Category 2 Dental Gas Relief Valves

  • Tuesday, July 08, 2025 12:26 PM
    Quote
    Message # 13518589
    David Osborn

    We had a situation arise recently during a certification inspection on a new dental facility. The situation involved the design team, the facility owners, the county plumbing inspector, and us. The issue was about the necessity of running the pressure relief valves for the O2 and N2O outside of the building. I and my team poured through the NFPA 99, 2021 (this particular county adopted 2021 a couple of years ago, ahead of the rest of the state) Chapter 15 to ensure that none of us were missing anything, but we found that a category 1 dental facility has the following requirement:

    15.3.2.1.4 Central Supply Systems: Category 1 systems shall comply with 5.1.3.5 


    If we look at 5.1.3.5, especially in 5.1.3.5.6.1(4) (talking about relief valves), it states, "They shall be vented to the outside of the building, except that relief valves for compressed air systems having less than 84,950 L (3000 ft3) at STP shall be permitted to be diffused locally by means that will not restrict the flow."


    The problem that we have is that this is a Category 2 Dental facility though! If we look at the requirements for Category 2 in 15.4.2.5.5 and 15.4.2.5.6, it doesn't have any requirement to have the relief valves vented to the outside of the building. There is no reference to comply with Chapter 5 either. 


    My question is, why not? We are talking about the same gases (Oxygen and Nitrous Oxide), the same volume, and the same issues of potential explosion hazards and even asphyxiation hazards if enough N2O is released. We referenced 15.2: Nature of Hazards of Gas and Vacuum Systems: "Potential fire and explosion hazards associated with positive-pressure dental gas systems and vacuum systems SHALL be considered in the design, installation, testing, operation, and maintenance of these systems". in our response to the design team and facility owner's objections to paying for 8' of 1/2" pipe being ran. Does anyone have any other references to help combat the usual cheap is better than safe mentality we see too often within the dental world?


    Thanks in advance for your consideration!

     
  • Wednesday, July 09, 2025 8:51 AM
    Quote
    Reply # 13518961 on 13518589
    Cary Darden (Administrator)

    Hi Dave,


    I agree with you that NFPA 99 is silent on the question of Category 2 dental oxygen & nitrous oxide manifold relief valves having to be vented outdoors.  This has been the case going back to when all of the dental requriements came from chapter 5 in section 5.3.  The language in 5.3.6.21.5 & 5.3.6.21.6 (2012 edition) is exactly the same in 15.4.2.5.5 & 15.4.2.5.6 (2024 edition).  


    I know in the case of medical air there has always been an exception for having to vent reliefs outdoors if the total amount of gas is < 3000 cu. ft.  I have a vague recollection of a conversation or maybe an old presentation that used that same logic for oxygen / N2O in a dental setting.  Maybe someone else can remember more specifics on that, or it is possible I am making a connection that never existed.  


    A quick look at a couple of the installation manuals from manufacturer's who make these Cat 2 dental manifolds has wording that calls piping those relief ports outside as optional, not mandatory.  So the manufacturer's also agree that NFPA 99 isn't mandating it.


    The question of "Should it be done" is MGPHO should discuss.  Typical Cat 2 dental manifold rooms like this will have (2) oxygen cylinders and (2) N2O cylinders.  That equals a total of about 1500-2000 cu. ft. of gas depending on if those cylinders are all H or K size. 


    In a Cat 1 installation there will be double the amount of cylinders, (4) oxygen and (4) N2O, which will put the facility right at the 3000 cu. ft. threshold.  I'm not sure if this math makes any practical sense as far as the need to vent the reliefs outdoors or not, but it is the only item I can find the could be reasonably responsible for when to turn the outdoor venting requirement on or off.
  • Monday, July 14, 2025 9:08 AM
    Quote
    Reply # 13520478 on 13518589
    Corky Bishop

    Many of the relief valves on dental manifolds are not threaded to attach any vent piping.  That was why it was important to reintroduce the paragraph about venting the room to the outdoors.

    NFPA 99, 2024; 15.4.2.4.4  Natural or mechanical ventilation for oxygen and nitrous oxide manifold locations shall be in accordance with 9.3.6.5.

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