On December 11, 1995, at Hanford, craftsmen were renovating and decontaminating a hot cell in Building 325 when a continuous air monitor connected to an adjacent tent alarmed. The airborne contamination came from metal and paint particles generated by an iron worker grinding a door jamb at the entrance to the hot cell. A laborer was exposed to contaminated air that entered his air-purifying respirator. Health Physics technicians estimated the air in the tent to be at least 7,000 derived air concentrations. The principle radionuclides were plutonium and americium. Radiological control technicians conducted whole body surveys of three craftsman and a radiological control technician and found no detectable contamination. This event is significant because unanticipated air contamination and inappropriate placement of a contaminated air alarm caused a laborer to be exposed to contaminated air. (ORPS Report RL--PNL-325-1995-0034)
Installation of a water dam at the entrance to the hot cell necessitated the grinding of a door jamb to prepare the metal surfaces for welding. A tent had been erected on the outside of the hot cell during the two-year renovation period to provide a contamination barrier and positive airflow. The stainless steel interior walls had been decontaminated several times during the two years with chemicals, steam and damp rags. The painted, carbon-steel door jamb was also cleaned, but contamination was impregnated in the paint and rust was not removed. The grinder wore a plastic bubble suit and the laborer wore an air-purifying respirator.
A monitor was installed outside the tent with a tube to the inside. The alarm was set at 30 cpm. As the grinder was completing the last part of the weld preparation, he rotated the grinder 180 degrees which caused contaminated particles to enter the tent. The monitor alarmed and indicated approximately 35 cpm. Because it was outside the tent, the grinding noise masked the alarm. The only visual indication was a small light on the monitor which was not visible from the inside.
A radiological control technician monitoring the job from outside the work area was not aware that the job included grinding. After the alarm sounded, she investigated and determined that the alarm was valid. She alerted the craftsman and directed them to make a controlled exit.
Radiological control technicians conducted whole body chest counts on the three workers and the radiological control technician. Results of this survey were inconclusive. On December 13, technicians conducted a second count on the exposed laborer that was negative. The technicians also took bioassay samples of the worker. Results of the short term fecal sample indicated no uptake, but long term results are pending.
The building manager suspended work in the cell. Work resumed after radiological technicians decontaminated the tent and the radiological engineer evaluated engineered controls for the job. As a corrective action a remote device was installed in the hot cell to provide audio and visual alarm indication.
This event illustrates the importance of radiological control technician involvement with radiological work and proper placement of alarms in potentially contaminated areas. In this instance, the technician did not attend the pre-job briefing and did not know of the grinding activity. Also, craftsman were not aware that they were in a highly contaminated atmosphere until informed by the technician.
DOE/EH-0256T, DOE Radiological Control Manual, section 324, specifies that cognizant radiological control personnel should attend pre-job briefings. Section 555 of the Manual requires continuous air monitoring equipment to have alarm capability and sufficient sensitivity to alert personnel that immediate action is necessary to minimize or terminate inhalation exposures. Radiological Control Managers should review their programs to determine if their radiological control technicians are adequately involved in all aspect of radiological work and if placement of monitor alarms is adequate to protect personnel.