Announcement

Collapse
No announcement yet.

Precedence of Emergency Branches

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Precedence of Emergency Branches

    Why does the Life safety branch take precedence over the critical branch? And why call it critical when it is truly life supporting over all else? Id think ventilators would need power first and before all else.



    Hospitals require a large amount of emergency power because lives depend on the ability of many services in the hospital to remain functional at all times. As described previously, code requires that the emergency power is segregated into four different branches. When the generator starts up, the power branches are started sequentially to prevent the generator from being overloaded by all systems starting at once. The life safety branch starts first, followed by the critical power, the equipment, and finally the X-ray branch. Now that the X-Ray is served by a UPS, there will be no problems with starting this last.

    #2
    possibly 517.42 is some help Mr MBrooke......but even that gets off on a tangent>

    Informational Note No. 2: For more information see NFPA
    99-2015, Health Care Facilities Code.
    ~RJ~

    Comment


      #3
      Originally posted by romex jockey View Post
      possibly 517.42 is some help Mr MBrooke......but even that gets off on a tangent>



      ~RJ~
      I'll give that a look.

      Comment


        #4
        Originally posted by romex jockey View Post
        possibly 517.42 is some help Mr MBrooke......but even that gets off on a tangent>



        ~RJ~
        Explain, All I'm reading is limited care facilities.

        Comment


          #5
          Originally posted by mbrooke View Post
          Why does the Life safety branch take precedence over the critical branch? And why call it critical when it is truly life supporting over all else? Id think ventilators would need power first and before all else.
          IMO the life safety branch is focused on supplying loads that are needed to evacuate the building when it is not safe to stay in the building. If a hospital is on fire the patients on life support will need to be evacuated and connection to life support systems would not really matter.

          Comment


            #6
            Originally posted by packersparky View Post
            IMO the life safety branch is focused on supplying loads that are needed to evacuate the building when it is not safe to stay in the building. If a hospital is on fire the patients on life support will need to be evacuated and connection to life support systems would not really matter.
            That's also my thinking. Needs of the many (to move around and maybe get out) over needs of the few.

            Comment


              #7
              Originally posted by packersparky View Post
              IMO the life safety branch is focused on supplying loads that are needed to evacuate the building when it is not safe to stay in the building.
              That notion had never occurred to me. But looking at the list of the only things that are allowed to be on the LS branch, in 517.32(A) through (H), it makes sense. Thanks for sharing.

              Charles E. Beck, P.E., Seattle
              Comments based on 2017 NEC unless otherwise noted.

              Comment


                #8
                Originally posted by packersparky View Post
                IMO the life safety branch is focused on supplying loads that are needed to evacuate the building when it is not safe to stay in the building. If a hospital is on fire the patients on life support will need to be evacuated and connection to life support systems would not really matter.



                But I don't see a fire today getting that large to the point where 1,500 patients need to be evacuated.


                Originally posted by charlie b View Post
                That notion had never occurred to me. But looking at the list of the only things that are allowed to be on the LS branch, in 517.32(A) through (H), it makes sense. Thanks for sharing.


                What year did the code mandate the separation of the life safety and critical branch? And idea of the substantiation? I remember old hospitals just mixed the two branches- at least in practice.

                Comment


                  #9
                  Originally posted by mbrooke View Post
                  Why does the Life safety branch take precedence over the critical branch? And why call it critical when it is truly life supporting over all else? Id think ventilators would need power first and before all else.
                  I've wondered about that a lot also. Only the LS branch has to comply with the stricter requirements in 700. So its obviously considered more important.

                  Originally posted by packersparky View Post
                  IMO the life safety branch is focused on supplying loads that are needed to evacuate the building when it is not safe to stay in the building. If a hospital is on fire the patients on life support will need to be evacuated and connection to life support systems would not really matter.
                  Hospitals are usually designed with a "defend in place" strategy for a fire event, since some patients can't be moved.

                  So I would probably add to that statement that the LS branch is also to provide things like emergency lighting needed to assist fire fighting and emergency operations.

                  BTW, I'm not sure, but I think ventilators are more commonly powered by compressed medical air. So it makes sense to have the Med Gas Alarm panels on the LS branch.

