NSF Standard 50: Circulation System Components and Related Materials for Swimming Pools, Spas and Hot Tubs David Purkiss General Manager Water Distribution Systems NSF International Ann Arbor, MI, USA ABSTRACT NSF/ANSI Standard 50 is the American National Standard for circulation system components used in swimming pools, spas and hot tubs. Twenty eight states in the USA require public facilities to utilize equipment that conforms to this standard. NSF 50 sets minimum criteria for the performance, hygiene, durability and safety of these products. This paper provides a review of the current requirements of the standard, the benefits that the standard and certification program provides for the public, product manufacturers and public health regulators, as well as directions for the future development of the standard. INTRODUCTION The purpose of NSF/ANSI Standard 50 (NSF 50) is to establish minimum requirements for materials, design, construction, and performance of equipment commonly included in the water circulation systems of residential and public swimming pools, spas, or hot tubs. NSF 50 was first published in 1977 and incorporates requirements for products previously covered by the following individual NSF standards: • • • • • • • •

Standard 9 - Diatomite-type filters for swimming pools; Standard 10 - Sand-type filters for swimming pools; Standard 11 - Recessed automatic surface skimmers for swimming pools; Standard 17 - Centrifugal pumps for swimming pools; Standard 19 - Adjustable output rate chemical feeding equipment for swimming pools; Standard 27 - Multiport valves for swimming pools; Standard 28 - Cartridge-type filters for swimming pools; and Standard 47 - Flow through chemical feeding equipment.

Since it was first adopted, NSF 50 has been revised to include various types of process treatment equipment and many other components. The standard is a dynamic document and continues to be reviewed and revised on an annual basis by the NSF Joint Committee on Swimming Pools and Spas. The Joint Committee consists of Regulatory Officials from various US States, Industry Representatives as well as product users.

REGULATORY ENFORCEMENT Currently 28 U.S. states have swimming pool and/or spa regulatory codes that specifically require compliance or third party certification of circulation system components to NSF Standard 50. Many counties and cities in states across the USA also have Pool and Spa codes that require compliance with NSF 50. Overall, regulatory oversight in the USA is strongest for commercial swimming pools rather than residential. Regulatory acceptance/oversight usually occurs at two levels: • Before and after construction. • On-going annual inspections. Most jurisdictions require permits for the construction of residential and commercial swimming pools/spas, which typically require a plan review to the applicable code. Residential and commercial pools may receive an inspection after construction, but on-going annual inspections are typically not required for residential pools. Most jurisdictions do perform annual inspections of commercial pool and spa facilities. However few jurisdictions are able to perform more than one or two inspections per year of regulated facilities. Hydromassage bathtubs, and therapeutic spas intended for medical care facilities are typically covered separately under plumbing codes, which typically receive inspections once after construction. Portable spas are typically not covered under any type of regulation. SCOPE OF NSF STANDARD 50 The scope of NSF 50 currently includes criteria for the following materials, components and devices: • • • • • • • • • •

Materials; Pipe and Fittings; Suction Fittings; Filters; Pumps; Multiport Valves; Surface Skimmers; Mechanical Chemical Feeders; Flow-Through Chemical Feeders; Process Equipment including: o Ozonators; o UV treatment systems; o Electrolytic Chlorinators and Brominators, in-line and brine tank; and o Copper/Silver Ion Generators.

