On October 6, 1993, at the Savannah River Site, an operator at the Old HB-Line observed an air flow reversal from a contaminated room into a corridor, resulting in the spread of plutonium-238 contamination and the internal contamination of a worker. Personnel investigating the abnormal air flow discovered a piece of craft paper obstructing the exhaust vent of the room. They concluded that the lack of exhaust pressurized the room causing the room air flow to reverse into the corridor. Facility personnel removed the blockage from the exhaust and reestablished normal air flow. This condition was significant because negative differential pressure is used as an engineered control to preclude the spread of contamination from radiologically controlled areas. Normal ventilation and air flows dictate that air flow from less contaminated areas to areas of higher levels of contamination. Facility decontamination and decommissioning activities were in progress at the time of the occurrence.
After the air reversal, Health Protection personnel performed contamination surveys of the corridor and discovered a maximum of 100,000 dpm/100cm2 alpha contamination. Analysis of the filter paper from the constant air monitor installed away from the ventilation reversal showed 534 DAC (Derived Air Concentration) for the entire counting period. Facility personnel are investigating why the constant air monitor did not alarm and why Health Physics personnel did not obtain air samples immediately following the event. The DOE Radiological Control Manual requires obtaining air samples for this type incident. Health Physics personnel placed the affected areas on respiratory protection, and administered nasal and saliva smears to seven employees present in the corridor at the time of the occurrence. The smears did not detect any contamination, although initial gross fecal counts showed one worker had internal contamination.
A contamination incident at the HB-Line facility on July 25, 1991, resulted in one personnel assimilation and four personnel uptakes. Savannah River Site personnel define an assimilation as an uptake of radionuclides into the body that results in an annual effective dose equivalent of 0.1 rem. In this event, five workers were contaminated when an operator opened an empty plutonium-238 shipping container. The container was not identified by a radiological control label to indicate that the interior was contaminated. The assimilation resulted in a committed effective dose equivalent of 16 rem. The four other individuals received uptakes resulting in committed effective dose equivalents ranging from 0.035 to 0.9 rem. (ORPS Report SR--WSRC-HBLINE-1991-1013)
There have been numerous other events at DOE facilities concerning sudden air reversals that resulted in the potential for the spread of contamination. An example of these events include the following.
On May 29, 1992, personnel at Rocky Flats Building 371 noticed an air reversal from a contaminated room into a hallway. Follow-up investigation determined that several High Efficiency Particulate Air filters in adjacent rooms had clogged, resulting in pressurization of the room. Workers had installed the filters in an effort to contain the existing contamination in the adjoining rooms. (RFO--EGGR-371OPS- 1992-0053)
On April 30, 1992, personnel at the Hanford 324 facility discovered air flowing out of a radiation area and into an uncontrolled area. The event investigators concluded that someone working in the area violated operating procedures when they opened the dampers to provide more air flow in an effort to reduce the temperature in the room. (ORPS Report RL--PNL-324-1992-0011)
On March 2, 1992, personnel at the Savannah River Old HB-Line facility encountered an air reversal that affected eighteen workers. Investigators determined that the reversal was caused by a combination of multiple doors being open at the same time resulting in a breached airlock. One of the primary doors establishing the airlock, which would have prevented this incident, was found to have no latching mechanism. (SR--WSRC-HCAN-1992-0012 Final Report)
On February 12, 1992, personnel at the Savannah River Old HB-Line facility identified an air reversal that resulted in an increase in airborne activity in a corridor. Prior to the event, a worker adjusted a ventilation system damper in an attempt to reduce a higher-than-usual airborne radioactivity level in an airlock located in another corridor. Although the worker did not notice an immediate change in the air flow after the adjustment, opening the damper caused a decreased capability for the room to exhaust and a resultant pressurization. (SR-- WSRC-HCAN-1992-0009)
These events illustrate the importance of thoroughly understanding facility ventilation systems prior to initiating work activities. When applicable, facility personnel may consider performing a study of facility air flow directions and differential pressures under all expected upset conditions to provide actual system ventilation data and verify that the air flow differentials between radiologically controlled areas and contamination areas are acceptable. These occurrences also emphasize the importance of heightened awareness during periods of change to facility primary systems. Planning reviews of work packages and facility modifications should be conducted to help facility personnel recognize and consider the potential impact of these activities. Each modification should also be carefully coordinated in such a way that installation does not adversely affect the facility operating status or compromise operation of a primary system such as confinement ventilation systems.
It is important that the integrity of all airlocks throughout a facility be maintained in accordance with standard operating and maintenance practices and that these airlocks have latching mechanisms. Consideration should also be given to posting signs at the appropriate locations that specify air lock operations (one door open at any one time). In addition, ventilation system vents should be periodically inspected to ensure that there are no obstructions and dampers are in the proper position.