of the explosions rather than the effects of chlorine since the toxic gas is readily dispersed and diluted in the atmosphere by the blast. in some bombings, over a hundred civilians were hospitalized due to breathing difficulties. the iraqi authorities tightened security for elemental chlorine, which is essential for providing safe drinking water to the population. on 23 october 2014, it was reported that the islamic state of iraq and the levant had used chlorine gas in the town of duluiyah, iraq. laboratory analysis of clothing and soil samples confirmed the use of chlorine gas against kurdish peshmerga forces in a vehicle-borne improvised explosive device attack on 23 january 2015 at the highway 47 kiske junction near mosul. another country in the middle east, syria, has used chlorine as a chemical weapon delivered from barrel bombs and rockets. in 2016, the opcw-un joint investigative mechanism concluded that the syrian government used chlorine as a chemical weapon in three separate attacks. later investigations from the opcw's investigation and identification team concluded that the syrian air force was responsible for chlorine attacks in 2017 and 2018. biological role the chloride anion is an essential nutrient for metabolism. chlorine is needed for the production of hydrochloric acid in the stomach and in cellular pump functions. the main dietary source is table salt, or sodium chloride. overly low or high concentrations of chloride in the blood are examples of electrolyte disturbances. hypochloremia (having too little chloride) rarely occurs in the absence of other abnormalities. it is sometimes associated with hypoventilation. it can be associated with chronic respiratory acidosis. hyperchloremia (having too much chloride) usually does not produce symptoms. when symptoms do occur, they tend to resemble those of hypernatremia (having too much sodium). reduction in blood chloride leads to cerebral dehydration; symptoms are most often caused by rapid rehydration which results in cerebral edema. hyperchloremia can affect oxygen transport. hazards chlorine hazards ghs labelling: pictograms signal word danger hazard statements h270, h315, h319, h330, h335, h400 precautionary statements p220, p233, p244, p261, p304, p312, p340, p403, p410 nfpa 704 (fire diamond) 3 0 0ox chlorine is a toxic gas that attacks the respiratory system, eyes, and skin. because it is denser than air, it tends to accumulate at the bottom of poorly ventilated spaces. chlorine gas is a strong oxidizer, which may react with flammable materials. chlorine is detectable with measuring devices in concentrations as low as 0.2 parts per million (ppm), and by smell at 3 ppm. coughing and vomiting may occur at 30 ppm and lung damage at 60 ppm. about 1000 ppm can be fatal after a few deep breaths of the gas. the idlh (immediately dangerous to life and health) concentration is 10 ppm. breathing lower concentrations can aggravate the respiratory system and exposure to the gas can irritate the eyes. when chlorine is inhaled at concentrations greater than 30 ppm, it reacts with water within the lungs, producing hydrochloric acid (hcl) and hypochlorous acid (hclo). when used at specified levels for water disinfection, the reaction of chlorine with water is not a major concern for human health. other materials present in the water may generate disinfection by-products that are associated with negative effects on human health. in the united states, the occupational safety and health administration (osha) has set the permissible exposure limit for elemental chlorine at 1 ppm, or 3 mg/m3. the national institute for occupational safety and health has designated a recommended exposure limit of 0.5 ppm over 15 minutes. in the home, accidents occur when hypochlorite bleach solutions come into contact with certain acidic drain-cleaners to produce chlorine gas. hypochlorite bleach (a popular laundry additive) combined with ammonia (another popular laundry additive) produces chloramines, another toxic group of chemicals. chlorine-induced cracking in structural materials chlorine is widely used for purifying water, especially potable water supplies and water used in swimming pools. several catastrophic collapses of swimming pool ceilings have occurred from chlorine-induced stress corrosion cracking of stainless steel suspension rods. some polymers are also sensitive to attack, including acetal resin and polybutene. both materials were used in hot and cold water domestic plumbing, and stress corrosion cracking caused widespread failures in the us in the 1980s and 1990s. chlorine "attack" on an acetal resin plumbing joint resulting from a fractured acetal joint in a water supply system which started at an injection molding defect in the joint and slowly grew until the part failed; the fracture surface shows iron and calcium salts that were deposited in the leaking joint from the water supply before failure and are the indirect result of the chlorine attack chlorine-iron fire the element iron can combine with chlorine at high temperatures in a strong exothermic reaction, creating a chlorine-iron fire. chlorine-iron fires are a risk in chemical process plants, where much of the pipework that carries chlorine gas is made of steel.