Here's a closer look at the various kinds of testing required of a medical gas system before it can be put into operation.

Author's note:This article is intended to acquaint plumbing contractors and engineers with the healthcare medical gas project testing that is required for the protection of the user and patients. It is not intended to cover all requirements in minute detail. The requirements have been paraphrased to make them easier to read and to conserve space. Though I am a member of the technical committee on medical gas and vacuum piping of the National Fire Protection Association, please note that this article is based on my own experiences and does not represent the opinions, position or interpretations of any other individual committee member, the committee as a whole or the NFPA. Please refer to the actual text of the referenced standards, such as NFPA 99, for the exact wording.

The Medical gas system tests are first conducted by the installer, and after they are completed, by a verifier. A verifier is a highly trained and certified individual directly responsible for the final inspection, testing and integrity of all complete medical gas and vacuum systems. This includes all compressed gases, such as medical oxygen and compressed air sources (including dryers, filters and regulators), vacuum sources, alarms and safeguards that monitor system components, isolation valves, and service inlets and outlets. All components of new piped systems (gas, patient vacuum and waste anesthesia gas disposal), as well as all additions, renovations, temporary installations and repaired systems, should be tested.

The end result is that, once placed in operation, there is complete assurance that the entire medical gas and vacuum system is safe to use and conforms to all requirements of the NFPA 99 code.

A verifier can work at the request of the contractor (the most common), the healthcare facility in which the systems have been installed or the engineering firm that designed the systems. For government work, where a separate verifier is frequently called in for Department of Defense contracts, an independent verifier is often used to compare test results.

A written report will be made of all findings and results. This written report from the verifier is submitted to the person or organization that ordered the tests. For the engineer or healthcare facility that ordered the report, this arrangement is often satisfactory. If the installing contractor ordered verification, frequently the contractor requests payment prior to giving the report to a third party. All documentation would be retained at the site.

NFPA 99 requires the verifier to be qualified to ASSE 6030 standards. This qualification can be obtained through the National Inspection, Testing and Certification program in California. In addition to this mandated qualification, a voluntary standard, not required by NFPA 99, is the Medical Gas Professional in Healthcare Organizations qualification, which can be roughly equated to the possession of a professional engineering license.

This additional qualification further tests the knowledge of equipment, calibration, codes, etc. The MGPHO certification is becoming increasingly important to the industry in order to bring the verification process to a higher level of competence. It's important to add this requirement to the specifications to assure that a qualified verifier is selected. In addition, the chosen verifier should submit data that can be used to assure that a qualified verifier is selected.

Contractor Tests

Before the verifier is called, the installing contractor is required to perform certain tests on the systems prior to installation of manufactured assemblies but after the installation of inlet/outlets. These tests must be documented, and include:

  • Initial Blow-Down Test: This will indicate that the piping system has been blown clear and is free of larger particulate matter left behind during construction. It is accomplished by using category Nitrogen National Formulary (especially pure in content and particulate) after the distributing piping only has been installed, before installation of other components of the system.

  • Initial Pressure Test: This is done after installation of capped piping at each station's inlet/outlet rough-in assemblies. The test pressure for pressurized systems shall be 150 psig (1,035 kPa) minimum, or 1.5 times the working pressure. For vacuum systems, the pressure shall be 60 psig (415 kPa).

  • The Cross-Connection Test: For each gas and vacuum system. This is done with all systems at atmospheric pressure. One system only shall be charged with Nitrogen NF to a pressure of 50 psig (345 kPa). Each system in turn shall be tested to assure that the test gas only flows from the tested system.

  • The Piping Purge Test: This test shall be done on each system to remove any remaining particulate matter. This is accomplished by starting at the furthest point of the system and injecting a high volume of heavy gas through each piping system intermittently. At each outlet, the purge process shall produce no discoloration or other evidence of particulate matter on a clean white cloth.

  • Standing Pressure Test For Pressurized Systems: This test shall be done only after the initial pressure test is completed and all system components have been installed. It consists of charging the entire system with Nitrogen NF from the source shutoff valve to bring it to a pressure of 20 percent above system pressure for a period of 24 hours.

