Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!dayton!jad
From: jad@dayton.UUCP (J. Deters)
Newsgroups: sci.electronics
Subject: Re: Are checkout-counter lasers hazardous?
Summary: No.
Message-ID: <6911@dayton.UUCP>
Date: 10 Jan 90 16:41:20 GMT
References: <189@bucsb.UUCP>
Reply-To: jad@dayton.UUCP (J. Deters)
Organization: Dayton-Hudson Dept. Store Co.
Lines: 61

> Article <189@bucsb.UUCP> From: erics@bucsb.UUCP (Michael L. Ardai)

>I was in the supermarket today, and while walking past the checkout
>counter, I got zapped in the face with the laser.  Does anyone know
>if this is unsafe?  The first thing that I learned about lasers was
>never to shine one in someones eyes. (The second was that laser tubes
>retain a charge after they are unplugged, but that is a different 
>story :-}  The tube looked like it was about a 5 mW unit. Any idea
>what to do about this (other than wearing blue sunglasses)
>
>Michael L. Ardai   Teradyne EDA   ...!sun!teraida!maven.decnet!ardai

I've been working with various scanner manufacturers for a couple of
years now, and I've found that all the lasers used in all of the different
types of scanners used in a retail environment (hand-held, flat bed, etc.)
are "Class II".  This means that they are safe within normal eye reaction
time.  They have a 1.0 mW max output, and health-wise do not constitute a
threat when used as directed.  The directions (and various warning stickers)
all say "DO NOT STARE INTO BEAM."  So of course, I stare into the beams :-).
Normal blink reflex closes your eyelids after maybe 1/4 second.  By forcing
myself to consciously stare into the beam, my blink reflex takes over after
about 1/2 second.  The beams are painful, but do not cause any permanent
damage in limited amounts.

You may be interested in knowing about the safety circuits built into the
different scanners.  All "checkout" laser scanners use a "moving beam" --
a beam that is constantly deflected by a moving mirror of some sort.
This insures that you, the user, will not have the opportunity to stare
into a straight beam.  Consider the fan-out of the beam vs. the diameter
of the pupil.  Worst case is if you take the hand-held type and hold it
as close to your eye as possible.  The fan-out is already at 2", and your
pupil is probably about 1/8".  This means you will never see more than 6%
of the total beam, and that takes a lot of effort.  The typical grocery
store flatbed scanner has between 16 and 64 scan beams (although some grocery
store flatbeds operate at 5.0 mw, as you guessed).  If you are of average
height you probably stand 30" above the scanner face.  At that distance, the
fan-out of any one beam is approximately 30".  Assuming 16 scan beams, your
pupil received .02% of the output of a 5mw laser, or 1.3 microwatts.  Not
exactly enough to run off to OSHA about (but maybe enough for a lawyer?? :-)

There is also control circuitry that either shuts off the laser or closes
an aperture if the mirror motion is prevented or if the mirror motor fails.
I jammed a mirror against the side of the case to try to get a straight
beam out of a hand-held unit, and the laser would not stay on, so their
circuit must have been functioning properly.

I certainly wouldn't worry about occasional eye contact with the beams
used in any retail application.

DISCLAIMER:  This letter does *NOT* reflect any opinion whatsoever of
the Dayton-Hudson Department Store Co.  It's just stuff I've learned
from the various vendors I deal with, and the occasional shining we
get playing with them.  I'm not trying to defend our use of lasers, it's 
just that I don't want to hear a panic like they are starting with VDTs.

-j
-- 
J. Deters
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