Chlorine

Chlorine was discovered in 1774 by Carl Wilhelm Scheele, who called it "dephlogisticated marine acid air" [1]. Its large-scale production became practical in the 1890s with electrochemical chlor-alkali cells, and its use expanded into water treatment (first applied to the US water supply in Jersey City, NJ in 1908, dramatically reducing typhoid fever mortality), bleaching, and chemical synthesis. Its military career began in World War I when German forces released 168 tons of chlorine gas at Ypres in April 1915, killing or injuring 15,000 Allied soldiers — the first large-scale use of chemical weapons [2]. Today chlorine is one of the highest-volume industrial chemicals in the US, produced at about 13 million tons annually. It is transported by rail and pipeline, and accidents at water treatment plants, industrial facilities, and during transportation create community emergency scenarios [3]. Swimming pools and bleach-based cleaning products are the most common consumer contact points.

Consumer exposure to chlorine primarily comes from bleach-based cleaning products (chlorine gas is released when bleach is mixed with ammonia or acids — a common accidental poisoning scenario), from swimming in chlorinated pools, and as a byproduct of drinking water disinfection [1]. The disinfection byproducts of chlorine in drinking water (trihalomethanes, haloacetic acids, chloroform) are more concerning for chronic health effects than dissolved chlorine itself. Industrial accident exposure occurs in communities near chlor-alkali plants, bleach manufacturing, and during rail or road tanker accidents [2]. Water treatment plant workers manage chlorine handling risks on a daily basis. The reaction of bleach with household ammonia (in many cleaners and glass cleaners) generates chloramine gas in the home — a significant source of accidental indoor toxic gas exposure [3].

Chlorine gas is a potent respiratory irritant and at high concentrations a pulmonary toxin [1]. It reacts with moisture in the airways to form hydrochloric acid and hypochlorous acid, damaging the epithelial lining from the nose to the alveoli. Mild exposures cause burning in the nose, throat, and eyes, with coughing and shortness of breath. Higher exposures cause pulmonary edema — fluid accumulation in the lungs — that can be life-threatening 12–24 hours after the initial exposure [2]. Long-term effects of industrial chlorine exposure include chronic respiratory disease, asthma, and reduced lung function. The occupational cohort of chlor-alkali workers shows elevated rates of respiratory illness. The disinfection byproducts generated in chlorinated water are the primary chronic cancer concern for the general population [3].

Water treatment plant workers, chlor-alkali plant workers, and bleach manufacturing workers face the highest occupational chlorine exposures [1]. People who use bleach and ammonia-containing cleaners in the same space — a common accident in home cleaning — create chloramine gas exposures. Competitive indoor swimmers and pool workers breathe chlorinated pool air containing chloroform and chloramines at concentrations that cause respiratory irritation [2]. Communities near chlorine manufacturing, transportation routes, and water treatment facilities face emergency exposure risk in accident scenarios.

Never mix bleach with ammonia, other cleaners, or acidic products like vinegar — the reactions generate toxic gases including chloramines and chlorine [1]. Store bleach in its original container, away from other chemicals. Ensure good ventilation when using bleach-based cleaning products [2]. For pools: ensure your pool's free chlorine is maintained at proper levels — both under-chlorination (inadequate disinfection) and over-chlorination (excess gas) are problems. Outdoor pools have better ventilation than indoor pools. For water treatment chemical exposure: use certified respiratory protection and follow emergency response protocols during chlorine handling [3]. If you are near a chlorine release emergency, move away from the release perpendicular to wind direction (don't move downwind), and seek higher ground if outdoors as chlorine is denser than air.