Re: Safety question re electron beam curing device

["Scott D. Kniffin" <Scott.D.Kniffin.1@gsfc.nasa.gov>]

Wayne, 

Your reference to the event at the industrial facility was exactly what I
was going to recommend that you check out.  I know all the inside details
of that event.  I'm not allowed to mention specifics, but I can tell you
what the facility did (or at least most of what they did) to prevent this
from happening again.  

The area with the carts containing product was completely fenced off except
for narrow slots where the trays could be swapped out and a gated access
point 
for workers.  Every concievable means of entrance to the conveyor area was 
alarmed: audibly, visually (strobe), and wired to automatically shut down
the entire beam, current and voltage upon unauthorized entry.  Several
cameras and photoeyes were also installed, along with a caveat that no one
could operate alone (had to be at least one other person in the facility).
A portable meter must be taken with anyone going into the target area for
any reason, beam off or not.  The operators console was rewired to prevent
voltage only condition.  That does result in a little drift each time you
fire the beam back up, but it is quickly compensated for if you have either
a well trained operator or good automatic equipment.  There was the
necessary slew of administrative and procedural changes as well, but I hope
they don't pertain since the idea is that you won't make these mistakes in
the first place, right?  

Be safe and good luck,
Scott Kniffin

Scott.D.Kniffin.1@gsfc.nasa.gov
RSO, Unisys Corp. @ Lanham, MD
CHO, Radiation Effects Facility, GSFC, NASA, Greenbelt, MD

The opinions expressed here are my own.  They do not necessarily represent
the views of Unisys Corporation or NASA.  This information has not been
reviewed by my employer or supervisor.  

At 08:24 12/22/97 -0600, you wrote:
>Does anyone have any experience or information about electron "dark
>current" or other radiation safety concerns with electron beam curing
>devices?  One of our registrants has an Energy Sciences, Inc. electron beam
>curing machine.  This thing is big and heavy-duty.  Manufacturer's
>literature indicates an electron dose of about 4 Mrad at a product
>throughput speed of 1300 ft/min. for example.
>
>I am less concerned with radiation problems during operation than with the
>possibility of "dark current" doses during maintenance or setup.  The front
>end of the machine rolls forward and individuals can stand in front of the
>beam port (a thin metal plate).  My concern is that the current source
>could be turned off while the accelerating voltage could remain applied.
>At 400 kV or more, it seems to me there could be enough stray electrons to
>set up a substantial "dark current" and dose workers standing before the
>beam port.  I cannot get out of my mind the 1993 report in Health Physics
>(V. 65, no. 2) about the "dark current" incident at an industrial
>accelerator facility in which the current source was turned off but the
>accelerating voltage remained at operating levels.
>
>Although I will speak to them again, the manufacturer was not able to tell
>me much about the potential for this kind of occurrence the first time I
>asked.  Any help appreciated.
>
>(Usual disclaimers.)
>wayne johnston
>nh bur. rad. health
>6 hazen drive
>concord, nh  03301-6527
>603-271-4842
>wjohnsto@dhhs.state.nh.us
>