  • Standing Pressure Test For Vacuum Systems: Similar to the above test, the entire system shall be subject to a negative pressure of 12 inches (300 mm) of water for 24 hours. Except for pressure changes due to changes in temperature or pressure, the system shall remain unchanged.

    At the conclusion of these tests, all leaks shall be found, repaired or replaced as required, and then the system must be re-tested.

    Verifier Tests

    After the installer has successfully completed these tests, the verifier will perform another round of tests to further assure that the systems are in compliance with NFPA 99 code requirements before they are placed into service. The verifier's tests include:

  • Standing Pressure Test: This is a 10-minute test at system operating pressure with all zone and source valves closed. The pressure shall remain unchanged.

  • Individual Pressurization Test: After all systems have been reduced to atmospheric pressure, and all of the inlets and outlets are connected, each system, including vacuum, in turn shall be tested to ascertain that only gas is discharged from the inlets/outlets tested.

  • Pressure Differential Test: With the pressure (or vacuum) in all systems set at predetermined code limits, each individual inlet/outlet on the system shall be tested with a gauge calibrated with the pressure indicator for that system. The readings must match.

  • Cross-Connection Test: After all the walls are completed, the verifier has the option of using the individual pressurization or pressure differential test to determine that no cross-connection exists.

  • Valve Test: Each valve installed on each individual system shall be tested to verify proper operation.

  • Alarm Test: Each component of all of the alarm systems for each medical gas and vacuum system shall be tested to assure proper operation. This test shall be performed only after the cross-connection test. All systems with master alarms shall be tested. Alarms shall verify an audible and noncancelable signal if the pressure in the system increases or decreases more than 20 percent of the normal operating pressure.

    Area alarms shall be tested to verify an alarm signal if the system pressure falls below or increases more than 20 percent.

  • Piping Purge Test: In order to assure that the piping system has no remaining large particulate matter, a minimum, interrupted purge rate of 8 standard cubic feet per minute (scfm) (225 Nl/min) shall be discharged from each outlet. No discoloration of a clean, white cloth shall be observed. Only a proper adapter for each system is allowed to be used.

  • Piping Particulate Test: This test is used to assure that the piping system does not have small particulate matter remaining in the system. A total of 35 cubic feet of Nitrogen NF at a flow rate of 3.5 scfm shall be filtered through a 0.45-micron filter. This shall be performed on 25 percent of the zones. The filter shall not accumulate more than 1 mg (0.001 g) from any outlet tested.

  • Piping Purity Test: Each positive pressure system shall be tested for the presence of total hydrocarbons, such as methane, and halogenated hydrocarbons, along with the dew point. These tests shall be taken at the most remote outlets.

  • Final Tie-In Test: Each joint in the final connection between new work and existing shall be tested with gas at system operating pressure. Any leaks found shall be repaired.

  • Operational Pressure Test: The purpose of this test is to assure that the required flow through the outlets does not have an excessive pressure drop. Using Nitrogen NF or the system gas for the test, the delivery of a set volume of gas for the various systems should not create an excessive drop in the piping. Vacuum inlets delivering 3 scfm (85 Nl/min) are tested the same way.

  • Medical Gas Concentration Test: The purpose of the test is to assure that the concentration of the different gases meets NFPA 99 criteria. This is accomplished by using specific analyzers to test for different gases.

  • Medical Air Concentration Test: This test is performed to analyze the medical compressed air for contaminant and concentration based on predetermined levels.

  • Labeling: The presence and correctness of the various systems shall be verified.

  • Oxygen, Air and Vacuum Source Operation: The source equipment for the various systems shall be tested for proper operation, including lead/lag time, switch to secondary supply, etc.

    "Standard for Health Care Facilities," NFPA-99, 2002.

    "Professional Qualifications Standard for Medical Gas Systems Installers, Inspectors and Verifiers," ASSE series 6000, revised Feb. 15, 2001.