The recent chlorine leak at a sports club in Mentana, just outside Rome, has brought renewed attention to the safety of systems that use chlorinated products for water treatment. However, it’s important to clarify one point right away: the presence of chlorine in water, when properly dosed and controlled, does not equate to a health risk.
Disinfection is essential to contain the proliferation of bacteria, viruses, fungi, and other microorganisms. Risks, however, arise from anomalies in the design, maintenance, or management of the system, such as incorrect dosages, malfunctions, poor ventilation, or contact between chemically incompatible substances. Therefore, the issue concerns not only the product used, but the entire water treatment system.
Chlorine in water and chlorine in the air are not the same thing. A distinction must be made between chlorine present in water, as a disinfectant, and chlorine gas, which can be accidentally released into the environment. In the former case, the product is dosed in controlled quantities to keep the water microbiologically safe. In the latter case, however, we are faced with a chemical emergency, often caused by the reaction between incompatible products. In public swimming pools, the commonly used reference values include a free active chlorine between 0.7 and 1.5 mg/L, a combined active chlorine no higher than 0.4 mg/L, and a pH between 6.5 and 7.5.
Chlorine is a highly irritating gas. When inhaled, it reacts with water present on the mucous membranes of the eyes, nose, throat, and respiratory tract. This reaction generates acidic and oxidising substances capable of damaging surface tissues. The effects depend on the gas concentration, the duration of exposure, the ventilation of the environment, the distance from the source, and the health conditions of the person involved. The intensity of breathing activity can also affect the amount of substance inhaled:
- At low concentrations, burning eyes, watery eyes, nasal irritation, sore throat, and cough may occur;
- At medium concentrations, difficulty breathing, chest tightness, wheezing, and bronchospasm may occur;
- At high concentrations, pulmonary edema may develop, with worsening symptoms occurring even after several hours.
Children are more vulnerable because they are particularly sensitive to environmental chemicals. Compared to adults, they breathe a greater amount of air relative to their body weight and have a still-developing respiratory system. Furthermore, their smaller stature represents an additional risk factor, as gases heavier than air can tend to accumulate in low-lying and poorly ventilated areas. More intense exposures can cause temporary changes in respiratory function and, in some cases, persistent asthma-like conditions. The presence of children therefore makes the proper design of utility rooms, dosing systems, and emergency procedures even more important.
The typical “pool odour” does not necessarily indicate excess free chlorine. It is most often due to chloramines, compounds formed when chlorine reacts with organic substances present in the water, such as sweat, urine, cosmetics, skin cells, and residues introduced from the environment. The formation of chloramines has two negative effects:
- It reduces the amount of chlorine available for disinfection;
- It generates irritating compounds that can pass from the water into the air.
A room with a strong pool odour is therefore not necessarily a “highly disinfected” room. On the contrary, it could be a sign of an incorrect chemical balance, insufficient water exchange, or inadequate ventilation.
Chlorine gas releases can occur in many situations, primarily due to a lack of adequate knowledge and technical protection. One of the most dangerous scenarios is contact between hypochlorite and acidic products used for pH adjustment, as mixing them can rapidly release chlorine gas. This problem can arise due to:
- incorrect connections of dosing lines;
- transferring a product to the wrong tank;
- dosing operation without water flow;
- backflow of one reagent into the other line;
- maintenance work performed without proper procedures;
- uncoordinated restart of the system after a circulation stop.
For this reason, dosing systems must be interlocked with the recirculation pump. In the absence of flow, the chemical feed must stop automatically. The lines must also be clearly identified, separated, and protected against backflow and accidental overflow.
Safety must be planned at the design stage. The safe management of chemicals cannot be left solely to the operator’s experience; it must be integrated into the plant design.
Technical rooms must be separated from publicly accessible areas and reserved for authorised personnel. Incompatible products must be stored in separate areas, with dedicated containment basins and adequate ventilation. Tanks, pipes, and dosing lines must be clearly identified.
Control instruments must be accessible, verifiable, and subject to periodic calibration. Alarms, sampling points, and intervention recording must be part of a clear and documented management logic. The data displayed on the control unit must be considered part of a broader control system, not a guarantee. For this reason, safety always requires that automation be complemented by professional operator training, including periodic manual checks, scheduled maintenance, and parameter recording.
The filling, maintenance, and replacement of containers must also be defined through precise procedures consistent with the plant’s characteristics. Indoor air conditioning must also be carefully designed: simply controlling temperature and humidity is not enough; ventilation must prevent the accumulation of irritants near the water surface and in areas frequented by users.
What to do in case of fumes? A suddenly intense and pungent odor, accompanied by burning eyes, coughing, or difficulty breathing, must be treated as an emergency. In these cases, you must:
- Immediately leave the area and reach an open, well-ventilated space;
- Prevent other people from entering;
- Call 112;
- Do not re-enter until authorised by emergency services.
Do not attempt to locate or neutralise the leak without specific training and adequate protective equipment.
Chlorination, if properly designed, dosed, and monitored, remains one of the most effective systems for microbiological control of water.
Safety, however, depends on the entire system: when designing a swimming pool or fountain, water treatment is not a technical accessory to be defined at the end. It is an integral part of the project and must be addressed from the earliest stages of the project.
