Many states have only general aquatic guidelines, but those that have detailed, comprehensive pool codes, such as Florida and Nevada, along with the most in-depth service technician/operator certification programs, emphasize the importance of proper filtration and circulation.
Along with sanitation regulations, user, structural, electrical safety requirements, circulation and filtration are also a key focus, yet by all indications, there is an oversight in the aquatic industry, and the Center For Disease Control (CDC), based on its published proposed modules, is poised in its Model Aquatic Health Code (MAHC) to be equally remiss in providing for bather health.
It is mind-boggling that only half of the states even require a pool operator to receive formal training and certification by an authorized industry organization, such as the National Swimming Pool Foundation (NSPF) or Association of Pool and Spa Professions (APSP).
At best, the codes include minimum turnover rates, almost universally requiring at least one turnover every four hours for public pools (cf. Southern Nevada Pool Code, section 610.10 Filtering and Circulation), or six per every 24 hours.
They include maximum velocity rates, often not to exceed 10 feet per second (cf. Florida Administrative Code (FAC), Chapter 64E-9.007 (10) Public Swimming Pools and Bathing Places, Recirculation and Treatment System Requirements).
Some require a “portable or plumbed-in vacuum-cleaning system” (FAC, supra, subsection 12). However, nowhere are there any regulations or even guidelines that require:
- Minimum or even continuous filter flow rates
- Minimum filtering porosity (the size of the holes in a filter element)
- Specifics in regards to vacuum-cleaning systems.
Without these requirements, bathers are subject to exposure from virtually all pathogens (disease-causing organisms) not removed by sanitation, which by itself is inadequate.
In addition, the prescribed turnover rates are misleading. They imply that every four hours for a public pool and varying other time periods for other types of pools and spas, the entire volume of the pool is required to be filtered.
As discussed below, the historic Gage and Bidwell Law of Dilution, dating to 1926, debunked that myth. Turnover actually is a quantitative, not qualitative standard.
Slipping Through The Cracks
It is estimated by industry sources and these programs that the great majority of all commercial (and in most cases, public) pools use high-rate sand filters, with a porosity of 20 to 50 microns.
There is a growing trend toward using diatomaceous earth (D.E.) filters with porosities below 5 microns, but they are expensive to purchase and maintain. Older public pools most often use high-rate filters or the less-efficient predecessor, rapid-rate sand filters.
A number of dangerous contaminants and unsightly debris, such as fine sand, silt, algae, and bacteria, are well below 20 microns in size. The majority of these pathogens are between 2 and 20 microns.
For example, the single most-focused recreational water pathogens focused on by the NSPF and the CDC are Cryptosporidium and Giardia, which according to Duke University’s Cruising Chemistry educational module, are 3 to 4 microns and 5 to 6 microns in diameter, respectively.
E.coli, arguably the most generally known and feared pathogen found in pools, along with that which causes Legionaire’s Disease (the more prevalent one with fatal consequences), is estimated to be 2 microns in length according to an article published by the American Ground Water Trust in the American Well Owner (2002, Number 2).
While some of the most common pool contaminants–such as viruses–are below 2 microns, the majority can be dealt with by a filter that has porosity smaller than 20 microns, such as D.E. filters or most high-end robotic cleaners and some handheld battery-powered pool and spa vacuums. But no regulation mandates their use.
Sanitation And Oxidation
Sanitation and oxidation will kill most pathogens, but any remnants still must be filtered out of the water. Here also lies a major misconception, namely that sanitizing a pool by adding disinfecting chemicals will remove the remnants of the killed pathogens.
Overlooked is the fact that circulating any chemical throughout an entire pool is a slow process, taking several hours in many instances. The code requirement that a pool-cleaning system must have a vacuum available, and the ones that require brushing, imply this will be sufficient to rid the pool of dirt, debris, and pathogens.
The accepted idea is that the debris on the walls, steps, floors, and everywhere else in a pool that static particles adhere to will be brushed into the water and, as it settles on the bottom, will be vacuumed into the filter system and removed.
The problem with this notion is that the only particles that will be removed are those larger than the porosity of the filter. At best, in sand filters, the debris goes in one end and out the other, and right back into the pool–continuing to expose bathers.
There are maximum-velocity requirements for two primary reasons:
- Creating a greater suction, which increases the risk of bather entrapment
- Preserving the life of the PVC piping system.
Probably the greatest misconception perpetuated involves turnover rates, with the Gage and Bidwell Laws of Dilution being inaccurately paraphrased. This writer has only been able to find one such law and only references it, and he continues to seek the original report.
In 1926, at the 56th Annual Meeting of the American Public Health Association (APHA), Stephen DeM. Gage, Chairman of the Public Health Engineering Section, in a report by the Joint Committee on Bath Places of the APHA, wrote:
“It can readily be demonstrated by computation and by experiment that 7 turnovers are required to effect a removal of 99.9 percent of the dirt present in the water of the pool when recirculation was started. At the end of the first turnover the purification will be about 63 percent, after two turnovers about 86 percent, at the end of three turnovers about 95 percent, after four turnovers about 98 percent, after five turnovers 99.3 percent, and after six turnovers 99.7 percent. To accomplish a purification of 99.99 percent, 10 turnovers will be required.”
The raw data and any detailed report do not appear to have been preserved, or at least are not readily available, but those who refer to them play fast and loose with these numbers.
The National Parks and Recreation Association’s Certified Aquatic Facility Handbook states that the first turnover will filter less than half the water, and even includes that as a question on its certification examination. There are no data to even imply modern filter systems have improved the numbers, nor any claim they have.
Despite this lack of concern as to the accuracy of Drs. Gage and Bidwell’s findings, it is obvious those in the know are well aware that current regulations are inadequate to protect bathers from the constant risks in a swimming pool. It only takes exposure to a few molecules of a pathogen to infect an unsuspecting bather or swimmer.
No process will entirely remove this risk, but there are methods and equipment to significantly lessen the risk, but only if the regulations address them.
It would be presumptuous to speculate on why this vital ingredient in aquatic safety has been delegated to secondary status in the regulations and certification courses.
Neither the APSP 4-day, 10-hours-a-day Certified Service Technician’s course and accompanying 500-page tech manual used as the course guide for its Certified Maintenance Specialist and the highest-level certification in the industry its Certified Service Professional, the NSPF’s prestigious Certified Pool and Spa Operator (CPO) certification course and handbook, the NRPS-certified Aquatic Facility Operator (AFO) course and handbook or the Aquatic Training Institutes certified Pool Technician course and handbooks give more than a passing reference, if that, to the importance of removing particles smaller than 20 microns from the pool.
They and the regulations do not require any constant minimum filtration flow rates, nor do they mention, much less promote, any need for pool vacuums that will filter these dangerous, sub-20 micron contaminants, despite the fact there have long been cleaners and vacuums that will filter particles as small as 2 microns.
Bather safety is clearly a humane mission of legislators, health and safety departments, and certainly eminent organizations like the CDC and NSPF. The need for a uniform, if not a national aquatic safety code, is obvious.
However, to be truly effective in protecting bathers from the risks caused by dangerous pathogens, more stringent regulations are necessary.
Richard K. Cacioppo, Sr., J.D., is director of the Institute For Public Pool Studies in Princeton, N.J. He can be reached at firstname.lastname@example.org.