Excessive chlorine exposure can cause acute, short-term health issues. Chlorine is introduced to pool water to act as a sanitizer, destroying pathogens and organic contaminants, which is essential for safe swimming. However, when the concentration exceeds recommended limits or its byproducts accumulate, it shifts from a protective agent to an irritant. Understanding the difference between proper sanitization levels and chemical overdose is key to maintaining a safe aquatic environment.
Acute Health Effects of High Chlorine
High concentrations of the active sanitizer, hypochlorous acid, can immediately irritate the body’s mucous membranes and skin. Ocular irritation is common, presenting as redness, burning, stinging, and temporary blurring of vision. This irritation occurs because the chemical disrupts the protective tear film layer that coats the surface of the eye.
The skin is also vulnerable to irritation from over-chlorinated water, which can lead to dryness, itching, and the development of a rash. In extreme cases, direct contact with highly concentrated chlorine can cause a burning sensation or chemical burns.
Chlorine exposure can also provoke respiratory symptoms, particularly in indoor swimming areas where ventilation may be insufficient. Inhaling the gases that off-gas from the water can irritate the nose, throat, and lungs, resulting in coughing, chest tightness, or difficulty breathing. This condition, sometimes referred to as “chlorine cough,” is especially relevant for individuals with pre-existing conditions like asthma.
Understanding the Irritants: Free Chlorine vs. Chloramines
Irritation symptoms are often mistakenly blamed on high levels of free chlorine, the active form of the chemical used to sanitize the water. Free chlorine is necessary and, at proper levels, does not produce the pervasive chemical odor most people associate with a pool. The strong, pungent smell and severe irritation are primarily caused by volatile compounds called chloramines, or combined chlorine.
Chloramines form when free chlorine reacts with organic waste introduced by swimmers, such as sweat, urine, body oils, and cosmetics. When the level of these byproducts increases, the active sanitizer is “used up,” leading to less effective germ killing and more irritation. Chloramines are heavier than air, concentrating just above the water’s surface where swimmers are most likely to inhale them, causing respiratory and eye discomfort.
The process used to eliminate these irritating chloramines is called breakpoint chlorination, or “shocking” the pool. This involves adding a large dose of chlorine to raise the free chlorine level high enough to break the chemical bonds of the chloramines and convert them into harmless nitrogen gas, which then escapes into the atmosphere. This process restores the pool’s sanitizing power and removes the irritating compounds.
Identifying and Correcting Pool Chemistry Imbalances
Maintaining the correct balance requires regular testing, most often done with test strips or liquid test kits. The recommended safe operating range for free chlorine in a pool is between 1.0 and 4.0 parts per million (ppm). The level of combined chlorine, the irritating chloramines, should ideally be kept at 0.2 ppm or less.
Accidental over-chlorination can occur from over-dosing during shocking or from a malfunctioning chemical feeder. If testing reveals a dangerously high chlorine level, one of the simplest methods for reduction is to stop adding any chlorine and remove the pool cover. Direct sunlight and heat naturally accelerate the breakdown and dissipation of chlorine.
For a faster reduction, a partial drain and refill with fresh water is an effective dilution method. Chemical neutralizers, such as sodium thiosulfate, can also be added to the water to quickly break down the excess chlorine. It is important to retest the water after any correction method to ensure levels are brought back into the safe and effective range.
Immediate Steps After Exposure
If a swimmer experiences acute irritation or symptoms of sickness from pool exposure, the first action is to remove them from the water and the immediate pool area to a location with fresh air. For eye irritation, the eyes should be flushed immediately and continuously with clean, running water for at least 15 minutes. Any contact lenses should be removed before rinsing begins.
Affected skin areas should also be washed thoroughly with soap and water to remove any chemical residue. Any clothing that may have been contaminated with highly concentrated chemicals should be removed. It is important to seek medical attention if symptoms persist, especially if there is persistent coughing, severe difficulty breathing, vomiting, or signs of chemical burns on the skin.