk...&lt;p&gt;This says dental x-rays are about 2-3 mrem:
&lt;a href=&quot;http://www.physics.isu.edu/radinf/dental.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.physics.isu.edu/radinf/dental.htm&lt;/a&gt;&lt;p&gt;This says BS is about .006-.009 mrem:
&lt;a href=&quot;http://science.howstuffworks.com/innovation/backscatter.htm&quot; rel=&quot;nofollow&quot;&gt;http://science.howstuffworks.com/innovation/backscatter.htm&lt;/a&gt;&lt;p&gt;Keep in mind that under certain models (the &apos;no-threshold model&apos;), any amount of exposure (even a tiny amount) to an X-ray is a slight increase in the chance that that person will get cancer.&lt;p&gt;Now you might think that because dental x-rays are about 300 times more powerful than BS, dental x-rays have a much higher chance to cause cancer. Sure, individually, my chances of getting cancer from a BS are much lower than my chances of getting cancer from a dental x-ray. It is even higher from daily background radiation, or from the radiation that you get from flying in an airplane.&lt;p&gt;But everything is about context. How many people fly each day? 2 million or so? How many people do we propose to put through the BS machine? All of them? (I assume the intent is to eventually replace the metal detectors with these). If you are putting 2 million people through the BS each day, that is actually large amount of radiation exposure. Probabilistically, someone will get cancer from the BS.&lt;p&gt;There are certain types of radiation that you can avoid (x-raying your foot for fun! backscatter machines), and there are certain types of radiation that you cannot avoid (background cosmic).&lt;p&gt;I don&apos;t see how the argument that it is &apos;nothing&apos; in comparison to other forms of radiation really stands up, in that I could potentially avoid backscatter radiation, whereas I couldn&apos;t conceivably avoid the other types.&lt;p&gt;(This doesn&apos;t take into account other real issues, like &apos;what if the machine breaks down and we start blasting people with focused beams of radiation&apos;... while trained to run the machine, I doubt that the TSA people are trained to maintain the machine, or would even know if something had gone horribly wrong with it).</text></item><item><author>yummyfajitas</author><text>Just curious, does anyone have some hard evidence that the MWBS is a cancer risk?&lt;p&gt;I ask this simply because anti-X activists have pushed junk science claims of the form &quot;X causes CANCER&quot; many times [1], so I&apos;m a little dubious. I don&apos;t think fighting civil liberties violations with junk science is a useful tactic, if that is indeed what is happening here.&lt;p&gt;[1] For example, feminists pushed the &quot;silicone gel implants cause breast cancer&quot;, anti-bioscience types push &quot;GMO foods cause cancer&quot;. Drug warriors have pushed &quot;pot causes cancer&quot; and anti-abortion crusaders pushed &quot;abortion causes cancer&quot;.</text></item></parent_chain></comment><story><title>When we got to the scanner, I opted out. Then they opted out.</title><url>http://blog.izs.me/post/1591805056/tsa-success-story</url></story>
<instructions>Your goal is to analyze the following comment and estimate how highly it will be upvoted by the Hacker News community.</instructions><comment><author>ohyes</author><text>It is hard to think that a flashlight or cellphone would have a power supply strong enough to do that much damage. (Although actually, metal halide lamps can sometimes cause UV radiation burns if they are damaged... &lt;a href=&quot;http://archpedi.ama-assn.org/cgi/content/full/158/4/372&quot; rel=&quot;nofollow&quot;&gt;http://archpedi.ama-assn.org/cgi/content/full/158/4/372&lt;/a&gt; ).&lt;p&gt;As long as the backscatter machine doesn&apos;t run on Double A&apos;s, my fears are actually more reasonable than yours.&lt;p&gt;The backscatter machine presumably uses some sort of electrical plug to connect to power. It isn&apos;t inconceivable that it could receive more power than intended and produce more x-rays, or that something could go wrong with the shielding allowing x-rays to leak, or that something could go wrong with the x-ray bulb and we could produce the wrong type of radiation.&lt;p&gt;And it doesn&apos;t have to be &apos;burning your head off&apos; to be a problem, it could simple produce an order of magnitude or two more radiation than intended, and be a health risk.</text><parent_chain><item><author>yummyfajitas</author><text>&lt;i&gt;(This doesn&apos;t take into account other real issues, like &apos;what if the machine breaks down and we start blasting people with focused beams of radiation&apos;...&lt;/i&gt;&lt;p&gt;What if my flashlight breaks down and I start blasting people with focused beams of laser light? What if my cell phone breaks down and the microwaves melt the brains of everyone within 6 feet of me?&lt;p&gt;I don&apos;t know a great deal about the engineering of MWBS, but I see no reason to believe that your fear is any more likely than mine. Most machines just don&apos;t work that way. Do you have evidence that MWBS is different?</text></item><item><author>ohyes</author><text>edit: s/mwbs/bs/g; per comment below&lt;p&gt;Well, X-rays cause cancer. BS uses X-rays So it is a cancer risk. 
