Re: [at-l] UV pen

["David F. Addleton" <dfa@wimlaw.com>]

Jim,

I'm glad to have physicists and physicians on this list, since I'm neither,
and definitely appreciate your input, critique, and etc. I *expect* to be
wrong about some of this stuff, since my science education is limited to
first level and a few second level college courses from the early 70s.

> > I will beg to differ from you on this. In my experience solar uv works
> > quite well to purify water.
> > 
> This is the kind of unscientific statement I have a problem with.

Agreed that anecdote doesn't a peer-reviewable scientific statement make,
since it comes without appropriate measurements and counts etc. But it
remains *scientific* in a generic, empirical sense, since it arises from
direct experience. If between two people all intake remains identical but
the water source, and one of them gets sick, we don't have a large sample,
but I'm willing to bet on the water source identified with the well person
and to neglect the water source used by the guy who got sick.

> How can
> you say that solar uv works well without any testing? 

You're completely correct: I cannot make a statement regarding counts of
the various pathological causes in water subjected to solar uv radiation
before or after. I can empirically state, however, I and my family and
friends did not get sick drinking from streams with the characteristics
previously mentioned; that I have used solar radiation to make tea in glass
jars and did not get sick subsequent to drinking it. And at some level we
really don't care about the actual counts of pathogens from filters,
iodine, boiling, or whatever, so long as the count is sufficiently low we
don't get sick.

> Only a before and
> after test is valid (test for "bugs" and find them - radiate them - test
and
> they're gone).

For peer-reviewed science I agree; for practical everyday empirical
reasoning, I don't agree. The kings of old who used slaves to test their
food and drink to assure it hadn't been poisoned, for example, conducted an
empirical experiment each time they brought in the poor slave. The miner's
canary served as an adequate meter for certain gases. Triangulating among
three or four distant mountain peaks, leaving your landrover for a long
hike into the mountains, and subsequently returning on camels days later,
directly to the landrover's location, may not result in accurate geometric
measurements, but it kept us from getting lost on our way back to the
vehicle.

> I can say the same thing about my PUR filter - in my
> experience it works fine. But I haven't tested it so the statement is
> meaningles. I've never gotten sick while using it but then maybe I never
> filtered any bad water.

The statement isn't meaningless, it's just packs less meaning than a
rigorous scientific test. Next time we go out on the trail we'll go
together and conduct an experiment on your pur filter. I will select the
stream from which I will drink untreated water. You will drink only boiled
or pur filtered water. If I get sick and you don't you'll have sufficient
empirical evidence to state that the pur filter works.

> I'm just questioning the claims from this little
> pen.

And I'm just trying to find out the basis for your questions about this
little pen, pointing out my *experience* with solar radiation, uv light,
and drinking water.

> 	I stand by the original statement - but I need to clarify. Solar
> radiation may purify but it takes a long time. For this small pen to do
the
> job in a short period of time would take a lot of energy output.

I agree with the reasoning so far as it goes, but don't agree that this
reasoning explains why a uv pen ought not be trusted in theory to disinfect
a cup of water, IF we believe the specs on the pen and the tables for uv
energy necessary to knock out specific pathogens.

> A milliwatt second per centimeter squared is just energy per unit area
> (Joules/square meter). Energy is expressed in Joules which are
watts/second,
> and area is expressed in square meters. 

Just using the industry's units instead of the physics; the numbers should
work out either way, shouldn't they, as long as we make the necessary
conversions.

> http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

Thanks! I needed that.

> A solid state laser (semiconductor) could be
> possible in the uv range though.

Tell me more ... maybe we can beat the steripen folks to the market with a
better pen.

> 	Keep looking. This is ALWAYS the test to see if a claim is valid. If
> a product makes claims that are legitimate then they will get it tested.

You bet they will. They'll get tested by the competition and by the
customers who use the product, and when they get sick they'll go after the
manufacturer to test them again against twelve peers.
 
> Please don't take my comments as being critical of your research or
ideas. I
> am just a skeptic and I believe in analyzing these things very critically
> from a scientific/engineering standpoint. Keep researching and let us
know
> if you find any independent test results. I will be the first one to swap
my
> heavy PUR filter for a ster-pen if it really works!

I don't take this stuff very personally, I can assure you. I am interested
in the subject matter and appreciate the presence here of people more
educated in the scientific issues than me. I'm pretty much of a skeptic,
too. I value your comments ... for instance, my memory was clearly wrong on
cube vs square thing, but you knew enough to know what I was trying to
remember for two or three decades ago.

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