EH-89-4 Lead Glass Shielding Problems on E-Beam Welders
                        ENVIRONMENT, SAFETY & HEALTH

                                   BULLETIN

Assistant Secretary for                              U.S. Department of Energy
Environment, Safety, & Health                        Washington, D.C. 20585

DOE/EH-0099                     Issue No. 89-4                  September 1989

Lead Glass Shielding Problems on E-Beam Welders

The Problem:

On March 7, 1988 four persons working on an E-Beam welder (Leybold Heraeus
model EBW-7.5) heard a loud, unusual bang which seemed to come from somewhere
near the south side of the unit in which they were working.  After a brief,
non-productive search to determine the cause of the noise, they resumed work
with the welder.

On the morning of April 14, 1988, a maintenance worker, who had come to
inspect a table drive motor, discovered the cause of the bang. A lead glass
plate window, which is normally positioned in the window opening of the door,
was lying on the floor.  All welder operations were halted and Health Physics
personnel called.  Lead glass plate windows provide shielding from x-ray while
allowing visual contact with the contained room.  Personnel working the E-Beam
welder between March 7 and April 14, 1988 lacked this normal Lead (Pb) glass
protective shielding and risked unusual exposure to x-ray.  Calculation for
exposure provided by the chief operator for this time period, indicated that
the total x-ray exposure received by 11 individuals was less than 400
millirem.  The low exposure is explained by the fact that the E-Beam welder
was used for only 2.25 hours during the 27 days in question and that the
distance from the welder to the closest routinely used work station is
approximately 15 feet away.

Primary Cause:

The cause of the incident was that 3 of 6 screws used to compress the Pb-glass
shield window against the vacuum glass window had loosened.  As a result the
full weight of the Pb-glass plate rested on a 3/16" lead support strip
soldered directly below the glass.

The solder had given way and the lead strip was folded back against the door
allowing the glass shield to slip down between the door and the access panel
(see figure 1.) The loosening of the 3 screws was attributed to cold flow of
sheet lead gaskets under the "z" shaped clamping brackets on either side of
the glass plate and normal aging and shrinkage of polymer lead gaskets and
port "o" ring.

Corrective Action:

As a result of this incident both doors of this E-Beam welder, 3 other similar
Leybold units and 2 Hamilton Standard units were shut down for evaluation and
corrective action.  All units exhibited similar wear problems.

Immediate corrective action included designing a new steel support bracket to
replace the failed bracket.  For those units which had not yet failed, 2" x 8"
wood planks were cut to fit between the Pb-strip and the bottom of the door
frame to provide added support.

Leybold-Heraeus Vacuum Systems, Inc. of Enfield, CT was contacted and informed
of the design defect.

Recommendations:

     o    Regular preventive maintenance on E-Beam welders should include
          instructions for inspection of the window support bracket screws
          during annual maintenance.

     o    While a chart recorder should run continuously during welder use,
          the record of run time, beam current and voltage is not saved when
          the paper is changed.  In this incident, the paper had been changed
          during the time in question and the chief operator had to recreate
          the record to provide the data on possible dose rates.  Until
          semi-annual x-ray surveys are conducted to indicate proper equipment
          performance, saving chart records would simplify run time
          calculations and provide valuable documentation in the event of it
          shielding failure.

     o    Signs should be conspicuously posted warning personnel to stay
          clear of the doors during welder use.



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This publication is one of several series of bulletins published so that DOE
program managers and contractors can share information about potential
occupational safety problems relevant to DOE operations.  For more information
or additional copies, contact the Performance Evaluation Division, Office of
Safety Compliance, Assistant Secretary for Environment, Safety & Health, U.S.
Department of Energy, Washington, DC 20545; telephone FTS 233-3294, Commercial
(301) 353-3294.
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