Re: RETAIL SCANNERS - RADIATION BURNS

["David Bromwich" <D.Bromwich@ens.gu.edu.au>]

> From:          king@reasoning.com
> To:            Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Subject:       Re: RETAIL SCANNERS - RADIATION BURNS 

Ah, a touch of flame!
> >> to deliberately stare into the beam.  On the positive side, 
> >> supermarkets are usually well lit, so the pupil of the eye would be 
> >> relatively small, giving a small target for the beam.
> 
> This is no protection. 
> The beam must be small [it has to be narrower than the smallest element of the
> bar code to do any scanning] and the pupil doesn't get that small.

Wrong.  The target is smaller, so the chance of the beam entering the 
eye is reduced.

> 
> >>							  Also, the beam 
> >> is usually scanning so that it can read barcodes, so the beam would 
> >> sweep across the eye and little energy would be deposited.
> 
> This is substantially more important.
> 
> And of course the small pupil is illuminated for a shorter time.
> 
> -dk
Agreed - the exposure is reduced by either moving the pupil/beam or 
reducing the size of the pupil.

I should mention the classification of Class 2 is one the time it 
takes to blink, about 0.25 seconds.  If the energy deposited in this 
time for a visible beam in 0.25 seconds is enough to damage the eye 
(retina) then the laser is a class 3 or 4.  Invisible beams (IR 
lasers) cannor be seen, so you have to assume the person has taken to 
staring at the beam and is not protected by the blink reflex.  I have 
been somewhat horrified by people demonstrating their you beaut Class 
4 CO2 (IR) laser whilst wearing shiny rings or watches.  The use of 
lasers is almost a free for all here.


David Bromwich, CIH 
Lecturer, Occupational Hygiene     tel (+617) 8757487
Faculty of Environmental Sciences  fax (+617) 8757459
Griffith University, Nathan Q 4111 AUSTRALIA