Safe Gas Systems and Office-Based Anesthesia

Jonathan L. Wong, DMD, and Gerhard Gschwandtner, PEng

Current Trends in Outpatient Anesthesia

Figure 1: Outpatient office where anesthesia can be delivered.

Outpatient sedation and anesthesia is nothing new. Ambulatory surgical centers are commonplace and widely accepted as a safe, convenient, and cost-effective means of delivering surgical care. Off-site anesthesia in locations remote to the operating room is also becoming increasingly prevalent. Office-based anesthesia (Figure 1) qualifies as a remote location and continues to grow in obstetrics and gynecology, plastic surgery, fertility clinics, ophthalmology, gastroenterology, and dentistry.

Dentists pioneered many of the techniques of anesthesia in an outpatient setting and were at the forefront of office-based anesthesia as well. So why are dental offices under such criticism? One major reason is that many dentists and oral surgeons continue to practice as operator anesthetists without adequate training of their support personnel and a lack of appropriate equipment. This was the basis of the unfortunate circumstances in California that led to the proposal of Caleb’s Law after six-year-old Caleb Sears died during anesthesia administered by his oral surgeon. However, several of the recent public tragedies in dental offices have involved separate anesthesia professionals. These clinicians include physician anesthesiologists, certified registered nurse anesthetists (CRNAs), and dentist anesthesiologists. One of the possible causes of morbidity and mortality is the lack of safety checks in dental offices. One such safety check that is almost entirely overlooked is that of the medical gas system.

NFPA and NFPA 99

The National Fire Protection Association (NFPA) is a global nonprofit organization, established in 1896, devoted to eliminating death, injury, and property and economic loss due to fire, electrical, and related hazards. It is widely known as a codes and standards organization that continually updates codes on a three- to five-year cycle in a process that is open and consensus-based. Technical committee members are typically volunteers. As Mr. Rusty Chase, a fire marshal, certified fire inspector, and paramedic, stated, “Many code items are developed to address issues that have severely injured or killed people in the past (personal communication).”

NFPA 99 is the Healthcare Facilities Code. It is updated every three years. NFPA 99 is the national code (American National Standards Institute or ANSI) for all medical and dental gas installations in the United States. It is also adopted by reference in the International Plumbing Code and International Fire Code, which are the basis for a majority of state and local building codes (these vary by locality).

Many anesthesiologists, nurse anesthetists, oral and maxillofacial surgeons, and dentists mistakenly believe that the NFPA 99 is merely about fire safety. This is a misconception. NFPA is actually about patient safety and prevention of medical gas mistakes.

Figure 2: Zone Valve Box: A – 3 piece full port shut-off valve, B – Zone Valve Assembly label, C – Patient side vacuum/pressure indicator gauge.

NFPA 99 contains the minimum requirements for piped gas systems, equipment, materials, alarms, installations, testing, verification, and maintenance. The requirement applies to all health care facilities in the U.S., including hospitals, outpatient facilities, clinics, medical offices, and dental offices. Since at least 1996, NFPA code has required dental offices providing sedation and anesthesia to be compliant with these minimum standards.

NFPA 99 defines 3 categories (previously called levels) of medical and dental gas systems (Table 1). These categories define the specific minimum requirements for each system. The assessment of which category a facility or dental office falls under is based on a risk assessment and not by facility type or occupancy permit. NFPA has assigned certain depths of anesthesia and sedation to each of its three categories. The NFPA adopts the definitions of minimal, moderate, and deep sedation and general anesthesia from the American Society of Anesthesiologists’ “Continuum of Depth of Sedation” Guideline.1 In addition, the above definitions were reiterated and both minimal and moderate sedation further described in the latest Practice Guidelines for Moderate Procedural Sedation and Analgesia.2

These designations also do not change even if such services are only offered on a nonroutine basis. The designations do not change even if fewer than four individuals could be incapacitated at the same time. There is a popular misconception that dental offices do not need to comply with NFPA 99. This misconception may stem from the NFPA 101 Life Safety Code, which relates to occupancy and applies when four or more individuals could be incapacitated (under or recovering from sedation/anesthesia) at the same time; an office is not exempt from following the NFPA 99 guidelines.

