Hypochlorite solutions

Hypochlorites are among the most commonly used disinfectant solutions. They are fast acting, inexpensive and readily available, and have a wide spectrum of activity. Their major disadvantages are that organic matter readily inactivates them and working solutions tend to decompose quickly (the latter is however an advantage for disposal of hypochlorite solutions).

The concentrated liquid solutions of sodium hypochlorite and potassium hypochlorite also degrade over time; open containers lose up to 50% of their original concentration within one month (Quinn and Markey 2001). Powder formulations, although significantly more stable, can react with moisture if open to the air.

As shown in Table 4.4, the available chlorine levels produced by different chlorine disinfectants vary significantly. Sodium hypochlorite is commonly supplied in a solution containing 14% (wt/vol) active chlorine (but this may vary from 1% to 15%). Calcium hypochlorite is generally 65% active chlorine. Using these products, either 1 litre of sodium hypochlorite (at 14% available chlorine) or 216 grams of calcium hypochlorite mixed with 140 litres of fresh water produces a solution containing 1000 mg/L available chlorine.

The chlorine concentration in the initial dose and residual levels of chlorine (see Section 7.8.2 for an explanation of initial dose and residual levels) should both be confirmed. Chlorine test kits are readily available from pool supply or aquarium stores.

Section 7.1 and Tables 4.6 to 4.9 contain further details on hypochlorite disinfectants. The recommended doses for various disinfectant applications are shown in Table 7.3.

7.1.1 Advantages

  • Wide spectrum of activity — effective against bacteria, fungi, viruses, protozoa and spores.

  • Rapid disinfecting action.

  • Nonfoaming action and easily rinsed from surfaces.

  • Not affected by cold temperatures.

  • Not affected by hard water unless pH is high.

  • Low toxicity at dilute concentrations.

  • Ease of use.

  • Readily available.

  • Relatively low cost.

7.1.2 Disadvantages

  • Working solutions degrade rapidly.

  • Concentrate solutions tend to degrade over time.

  • Readily inactivated by organic matter.

  • Disinfecting ability significantly affected by pH, with loss of activity above pH 8.5.

  • No wetting capability.

7.1.3 Availability

Hypochlorite disinfectants are readily available, in a range of concentrations, from commercial cleaning supply wholesalers, swimming pool supply stores and chemical wholesalers.

7.1.4 Environmental and workplace safety considerations

  • Adhere to recommendations and safety advice from the manufacturer and in the material safety data sheet.

  • Hypochlorites are toxic to fish, but they are rapidly neutralised by organic matter, and therefore any effects are short lived.

  • Hypochlorites are inactivated by thiosulfate.

  • Hypochlorites are powerful oxidising agents, and some compounds may cause fire or explosion or produce severe burns. Concentrate preparations should not come into contact with other chemicals (especially acids) or with combustible material such as paper, fabric, sawdust or kerosene.

  • Concentrate preparations should be stored in dry, well-ventilated areas away from sunlight.

  • Hypochlorites should not be mixed with other chemicals or with different types of chlorinating chemicals.

  • Concentrate preparations can irritate eyes, nose, throat and skin. Avoid contact with skin, eyes, and clothing. Avoid breathing dust or vapour.

  • Hypochlorites liberate chlorine gas at low pH and therefore should not be mixed with acids.

7.1.5 Applications

  • As a basic disinfecting agent for most applications (taking into account the points listed above).

  • On clean surfaces.

  • Disinfection of water.

  • Disinfection of previously cleaned buildings, equipment, vehicles, tanks and pipework.

  • Not recommended for disinfection of slurries, manures, carcases, uncleaned surfaces or other situations with high levels of organic matter.

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