SPECIFIC REQUIREMENTS Material Requirements NSF 50 requires materials to be corrosion resistant and to meet minimum criteria established to ensure that the materials do not contribute harmful contaminants to the water. Materials that have more than 650 square centimeters of water contact area are required to meet leaching test requirements designed to identify harmful contaminants that may migrate out of the material and into the water. Material samples are exposed to a defined extraction water for three 24-hour periods. The extractant water from the final 24-hour exposure period is analyzed for contaminants, which must be below acceptable levels based on USEPA drinking water standards. Materials are exempt from this requirement if the materials comply with the requirements of US Code of Federal Regulations 21 CFR 170-199. Alternately, materials are also acceptable if they comply with the American National Standard for drinking water materials: NSF/ANSI Standard 61: Drinking Water System Components – Health Effects. NSF 61 has defined exposure protocols for various types of materials and components, which are more aggressive than the NSF 50 exposure protocol. Allowable levels of contaminants under NSF 61 are based on USEPA and Health Canada levels for drinking water. NSF 61 also contains toxicology evaluation criteria for unregulated contaminants. Chemicals that are used as an integral part of a system covered by NSF 50 are considered acceptable if they meet the requirements of the American National Standard for drinking water treatment chemicals: NSF/ANSI Standard 60: Drinking Water Treatment Chemicals – Health Effects. Circulation System Components NSF 50 has specific design, flow, durability and safety requirements for the integral components of the circulation system, including pumps, skimmers, pipe and fittings, suction fittings and valves. Plastic pipe and fittings are required to conform to the American National Standard NSF/ANSI Standard 14 that establishes material, performance and durability requirements for plastic piping components. The safety and applicability of suction fittings is addressed via ASME A112.19.8M. Centrifugal pumps are required to withstand a hydrostatic pressure of 150% of the maximum working pressure. There are design criteria for strainers, drain plugs and shaft seals. Each pump must be sold with operating instructions that must include a manufacturer’s pump performance curve. NSF 50 includes a test method to verify these pump performance curves. Multiport valves are required to meet a burst pressure of 4 times the maximum working pressure and shall not leak, rupture, or burst when subjected to 1.5 times the maximum working pressure for 5 minutes. The ability of a multiport valve to seal off ports not in use during the filter and backwash cycles is judged by a differential pressure/leakage test. Valves are tested to verify the pressure loss claims of the manufacturer, and waste ports are tested for leakage.

Recessed automatic surface skimmers are required to meet dimensional requirements of NSF 50 for the housing, weirs and strainer basket. The structural integrity of a skimmer housing is evaluated by subjecting the housing to a vacuum of 85kPa for 5 minutes. Weirs are required to automatically adjust to changes in the water level when operating at the maximum design flow rate. Skimmers for commercial pools are required to have an equalizer line that prevents air from becoming entrained in the suction line. Leakage of water through the equalizer is not allowed to exceed 10% of the total flow through the skimmer under normal operating conditions. Electrical Requirements All electrical components of equipment are required to meet the requirements of the National Electric Code and referenced standards. Filtration Systems NSF 50 establishes criteria for cartridge filters, diatomaceous earth filters and sand type filters. In addition to the material requirements mentioned previously, NSF 50 addresses structural durability, and filtration performance. Filters must meet structural durability requirements that include: • Design burst pressure equal to 4 times the maximum working pressure. • Hydrostatic pressure equal to 1.5 times the maximum working pressure for 5 minutes. • 20,000 low-pressure (207 kPa) cycles followed by 2 times the maximum working pressure for 1 minute. • Vacuum filters shall be designed to withstand 1.5 times the vacuum pressure developed by the weight of the water in the tank. • Vacuum filters shall sustain a 5 minute vacuum of 85 kPa without leak, rupture or collapse. Filtration performance is mainly measured by turbidity reduction requirements where filters must reduce influent turbidity of 45 +/- 10 NTU by 70%. The startup effluent of a DE filter system is not to exceed 10 NTU during the first 60s of flow. Pressure head loss from the filter inlet to the filter outlet is not to exceed the maximum head loss specified by the manufacturer. There is also a verification test of manufacturer’s cleaning procedures. Cartridge, sand type and DE filters must meet defined filtration rates based on filter design and the intended application (i.e. residential/commercial, and pool/spa). NSF 50 also establishes criteria for filter media in sand type filters. The standard currently has specifications for filter sand in terms of content, particle size, and uniformity coefficient. NSF 50 allows the use of alternative medias in filters where the media is specified on the data plate of the filter. The filter must meet all applicable requirements of NSF 50 when tested with the alternate media.

