ZDC CTLR OBTAINS AN INCOMPLETE POS RELIEF BRIEFING AND BECOMES INVOLVED IN A LOSS OF SEPARATION WHEN HE ISSUES A DSCNT CLRNC TO A BE58 THROUGH A C208 1000 FT BENEATH.

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WIDESPREAD IFR DAY ACROSS ENTIRE CTL AREA; RAIN AND ICING RPTS EARLIER IN THE SHIFT. NOW THAT SUN HAD SET; FOG MOVING IN. ANOTHER OPERROR OCCURRED IN MY AREA OF SPECIALIZATION -- BAY 3 -- ABOUT 3 HRS BEFORE; RESULTING IN 3 FPL'S AND 1 DEVELOPMENTAL BEING REMOVED FROM STAFFING DUE TO INVESTIGATION. I CAME BACK FROM A BREAK AND STARTED TO RELIEVE THE CTLR AT THE R05 AND R02 COMBINED POS. EVEN THOUGH A CHKLIST WAS USED; THE BRIEFING WAS RUSHED AND NOT IN A CONTINUOUS FLT. WE KEPT BEING INTERRUPTED BY SEVERAL ACFT WITH REQUESTS AND BY CTLRS ATTEMPTING TO COORDINATE WITH US. I HASTILY ACCEPTED THE POS AND STARTED ISSUING CLRNCS. MORE CALLS FROM OTHER CTLRS CAME. THEN; ACFT #1 AT 7000 FT REQUESTED AN APCH. I DID NOT UNDERSTAND HIM AND ASKED HIM TO REPEAT HIS REQUEST. IT WAS ONLY THEN THAT I REALIZED ACFT #1 WAS LNDG AT AN ARPT WITHIN MY JURISDICTION; AND HE WAS ONLY 7 MI S OF THAT ARPT. I KNEW THAT THE PROC TURN WOULD TAKE THE ACFT CLOSE TO AN ADJACENT APCH CTLR'S AIRSPACE; BUT WAS NOT SURE IF IT WAS A R TURN OR L TURN. I STOOD UP AND SEARCHED FOR THE REF BOOK; SO THAT I COULD VERIFY THE APCH. AS MY D-SIDE AND I SEARCHED FOR THE APCH PLATE; A SMALL GROUP OF CTLRS AND SUPVRS GATHERED 4-5 FT BEHIND ME. THEY WERE DISCUSSING THE ONGOING INVESTIGATION OF THE OPERROR THAT HAD OCCURRED EARLIER. WITH ALL OF THE DISTRS; BOTH ON THE RADAR AND IN MY SURROUNDING ENVIRONMENT; I NEVER GAINED A COMPLETE AND THOROUGH PICTURE OF MY TFC. WHEN ACFT #1 ASKED FOR LOWER; I DSNDED HIM FROM 7000 FT TO 5100 FT; MY MINIMUM IFR ALT. I CONTINUED ISSUING CLRNCS TO OTHER ACFT; SCANNING THE WHOLE SECTOR NOW; WHEN I REALIZED THAT ACFT #1 HAD ACFT #2 UNDERNEATH HIM AT 6000 FT LESS THAN 2 MI W OF HIS POS. THE CONFLICT ALERT ACTIVATED AND I TURNED ACFT #1 TO A 090 DEG HDG; WHICH WAS APPROX A 60 DEG TURN TO THE R. DUE TO THE PROX TO THE ARR ARPT; ACFT #1 WAS DSNDING RAPIDLY; SO I CHOSE NOT TO STOP HIS DSCNT; BUT LET HIM CONTINUE TO 5100 FT TO GET BELOW ACFT #2. I DID NOT TRY TO CLB HIM BACK TO 7000 FT; FEARING THAT SEPARATION WOULD BE LOST A SECOND TIME. SEPARATION WAS REGAINED LATERALLY AND I WAS RELIEVED FROM THE POS. IN REVIEWING THIS ERROR; I NOW SEE MANY CONTRIBUTING FACTORS. FIRST; THE POOR WX AND INCOMING FOG INFLUENCED ME TO RUSH THE APCH SO THAT ACFT #1 COULD GET ON THE GND ASAP. SECONDLY; THE REDUCED STAFFING; DUE TO THE OTHER OPERROR; HAD MEANT LONGER TIME ON POS THAT EVENING -- FATIGUE WAS SETTING IN. THE THIRD FACTOR WAS MY HAVING TO ISSUE MULTIPLE CLRNCS AND RECEIVE MULTIPLE COORDS; AS SOON AS I TOOK THE SECTOR DISTRACTING ME FROM CORRELATING DATA BLOCKS AND FLT PLAN INFO AS I NORMALLY DO. ANOTHER CONTRIBUTING FACTOR WAS MY INABILITY TO COMPREHEND THE PLT'S REQUEST; AND THEN BEING UNFAMILIAR WITH THE FULL APCH. I SHOULD HAVE FULLY ABSORBED THE INFO BEFORE I ISSUED THE DSCNT CLRNC. ADDITIONALLY; HAVING ANOTHER OPERROR THAT EVENING; AND LISTENING TO THE SPECULATION AND RUMORS CAUSED ALL OF BAY 3 TO BE ON EDGE. DISCUSSING IT ON THE CTL ROOM FLOOR CREATED A LOT OF BACKGND NOISE. THE NEW DSR ROOMS HAVE SECTORS MUCH CLOSER TO EACH OTHER; SO NORMAL TONE OF VOICE APPEARS TO BE AMPLIFIED. I WAS UNABLE TO TUNE THAT NOISE OUT. LASTLY; AND MOST IMPORTANTLY; I ASSUMED RESPONSIBILITY OF THE RADAR POS PREMATURELY BEFORE I HAD THE COMPLETE PICTURE IN MY MIND. THE RUSHED RELIEF BRIEFING STARTED THE ERROR CHAIN. HAD I TAKEN THE TIME AND DEVELOPED A FULL UNDERSTANDING OF ALL OF THE TFC; THIS OPERROR COULD HAVE BEEN AVOIDED.