It has been determined that during a painting and insulation replacement: job on the exterior of the D-15 vessel at the Solvents Plant at Dow's Plaquemine manufacturing complex, a radiation shield was not locked out on a 500 mCi
Cs-137 radiation source used for level detection. The zone of potential exposure was approximately 3 inches wide by 14 inches long on the external top of the tank. The work that was being performed was in such a manner that there could have been a possibility of hand or arm exposure. During the six day period it was determined that up to 16 persons had the potential to be exposed while completing the insulation replacement. A conservative estimate of 5 minutes total continuous exposure time over this period at a distance of 5 inches from the source yield a potential exposure of 421 mrems. A two minute total continuous exposure at a distance of 14 inches would yield a potential exposure of 31 mrems. The cause of the incident was failure to lock out a radiation shield prior to commencement of work. Lock out procedures for the facility have been reviewed and strengthened to prevent reoccurrence. Medical screening was performed on all potentially exposed personnel and the results were reviewed with the personnel. No effects were observed.