Do You Know Your Chlorine-Based Biocide?  A Quick Synopsis Regarding Chlorine Chemical Nomenclature



Written by: Selective Micro Technologies 

Did you know that the type of chlorine-based biocide one uses for decontamination not only plays a role in how effectively surfaces are disinfected, but also may impact health and safety even at particularly low use concentrations. Chlorine bleach is a commonly known biocide, and has been grandfathered in for so many uses.

Chlorine itself comes in a number of forms:

  • Chlorine gas, which can destroy the respiratory organs, and cause death by asphyxiation
  • Sodium hypochlorite "bleach" & calcium hypochlorite HTH tablets / granules
  • Organo chloro compounds which can release chlorine on contact with water; eg dichlorodiisocyanurate
  •  Free chlorine, which can be hypochlorous acid (HOCl) or hypochlorite (OCl–) ion or bleach
  • Combined chlorine, which is when ammonia or nitrogen may combine with free chlorine 

Chlorine itself has advantages such as presenting end-user familiarity and being a cost effective disinfectant. However, disadvantages include it is highly corrosive (in all forms, including chorine gas, free chlorine, and combined chlorine). It is toxic (in all forms); HOCl can produce disinfection byproducts, which are carcinogenic. Also, it's efficacy against microbial organisms is very pH dependent. Unlike chlorine gas, pure chlorine dioxide does not hydrolyze in water to form ionic impurities, nor does pure chlorine dioxide form harmful byproducts, like chlorine bleach. Selective Micro® offers ultra-pure chlorine dioxide at the point of use, which is a very user-friendly (just add water), highly compatible, and environmentally-aware method to harness the decontamination power of the chlorine dioxide molecule. This is accomplished through the company’s patented membrane technology, which delivers >99% pure chlorine dioxide in solution. For more information, please visit:

In summation, here are some other points to consider before using chlorine itself opposed to pure chlorine dioxide for decontamination and deodorization protocols:

  • It is highly reactive and hence affected by suspended solids and organics in water
  • It is very weak at removing bio-slime
  • It has very poor material compatibility, therefore very high corrosivity issues 
  • It produces an unpleasant working environment due to potential health hazards and its ability to readily generate disinfection byproducts
  • It is important to know the difference between "free" chlorine and "combined" chlorine. Free chlorine relates to HOCl in the pH range of 7 - 7.5 and combined chlorine relates to the OCL - ion or reaction solutions, e.g., chloramines. The latter (OCL- and chloramines) have VERY POOR disinfectant capabilities.