And it is a little more founded than someone randomly saying&apos; this causes cancer&apos;.&lt;p&gt;In terms of risk...&lt;p&gt;This says dental x-rays are about 2-3 mrem:
&lt;a href=&quot;http://www.physics.isu.edu/radinf/dental.htm&quot; rel=&quot;nofollow&quot;&gt;http://www.physics.isu.edu/radinf/dental.htm&lt;/a&gt;&lt;p&gt;This says BS is about .006-.009 mrem:
&lt;a href=&quot;http://science.howstuffworks.com/innovation/backscatter.htm&quot; rel=&quot;nofollow&quot;&gt;http://science.howstuffworks.com/innovation/backscatter.htm&lt;/a&gt;&lt;p&gt;Keep in mind that under certain models (the &apos;no-threshold model&apos;), any amount of exposure (even a tiny amount) to an X-ray is a slight increase in the chance that that person will get cancer.&lt;p&gt;Now you might think that because dental x-rays are about 300 times more powerful than BS, dental x-rays have a much higher chance to cause cancer. Sure, individually, my chances of getting cancer from a BS are much lower than my chances of getting cancer from a dental x-ray. It is even higher from daily background radiation, or from the radiation that you get from flying in an airplane.&lt;p&gt;But everything is about context. How many people fly each day? 2 million or so? How many people do we propose to put through the BS machine? All of them? (I assume the intent is to eventually replace the metal detectors with these). If you are putting 2 million people through the BS each day, that is actually large amount of radiation exposure. Probabilistically, someone will get cancer from the BS.&lt;p&gt;There are certain types of radiation that you can avoid (x-raying your foot for fun! backscatter machines), and there are certain types of radiation that you cannot avoid (background cosmic).&lt;p&gt;I don&apos;t see how the argument that it is &apos;nothing&apos; in comparison to other forms of radiation really stands up, in that I could potentially avoid backscatter radiation, whereas I couldn&apos;t conceivably avoid the other types.&lt;p&gt;(This doesn&apos;t take into account other real issues, like &apos;what if the machine breaks down and we start blasting people with focused beams of radiation&apos;... while trained to run the machine, I doubt that the TSA people are trained to maintain the machine, or would even know if something had gone horribly wrong with it).</text></item><item><author>yummyfajitas</author><text>Just curious, does anyone have some hard evidence that the MWBS is a cancer risk?&lt;p&gt;I ask this simply because anti-X activists have pushed junk science claims of the form &quot;X causes CANCER&quot; many times [1], so I&apos;m a little dubious. I don&apos;t think fighting civil liberties violations with junk science is a useful tactic, if that is indeed what is happening here.&lt;p&gt;[1] For example, feminists pushed the &quot;silicone gel implants cause breast cancer&quot;, anti-bioscience types push &quot;GMO foods cause cancer&quot;. Drug warriors have pushed &quot;pot causes cancer&quot; and anti-abortion crusaders pushed &quot;abortion causes cancer&quot;.</text></item></parent_chain></comment><story><title>When we got to the scanner, I opted out. Then they opted out.</title><url>http://blog.izs.me/post/1591805056/tsa-success-story</url></story>