Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Total 20563
Human-Machine Interface; Situational Awareness; Troubleshooting
Aircraft Equipment Problem Less Severe; Flight Deck / Cabin / Aircraft Event Illness / Injury
Flight Crew Became Reoriented; Flight Crew Landed in Emergency Condition; General Physical Injury / Incapacitation
Aircraft
After a 1R door slide replacement by Maintenance; the number 1 Flight Attendant had trouble arming the 1R door at the gate. Maintenance was called. Maintenance found a broken piece of dish under the arming lever. After the piece was removed; the door was able to be armed; but the arming lever was more difficult than usual to move. Maintenance signed off the 1R door arming lever as operational and we departed. After takeoff; at about 500 feet the number 1 Flight Attendant called the flight deck and told us that he had a flashing cabin pressurization warning light. He was told to standby while the flight crew continued to fly and identify the problem. The 1R door armed light was found to be extinguished. The aircraft was leveled at 10;000 feet for analysis. After determining there was no issue with the aircraft pressurization system and that the problem was likely associated with the arming issue experienced at the gate; we elected to continue the flight as planned.The flight attendants were notified along with an explanation as to what was occurring. Approximately 10 minutes after leveling at cruise at 36000 feet; the number 1 Flight Attendant called to inform us that the other two flight attendants were experiencing symptoms of hypoxia. The cabin altitude at 36000 feet was approximately 7100 feet and holding stable with no adverse pressurization indications. A lower altitude of 24000 feet was immediately requested and obtained. After leveling at 24000 feet; the Captain checked on the flight attendants. The Captain was informed that their symptoms were worsening. We immediately [advised ATC].  The portable O2 bottles were used by each affected flight attendant; an onboard doctor began monitoring the situation; and the paramedics were requested to meet us at the gate. Upon arrival at the gate; their symptoms had subsided and the flight attendants reported fit for duty for their next leg. This event occurred due to an equipment failure in flight. If the door arming lever would not have changed status to 'disarmed' after takeoff; this event would not have occurred.I recommend informing both Maintenance and flight attendants that if a door arming lever is difficult to move after a slide replacement; even if the door is able to be armed; do not take the aircraft. The aircraft should be removed from service until the arming lever not only arms; but also moves with the normal amount of force application.
[Report narrative contained no additional information.]
Air carrier flight crew reported a cabin pressure issue and flight attendants experiencing hypoxia.