Sodium Hypochlorite


Sodium hypochlorite is a chemical compound with the formula NaClO. [1] It is a clear, slightly yellowish solution with a characteristic odour. Sodium hypochlorite is unstable. Chlorine evaporates from the solution and when heated, the sodium hypochlorite disintegrates. This also happens when sodium hypochlorite comes in contact with acids, sunlight, certain metals and poisonous and corrosive gasses, including chlorine gas. It is a strong oxidator and reacts with flammable compounds and reductors. Sodium hypochlorite solution is a weak base that is inflammable.[2]

Uses [2]

Sodium hypochlorite is used on a large scale. For example in agriculture, chemical industries, paint- and lime industries, food industries, glass industries, paper industries, pharmaceutical industries, synthetics industries and waste disposal industries. In the textile industry sodium hypochlorite is used to bleach textile. It is sometimes added to industrial wastewater. This is done to reduce odours. Hypochlorite neutralises sulphur hydrogen gas (SH) and ammonia (NH3). It is also used to detoxify cyanide baths in metal industries. Hypochlorite can be used to prevent algae and shellfish growth in cooling towers. In water treatment, hypochlorite is used to disinfect water. In households, hypochlorite is used frequently for the purification and disinfection of the house.

Sources and Routes of Exposure

Sources of Exposure [3]

  • Exposure to sodium hypochlorite can occur at low levels if you use disinfectants like household bleach.
  • Exposure may also occur when swimming in pools where it has been added to kill bacteria.
  • Drinking water from public drinking water supplies where sodium hypochlorite is added to kill bacteria can also be a source of exposure.
  • Workers employed in occupations where sodium hypochlorite is used to bleach paper and textiles may be subject to slightly higher levels of exposure.

Routes of Exposure [4]

The main routes of sodium hypochlorite is via ingestion, contact with the skin and eyes and inhalation of gases.

Health Effects [5]

Acute Exposure

Symptoms of sodium hypochlorite exposure may be immediate, or may be delayed for several hours.


The toxicity of sodium hypochlorite solution by inhalation is predominantly due to the mixing of bleach with acids and the release of highly irritant gases. Metabolic acidosis may occur in rare cases following significant inhalation of sodium hypochlorite. Mixing sodium hypochlorite with acids releases chlorine gas, although in most cases the concentration of chlorine liberated are not sufficient to cause adverse health effects. In rare cases, inhalation of chlorine gas, produced from mixing sodium hypochlorite with acid causes immediate burning of the throat and lungs, eye and nose irritation, chest tightness, coughing, sore throat, wheezing and dyspnoea. In severe cases, bronchospasm, pneumonitis, upper airway oedema, pulmonary oedema or oedema of the glottis may develop. Mixing sodium hypochlorite with ammonia-based solutions results in the formation of monochloramine and dichloramine, both of which are respiratory irritants. In most cases respiratory irritation occurs immediately, followed by a latent period of 5 minutes to 15 hours, after which time breathlessness and bronchospasm may occur. In most cases symptoms are usually resolved in 1 – 4 weeks [5, 8]. However, in some instances pulmonary damage may lead to long-term Reactive Airways Dysfunction Syndrome (RADS), a chemical irritant-induced type of asthma following an acute respiratory exposure to an irritant gas. In addition, Acute Respiratory Distress Syndrome (ARDS), as a result of pneumonitis, has been reported in patients following inhalation of chlorine following the mixing of bleach and other hydrochloric acid.


At low concentrations (up to 10 %), such as those used for household bleach, sodium hypochlorite is a mild to moderate irritant that rarely produces necrosis or significant mucosal injury. Ingestion is not expected to cause severe or permanent damage of the gastrointestinal tract and recovery is usually rapid. At higher concentrations (> 10 %) it is corrosive. The critical pH for corrosivity is thought to be 12.5. Ingestion of small volumes (up to 200 ml in adults; 50 ml in children) of sodium hypochlorite solution (< 10 %) usually causes minimal health effects. In some cases it may cause burns to the mouth, throat, oesophagus and stomach, pharyngeal pain and inflammation, gastrointestinal irritation, nausea and vomiting. Dysphagia, stridor, drooling, abdominal pain and dyspnoea may also occur. Severe irritation is uncommon unless contact is prolonged or a large volume is ingested. Ingestion of large amounts (approximately 300 ml in adults; 100 ml in children) of sodium hypochlorite (< 10 %) or more concentrated sodium hypochlorite (> 10 %) may cause corrosive oesophagitis, haematemesis, abdominal and retrosternal pain, diarrhoea and, in some cases, malaena and metabolic acidosis, although symptoms other than vomiting do not strongly correlate with the amount of sodium hypochlorite ingested. In rare cases, the gastrointestinal mucosa may become haemorrhagic, ulcerated and perforated, leading to shock. Hypernatraemia, hyperchloraemia, hypotension and cardiovascular collapse may rarely develop after ingestion of extremely large volumes of sodium hypochlorite (volumes not stated). Aspiration of sodium hypochlorite or aspiration of contaminated vomit may occur. This secondary source of pulmonary exposure may lead to ARDS.

