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From: siegman@sierra.Stanford.EDU (Anthony E. Siegman)
Newsgroups: sci.electronics
Subject: Re: Are checkout-counter lasers hazardous?
Message-ID: <446@sierra.stanford.edu>
Date: 9 Jan 90 05:17:28 GMT
References: <189@bucsb.UUCP>
Sender: siegman@sierra.STANFORD.EDU (Anthony E. Siegman)
Reply-To: siegman@sierra.UUCP (Anthony E. Siegman)
Organization: Stanford University
Lines: 23

I'd be very surprised if a supermarket laser scanner were hazardous.
The manufacturers must be very knowledgable about the safety issues --
including the knowledge that they have deep pockets, lasers have a
death ray image, and a supermarket checkout stand is a very public
place, all of which would make them very vulnerable to damage claims,
real or spurious.  I'd expect their concern for safety (including
every possible form of fail-safe design) to be very extreme.

In addition, a few milliwatt cw visible laser is really not that
hazardous.  It certainly can't burn skin or the outer surface of an
eye, and even if optimally focused within an eye on a continuous basis
my guess is it would still not do real physical damage (burning or
phase transformation) to the retina.  In addition, your natural blink
reflex will close the eyelid very rapidly.  And, the actual output
beam from a supermarket scanner unit may be more in the 10 to 100
microwatt range.

I've never heard of eye damage (or any other kind of damage) from a
milliwatt-level He-Ne laser.  It's the multi-watt cw ion lasers, or
the high energy pulsed lasers, that you really have to be careful
with.  In general, injuries from laser beams have been very, very few.
But, several people (including at least two students I know of) have
been electrocuted by laser power supplies in laboratory accidents.