exposure to chloramine can contribute to respiratory problems, including asthma, among swimmers. Respiratory problems related to chloramine exposure are common and prevalent among competitive swimmers. Though chloramine's distinctive smell has been described by some as pleasant and even nostalgic, its formation in pool water as a result of bodily fluids being exposed to chlorine can be minimised by encouraging showering and other hygiene methods prior to entering the pool, as well as refraining from swimming while suffering from digestive illnesses and taking breaks to use the bathroom. Safety US EPA drinking water quality standards limit chloramine concentration for public water systems to 4 parts per million (ppm) based on a running annual average of all samples in the distribution system. In order to meet EPA-regulated limits on halogenated disinfection by-products, many utilities are switching from chlorination to chloramination. While chloramination produces fewer regulated total halogenated disinfection by-products, it can produce greater concentrations of unregulated iodinated disinfection byproducts and N-nitrosodimethylamine. Both iodinated disinfection by-products and N-nitrosodimethylamine have been shown to be genotoxic, causing damage to the genetic information within a cell resulting in mutations which may lead to cancer. Synthesis and chemical reactions Chloramine is a highly unstable compound in concentrated form. Pure chloramine decomposes violently above . Gaseous chloramine at low pressures and low concentrations of chloramine in aqueous solution are thermally slightly more stable. Chloramine is readily soluble in water and ether, but less soluble in chloroform and carbon tetrachloride. Production In dilute aqueous solution, chloramine is prepared by the reaction of ammonia with sodium hypochlorite: NH3 + NaOCl → NH2Cl + NaOH This reaction is also the first step of the Olin Raschig process for hydrazine synthesis. The reaction has to be carried out in a slightly alkaline medium (pH 8.5–11). The acting chlorinating agent in this reaction is hypochlorous acid (HOCl), which has to be generated by protonation of hypochlorite, and then reacts in a nucleophilic substitution of the hydroxyl against the amino group. The reaction occurs quickest at around pH 8. At higher pH values the concentration of hypochlorous acid is lower, at lower pH values ammonia is protonated to form ammonium ions (), which do not react further. The chloramine solution can be concentrated by vacuum distillation and by passing the vapor through potassium carbonate which absorbs the water. Chloramine can be extracted with ether. Gaseous chloramine can be obtained from the reaction of gaseous