Improper Disinfection of Premise Plumbing Systems Can Damage Piping, Part 2

Last month we discussed how certain substances used in disinfection can damage plumbing systems, as well as guidance from the International Plumbing Code (IPC) and the Uniform Plumbing Code (UPC).

This month’s column is about the “disinfection methods” listed in the codes.

Currently, there is no consistent industry standard for flushing and disinfecting plumbing/building water systems, either prior to building occupancy or in response to a bacteriological problem or a closed, stagnant plumbing system. The pre-use/occupancy disinfection methods provided in the IPC and UPC are vague in their practical guidance and do not represent genuine methods at all.

In other words, these sections of code tell you “what” to do, e.g. B. filling the plumbing system with one of two chlorinated water solutions and leaving it in the plumbing for a specified period of time, but the details of “how” to accomplish this are missing. The regulations also require a minimum level of chemical concentration in parts per million (ppm), but not a maximum level.

The American Water Works Association (AWWA) standards C651 and C652 for disinfection of utility water pipes and water storage facilities referenced in the IPC are neither translatable nor easily adaptable for implementation in building plumbing systems with smaller pipe sizes. AWWA C651 is designed for flushing and disinfecting domestic water lines with pipe sizes 4 inches and larger, not for flushing and disinfecting building water systems.

The preface (which is for information only and does not form part of AWWA C651) and the scope and purpose of the standard inform that the standard is intended for water pipes, which are essentially supply water pipes (and water storage systems) and differ differs significantly from the on-site plumbing systems in terms of construction materials as well as size and functionality.

No one reading AWWA C651 or AWWA C652 would be able to competently apply the instructions contained therein to a premises/building plumbing system. For example, AWWA C651 specifies four disinfection methods, only one of which (continuous supply) has plausible application to a building/building's plumbing system.

Additionally, in the tables used to determine chlorine dosage and flush rate, the smallest pipe size considered in AWWA C651 is a 4-inch pipe (Tables 1 through 4); However, in most buildings the pipes are smaller than 4 inches. Only in essence can anything be learned from reading AWWA C651 that resembles an overall method that can be applied to plumbing systems in buildings.

The method would essentially simply be a comprehensive statement of the order of performance, which in my reading of AWWA C651 consists of the following:

1. Flush the system with water until the water runs clear and remove any visible dirt and debris.

2. Fill the system with a water-chlorine solution;

3. Close the valve of the system and wait a certain time depending on the chlorine concentration of the solution used.

4. Sampling/measuring the residue;

5. Safely flush the hyperchlorinated water from the system.

6. Check by bacteriological tests.

These steps stated in AWWA C651 are more numerous than the steps set forth in the mentioned sections of the IPC and UPC. These code sections do not require that sampling and measurement of residual water treatment chemical be performed during or after the waiting period or that the hyperchlorinated water be safely discharged.

Controlled rinsing and disinfection

ASHRAE Guideline 12, “Minimizing the Risk of Legionellosis Associated with Building Water Systems,” provides guidance for flushing a hot water system with very hot water as part of a high-temperature “heat and flush” decontamination effort. I have found that most water heaters are not designed to perform thermal disinfection at the temperature rise and flow rates required to quickly disinfect a system.

In addition, thermal disinfection only affects the hot water system. Note that a more detailed flushing procedure is currently being developed as an appendix to Guideline 12 (GL12). However, GL12 provides little guidance on hyperchlorination techniques for decontamination.

The plumbing manufacturer, plumbing designer and water treatment provider must work together to develop a controlled flushing and disinfection process that limits excessive chemical exposure and contact time with the plumbing system. The steps I would suggest are more numerous than the Code or AWWA C651 and include, but are not limited to:

1. Identify all pipe, fitting, valve, and equipment manufacturers, as well as all materials of construction.

2. Obtain manufacturers' chemical resistance data to determine the maximum allowable ppm levels and required contact time for the water treatment chemical to be used to minimize oxidation/damage to the system.

3. Document the materials, chemicals to be used, concentration in ppm, contact time and who is doing the work. Document the date, time and dates of the entire rinsing and disinfection process and maintain records to demonstrate that these processes were carried out.

4. Locate chemical injection points and flushing locations.

5. Identify testing methods for ppm of water treatment chemical to be used (test strips or chlorine meters).

6. Determine the maximum and minimum ppm levels and contact time required for effective disinfection.

7. Premix disinfectant chemicals in tanks or set up a flow rate pump that can be precisely controlled with a chlorine meter.

8. Establish a method for flushing the water at each fixture, a required number of fixtures to flush simultaneously, and a schedule for flushing times.

9. Turn off the hot water system and flush out hot water, which can affect the chemical oxidation rate.

10. Flush the cold and hot water systems with water at a rate of approximately 3 feet/second until the water at all fixtures runs clear. This removes dirt, sediment and debris.

11. Determine chlorine residual and perform bacteriological testing on source water to establish a baseline.

12. Fill the system with a water-chlorine solution; Allow water to flow from each faucet until there is sufficient water treatment chemical residue.

13. Close the system valve and wait a certain time depending on the chlorine concentration of the solution used.

14. Measure the water treatment chemical residues on the removed devices at the beginning, periodically and at the end of the contact time.

15. Safely flush all hyperchlorinated water from the system to prevent oxidation and corrosion damage.

16. Verify effectiveness by testing for residual chlorine and conducting bacteriological tests.

17. Repeat steps if bacteriological testing indicates the system is still contaminated.

18. If the source water is contaminated, notify the water utility to flush the water lines and check for water treatment chemical residues.

Good intentions, bad results

When I investigate Legionella outbreaks or new piping systems that are experiencing leaks, I see many installations where the piping system has been destroyed by the disinfection process. Without proper training, disinfecting a plumbing system can destroy the plumbing and expose building occupants to toxic levels of water treatment chemicals.

I have seen building owners and contractors “combine” the flushing instructions in GL12 with the chlorine-PPM solutions specified in the code to quickly disinfect their building water piping systems by flushing (rather than retaining) a water-chlorine solution in the piping system. Sometimes systems are filled with chlorine solutions at thousands of ppm because there was no good way to accurately dose the chemicals. I also saw large amounts of chemicals in the system.

In most cases, these activities are carried out after a case of legionellosis has been reported in a tenant. If a building is already in use, the process of hyperchlorination can be very disruptive to the building's occupants because no water is allowed to be used during the process of hyperchlorination; Sometimes there are temporary evacuations or water system shutdowns and bottled water distribution.

This highlights the need for an industry standard for emergency flushing and disinfection procedures for building water systems/domestic plumbing systems that takes into account the materials of the piping system, the water treatment chemicals and the required contact time at various concentrations with regard to corrosion/oxidation damage to the pipes and toxicity to humans.

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