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Chlorine

DESIGNATIONS

CAS No.: 7782-50-5
Registry name: Chlorine
Chemical name: Chlorine
Synonyms, Trade names: Chlorum
Chemical name (German): Chlor
Chemical name (French): Chlore
Appearance: greenish-yellow gas with pungent irritating odour

BASIC CHEMICAL AND PHYSICAL DATA

Empirical formula: Cl2
Rel. molecular mass: 70.91 g
Density: 0.567 g/cm3 (liquid, critical density at 144 C); 3.21 g/l (gas) at 0C, 1013 hPa
Relative gas density: 2.49
Boiling point: -34.05C
Melting point: -100.98C
Vapour pressure: 6.8 bar at 20C
Odour threshold: 0.05 ppm
Solvolysis/solubility: in water: 7.3 g/l at 20C
in tetrachloromethane: 176.5 g/l at 19C
Conversion factors: 1 mg/m3 = 0.339 ml/m3
1 ml/m3 = 2.947 mg/m3

ORIGIN AND USE

Usage:
Chlorine is used for numerous applications in the chemical industry, for example in the manufacture of chlorinated organic products (synthetics, solvents, insecticides, herbicides). It is also used in the cellulose/paper industry and in laundries as a bleaching agent. Drinking-water and swimming-pool water disinfection is a further application.

Origin/derivation:
In nature, chlorine is chiefly found as chloride (bonded to sodium, potassium and magnesium). A further important chlorine compound is hydrogen chloride. Nowadays, chlorine is primarily produced by electrolysis of alkali-metal chlorides (mercury method and diaphragm method). Use is also still made of chemical methods (SHELL chlorine method, KEL chlorine process, SOUTHWEST POTASH method).

Production figures (worldwide):
1975 = 22.5 million tons; 1983 = 30 million tons; 1994 = >40 million tons

Toxicity

Humans: LCLo 837 ppm/30 min, inhalation acc. UBA, 1986
2.5 mg/l air = immediately lethal acc. TAB. CHEMIE, 1980
Mammals:
Rat LC50 293 ppm/1 h, inhalation acc. UBA, 1986
Mouse LC50 137 ppm/1 h, inhalation acc. UBA, 1986
Guinea pig LCLo 330 ppm/7 h, inhalation acc. UBA, 1986
Dog LCLo 800 ppm/30 min, inhalation acc. UBA, 1986
Aquatic organisms:
Trout 0.08 ppm/ 168 h/ freshwater; TLm acc. UBA, 1986
Fish more than 0.05 mg/l lethal  

Characteristic effects:

Humans/mammals: Chlorine is an extremely caustic, poisonous gas. Symptoms of poisoning following inhalation are the irritation of the mucous membranes of the respiratory tract combined with breathing difficulties, coughing up of blood and low pulse rate. Humans become accustomed to odour and irritation if exposed for a long time or repeatedly. Symptoms may be delayed. Liquid chlorine is extremely caustic on the skin.

Plants: Any description of the damage to plants generally relates to the chloride impact although chlorine gas is also absorbed by plant leaves and destroys plant tissue partly by oxidation and partly by expulsion of hydrogen in organic compounds.

ENVIRONMENTAL BEHAVIOUR

Water:
Water hazard class 2. Destroys all aquatic life; kills bacteria as long as free chlorine can be detected. Chlorine reacts with water forming hydrogen chloride/hydrochloric acid depending on water content. Chlorine corrodes several materials when wet.

Air:
On expansion, chlorine gas (compressed gas) forms a cold mist which is denser than air; poisonous, corrosive mixtures form in air over the surface of water.

Soil:
Chlorine is only found in soil in ionised form of its salts (chlorides).

ENVIRONMENTAL STANDARDS

Medium/acceptor Sector Country/organ.

Status

Value Cat. Remarks Source
Air:   D

L

0.1 mg/m3 IW 1 1) acc. TA Luft, 1986
    D

L

0.3 mg/m3 IW 2 2) acc. TA Luft, 1986
    D

G

0.10 mg/m3   Monthly average, plants acc. LAU-BW
  Emiss. D L 5 mg/m3   mass flow > 50 g/h acc. TA Luft, 1986
  Workp D

L

1.5 mg/m3 MAK Peak limit I DFG, 1989
  Workp D

L

1.5 mg/m3 BAT   acc. LAU-BW
  Workp DDR

L

1 mg/m3     acc. LAB. CHEMIE, 1980
  Workp SU

(L)

1 mg/m3     acc. SORBE, 1988
  Workp USA

(L)

3 mg/m3 TWA   acc. SORBE, 1988
  Workp USA

(L)

9 mg/m3 STEL   acc. SORBE, 1988

Notes:

1) Annual arithmetic mean
2) 98 % of annual 30-minute average

Assessment/comments

Chlorine is a hazard to all types of water and in particular to drinking water because of its high toxicity and corrosiveness as well as its oxidising effect. Disaster alarm must be given if large quantities of the gas are liberated.


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