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Chemical Intervention in Swimming Pools: A Proposed Definition for Shock Treatment PowerPoint PPT Presentation

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Chemical Intervention in Swimming Pools: A Proposed Definition for Shock Treatment. Paul Chrostowski and Sarah Foster CPF Associates, Inc. NEHA 66 th Annual Educational Conference. This Presentation Will Discuss. Recreational waterborne disease Emerging infectious disease

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Chemical Intervention in Swimming Pools: A Proposed Definition for Shock Treatment

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Chemical Intervention in Swimming Pools: A Proposed Definition for Shock Treatment

Paul Chrostowski and Sarah Foster

CPF Associates, Inc.

NEHA 66th Annual Educational Conference

This Presentation Will Discuss

  • Recreational waterborne disease

  • Emerging infectious disease

  • Sources of microorganisms to pools

  • Pool disinfectants

  • Diagnosis of pool and spa problems

  • Shock treatment

  • Treatment protocols

  • Additional issues

Waterborne Disease Trends

Source: MMWR (May 2000).

Emerging Infectious Diseases

  • Once under control, now on rise

  • Human mobility (Ebola)

  • Food imports (Salmonella on strawberries)

  • Immunocompromised individuals

  • Sequelae more important than thought

Sources of Microorganisms to Pools

  • Accidental fecal release (also other body fluids)

  • Inadvertent shedding

  • Exogenous sources (dirt, leaves, other vectors)

  • Pool fill water

Potable Water Disease Outbreaks

Frequently Used

Less Frequently Used

Infrequently Used

Chlorine Products

Bromine Products


Ozone (plus halogen)

UV (with or without ozone)

Chlorine dioxide





Potassium permanganate

Electrolytic generation

Pool Disinfectants

Anatomy of a Pool Problem - Outbreaks

  • 15 outbreaks adequately reported

  • 12 routine outbreaks/3 incidents

    • 7 gastroenteritis

    • 5 dermatitis/folliculitis

    • 2 pulmonary

    • 1 mixed endpoint

Anatomy of a Pool Problem - Agents

  • Ps aeruginosa

  • Cryptosporidium

  • Legionella

  • E Coli O157

  • Enterovirus

  • Mycobacterium

  • Giardia

Anatomy of a Pool Problem -- Disinfectants

  • Chlorine

  • Ozone

  • Chlorine/bromine

  • Hydrogen peroxide

  • In all cases, disinfectant residual was inadequate or incorrectly measured

Survey of 15 Residential Spas

  • Used dichlor, cal hypo, electrolytic, or BCDMH

  • pH average: 7.5 (5.37-8.23)

  • Free Ox residual average: 13.04 ppm (0-59 ppm)

  • Total plate count average: 108 cfu/mL (0-TNTC)

  • 4/15 plates: TNTC or overgrown, free Ox residual 0-0.2 ppm

Pool Water  Drinking Water

Proposed Solution is Chemical Intervention

  • Shock treatment has potential to reduce incidence of waterborne-deisease

  • Shock treatment, superchlorination, breakpoint chlorination usage is haphazard and often ineffective

  • Manufacturers promote shock for aesthetics and organoleptic control, not disinfection

  • Definition of shock and protocol for usage is needed

Shock Treatment Proposed Definition

  • Shock is the addition of an immediately available, oxidizing disinfectant routinely or as intervention

  • Shock chemical must be effective against bacteria, viruses, fungi, protozoa, and algae with reasonable CT

  • Shock chemical must destroy organics and nitrogen compounds with reasonable reaction time

Shock Treatment Proposed Definition (Continued)

  • Shock dose must be measurable

  • Shock results should generally be visible

  • Routine shock involves raising free chlorine to a minimum of 10 ppm for 1-4 hours weekly for pools and daily for spas

  • Intervention shock for a water quality problem involves raising free chlorine to 20 ppm for 8 hours

Shock Treatment Proposed Definition (Continued)

  • Intervention shock for public health involves following Maryland-type protocol based on CT.

  • pH, water balance, and filtration should be maintained during shock treatment.

  • Bathers can safely re-enter the water when free chlorine is < 10 ppm.

Useful Shock Chemicals

  • Inorganic chlorine compounds such as sodium, lithium, or calcium hypochlorites all fit definition

  • Dichlor fits definition, if residual cyanuric acid is controlled

  • Inorganic brominated compounds may fit definition if residual bromate is controlled

  • Stabilized chlorine dioxide may fit definition, residuals hard to attain

Shock Protocols – Maryland DHMH

  • Maryland DHMH focuses both on prevention and intervention

  • Maryland DHMH Chemical intervention includes minimum FAC (10 ppm), pH 7.2-7.5, re-entry based on CT data

Shock Protocols – New South Wales/Health

  • NSW/Health includes prevention, education, chemical intervention including weekly shock at 10 ppm FAC overnight

  • Shock allows pool to catch up on disinfection

  • More effective against Crypto

  • Extra oxidation, aids filtration, clarification

  • Destroys biofilms that may harbor resistant organisms

Issues Associated with Shock

Resistant Microorganisms

  • Giardia, Cryptosporidium typically have highest CT values

  • CT for Crypto ranges from 7200 to 8400; 20 ppm for 6-7 hours

  • New studies suggest lower CTs might be effective, especially if chloramine is present

  • Good filtration always important

Bather Re-entry Halogen Level

  • Currently most states and NGOs recommend chlorine residuals up to 4 ppm

  • Some jurisdictions allow up to 10 ppm, especially in spas and kiddie pools

  • Toxicological data shows levels up to 10 ppm will have no adverse effect

  • Bather load and other conditions will rapidly reduce this residual

Disinfection Byproducts (DBPs)

  • Prudent to meet drinking water standards

  • Organic carbon is most significant determinant of DBPs – algal blooms, high bather load

  • Other factors including temperature and water age are also important

  • Type of disinfection not important

Shock and DBPs

  • Study on 114 U.S. residential pools showed no significant difference in THM levels between pools shocked or not shocked

  • Study on 20 Texas pools showed shocked pools can meet drinking water standards for THMs (averages 30-52 ppb)

  • Possible reason for low THM levels may be oxidation of organic precursors


  • Recreational waterborne disease is not losing significance as a environmental health problem

  • Most outbreaks may be prevented or treated by chemical intervention.

  • Shock treatment using a rigorous definition and with comprehensive protocols is an effective form of chemical intervention.

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