                  I've heard tale of a contractor that cut a medical air line, and the havoc that wrought. Nurses had to use the masks with the squeeze bulbs on them to keep patients breathing.

                  Also, would guess any electric ventilators would probably also have battery backup.

                  Comment


                    #10
                    Originally posted by steve66 View Post
                    I've wondered about that a lot also. Only the LS branch has to comply with the stricter requirements in 700. So its obviously considered more important.



                    Hospitals are usually designed with a "defend in place" strategy for a fire event, since some patients can't be moved.

                    So I would probably add to that statement that the LS branch is also to provide things like emergency lighting needed to assist fire fighting and emergency operations.

                    BTW, I'm not sure, but I think ventilators are more commonly powered by compressed medical air. So it makes sense to have the Med Gas Alarm panels on the LS branch.

                    I've heard tale of a contractor that cut a medical air line, and the havoc that wrought. Nurses had to use the masks with the squeeze bulbs on them to keep patients breathing.

                    Also, would guess any electric ventilators would probably also have battery backup.

                    Honestly, it would actually make sense if hospitals just required two equal branches. Failure of an ATS or branch results in all critical load being dropped or all life safety load being dropped. Mandating a few receptacles on normal power is silly when a blackout is causing it.


                    Regarding ventilators they are electric powered, but use piped medical gas (oxygen / air) instead of the air inside the critical care area.

                    Comment


                      #11
                      Originally posted by mbrooke View Post
                      But I don't see a fire today getting that large to the point where 1,500 patients need to be evacuated.

                      What year did the code mandate the separation of the life safety and critical branch? And idea of the substantiation? I remember old hospitals just mixed the two branches- at least in practice.
                      Hospitals are intended to be "defend in place" facilities, but in worst case scenarios it may be needed to evacuate a part or all of the building. The loads supplied by the life safety branch help facilitate evacuation.

                      http://www.paho.org/disasters/index....id=924&lang=en


                      Article 517 first appeared in the 1971 NEC and required separate branches. Before that there was just an article called "Flammable Anesthetics"
                      Last edited by packersparky; 06-20-19, 02:51 PM.

                      Comment


                        #12
                        Originally posted by packersparky View Post
                        Hospitals are intended to be "defend in place" facilities, but in worst case scenarios it may be needed to evacuate a part or all of the building. The loads supplied by the life safety branch help facilitate evacuation.

                        http://www.paho.org/disasters/index....id=924&lang=en


                        But worst case such a rarity that it must be weighed against the higher probability of loosing a critical feeder or system.

                        Comment


                          #13
                          Originally posted by mbrooke View Post
                          Why does the Life safety branch take precedence over the critical branch? And why call it critical when it is truly life supporting over all else? Id think ventilators would need power first and before all else.
                          Both the Life Safety and Critical branch are the same priority. Upon loss of power, the generator must start and pick up both branches within 10 seconds. Neither branch may be shed. The Life Safety branch feeds the loads necessary to evacuate the hospital. The Critical branch feeds the loads necessary to keep people alive in the hospital. The branches are separated to increase reliability. The more loads you add to any branch, the greater the chance that something will fail.

                          Comment


                            #14
                            Originally posted by d0nut View Post
                            Both the Life Safety and Critical branch are the same priority. Upon loss of power, the generator must start and pick up both branches within 10 seconds. Neither branch may be shed. The Life Safety branch feeds the loads necessary to evacuate the hospital. The Critical branch feeds the loads necessary to keep people alive in the hospital. The branches are separated to increase reliability. The more loads you add to any branch, the greater the chance that something will fail.
                            Regarding the last part if more load meant greater chance of failure we would be talking about loading restrictions or restrictions on the max size equipment that could be used.

                            Comment


                              #15
                              True. I guess I wasn't clear with what I was thinking. If you limit the loads to only certain loads as stated in 517 and NFPA 99, you will reduce the chance that other items may be added in the future that compromise the system, such as a large motor with an inrush that may trip an upstream circuit breaker. The life safety branch and critical branch serve such important purposes that we are limited to only specific loads that can be added.

                              From a practical standpoint, the actual loading on those two branches is somewhat limited as well based on the permitted loads, conductor lengths, building size, etc. I rarely end up with a life safety system over 100A, for example.

                              Comment

                              Working...
                              X