Table 1: NFPA 99 Categories of Medical/Dental Gas Systems

NFPA 99 2018 Edition
Category Type Category 3 Category 2 Category 1
Permissable Depth of Anesthesiaa Nitrous anxiolysis and minimal sedation Moderate sedation Deep sedation and general anesthesia
Zone Valvesb Required No Yes Yes
Zone Alarms Required No Yes Yes
Master Alarm Panel Yesc Single Duald
Controls for Line
Per manufacturer Maintain stable pressure and flow for peak demand Maintain stable pressure and flow for peak demand
Vacuum System Dental vacuum Simplexe Duplex,d,e separate from dental vacuum
Waste Anesthetic Gas Scavenging None Nitrous scavenging may run through dental vacuum system Separate Waste Anesthesitic Gas Disposal (WAGD) and medical vacuum from dental vacuum
Testing and Verification In dental offices using dental gas systems, follow local code and manufacturer specs American Society of Sanitary Engineers (ASSE) 6030 3rd Party Verifier American Society of Sanitary Engineers (ASSE) 6030 3rd Party Verifier
Installation Brazed, soldered, or fitted joints Brazed with nitrogen purge Brazed with nitrogen purge
Reserve Gas Supply Minimum not required One-day reserve supply One-day reserve supply
aNFPA adopts the definitions for sedation and anesthesia from the American Society of Anesthesiologists’ “Continuum of Depth of Sedation” verbatim
bZone Valves are mechanical shut offs for medical gas and vacuum supply lines to each anesthetizing location and each supplied zone such as the PACU. Per NFPA, pressures must be monitored downstream of the valve for each gas and upstream for each vacuum supply line (Figure 2).
cLimited, need not provide real time pressures, only low supply pressure
d2018 NFPA 99 Chapter 15 allows a simplex system in a dental office
eSimplex refers to a vacuum system that may have multiple vacuum sources, but cannot generate 100% of the demand independently, and therefore is not redundant. A duplex system has 100% redundancy and can operate at capacity with a single source failure.

Anesthesia Professionals and Medical Gas Systems

Anesthesia professionals are primarily trained in the operating room. Training also occurs in hospitals and ambulatory surgery centers. These facilities, even at remote sites, must comply with NFPA 99 standards. As professionals, we are not trained to deal with the technicalities of these medical gas systems. The authority having jurisdiction (AHJ) is often the fire marshal who is not always aware of the level of anesthesia to be provided in an office. This is especially true of dental offices, in which it is often assumed that the office will be using just nitrous oxide and a dental air system (Category 3). Compounding this problem is the fact that anesthesia professionals may mistakenly assume that dental (Category 3) systems are the same as other medical gas systems that are familiar to them. This is, in part, due to the fact that Category 3 systems are not routinely discussed in texts or training programs,3 as these nitrous dental gas systems were not intended for sedation and/or general anesthesia. Both dental and medical gas systems must be installed by an American Society of Sanitary Engineers (ASSE) 6010 Certified Medical Gas Installer, as there are strict rules for brazing and testing these piped systems. Plumbers that are not certified medical gas installers mistakenly install some of these systems. This has resulted in medical gas line cross-overs that have resulted in several deaths in dental offices due to hypoxic gas mixtures being delivered to patients. For this reason, all systems except dental Category 3 systems, even when installed by an ASSE 6010 Certified Medical Gas Installer, must then also be independently tested and verified by an ASSE 6030 Medical Gas Verifier (who has an additional two years of training with an associated certification when compared to the ASSE 6010) prior to use.

Additional patient and staff safety concerns arise from the dental air compressors and dental vacuum systems. Dental air compressors are designed simply for driving dental surgical instruments. It is highly unlikely that these systems could be mistaken for medical air, and thus will not be discussed further. However, dental vacuum pumps are designed to operate “wet” and do not have a collection canister to prevent contamination of the vacuum line. Instead, dental suctions have a “trap” built into the dental delivery unit to prevent large debris from entering the “wet” system. In the event of regurgitation, this system clogs with debris and will immediately fail. These vacuum pumps are designed to operate at high flow but low vacuum. For example, most dental vacuums operate at 10-13 inches of mercury, whereas a medical vacuum is required to maintain a minimum of 19 inches of mercury.

The variability in fresh gas and vacuum flows may also be a patient safety issue. The variability is due to the lack of compliant source systems and engineering of the gas plumbing. Connecting anesthesia machines, through the use of both gas supply and vacuum fittings and adaptors that allow connection to a Category 3 system could potentially cause fluctuations in the fresh gas and vacuum flows to the machine. The change in vacuum flow could potentially cause increases in positive end expiratory pressure (PEEP) as vacuum levels decrease with concomitant use of the dental vacuum. Inappropriate fresh gas piping sizes could lead to inadequate flows, especially when using the oxygen flush valve. These technical issues rarely cross the mind of anesthesia professionals, as they are accustomed to appropriately designed systems in the hospital.

NFPA 2018 Edition

The NFPA released the NFPA 99 Healthcare Facilities Code 2018 Edition in November of 2017. The NFPA worked with the American Dental Association and dental specialty groups to develop the latest edition. The lack of knowledge and adoption of code standards in dentistry was recognized by the NFPA. For example, The American Academy of Oral and Maxillofacial Surgeons (AAOMS) requires that all  “AAOMS fellow/members must have their offices successfully evaluated and re-evaluated by their component society every five years or in accordance with the state law, provided that the state law does not exceed six years between evaluations and otherwise meets AAOMS office anesthesia guidelines.”4 However, AAOMS Parameters of Care5 are silent on NFPA 99 adherence. Individual state dental board requirements are also highly variable and do not discuss NFPA 99 requirements. Therefore, NFPA 99 has explicitly included dental offices in Chapter 15 “Dental Gas and Vacuum Systems.”6 The NFPA decided to explicitly include dental facilities in their own chapter to address the issues discussed above. However, they did not “grandfather” in existing systems in dental offices. Instead, NFPA 15.1.5 states, “An existing system that is not in strict compliance with the requirements of this code shall be permitted to continue in use as long as the authority having jurisdiction has determined that such use does not constitute a distinct hazard to life.”7

