Narrative:

We were single pack operations. On departure; we took off bleeds closed; leveled off at 6;000 feet and followed the MEL operational procedure to swap the bleed air source to the right engine. This was accomplished successfully without any issues. We continued our climb to our cruise altitude of FL250 and upon climbing through FL200; we noticed that the right pack (the only operational pack) had shut off and the cabin altitude was climbing at a fast rate. We immediately stopped climbing; and we began a descent to 10;000 feet as I [advised ATC] and told them that we were experiencing pressurization problems. We both donned our oxygen masks and established communications. I told the first officer to continue flying the descent and take the radios while I ran the qrc and QRH procedures for emergency descent. We reached 10;000 feet and we both came off of O2. We requested a turn back to ZZZ and also requested a lower altitude to decrease cabin altitude and we were cleared to descend to 6;000 feet as I was running the QRH emergency descent procedure; we were descending through 9;000 feet and the cabin altitude was still below 9;000 feet so I made the choice not to deploy the passenger oxygen masks.after wrapping up the QRH procedure; I called the flight attendant with the emergency button and briefed her on the nature of the [situation] but told her that everything was under control and that we would be returning to ZZZ and landing in 15 minutes; there would be no need for brace positions on landing; it would be a routine approach and landing; and to secure the cabin for landing. I also asked the flight attendant if anyone was injured or was feeling ill and she replied that everyone was doing good and everyone was seated with their seatbelts on. I made a passenger announcement and briefed the passengers that we were returning to ZZZ. I finished running the unpressurized flight procedure in the QRH and then began helping to prepare for the approach and landing into ZZZ. Since the first officer (first officer) had been flying this whole time; we discussed that the he would continue flying and make the landing. I then briefed the approach. We ran a descent check and conducted the approach and landing as planned with no issues. Arff (aircraft rescue and firefighting) was waiting alongside the runway for our arrival and communicated with us as we vacated the runway. They asked if we had any injuries and we called the flight attendant again to verify no injuries and this was confirmed. After we shut the engines down at the gate and ran the shutdown check; I made a PA announcement in front of the passengers and explained what all happened and why we returned to ZZZ; and also asked one last time if anyone was feeling hurt or ill. EMS (emergency medical services) waited in the jet bridge just in case anyone wished to seek medical attention; but nobody did. Aircraft was then written up and maintenance was called.we are not sure what caused the right pack to shutoff. Never received any pack hi temperature or pack hi press caution messages and right pack was operated in automatic temperature control mode the entire flight.looking back on the event; we are trained to begin an emergency descent immediately once we realize the aircraft is not being pressurized; and we did this; however; after reviewing the events; I realized I did not try recycling the right pack. Not necessarily a mistake because this was not part of any of the QRH procedures; but had I recycled the pack and had it turned back on; it would have mitigated the risk involved with the emergency descent.

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Original NASA ASRS Text

Title: CRJ Captain reported that during climb and single pack operation; the remaining pack failed causing a return to the departure airport.

Narrative: We were single pack operations. On departure; we took off bleeds closed; leveled off at 6;000 feet and followed the MEL Operational Procedure to swap the bleed air source to the right engine. This was accomplished successfully without any issues. We continued our climb to our cruise altitude of FL250 and upon climbing through FL200; we noticed that the right pack (the only operational pack) had shut off and the cabin altitude was climbing at a fast rate. We immediately stopped climbing; and we began a descent to 10;000 feet as I [advised ATC] and told them that we were experiencing pressurization problems. We both donned our oxygen masks and established communications. I told the First Officer to continue flying the descent and take the radios while I ran the QRC and QRH procedures for Emergency Descent. We reached 10;000 feet and we both came off of O2. We requested a turn back to ZZZ and also requested a lower altitude to decrease cabin altitude and we were cleared to descend to 6;000 feet As I was running the QRH Emergency Descent procedure; we were descending through 9;000 feet and the cabin altitude was still below 9;000 feet so I made the choice not to deploy the Passenger Oxygen masks.After wrapping up the QRH procedure; I called the Flight Attendant with the Emergency button and briefed her on the nature of the [situation] but told her that everything was under control and that we would be returning to ZZZ and landing in 15 minutes; there would be no need for brace positions on landing; it would be a routine approach and landing; and to secure the cabin for landing. I also asked the Flight Attendant if anyone was injured or was feeling ill and she replied that everyone was doing good and everyone was seated with their seatbelts on. I made a passenger announcement and briefed the passengers that we were returning to ZZZ. I finished running the Unpressurized Flight procedure in the QRH and then began helping to prepare for the approach and landing into ZZZ. Since the FO (First Officer) had been flying this whole time; we discussed that the he would continue flying and make the landing. I then briefed the approach. We ran a descent check and conducted the approach and landing as planned with no issues. ARFF (Aircraft Rescue and Firefighting) was waiting alongside the runway for our arrival and communicated with us as we vacated the runway. They asked if we had any injuries and we called the Flight Attendant again to verify no injuries and this was confirmed. After we shut the engines down at the gate and ran the shutdown check; I made a PA announcement in front of the passengers and explained what all happened and why we returned to ZZZ; and also asked one last time if anyone was feeling hurt or ill. EMS (Emergency Medical Services) waited in the jet bridge just in case anyone wished to seek medical attention; but nobody did. Aircraft was then written up and maintenance was called.We are not sure what caused the Right pack to shutoff. Never received any PACK HI TEMP or PACK HI PRESS caution messages and right pack was operated in automatic temperature control mode the entire flight.Looking back on the event; we are trained to begin an emergency descent immediately once we realize the aircraft is not being pressurized; and we did this; however; after reviewing the events; I realized I did not try recycling the R pack. Not necessarily a mistake because this was not part of any of the QRH procedures; but had I recycled the pack and had it turned back on; it would have mitigated the risk involved with the emergency descent.

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.