Narrative:

Upon climbing through approximately 33;000 ft; I noticed a pressure bump with a large pressure change. It was obvious something had occurred to the pressurization system. I looked up and noticed the cabin vsi showing a rapid climb. As I was placing the mask on my face; the cabin altitude alert began to sound and the captain placed his mask on as well; and complied with the immediate action items for a loss of cabin pressurization. It was apparent the cabin was not controllable per the QRH; and we initiated a descent. The cabin masks had already deployed by the time I was instructed to deploy them per the QRH. The highest cabin altitude noticed was approximately 17-20;000 ft. It occurred within a very short time frame of likely less than 1 minute from the sound of the intermittent horn to the max cabin altitude. Upon descent there were no unusual sounds and at arrival at 10;000 ft altitude after conferring with the flight attendants; everything appeared normal in the rear of the aircraft as well; other than the cold air that entered the aircraft. Mmo/vmo was exceeded slightly as we were in the emergency descent. (As a side note; the pressurization controller in manual controlled the cabin altitude extremely erratically when at a lower altitude. A simple touch of the valve switch would change the cabin altitude vsi by +/-1500-2000 fpm and would not affect a change at all at higher altitudes.) we proceeded to ZZZ as an emergency aircraft and had medics standing by as a precaution to anyone needing medical attention. At the request of the captain; all the flight crew were all evaluated by the medics and released.

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Original NASA ASRS Text

Title: B737 flight crew experiences a loss of cabin pressurization passing FL330 in the climb. The cabin altitude cannot be controlled and an emergency descent is initiated and a return to the departure airport is accomplished. The crew reported problems in the cabin with both passenger and Flight Attendant oxygen systems.

Narrative: Upon climbing through approximately 33;000 ft; I noticed a pressure bump with a large pressure change. It was obvious something had occurred to the pressurization system. I looked up and noticed the cabin VSI showing a rapid climb. As I was placing the mask on my face; the cabin altitude alert began to sound and the Captain placed his mask on as well; and complied with the immediate action Items for a loss of cabin pressurization. It was apparent the cabin was not controllable per the QRH; and we initiated a descent. The cabin masks had already deployed by the time I was instructed to deploy them per the QRH. The highest cabin altitude noticed was approximately 17-20;000 ft. It occurred within a very short time frame of likely less than 1 minute from the sound of the intermittent horn to the max cabin altitude. Upon descent there were no unusual sounds and at arrival at 10;000 ft altitude after conferring with the flight attendants; everything appeared normal in the rear of the aircraft as well; other than the cold air that entered the aircraft. MMO/VMO was exceeded slightly as we were in the emergency descent. (As a side note; the pressurization controller in manual controlled the cabin altitude extremely erratically when at a lower altitude. A simple touch of the valve switch would change the cabin altitude VSI by +/-1500-2000 fpm and would not affect a change at all at higher altitudes.) We proceeded to ZZZ as an emergency aircraft and had medics standing by as a precaution to anyone needing medical attention. At the request of the Captain; all the flight crew were all evaluated by the medics and released.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.