Dermal/Ocular exposure

Sodium hypochlorite itself is corrosive and may irritate the skin or cause burning pain, inflammation and blisters. Skin damage may not be immediately apparent and may continue to develop over time. Ocular exposure to household bleach can cause mild irritation and temporary discomfort if eyes are washed immediately [1]. Irritation becomes more severe and prolonged if eyes are not washed. More concentrated solutions can cause pain, blepharospasm, lacrimation, conjunctivitis, photophobia, necrosis and chemosis of the cornea, clouding of the cornea, iritis, cataract formation and retinitis.

Chronic Effects

Dermal/Ocular exposure

Chronic dermal exposure to sodium hypochlorite solution may cause skin irritation.


No data were available from studies in humans on the carcinogenicity of hypochlorite salts and there was inadequate evidence for the carcinogenicity of hypochlorite salts in experimental animals. Overall, the IARC assigned hypochlorite salts to Group 3, i.e. compounds that are not classifiable as to their carcinogenicity in humans.

Reproductive and developmental toxicity

There are no data indicating that sodium hypochlorite, without severe maternal toxicity, is associated with adverse effects on reproductive function, pregnancy or lactation in humans.

Safety [6]

First Aid Measures

  • Ingestion: Rinse mouth with water immediately. If swallowed DO NOT induce vomiting. Give a 1-3 glasses of water to drink. If vomiting occurs, place victim head lower then hips to prevent vomiting entering lungs. Seek immediate medical assistance or contact the Poisons Information Centre immediately.
  • Eye: Hold eyelids apart and flush the eye continuously with running water. Continue flushing until advised to stop by the Poisons Information Centre or a doctor, or for at least 15 minutes.
  • Skin: If spilt on large areas of skin or hair, immediately drench with running water and remove clothing. Continue to wash skin and hair with plenty of water (and soap if material is insoluble) until advised to stop by the Poisons Information Centre or a doctor.
  • Inhaled: Remove victim from further exposure. Remove contaminated clothing and loosen remaining clothing. Allow patient to assume most comfortable position and keep warm. Keep at rest until fully recovered. Seek medical attention if effects persist.
  • Advice to Doctor: Treat symptomatically. Can cause corneal burns. Delayed pulmonary oedema may result.

Exposure Controls & Personal Protection

Engineering Control Measures

  • Ensure ventilation is adequate and that air concentrations of components are controlled below quoted Exposure Standards.
  • If inhalation risk exists, use with local exhaust ventilation or while wearing air supplied mask.
  • Keep containers closed when not in use.

Personal Protective Equipment

  • Wear overalls, face shield, elbow-length impervious gloves, splash apron and rubber boots.
  • Always wash hands before smoking, eating, drinking or using the toilet.
  • Wash contaminated clothing and other protective equipment before storage or re-use.
  • If risk of inhalation exists, wear air supplied respirator meeting the requirements of AS/NZS 1715 and AS/NZS 1716.


United States [7]

  • NIOSH: The National Institute for Occupational Safety and Health recommends an airborne recommended exposure limit (REL) of 0.5ppm for sodium hypochlorite for any 15 min work period.
  • AIHA: The American Industrial Hygiene Association recommends a workplace environmental exposure level (WEEL) of 2mg/m3 for sodium hypochlorite for a 15 min work period.

Australia [6]

No value assigned for this specific material by the National Occupational Health and Safety Commission. However, Exposure Standard(s) for decomposition product(s): Chlorine: Peak Limitation = 3 mg/m3 (1 ppm).

Peak Limitation – a ceiling concentration which should not be exceeded over a measurement period which should be as short as possible but not exceeding 15 minutes. These Exposure Standards are guides to be used in the control of occupational health hazards. All atmospheric contamination should be kept to as low a level as is workable. These exposure standards should not be used as fine dividing lines between safe and dangerous concentrations of chemicals. They are not a measure of relative toxicity.