Narrative:

This was the first leg of a four day trip and first flight of the day for the crj-200 aircraft ZZZ-ZZZ1. As we were climbing to FL230 we noticed that the cabin altitude was climbing at about 600 FPM at times and we heard a loud squeal from our main passenger boarding door. At about FL200 we were growing more suspicious of our climbing cabin and I asked ATC to level at FL230 to determine if we had a pressurization issue. Our hope was the cabin would stabilize. When we leveled at FL230 the cabin continued to climb at about 200 FPM and we received a cabin alt caution message. I began the QRH procedure. When I got to the portion of the procedure that attempts to swap cabin pressure controller (cpc) from one to the other; the cabin began to quickly climb. From here things happened very quickly; within less than 20 seconds we requested lower and I proceeded with the QRH and per the QRH attempted to control the cabin in manual mode. We received a cabin alt warning and complied with the immediate action items; emergency descent; and declared an emergency requesting lower. Upon initiation of the emergency descent; the cabin at one glance was climbing at 4;000 FPM and showed an altitude of 13;000 ft. By the time we got to the QRH cabin warning checklist; the passenger masks had deployed automatically. We were ultimately cleared by ATC to 10;000 ft and were able to descend without any level offs. During the later portion of the descent; I spoke to the flight attendant and advised her of our status. She informed me that everyone was fine and using their masks. She had to assist one passenger with the portable oxygen bottle as that passenger's mask had malfunctioned. ZZZ2 was only 50 miles to our 11 o'clock [position] when we began our descent so I advised ATC we would like to divert there.ATC quickly got us down to 5;000 ft on a vector for [runway] 27L. Once we got below 10;000 ft; I saw that the cabin altitude was in a 'normal' range and told ATC that we had normal cabin pressure and would like delaying vectors at this point. I told the first officer we could slow down and now take our time as the emergency was essentially over. I made a PA to the passengers that they could remove their masks and also reassured them that we would be landing safely in ZZZ2 shortly. I also once again spoke to the flight attendant to relay information and check on her and the passengers. She told me everyone was fine and I told her we were working on cooling the airplane as it had noticeably warmed due to the [passenger mask] oxygen generators. We sent the dispatcher a text advising them of what had happened and our plan to land in ZZZ2. We proceeded to get weather; landing numbers; and brief the visual approach to [runway] 27L in ZZZ2. We landed without incident and proceeded to gate D. During the taxi; we received a message from dispatch which indicated he had not received our text. We deplaned the passengers via ramp as we also had wheelchair passengers. The biggest threat to me was the time compression which took place from the point we received our initial indication of a problem to the point where we restored normal cabin pressure. What initially seemed to be an abnormality quickly turned into an emergency. It had been a couple years since my first officer and myself had been to ZZZ2; so it is not an airport we were as familiar with relative to most other airports. Otherwise good weather; fresh crew; experienced first officer (including a flight attendant who had recently had a pressurization emergency); and quick ATC response helped mitigate threats. We could have leveled a bit earlier than FL230; but we didn't think there was a possible issue until about FL200. I will expect the cabin to quickly climb when power is retarded and there is a pressurization leak; the incredible rate at which the cabin climbed caught me by surprise.

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Original NASA ASRS Text

Title: A Captain describes how quickly the Cabin Rate of Climb in their CRJ-200 aircraft had reached 4;000 FPM showing an altitude of 13;000 FT with a Cabin ALT Warning at FL230. Passenger masks auto deployed. Emergency declared with ATC to 10;000 FT; flight diverted to alternate airport.

Narrative: This was the first leg of a four day trip and first flight of the day for the CRJ-200 aircraft ZZZ-ZZZ1. As we were climbing to FL230 we noticed that the Cabin Altitude was climbing at about 600 FPM at times and we heard a loud squeal from our main passenger boarding door. At about FL200 we were growing more suspicious of our climbing cabin and I asked ATC to level at FL230 to determine if we had a pressurization issue. Our hope was the cabin would stabilize. When we leveled at FL230 the cabin continued to climb at about 200 FPM and we received a Cabin Alt Caution message. I began the QRH procedure. When I got to the portion of the procedure that attempts to swap Cabin Pressure Controller (CPC) from one to the other; the cabin began to quickly climb. From here things happened very quickly; within less than 20 seconds we requested lower and I proceeded with the QRH and per the QRH attempted to control the cabin in Manual Mode. We received a Cabin Alt Warning and complied with the immediate action items; emergency descent; and declared an emergency requesting lower. Upon initiation of the emergency descent; the cabin at one glance was climbing at 4;000 FPM and showed an altitude of 13;000 FT. By the time we got to the QRH Cabin Warning Checklist; the passenger masks had deployed automatically. We were ultimately cleared by ATC to 10;000 FT and were able to descend without any level offs. During the later portion of the descent; I spoke to the Flight Attendant and advised her of our status. She informed me that everyone was fine and using their masks. She had to assist one passenger with the portable oxygen bottle as that passenger's mask had malfunctioned. ZZZ2 was only 50 miles to our 11 o'clock [position] when we began our descent so I advised ATC we would like to divert there.ATC quickly got us down to 5;000 FT on a vector for [Runway] 27L. Once we got below 10;000 FT; I saw that the Cabin ALT was in a 'Normal' range and told ATC that we had normal cabin pressure and would like delaying vectors at this point. I told the First Officer we could slow down and now take our time as the emergency was essentially over. I made a PA to the passengers that they could remove their masks and also reassured them that we would be landing safely in ZZZ2 shortly. I also once again spoke to the Flight Attendant to relay information and check on her and the passengers. She told me everyone was fine and I told her we were working on cooling the airplane as it had noticeably warmed due to the [passenger mask] Oxygen Generators. We sent the Dispatcher a text advising them of what had happened and our plan to land in ZZZ2. We proceeded to get weather; landing numbers; and brief the visual approach to [Runway] 27L in ZZZ2. We landed without incident and proceeded to Gate D. During the taxi; we received a message from Dispatch which indicated he had not received our text. We deplaned the passengers via ramp as we also had wheelchair passengers. The biggest threat to me was the time compression which took place from the point we received our initial indication of a problem to the point where we restored normal cabin pressure. What initially seemed to be an abnormality quickly turned into an emergency. It had been a couple years since my First Officer and myself had been to ZZZ2; so it is not an airport we were as familiar with relative to most other airports. Otherwise good weather; fresh crew; experienced First Officer (including a Flight Attendant who had recently had a pressurization emergency); and quick ATC response helped mitigate threats. We could have leveled a bit earlier than FL230; but we didn't think there was a possible issue until about FL200. I will expect the cabin to quickly climb when power is retarded and there is a pressurization leak; the incredible rate at which the cabin climbed caught me by surprise.

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.