NFPA 99 and Anesthesia in Dental Practices

New dental offices should be aware of these new standards. The major dental equipment suppliers often offer design services, but are not well versed in medical gas systems. Local building inspectors often do not inspect dental offices for compliance unless the office specifically states that they offer certain sedation and anesthesia services. Professional engineers may be needed to design the gas system and mechanical closet. The thorough testing of medical gas systems is imperative as it ensures proper functionality of gas manifolds, alarms, and automated switchover valves and ensures against system leaks and medical gas line crossovers. This testing ensures that the medical gas system is performing properly much like a biomedical technician certifies the working order of anesthesia machines. The redundancy of these systems allows for additional patient safety and verification. For example, the requirement8 during general anesthesia for an in-line oxygen analyzer on anesthesia machines serves as a protection against delivery of a hypoxic gas mixture in the event of a gas line crossover. The American Dental Association’s Guidelines for the Use of Sedation and General Anesthesia by Dentists also requires either an in-line oxygen analyzer or “a functioning device that prohibits the delivery of less than 30% oxygen.”9 Of course, these devices may only be relied upon with adequate verification of the medical gas system installation, which is required by NFPA 99.


Existing offices should understand the regulatory issues included in NFPA 99 and the relevant society guidelines when introducing new sedation and anesthesia services. An existing Category 3 medical gas system is not permissible when adding sedation and anesthesia services, just because the system is already present at the dental office. This also applies when independent anesthesia professionals are brought into the office to assist in treatment of patients. In addition, offices providing sedation and anesthesia without the proper independent third-party certification of their gas system, may, at the very least, be responsible for notifying the authority having jurisdiction of such. As one state-level AHJ and professional engineer stated, “This, however, does not relieve the building owners, contractors, architects, engineers, material suppliers, and anyone involved including the dental practitioners in the construction of the medical gas systems from complying to this code (personal communication).”  The best practice is to ensure that an independent ASSE 6030 medical gas verifier has evaluated the medical gas system for any new installation or repair and whenever adding additional sedation or anesthesia services to any office or facility. Although not required by the NFPA, routine maintenance and certification of the gas system is also recommended, just as it is for anesthesia machines.

Dr. Wong is a dentist anesthesiologist in private practice at Coastal Pediatric Dental & Anesthesia in Norfolk, VA.

Gerhard Gschwandtner is a professional engineer, certified health care safety professional, and credentialed medical gas verifier at Comprehensive, Inc in Cary, NC.

Both authors have no disclosures relevant to the content of this article.

Special acknowledgment to Dr. Jan Ehrenwerth for serving as guest editor. Dr. Ehrenwerth presently serves on the APSF editorial board.


  1. Continuum of depth of sedation: definition of general anesthesia and levels of sedation/analgesia. American Society of Anesthesiologists Committee of Quality Management and Departmental Administration; 2014;p. 1–2.
  2. Practice guidelines for moderate procedural sedation and analgesia 2018: A report by the American Society of Anesthesiologists Task Force on Moderate Procedural Sedation and Analgesia, the American Association of Oral and Maxillofacial Surgeons, American College of Radiology, American Dental Association, American Society of Dentist Anesthesiologists, and Society of Interventional Radiology. Anesthesiology 2018;128:437–79.
  3. Malayaman SN, Mychaskiw G, Ehrenwerth J; Medical gases: storage and supply, Chapter 1 in Ehrenwerth J, Eisenkraft J, and Berry J: Anesthesia equipment: principles and applications. Second Edition. Elsevier, Philadelphia, 2013.
  4. Office-Based anesthesia provided by the oral and maxillofacial surgeon: White Paper. American Association of Oral and Maxillofcial Surgeons; 2016; p. 3.
  5. Anesthesia in outpatient facilities. Parameters of care: clinical practice guidelines for oral and maxillofacial surgery (AAOMS ParCare 2012). 5th ed. Rosemont, IL: American Association of Oral and Maxillofacial Surgeons; 2012;e31–e49.
  6. NFPA 99: Health Care Facilities Code, 2018 ed. Boston, MA: National Fire Protection Association; 2017.
  7. NFPA 99: Health Care Facilities Code, 2018 ed. Boston, MA: National Fire Protection Association; 2017; Section 15.1.5, p. 122.
  8. Standards for basic anesthetic monitoring. American Society of Anesthesiologists Committee of Standards and Practice Parameters; 2015, p. 2.
  9. Guidelines for the use of sedation and general anesthesia by dentists. Chicago, IL: American Dental Association; 2016; p. 10 & 13.