Narrative:

While at cruise we noticed that it was CAT 2 ILS minimums into ZZZ. We briefed the CAT 2 while in cruise. At about 30 miles from zzzzz; we were asked if we were CAT 2 capable at 1000 ft RVR. We told center; we are limited to 1200 ft RVR. ATC then instructed us to hold at zzzzz. After setting up the hold; communicating with dispatch and calculating our bingo fuel to leave the hold; I asked the flight attendant (flight attendant) if I could use the restroom. Just prior to me leaving the flight deck; the first officer (first officer) pulled out his oxygen mask and it began to leak; after seeing there was a tear in the line the first officer realized he was not going to stop the leak. I told the flight attendant to hold off on me going back. Just then center asked if we could do 1200 ft RVR CAT 2 and then cleared us to ZZZ via the arrival and to descend via the [arrival]. I pulled up the oxygen page on the mfd; the oxygen was quickly draining out of our bottle. I pulled out the QRH and looked in the index for oxygen leak. Not seeing anything in the index related to that I assumed there was no procedure for it. I asked center if we could get priority descent. The controller took us off the 'descend via' and gave us decent to 12000 ft and then 6000 ft within 60 seconds. I looked at our alternate and noticed that they had us planned at FL210; with the oxygen running out; we were limited to 10000 ft. I texted dispatch about the leak and asked for an alternate that was closer. The dispatcher came back with ZZZ1 as our new alternate. The first officer and I both agreed that would be much better. Shortly thereafter we got oygen lo press; I went back to the QRH and ran this checklist. By this time we were now at 6000 ft about to intercept the localizer and the first officer realized we had not yet run the arrival checklist from the CAT 2 QRH procedure. I ran that checklist and we were cleared for the approach shortly afterwards. We broke out at minimums and landed the aircraft safely. At the gate we called maintenance. The first one to show up asked us what the pressure was. I told him it was around 10 psi; and he mentioned that below 40 psi they have to replace the entire bottle. We explained to him where the leak was coming from and I wrote up the discrepancy in the [logbook].on our next leg; my first officer and I were discussing whether or not to report this incident. Seeing it was aircraft damage; we figured it would fall under a mandatory reporting event. In discussing the events and replaying them back in our head; I was looking at the QRH and realized that there is a procedure for oxygen leak; because we were so busy I did not even see the checklist directly below the oxygen lo press. In reading this checklist it would have had us shut off the oxygen cylinder behind the first officer. In looking at the QRH after the fact; I see in the index; oxygen leak under unannunciated procedures (no EICAS message). Once the leak started; I now realized that I overlooked the proper procedure in the index because I was task saturated with holding instructions; fuel concerns; alternate concerns; having the minimum RVR for the CAT 2 approach; communicating with dispatch; my crew and ATC and switching to a closer alternate due to the leak.furthermore; in studying the oxygen leak QRH procedure; one item that is very unclear and confusing is line number 5 which states: 'test and shutoff sliding control - actuate'the test 'button' is clear; but the shutoff sliding control; I assume that this is the valve on the back of the mask that you can twist from emergency; 100% to norm. This checklist would be clearer if it said; twist from 100% to emergency to norm. I can only assume this is to check and see if the button and or mask twisted to an abnormal position. A situation occurred which I had never seen before; oxygen leak. Very high task saturated situation; CAT 2 ILS minimums; fuel concerns; alternate concerns; altitude concerns; holding etc. I miss read the QRH index; and could not find the procedure for oxygen leak. Theoxygen was leaking and leaked out completely. One thing that would have helped me is using the tabs on the QRH. Had I just gone straight to the oxygen tab I would have immediately seen the oxygen leak checklist.

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Original NASA ASRS Text

Title: ERJ-145 flight crew reported an oxygen leak from the First Officer's mask and confusion with the QRH procedure.

Narrative: While at cruise we noticed that it was CAT 2 ILS minimums into ZZZ. We briefed the CAT 2 while in cruise. At about 30 miles from ZZZZZ; we were asked if we were CAT 2 capable at 1000 ft RVR. We told center; we are limited to 1200 ft RVR. ATC then instructed us to hold at ZZZZZ. After setting up the hold; communicating with dispatch and calculating our bingo fuel to leave the hold; I asked the FA (Flight Attendant) if I could use the restroom. Just prior to me leaving the flight deck; the FO (First Officer) pulled out his oxygen mask and it began to leak; after seeing there was a tear in the line the FO realized he was not going to stop the leak. I told the FA to hold off on me going back. Just then center asked if we could do 1200 ft RVR CAT 2 and then cleared us to ZZZ via the arrival and to descend via the [arrival]. I pulled up the oxygen page on the MFD; the oxygen was quickly draining out of our bottle. I pulled out the QRH and looked in the index for OXYGEN LEAK. Not seeing anything in the index related to that I assumed there was no procedure for it. I asked center if we could get priority descent. The controller took us off the 'descend via' and gave us decent to 12000 ft and then 6000 ft within 60 seconds. I looked at our alternate and noticed that they had us planned at FL210; with the oxygen running out; we were limited to 10000 ft. I texted dispatch about the leak and asked for an alternate that was closer. The dispatcher came back with ZZZ1 as our new alternate. The FO and I both agreed that would be much better. Shortly thereafter we got OYGEN LO PRESS; I went back to the QRH and ran this checklist. By this time we were now at 6000 ft about to intercept the LOC and the FO realized we had not yet run the arrival checklist from the CAT 2 QRH procedure. I ran that checklist and we were cleared for the approach shortly afterwards. We broke out at minimums and landed the aircraft safely. At the gate we called maintenance. The first one to show up asked us what the pressure was. I told him it was around 10 PSI; and he mentioned that below 40 PSI they have to replace the entire bottle. We explained to him where the leak was coming from and I wrote up the discrepancy in the [logbook].On our next leg; my FO and I were discussing whether or not to report this incident. Seeing it was aircraft damage; we figured it would fall under a mandatory reporting event. In discussing the events and replaying them back in our head; I was looking at the QRH and realized that there is a procedure for OXYGEN LEAK; because we were so busy I did not even see the checklist directly below the OXYGEN LO PRESS. In reading this checklist it would have had us shut off the oxygen cylinder behind the FO. In looking at the QRH after the fact; I see in the index; OXYGEN LEAK under UNANNUNCIATED PROCEDURES (NO EICAS MESSAGE). Once the leak started; I now realized that I overlooked the proper procedure in the index because I was task saturated with holding instructions; fuel concerns; alternate concerns; having the minimum RVR for the CAT 2 approach; communicating with dispatch; my crew and ATC and switching to a closer alternate due to the leak.Furthermore; in studying the OXYGEN LEAK QRH procedure; one item that is very unclear and confusing is line number 5 which states: 'Test and Shutoff Sliding Control - ACTUATE'The test 'button' is clear; but the Shutoff Sliding Control; I assume that this is the valve on the back of the mask that you can TWIST from EMER; 100% to NORM. This checklist would be clearer if it said; TWIST from 100% to EMER to NORM. I can only assume this is to check and see if the button and or mask twisted to an abnormal position. A situation occurred which I had never seen before; oxygen leak. Very high task saturated situation; CAT 2 ILS minimums; fuel concerns; alternate concerns; altitude concerns; holding etc. I miss read the QRH index; and could not find the procedure for OXYGEN LEAK. Theoxygen was leaking and leaked out completely. One thing that would have helped me is using the TABS on the QRH. Had I just gone straight to the OXYGEN TAB I would have immediately seen the OXYGEN LEAK checklist.

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.