Possible Future Requirements for Filtration Systems under NSF Standard 50 Currently specifications for zeolite are being drafted for incorporation into the standard. Future requirements may include ammonia and chloramine reduction requirements for zeolite filters. Particle reduction tests resulting in ratings for cartridge filters based on particle size may be developed in the future. Using particles as a surrogate for cryptosporidium reduction performance tests may also be considered. Disinfection Systems NSF Standard 50 contains criteria for a wide range of equipment that is designed to disinfect pools and spas. These include chemical feeders, (mechanical and flow through), as well as electrolytic chlorinators and brominators, ozonation and UV systems, and copper/silver ion generators. Chemical feeders are required to sustain a hydrostatic pressure of 1.5 times the maximum working pressure for 5 minutes without distortion or leakage. Chemical feeders are subjected to a chemical resistance test to ensure the materials are resistant to degradation. Mechanical feeders are also subjected to an erosion test using dry chemicals or a DE suspension for slurry feeders. Mechanical feeders are subjected to a 3000 hour life test and must meet uniformity of output requirements +/- 10% of feeder setting from 25% to 100% of rated capacity. Flow through feeders are not subjected to an extended life test, but they must meet uniformity of output requirements. The nature of the chemical type, size, and configuration greatly effects the performance of flow through feeders. Using the wrong the type of chemical in a flow through chemical feeder can result in over or under dosing of disinfectant, or cause serious hazards such as fire or explosions. There are many incidents reported each year where calcium hypochlorite and Trichloroisocyanuric acid are inadvertently mixed in flow through feeders, resulting in explosions. For this reason flow through feeders are evaluated for use with specific chemicals (chemical type, configuration, trade designation). NSF 50 requires manufacturer’s instructions and caution statements on the unit to advise the user of the chemicals recommended by the manufacturer. Process equipment such as ultraviolet light (UV), ozone, electrolytic chlorinators/brominators and ion generators are required to meet 3000 hour life tests. Ion generators and chlorinators/brominators are required to meet uniformity of output requirements, as well as chemical resistance requirements. NSF Standard 50 contains a disinfection efficacy test procedure for process equipment. The procedure currently requires a 3 log reduction in challenge organisms within 30 minutes of activation. It also requires the equipment to meet or exceed the reduction in challenge organisms achieved by dosing hypochlorite into a tank so that a concentration of 2ppm is achieved in 30 minutes. This disinfection efficacy test is problematic in that the test method evaluates the level of organisms in the tank, making the test virtually impossible to pass for technologies that do not produce residual levels of disinfection chemical. While the effluent of the unit may meet the reduction criteria, bacteria adhering to the sides of the tank will cause the unit to fail the test. Since NSF 50 current requires all disinfection systems to be used along with residual disinfection

chemicals, the test is viewed by many as overly stringent. For that reason it is currently under review by the committee that oversees the standard. NSF 50 requires UV systems, Ozone and Ion Generators to be utilized with residual levels of chemical disinfectants. • Ion generators shall be used in conjunction with not less than 0.4 ppm free chlorine or 0.8 ppm bromine. • UV systems are required to be used with not less than 1 ppm free chlorine or 2 ppm bromine. • Ozone systems are also required to be used with residual disinfectants and also ensure the ozone concentration in the finished product water does not exceed 0.1ppm.

NSF CERTIFICATION: NSF International provides testing and certification of products to the requirements of NSF/ANSI Standard 50. The certification process involves a review of product data, inspection of the production facility, and testing of products to the requirements of the standard. NSF performs annual unannounced inspections of each certified production location to ensure products continue to be produced in exactly the same manner as the original product that was tested. Any modifications to certified products require authorization from NSF in advance. NSF Certified products are listed at www.nsf.org, where listings are updated daily. Currently NSF has certified over 5800 products manufactured by over 100 companies.

BENEFITS OF CERTIFICATION: NSF Standard 50 and the NSF Certification process provide benefits for product manufacturers, product regulators, and the general public. Protection of public health and safety is the ultimate goal of any product standard. Establishing minimum requirements that all products must meet benefits all stakeholders. NSF 50 provides a uniform set of requirements that has been adopted across the USA. This saves local regulatory agencies time and effort in drafting their own individual requirements. It saves manufacturers time and money because their products only have to meet one set of requirements, instead of a wide array of requirements that may vary by locality. Third party certification of products benefits product users and regulators from having to evaluate products on a case-by-case basis. They only need to reference the product listings on the NSF website to ensure themselves that products meet standard requirements.

REFERENCES: NSF/ANSI Standard 50: Circulation system components and related materials for swimming pools, spas/hot tubs1 NSF/ANSI Standard 61: Drinking water system components – Health Effects1 NSF/ANSI Standard 60: Drinking water treatment chemicals – Health Effects1 NSF/ANSI Standard 14: Plastics piping system components and related materials1 FDA, 21 CFR 170-199, Code of Federal Regulations2 ASME/ANSI A112.19.8 M Suction Fittings for Use in Swimming Pools, Wading Pools, Spas, Hot Tubs and Whirlpool Bathtub Appliances3 NFPA, 2005 National Electric Code (NEC)4

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