Risks and Hazards of Chlorine


CAS no.  (Chemical Abstracts Service Registry Number): 7782-50-5


Chlorine (dichlorine, diatomic chlorine, bertholite, sodium hypochlorite, molecular chlorine) is a greenish-yellow gas. It has a very pungent odour similar to the smell of bleach. Chlorine is mildly soluble in water, becoming hypochlorous acid and hypochloric acid.

As chlorine is heavier than air (approximately 2 ½ times), in areas with limited ventilation or air movement it will often accumulate and spread through low lying areas.

Liquid chlorine will evaporate into the air very quickly. Chlorine combines easily with all gases except for nitrogen and any of the rare gases (excluding xenon). Chlorine itself is not flammable but, being very reactive, it may explode or form explosive compounds when exposed to substances such as ammonia, hydrogen, natural gas or turpentine.

Often for shipping or storage, chlorine is cooled and pressurized turning into liquid chlorine.

  • Melting Point: -100.98°C
  • Boiling Point: -34.6°C
  • Specific Gravity: 1.4085
  • Vapour Density: 2.5
  • Formula weight 70.906


Chlorine is used in the manufacturing of many consumer products (rubber, plastic, paper, solvents, pesticides, titanium dioxide pigment) as well as industrial (food processing, water purification, sewage treatment) and household (swimming pool sanitation, cleaners) disinfectants.

During World War I, chlorine was used for chemical warfare as a choking agent.


According to Safe Work Australia, chlorine is classified as a “Hazardous Chemical”. It is also classified by the Australian Dangerous Goods Code as “Dangerous Goods” for transport by road or rail.

Occupational Health Exposure Standards

Occupational Exposure Limits ILV (EU) – 15 min – [mg/m³] : 1.5

ILV (EU) – 15 min – [ppm] : 0.5

DNEL: Derived no effect level (Workers) Inhalation-short term (local)[mg/m3]: 1.5

Inhalation-short term (systemic)[mg/m3]: 1.5

Inhalation-long term (local) [mg/m3]: 0.75

Inhalation-long term (systemic)[mg/m3]: 0.75

PNEC: Predicted no effect concentration Aqua (freshwater) [mg/l]: 0.00021

Aqua (marine water) [mg/l]: 0.000042

Aquatic, intermittent releases [mg/l]: 0.00026

Micro-organisms or PNEC sewage treatment plant (STP) [mg/l]: 0.03 8.2.

 0.5 ppm (1.45 mg/m3) 15-minute CEILING

OSHA PEL: 1 ppm (3 mg/m3) CEILING

1-hour EEGL: 3 ppm

24-hour EEGL: 0.5 ppm

A concentration of 34 to 51 ppm has been reported to be lethal in 1 to 1.5 hours [Freitag 1941] while 14 to 21 ppm has been suggested as being dangerous within 0.5 to 1 hour [NPIRI 1983].

Exposure controls

Appropriate engineering controls

An appropriate chlorine detection system should be installed and portable instrument worn for maximum worker protection. Further oxygen detectors should be used when asphyxiating gases may be released.

  • Provide adequate general and local exhaust ventilation.
  • Ensure exposure is below occupational exposure limits (where available).
  • Systems under pressure should be regularly checked for leakages.
  • Consider work permit system e.g. for maintenance activities.

Individual protection measures e.g. personal protective equipment

A risk assessment should be conducted and documented in each work area to assess the risks related to the use of the product and to select the PPE that matches the relevant risk.

The following recommendations should be considered: PPE compliant to the recommended EN/ISO standards should be selected.

  • Eye/face protection: Wear safety glasses with side shields. Standard EN 166 – Personal eye-protection.
  • Skin protection:
    • Hand protection: Wear working gloves when handling gas containers. Standard EN 388 – Protective gloves against mechanical risk.
    • Other: Wear safety shoes while handling containers. Standard EN ISO 20345 – Personal protective equipment – Safety footwear.
  • Respiratory protection: Self contained breathing apparatus (SCBA) or positive pressure airline with mask are to be used in oxygen-deficient atmospheres. Standard EN 137 – Self-contained open-circuit compressed air breathing apparatus with full face mask.

Short Term Exposure Risks


The most common hazardous exposure is through inhalation. Although chlorine’s odour may provide early warning signs it may also cause olfactory fatigue, minimizing an individuals perception of danger.

Low level exposure can cause blurry vision, coughing, sore or burning throat, or nausea.

More acute, high level exposure can lead to symptoms such as wheezing, difficulty breathing, chest tightness, vomiting, dyspnea and bronchospasm.

Lung edema (noncardiogenic pulmonary edema), otherwise known as fluid in the lungs, can occur in severe cases. Symptoms often don’t appear for a few hours after exposure. It is very important that anyone exposed to high levels of chlorine should rest and be observed by a medical professional for up to 24 hours after exposure. Although extreme exposure may be fatal, most people recover fully after exposure.

Skin & Eye Contact

Direct contact with skin is much less common given that chlorine is a gas at room temperature. Gas exposure can cause skin and eye irritation at low levels and severe chemical burns at high levels. Skin contact with liquid chlorine can cause frostbite.

Long Term Exposure Risks

If high level, short term exposure has occurred it may result in long term symptoms or complications. In cases where pulmonary edema has occurred there is risk of permanent respiratory tract and lung damage.

Long term, repeated exposure has a similar effect of chronic lung and respiratory inflammation and difficulty breathing.



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