Narrative:

Event began with phone conversation to [maintenance] from hotel prior to walking to the airport. Subject inbound writeup at XA08 to ZZZ low oxygen quantity. I was told the jet was just blocking in (XA43) our departure was at XB50. I arrived at the jet at approximately XB25; after going by flight operations for planning.I discovered the O2 hadn't been serviced and displayed 970 psi. I immediately called maintenance and requested servicing as the visibility was now 1/2 mist; and our takeoff alternate was ZZZ2. Having a basic understanding of the crew oxygen system dispatch limits 850/550 psi and other [company] publications that quantifies the dispatch limit that states a crew has approximately 15 minutes of O2 in case of cockpit smoke; I concluded - based on takeoff weather/takeoff alternate; and enroute planning where we would be on the hose from airborne to ground rollout; the safest and most prudent and course of action would be to have the O2 serviced. I continued with preflight duties while monitoring the maintenance frequency. A few minutes later; maintenance told me they weren't going to service the O2; because they would have to deplane our passengers.I told them that I didn't think this was the correct procedure; and I immediately called maintenance. He said a [report] would be initiated. At that point I sent a [maintenance request] at XB41 (9 mins before scheduled departure and due to maintenance's request as mentioned earlier; I had notified ZZZ maintenance approximately 16 minutes prior to this. In the end; ZZZ maintenance made the decision to deplane everyone. In the end; we deplaned; serviced system; reboarded and departed 55 minutes late.47 minutes into the flight we had already lost 110 psi; noted on an info only write up.as a side note; existing ZZZ2 weather and takeoff alternate aside; actual enroute data placed us 4nm on top of ZZZ3 at FL320. Using ZZZ3 as the closest airport would require 18 minutes leaving us with a possible 3 minute deficit and all of this in a perfect world.

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Original NASA ASRS Text

Title: A320 Captain reported issues between the aircraft advisory display; maintenance limits and dispatch limits for servicing the crew oxygen system.

Narrative: Event began with phone conversation to [Maintenance] from hotel prior to walking to the airport. Subject inbound writeup at XA08 to ZZZ Low Oxygen Quantity. I was told the jet was just blocking in (XA43) our departure was at XB50. I arrived at the jet at approximately XB25; after going by Flight Operations for planning.I discovered the O2 hadn't been serviced and displayed 970 psi. I immediately called Maintenance and requested servicing as the visibility was now 1/2 mist; and our takeoff alternate was ZZZ2. Having a basic understanding of the Crew Oxygen System dispatch limits 850/550 psi and other [company] publications that quantifies the dispatch limit that states a crew has approximately 15 minutes of O2 in case of cockpit smoke; I concluded - based on takeoff weather/takeoff alternate; and enroute planning where we would be on the hose from airborne to ground rollout; the safest and most prudent and course of action would be to have the O2 serviced. I continued with preflight duties while monitoring the Maintenance frequency. A few minutes later; Maintenance told me they weren't going to service the O2; because they would have to deplane our passengers.I told them that I didn't think this was the correct procedure; and I immediately called Maintenance. He said a [report] would be initiated. At that point I sent a [Maintenance Request] at XB41 (9 mins before scheduled departure and due to Maintenance's request as mentioned earlier; I had notified ZZZ Maintenance approximately 16 minutes prior to this. In the end; ZZZ Maintenance made the decision to deplane everyone. In the end; we deplaned; serviced system; reboarded and departed 55 minutes late.47 minutes into the flight we had already lost 110 psi; noted on an info only write up.As a side note; existing ZZZ2 weather and takeoff alternate aside; actual enroute data placed us 4nm on top of ZZZ3 at FL320. Using ZZZ3 as the closest airport would require 18 minutes leaving us with a possible 3 minute deficit and all of this in a perfect world.

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.