Area alarm

  • Monday, August 07, 2017 6:54 PM
    Message # 5017396

     You're doing an annual test at a hospital where the normal oxygen pressure is 55 psi. 

     You note that the area alarm does not activate when you put 60 PSI pressure to the sensor. 

     What should you do? 

    A)  Tell the hospital that their pressures high in their oxygen system and adjust the oxygen system appropriately. 

    B)  Note that there was a high alarm failure at 60 PSI in your report. 

    C)  Raise the pressure on the sensor till you get a high alarm and note the activation point. 

    D)  Notify the hospital that they need their system serviced in your report. 

  • Tuesday, August 08, 2017 7:29 PM
    Reply # 5019891 on 5017396

    E) Nothing

    *The high alarm would be required to activate at 66 psi if the normal line pressure is 55 psi (20% above). Wouldn't you bring the pressure up to that 66 psi to see if it activates? 

    Last modified: Tuesday, August 08, 2017 7:29 PM | Anonymous
  • Saturday, August 12, 2017 8:54 AM
    Reply # 5026327 on 5017396
    Al Moon (Administrator)



    Section #5.1.11 The normal pressures for Oxygen are 50-55 psig.

    So, 50 is normal, 51 is normal, 52 is normal,

    53 is normal, 54 is normal and 55 is also normal

    and within the standard code requirement.




    Section # Is the requirement for the area alarm 20% increase and decrease set points from the normal line pressure. That is the 50-55 psig range. COOL



    Section # The accuracy of the digital indicators in the area alarm panel can be off scale by (+ or - 5 percent) of the operating pressures.




    If a hospital has 50 area alarm panels and you do an annual on August 31 and the

    oxygen line pressure is 50 psig, the alarm set points are 40 and 60 psig.

    All is good right?

    Now on September 01 the hospital has a procedure to rotate the final line regulators each month and that regulator is set for 53 psig.

    Which is totally normal per #5.1.11.

    So are you going to tell hospital to go back and to all 50 alarms and re-set the hi and low set point? Remember to take in to account the + or - 5% differential at the area alarm digital read out.


    Is the hospital ready out of compliance ? 

    Are the patient ready in danger ?

    Is the equipment ready going to fail ?

    Are their any real mortality or morbidity case studies on this ? (i.e. a white paper)


    Conclusion In my opinion only.

    A oxygen system that is within the normal ranges of 50 to 55 psig,

    with the area alarm set at 40 psig low and 60 psig high is acceptable.



  • Saturday, September 09, 2017 5:36 AM
    Reply # 5071665 on 5017396
    Deleted user

    If an oxygen flow meter, ventilator, anesthesia machine, or other respiratory equipment deliver correct, steady flow between the 35 and 65 psi that would make the alarm pressure settings of 40 and 60 ideal.

  • Sunday, September 10, 2017 10:53 AM
    Reply # 5073150 on 5017396
    Al Moon (Administrator)

    Steve and I win:



    The effect on accuracy of flow due to variations in ambient temperature is standard accuracy +7.3% @ 32°F (0°C) and -3.0% @ 104°F (40°C). Most all USA flowmeters are calibrated at 50 psi (3.4 bar), 70°F (21°C), and standard atmospheric pressure.  

  • Sunday, September 10, 2017 7:33 PM
    Reply # 5073582 on 5017396

    I concede Al. 


    If we were to require master and area alarm set points to vary depending on pressures between 50 and 55psi, we would then have to say the line pressure relief valves would not meet code at 75psi since they are required to be 50% above normal line pressure. 


    Normal line pressure for oxygen 50-55psi, agreed. 

  • Sunday, September 17, 2017 2:30 PM
    Reply # 5265102 on 5017396

    Agree, gas systems with nominal operating pressure of 50 -55 psig are fine with alarm set points of 40 and 60 psig.

    This may be a good opportunity to briefly review how some respiratory care devises perform with changes in line pressure.

    Medical 02 and med air flowmeters are “back pressure compensated” to 50 psig and read accurately at 50 psig and their flow reading will vary if pressure changes. Back pressure compensated means the gas pressure within the flow tube is always under line pressure, even when turned off. This is why you may see the flowmeter ball raise and fall rapidly when pressure temporarily changes as when nearby ventilators start their inspiratory cycle, particularly when the flowmeter is turned off. Will flowmeter flow readings change if pressure varies within the 40 to 60 psig range? Yes. Is it clinically significant? Probably not.

    Ventilator inlet pressure requirements can vary somewhat from manufacturer to manufacturer and model to model, but generally will function as designed within the 40 and 60 psig range, but this should be verified for a specific vent. Flow, 02 concentration, and occasionally other parameters can vary as 02 and air inlet pressures change in relation to each other. Clinically significant within the 40 to 60 psig range? Maybe, maybe not.

    Oxygen/air mixers (blenders) are devices separate from ventilators, used to control a precise and constant oxygen concentration to patients. Their range is 21 to 100% 02. These devises will typically give the set 02 concentration, within their stated accuracy, provided the difference between 02 and air inlet pressures are within +/- 20 psig of each other. This is providing the devices receive periodic maintenance (including replacing internal components) as required by the manufacturer.

    Typically, ventilators and blenders will alarm when line pressure variation is significant.

    George Scott

    Last modified: Sunday, September 17, 2017 2:42 PM | George Scott
  • Friday, December 29, 2017 9:05 PM
    Reply # 5653100 on 5017396

    George wins!

    Back pressure of 50 - 55 psig assists in keeping all flowmeter literflow markings and FiO2 range indicators within 10% of accuracy. Something the RTs are required to monitor directly with analyzers as part of their patient care due diligence.

    Regarding the setting of the +20% of working pressure setting for high and low alarms on area alarm panels I have a few questions.

    Isn't the intent of NFPA 99 to set a minimum standard? 

    Isn't that standard here 20% of working pressure?

    That means a working pressure of 55 psig and a low alarm setting of 40 psig is now 27% below the working pressure.

    How can that ever meet this standard when there is a clear numeric limit of 20%?

    How about this possibility:

    1. Set all area alarm low settings at 45 psig and high alarm settings at 60 psig. 

    2. When the working pressure is 50 psig then the low is 10% below (more strict than code at 45 psig) and the high is 20% (minimum code standard at 60 psig). 

    3. When the working pressure is 55 psig then the high is 10% above (more strict than code at 60 psig) and the low is 20% (minimum code standard at 45 psig).

    You will never have to adjust the alarm High and Low settings again. If either setting goes outside the code required minimum of 20% it is because the line pressure of the gas monitored is outside the code required working pressure range.


16339 Kranker Drive, Stilwell, KS 66085