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Understanding DIN standards

glencoe after
Underwater images of the 25 m (82 ft) indoor pool at the Glencoe Club in Calgary, Alta., before and after the application of DIN filtration standards.

By Dennis Ashworth

When visiting a European aquatic facility, North American operators and designers would likely be in for a few surprises. In fact, when comparing what is acceptable in our region to a minimum European Deutsches Institut für Normung (DIN) standard, the results can be downright shocking.

Some believe Europe is almost 40 years ahead of North America when it comes to public swimming pools and spas, particularly in terms of water clarity, mandatory filtration requirements, disinfection levels and trihalomethanes/chloroform control and testing. In addition, European operators also seem more aware that trihalomethane (THMs), nitrogen trichloride (NCl3) and other chlorine compounds create risks for both the building envelope and a facility’s bathers and staff. Why these standards haven’t served as a blueprint for the North American pool industry is a question aquatic facility professionals need to ask themselves.

Setting the bar with DIN

DIN is a German national standards organization, known in English as the German Institute for Standardization. Founded in 1917 and operating out of Berlin, DIN currently has more than 30,000 standards in effect, covering all varieties of technology. These standards are available in numerous languages and adopted by many countries or re-written to apply to the countries requirements.

In Europe, DIN is the standard that must be adhered to when a public pool is designed, constructed and equipped. These standards are far stricter than North American equivalents, and tend to result in improved designs and the best possible water quality. The legislation demands quality and provides strict parameters to provide positive results.

This begs several questions: Why is it taking so long to adopt similar requirements in North America? Why is a system that appears to work so well totally disregarded? What do we accept as water and air quality minimums—and why? Is it time for those of us in Canada and the U.S. to re-evaluate our standards with DIN as a guide?

There are several possible reasons North American standards differ so greatly from DIN. One potential reason is that the European scientific community is given greater respect than its North American counterparts. While Canadian and U.S. researchers may be equally skilled and thorough, too often their findings go ignored or unnoticed. In addition, North American manufacturers may have a greater influence on the rules and regulations adopted by governments and testing bodies. In Canada specifically, operators and regulators tend to look to the U.S. as an example; however, 24 U.S. states do not have a pool health act. Standards are often changed to meet the pools, not the other way around. DIN, on the other hand, takes a different approach, one worth investigating in greater detail.

Finessing filtration

The design of the filtration system is critical and mandatory to meet DIN requirements. The depth and design of the filter media provides healthy water returning to the pool. In Germany and Austria, where regulations are strictest, sand is the industry standard, though in a very different form than North American operators are used to.

European-style filtration systems differ from their North American equivalents in many ways, including:

  • air release at the top of the filter;
  • a clear, wide view port for easy operator inspection;
  • pipe connectors located further apart from one another;
  • nozzle plate collection (instead of laterals);
  • filter bed depth greater than 1,200 mm (47.2 in.) of graded filter media;
  • filter backwashing with water and/or water and air;
  • diffuser/backwash piping sized to backwash without pressure;
  • mandatory use of flocculent; and
  • a large freeboard area (open space from the bottom of the diffuser to the top of the sand).

Slower flow rates per square foot are designed to provide superior water quality. The slower the flow, the higher the quality of the filtered water—and slow is good when swimming pool filters are designed correctly.

For filters with higher flow rates up to 667 litres per minute (lpm) per square metre (17 gallons per minute (gpm) per square foot), taller filters with multi-layer, multi-grade media are designed. This provides greater bed depth and extra contact time for flocculation, as well as more freeboard for media expansion during backwash.
If these designs are effective, one might wonder why North American filter manufacturers continue to build horizontal filtration systems with very shallow sand depths (some less than 305 mm [12 in.]). Removing bather waste in a heavily loaded public leisure facility would be nearly impossible at flow rates in excess of 57 litres per 930 cm2 (15 gallons per sf); a 1.2-m (48-in.) horizontal filter only provides approximately 610 mm (24 in.) of filter media depth. North American engineers also often specify filters to be able to fit through a typical building door; again, a practical, budgetary concern that does not necessarily reap the most benefits for water quality and user experience
Unfortunately, in North America, price often overrides quality. While these approaches might be healthy for the budget, they do not necessarily provide the safest and most comfortable environment for swimmers.

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