NFPA 99 defines the medical gas systems for all healthcare facilities based on a number of factors all related to the safety of the patients who are connected to them. Each medical gas “system” from the source equipment to the outlet/inlet termination point can be placed into one of three categories or “levels”. The least stringent requirements are applicable to Level 3 facilities which are typically (but not necessarily always) dental facilities.

One of the requirements for the oxygen and nitrous oxide piping systems for Level 3 facilities is that the line sizes for each of these gases be different so as to clearly distinguish separation of the piping systems as they are routed throughout the facility. Para. 5.3.10.10.3 of the 2005 edition of NFPA 99 dictates a minimum line size of (NPS 3/8” or ½” OD) for oxygen systems and (NPS ¼” or 3/8” OD) for nitrous oxide systems. The intent of this distinction is to prevent cross connection of these two gases as explained in Para. A.5.3.10.10.3.  Most of these source systems (manifolds) are manufactured as a common enclosure for both gases, with two copper feed lines extending out from the top of the enclosure.  Sometimes these feed lines are the same line size, which can be confusing, especially if these lines are not correctly labeled.

Recently, (March 2009) a terrible accident occurred in Togonoxie, KS when a patient in a dental office was given nitrous oxide gas instead of oxygen, as a practitioner intended.  According to news reports, this mistake was due to the “incorrect connection of the medical gas lines.” The full article on this medical gas mishap can be viewed at: http://www2.ljworld.com/news/2009/apr/22/medical-gas-accident-may-lead-policy-change/