Henderson Engineers 
does health care

By Christoph Lohr, P.E.

Phoenix and the surrounding metro area continue to grow the requirements for additional health care facilities in order to support population growth. In order to control costs, many health care providers are constructing support facilities outside of their hospital campuses.  

One such facility, the Center at Val Vista, a 3-story, 78,000  square-foot skilled nursing facility located in Gilbert, Arizona, began design in early 2015. Henderson Engineers (HEI) teamed with H&L Architects and Kitchell Contractors to build upon previous iterations of this project.

Specifically for plumbing there were two items that were approached differently:

Legionella Risk Mitigation. HEI designed a system that would attempt to minimize the risk of a Legionella outbreak in the facility.

Medical Gas Installation, Inspection, and Verification special requirements for Arizona and Gilbert AHJs.

Legionella risk mitigation

The standard way to design hot water systems for health care and many other facilities in the past has been to produce hot water at 140 F at the water heater system, and then reduce the temperature down to 120 F or 110 F via a master thermostatic mixing valve and recirculate hot water between from up to 120 F down to 100 F throughout the facility. The theory behind this methodology was to ensure that the water temperature was not too high to cause scalding at the end user plumbing fixtures by controlling the temperature at the source.  

The majority of health care facilities have been designed and built this way over the last several decades. The problem with this design approach is that it does not fully mitigate the risk of Legionella growth in the piping. Legionella grows in a water temperature range of 68 F to 122 F. Therefore, no matter how small of a temperature difference in the recirculation loop, since the hot water supply and return loop is less than 120 F, the Legionella would grow. Additionally, less frequently used plumbing fixtures could see their branch piping drop even further into this ideal growth range, exasperating the problem.

An argument might be made at this point that Legionella would be eliminated by the water heater system upstream of the master TMV. However, industry data shows that it takes Legionella five to six hours to be eliminated at a water temperature of 130 F, and 32 minutes to be eliminated at water temperatures of 140 F. When cold water is introduced at the master thermostatic mixing valve the cold water would not reside in the valve for long enough to eradicate the Legionella. In this case, there is a potential for that strain to multiply and grow within the hot water system and cause a facility-wide Legionella outbreak.   

In order to mitigate the risk of Legionella, the Center at Val Vista has a 140 F set point for their water heaters and hot water supply loop. The hot water return system is sized to bring back no less than 133 F water to the water heater system before being reheated and sent back out to the system. Additionally, the hot water supply and return branch piping were located as close as possible to the plumbing fixtures to minimize hot water delivery time and increase temperatures in the plumbing fixture branch piping.  

ASSE 1070 point-of-use thermostatic mixing valves were used at all hand-washing locations to prevent scalding while thermostatic/pressure balancing shower valves were provided to offer an extra layer of scald protection to the patients. A water softener system was utilized to reduce scale build up in the hot water supply and return piping. Scale provides a location for biofilm to increase, and conversely Legionella grows in biofilm. Scale control allows the water heater system to maintain rated efficiency; scale build up reduces heat transfer in water heating systems. Finally, laminar or non-aerating faucets were utilized throughout the facility to further mitigate the risk of Legionella becoming airborne.

These strategies should allow building occupants to use Legionella-free hot water throughout their stay at this facility.

Medical gas special requirements in Arizona

Many engineers and engineering firms that come to Arizona to do health care work are surprised to discover the “extra” requirements that the local AHJ’s (each city/county in Arizona is its own AHJ with its own plumbing code) require. Specifically, they are surprised by the requirements of the Special Inspection for Medical Gases, and the Arizona Department of Health Services Engineer Checklist.  

In NFPA 99, the 2012 edition adopted in the entire state of Arizona at the time of this article’s publishing, there are a number of requirements. The requirements are for installer testing (contractor), inspection (third party) and verification (third party) once medical gas systems have been installed. These tests verify particulate purity (i.e. confirming that nitrogen NF was used while brazing to prevent the interior of the pipe from oxidizing), standing pressure, cross-connections, etc.  

The Piping Industry Progress and Education (P.I.P.E.) Trust Fund Medical Gas Committee was established  to determine a method to ensure that the best possible medical gas systems were installed starting in Phoenix and surrounding metro-area municipalities. Together with the local AHJs, committee members determined a process that adds  a number of layers of checks and balances to assist the owner in ensuring a fully-functioning, safe and operational medical gas system is provided.

Starting in Phoenix and now also required in Gilbert and many other metro cities, a Medical Gas Special Inspection form is required to be signed by the design engineer of record (EOR) and submitted with the permit drawings. This form states that the design engineer is responsible for the parties that perform the inspections (and verification) of the medical gas systems. The engineer stamps and signs the top half of the form indicating that he  will be overseeing the inspectors/verifiers, and then signs  a second time at the bottom of the form, indicating that the completed system meets all requirements. If this form is not completed for facilities with newly-installed medical gas systems, then occupancy would be denied by the AHJ.

Furthermore, the ADHS requires that all health care projects with medical gas systems (excluding federal government) in Arizona require a letter with a completed checklist from the engineer, indicating that the following criteria have been met:


  • Installer and continuity certifications for all journeymen who worked on the project
  • Verifier and inspector certifications
  • Verifier's and Inspector’s reports, including purity test results, pressure tests, flow tests and cross connection test
  • Materials certifications
  • Bill of sale for medical gas piping materials
  • Contractors medical gas systems installation guidelines and checklist
  • Certification that medical gas materials used on this project is medically clean
  • Continuous observation reports  (city of Phoenix)

These documents are compiled and sent with the letter from the engineer of record to ADHS upon completion. If these documents are not received by ADHS, occupancy would be denied.

These are requirements that go well above and beyond the requirements of the health care code; however, they work in tandem for the engineer. TAs an engineer the second half of the special inspection form would not be signed until all of the items from the ADHS checklist are reviewed and found to be in compliance with code. Therefore, in Arizona, the engineer has authority to ask the contractor to provide the final medical gas reports and can indicate with confidence to the owner that the medical gas system is safe to operate.


The Center at Val Vista is currently under construction. Due to Arizona requirements for medical gas system, the EOR has some additional involvement including but not limited to: participating in the Project Kick-off Coordination meeting with the medical gas installing contractor (RKS Plumbing); witnessing some of the medical gas installer brazing (with Nitrogen NF purge); reviewing the engineer checklist for ADHS; and signing and submitting the special inspection form for the town of Gilbert.

In addition to the medical gas requirements, the usual site observations will occur on the hot water system to ensure that Legionella risk is mitigated properly. By providing scald control at the plumbing fixtures and water treatment to prevent biofilm, maintaining water heater efficiency, and supplying 140 F-water through the system, the hot water system is slated for a long life of service to the owner.  

Additionally, due to the Arizona requirement of having the engineer review the medical gas tests, an extra layer of confidence is given to the owner that the medical gas systems meet all requirements of NFPA 99. HEI has been very excited to work with H&L Architects and Kitchell Contractors (and RKS Plumbing) on this project and look forward to delivering the best possible plumbing and medical gas system to the Center at Val Vista. 


Christoph Lohr, P.E. (AZ, NV), CPD, LEED AP BD+C, is a plumbing engineer at Henderson Engineers (HEI). He is also the vice president of Legislative for the American Society of Plumbing Engineers (ASPE) Phoenix Chapter and co-chair of the P.I.P.E. Trust Medical Gas Committee. He can be reached at Christoph.Lohr@ hei-eng.com. 

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