A B737-700 FLT CREW DECLARES AN EMER AND EXECUTES AN EMER DSCNT FOR A PRESSURIZATION PROB. THEY FAILED TO WRITE UP THE PROB PROPERLY.

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DURING DSCNT FROM FL390 TO FL250; THE ALT WARNING HORN CAME ON AS THE CABIN ALT SLOWLY CLBED ABOVE 10000 FT. WE SILENCED THE HORN; INITIATED CHKLIST PROCS AND TOLD CTR WE WERE EXPERIENCING A DEPRESSURIZATION; REQUESTING 8000 FT. THEY INITIALLY ASSIGNED US 11000 FT AND WE EXPEDITED OUR DSCNT. THE CABIN ALT PEAKED AT APPROX 14000 FT; BUT BEGAN TO RECOVER AS WE DSNDED. FORTUNATELY; THE PAX OXYGEN MASKS NEVER DEPLOYED. WE INDICATED A LOSS OF L DUCT PRESSURE. AS WE CLOSED IN ON 11000 FT; CTR IMPLIED THEY WERE NOT GOING TO GIVE US OUR REQUESTED ALT. CONSEQUENTLY; AN EMER WAS DECLARED SIMPLY TO GET DOWN TO 8000 FT. CABIN ALT EVENTUALLY WENT BELOW 10000 FT ONCE WE DSNDED BELOW 10000 FT. AT 8000 FT; CABIN ALT RECOVERED AND WE TERMINATED THE EMER. UPON ARR AT THE GATE; WE NOTICED THE L PACK VALVE CIRCUIT BREAKER WAS OPEN. IT RESET AND OUR SUBSEQUENT LEG WAS UNEVENTFUL. DISPATCH WAS ADVISED. WE SPECULATED THE CIRCUIT BREAKER HAD OPENED SOMETIME DURING CRUISE FLT BECAUSE WE HAD BEEN OPERATING BOTH PACKS IN HIGH TO HELP CLR ANY SMOKE ODORS FROM THE ACFT. WE HAD JUST DEPARTED AN AREA AFFECTED BY WILDFIRES. WE ADVISED MAINT CTL OF OUR EXPERIENCE WITH SINGLE PACK OP AND THEY SAID THEY WOULD SET UP A LEAK CHK ON THE ACFT. SUPPLEMENTAL INFO FROM ACN 597855: I'M WRITING THIS RPT AS A RESULT OF BEING INFORMED BY MY CHIEF PLT THAT AN INVESTIGATION IS BEING LAUNCHED; DUE TO A LACK OF MAINT ITEM WRITE-UP FOR THE PARTIAL CABIN DEPRESSURIZATION INCIDENT OF FLT NUMBER. THE FACT THAT PROPER WRITE-UP PROCS WEREN'T FOLLOWED CAME AS A SURPRISE TO ME. AT THAT TIME; I ALSO OBSERVED THAT THE PACKS WERE ON HIGH. I SWITCHED THE PACKS TO AUTO; AS I HAD DONE ON PREVIOUS LEGS THAT DAY; AND REACHED DOWN TO GRAB THE OXYGEN MASK. I OBSERVED AN IMMEDIATE REVERSAL OF THE CABIN RATE FROM CLB TO A DSCNT. WHILE CONTINUING TO PERFORM THE MEMORY ITEMS FLOW OF RAPID CABIN DEPRESSURIZATION; I REACHED UP TO CLOSE THE OUTFLOW VALVE. I OBSERVED AGAIN THAT THE CABIN WAS STILL DSNDING AND THAT THE ACFT WAS PRESSURIZING. I SHOWED IT TO THE CAPT AND ASKED IF HE WOULD LIKE FOR ME TO CONTINUE WITH THE PROC. HE SAID NO. I AGREED BECAUSE IT APPEARED THAT THE CABIN WAS PRESSURIZING NORMALLY.