A B737-700 ON INITIAL CLB AT 12000 FT HAD L EYEBROW WINDOW FAIL. ACFT WAS DEPRESSURIZING WITH LOUD NOISE THAT MADE COMMUNICATION BETWEEN CREW AND WITH ATC VERY DIFFICULT.

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LEAVING ZZZ ON THE RNAV DEP. JUST FINISHED THE CLB CHECK PASSING 12000 FT MSL. ALL OF A SUDDEN AN EXTREMELY LOUD CONSTANT NOISE BEGAN. MY L-5 WINDOW SHATTERED AND PARTIALLY SEPARATED FROM THE ACFT. THIS LOUD CONSTANT NOISE WAS THE PLANE LOSING CABIN PRESSURE. MY SENNHEISER HEADSET WAS FORCED OFF MY HEAD. BOTH PLTS IMMEDIATELY DONNED OXYGEN MASKS AND TRIED TO ESTABLISH CREW COMMUNICATIONS. I DISENGAGED THE AUTOPLT AND ARRESTED MY CLB RATE AND STARTED A SLOW SMOOTH TURN BACK TO ZZZ. I BELIEVE THE INITIAL HDG WAS 360 DEGS. I ALSO STARTED A DSCNT BACK DOWN TO 10000 FT. I THINK THE HIGHEST ALT WE CLBED TO WAS 12500 FT MSL AND I NOTED THE HIGHEST CABIN PRESSURE WAS 8500 FT. MY MAIN PRIORITY WAS TO GET BELOW 10000 FT MSL WHILE CLEARING FOR TFC AND STAYING CLEAR OF TERRAIN. WE SQUAWKED 7600 FOR SEVERAL MINUTES BECAUSE COMMUNICATION IN THE COCKPIT AND WITH ATC WAS VERY DIFFICULT. ONCE THE FO WAS ABLE TO TALK TO APCH AND ESTABLISH COMMUNICATION; WE SQUAWKED 7700 AND DECLARED AN EMER. ESTABLISHED AT 10000 ON A 020 DEG ATC VECTOR I CALLED FOR THE CABIN ALT WARNING HORN/ABNORMAL PRESSURIZATION QRH CHKLIST; BUT THE FO COULD NOT HEAR ME. SO I GOT OUT THE QRH AND TURNED TO THE CHKLIST I WANTED AND SHOWED HIM. THE FO HANDLED ALL THE QRH ITEMS WHILE I MONITORED. WE USED NOTES AND HAND SIGNALS TO COMMUNICATE. WE USED THE OLD WX DATA; RAN THE OPC FOR 125000 GW (131 136); ACCOMPLISHED THE DSCNT CHKLIST AND BRIEFD OUR ARR. THE NOISE WAS STILL VERY LOUD SO WE CHOSE TO GO MANUAL ON THE PRESSURE SELECTOR AND FULL OPEN ON THE VALVE. THE NOISE DIED DOWN A LITTLE. I ALSO REDUCED MY SPD TO 210 KTS AND THAT REALLY DIMINISHED THE NOISE. ONCE ALL THIS WAS ACCOMPLISHED; WE COULD COMMUNICATE CROSS COCKPIT BY YELLING AT EACH OTHER. ATC PUT US ON A MODIFIED DOWNWIND AT 7000 FT MSL. I HOOKED UP THE AUTOPLT; AND REALIZED I HADN'T INFORMED THE FLT ATTENDANTS OR PAX WHAT WAS GOING ON; SO I TOLD THE FO TO TRY TO ESTABLISH COMMUNICATIONS WITH THEM WHILE I RETRIEVED MY HEADSET. WE CHOSE TO SECURE THE CABIN FOR LNDG; RATHER THAN PREPARE THE CABIN. FROM THIS POINT ON; IT WAS UNEVENTFUL; A LITTLE NOISY; BUT I COULD COMMUNICATE WITH THE FO AND ATC. WE BROUGHT IT AROUND AND LANDED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THIS AIRPLANE WAS PREVIOUSLY FLOWN ABOVE 35000 FT WITH NO PROBS. THE OUTER PANE SHATTERED AND THE INNER VINYL STRUCTURAL MEMBER TOP AFT OR UPPER PORTION WAS OPEN THREE INCHES TO THE OUTSIDE. RPTR INDICATED THAT MAINT DID NOT RPT THE CAUSE OF THE INNER VINYL PANE FAILURE BUT THE UPPER FRAME APPEARED INTACT AND ONLY THE UPPER PART OF THE VINYL PANE WAS EXPOSED.