Category 3 Warning / Alarms

  • Sunday, January 20, 2019 11:17 AM
    Message # 7011416
    Al Moon (Administrator)

    A true dental facility has a oxygen and nitrous oxide manifold system outside (i.e  the room is per code - just out the back door).

    In the main corridor of the facility is zone valve box for the oxygen & nitrous oxide. This box has single handle (i.e. when you pull it down both gases, oxygen & nitrous oxide are shut off)

    There is an alarm panel next to this zone off valve. Typical dental category 3 type alarm panel. FYI: the equipment is from a major supplier of dental oxygen & nitrous oxide systems.

    When the zone valve handle is shutoff and the gas lines are reduced to below 40 psig, this single only alarm panel provides an visual and audible signal. It also shuts off the gas manifold.

    Now the fun part:

    When you shut off the the zone valve box and then shut off the gases at the manifold (i.e. the cylinders) and drop the pressure in the lines between the zone valve box and gas manifold.

    There is NO alarm for the low main line pressure, that is listed in (1 & 4). 

    Is this per code ?

    Should we not have both main line alarm signals and zone valve box alarm signals ?  Category 3 Warning Systems.  Warning systems for medical gas systems (oxygen and nitrous oxide) in Category 3 facilities shall provide the following alarms: 

    (1) Oxygen main line pressure low

    (2) Oxygen main line pressure high

    (3) Oxygen changeover to secondary bank or about to changeover (if automatic)

    (4) Nitrous oxide main line pressure low

    (5) Nitrous oxide main line pressure high

    (6) Nitrous oxide changeover to secondary bank or about to changeover (if automatic)  Warning systems shall have at least one single alarm panel in each treatment facility served by the medical gas source equipment.  Alarm panels shall be located in an area of continuous surveillance while the facility is in operation.  Pressure switches/sensors that monitor main line pressure shall be mounted at the source equipment with pressure alarm indicators (lamp or LED) at the alarm panel.  Audible and noncancelable alarm visual signals shall indicate if the pressure in the main line increases or decreases 20 percent from the normal operating pressure.  Visual indications shall remain until the situation that caused the alarm is resolved.  Pressure switches/sensors shall be installed downstream of any emergency shutoff valves and any other shutoff valves in the system and shall cause an alarm for the medical gas if the pressure decreases or increases 20 percent from the normal operating pressure.  A cancelable audible indication of each alarm condition that produces a sound at the alarm panel shall reinitiate the audible signal if another alarm condition occurs while the audible signal is silenced.

    Last modified: Monday, January 21, 2019 2:12 PM | Al Moon (Administrator)
  • Wednesday, January 23, 2019 9:14 AM
    Reply # 7073587 on 7011416  Pressure switches/sensors shall be installed downstream of any emergency shutoff valves and any other shutoff valves in the system and shall cause an alarm for the medical gas if the pressure decreases or increases 20 percent from the normal operating pressure.

    This was discussed at the last meeting with Dan Shoemaker.  He believes, as do I, that no sensors shall be upstream of any valves.  He told a story of a valve under the cabinet that was half closed and they had a patient needing oxygen due to a cardiac arrest (?).  And they couldn't get the flow rates they needed due to a valve being shut...They had to drag the patient down the hall to another room to give them oxygen.  He stated no valves should be allowed where they can shutoff they supply without an alarm / sensor going off.

  • Wednesday, January 23, 2019 3:09 PM
    Reply # 7090536 on 7011416


    To answer your question directly: There should be two sets of alarms in the scenario you described.  One set after the "Source Valve" and one after the "Zone Valve". basically says: Valve = Alarm Sensor Downstream (Patient Side).  As Jonathan already stated Dan Shoemaker awoke me to this.  He had a great presentation and that story about the quarter turn valves at the point of use has always stuck with me.  


  • Monday, January 28, 2019 11:12 AM
    Reply # 7133286 on 7011416

    Hi Al,

    You have described a remotely located manifold serving a single treatment facility.  This arrangement involves 5 extra requirements:

    1.  Lock the manifold room door.

    2.  Install an Emergency Shutoff Valve for O2 & N2O that is accessible from all use points.

    3.  Provide an automatic switching manifold.

    4.  Provide Changeover to Secondary alarm signals.

    5.  The High/Low switches must be on the patient side of the emergency shutoff valves.

    The NFPA 99, 2012 edition is easiest to find these rules in 5.3.  

    Keep it simple Al.  None of these rules apply when the manifold is not remote.  Dental manifolds come with the High/Low pressure switches attached to the manifold.  A manifold that is not remote does not require any valves in the piping.  You close the cylinders instead.

    The valves mentioned are not called zone valves on purpose.  The Emergency Shutoff Valves are typically inside the same room or area as all of the use points (dental chairs).  They come with High/Low switches on the patient side of the valves.  See the attached diagram.  It shows the valve box and the wiring.

    The goal of requiring alarms downstream of all valves was to discourage installing ball valves at each chair.  It might have been better understood to have prohibited valves at the use points and required demand check outlets (DISS).

    My final answer is that Al described a perfectly compliant Category 3 Dental med gas system. 

    Of course, in the new 2018 chapter 15.4 Dental section, it is now called Category 2.  ;-)

    Last modified: Monday, January 28, 2019 11:15 AM | Corky Bishop
  • Monday, January 28, 2019 9:29 PM
    Reply # 7134338 on 7011416
    Al Moon (Administrator)

    Not all dental equipment supplier do it the same:

    The scenario I listed was real and via Porter 

    check out page 35 & 36

    Last modified: Monday, January 28, 2019 9:34 PM | Al Moon (Administrator)
  • Tuesday, January 29, 2019 5:12 PM
    Reply # 7135981 on 7011416

    Page 34 is where the more expensive automatic switching manifold is.  That is the one to use for a remotely located dental manifold.  Notice there is no source valve, only the emergency shutoff (zone) valve inside the space.  

    This valve is similar to the main valve inside a hospital for a bulk oxygen system.  Your pressure switch is to be located on the patient side of the main valve if it exists, right?  You don't put in 2 sets of pressure switches, one for the underground main and the other for the piping inside the hospital.

    The attached diagram you referred to on page 36 is perfectly compliant for a category 3 dental system with a remotely located manifold.  Notice the manifold room is not attached to the office space.

  • Wednesday, January 30, 2019 8:06 AM
    Reply # 7136912 on 7011416
    Al Moon (Administrator)

    I totally disagree with your conclusion.

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