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Product Safety Assessment (PSA): Caustic Soda

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Names
Product Overview
Manufacture of Product
Product Description
Product Uses
Exposure Potential
Health Information
Environmental Information
Physical Hazard Information
Regulatory Information
Additional Information
References

Names

CAS No. 1310-73-2 Sodium hydroxide (NaOH)
Caustic soda Lye
Caustic


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Product Overview

  • Caustic soda is an essential ingredient in an array of industrial applications. In addition, consumers use caustic soda when using cleaners, such as oven and drain cleaners. See Product Uses.
  • Caustic soda is highly corrosive and reactive. Caustic soda can be irritating to the skin, eyes and gastrointestinal tract. See Health Information and Physical Hazard Information.
    Occupational and consumer exposure is dependent upon the conditions under which caustic soda is used. See Exposure Potential.
  • Although caustic is only slightly toxic to aquatic organisms, a large discharge can change the pH of the aquatic system which may be toxic to aquatic organisms. See Environmental Information.

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Manufacture of Product

  • Capacity – Dow is the largest producer of caustic soda in the world.1 Dow has production sites in the U.S., Brazil, Canada and Germany, with total annual caustic production exceeding 15 billion dry pounds (6.8 million metric tons).
  • Process – The chlor-alkali process uses naturally-occurring salt (in the form of brine) to produce two major products: caustic soda and elemental chlorine, plus hydrogen. The sodium chloride brine is electrolyzed to produce chlorine at the positive electrode (anode) and sodium hydroxide and hydrogen at the negative electrode (cathode). The electrolysis reaction is shown below.

caustic soda reaction formula

Electrolysis is the same process that energizes batteries. Dow uses two electrolytic processes to produce caustic soda and chlorine.

  1. Diaphragm cell
  2. Membrane cell

The anode and cathode chambers are separated by a barrier to prevent the sodium hydroxide and hydrogen from reacting with the chlorine. This barrier is either an ion-selective membrane or porous diaphragm. The membrane is more “selective,” meaning that sodium chloride (NaCl) cannot readily pass through the membrane, resulting in lower salt in the final caustic. For some applications, low-salt caustic is specified.

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Product Description

Caustic soda, typically sold by Dow as a 50% solution in water, is an odorless and colorless liquid. Sodium chloride, sodium carbonate, and sodium sulfate are impurities that can be found in caustic soda.

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Product Uses

Uses for Caustic Soda

Caustic soda is used in the following industries and applications:2,3

  • Pulp and paper – the largest application for caustic soda world wide. Uses include the de-inking of waste paper and water treatment as well as being a raw material in the pulping and bleaching process.
  • Textiles – used to process cotton and dye synthetic fibers, such as nylon and polyester.
    Soap and detergents – used in saponification, the chemical process that converts fat, tallow and vegetable oils into soap. Caustic soda is used to manufacture anionic surfactants, a crucial component in most detergents and cleaning products.
  • Bleach manufacturing – used to make bleach which has industrial and consumer applications such as mold and mildew control around the home or to control microbial levels in swimming pools and hot tubs.
  • Petroleum products – used to explore, produce and process petroleum and natural gas. Caustic soda removes objectionable smells from these materials that result from the presence of hydrogen sulfide (H2S) and mercaptans.
  • Aluminum production – used to dissolve bauxite ore, the raw material for aluminum production.
  • Chemical processing – used as a basic feedstock for a wide range of downstream products, including solvents, plastics, fabrics, adhesives, coatings, herbicides, dyes, inks, pharmaceuticals, etc.
  • Other small applications for caustic soda include water treatment, cleaners for beverage bottles, cleaning products such as drain and pipe cleaners, oven cleaner and other household cleaning products and home soap making.

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Exposure Potential

Because caustic soda is corrosive, precautions should be taken to minimize potential harm to people, pets and the environment. Such precautions include using appropriate personal protective equipment when handling caustic soda and following all label instructions and warnings on consumer products. Based on the uses for caustic soda, the public could be exposed through:

  • Workplace exposure – Exposure can occur either in a caustic soda manufacturing facility or in the various industrial facilities that use caustic soda. Caustic soda has been used for more than 100 years by industry. When exposures occur, they are most frequently to the skin and eyes, although oral exposure and ingestion are possible. Good industrial hygiene practices minimize the risk of exposure. Additionally, most processes using caustic soda use closed tanks and vessels.
  • Consumer exposure to products containing caustic soda – Although Dow does not sell caustic soda through retail stores, caustic soda may be an ingredient in some consumer products. For example, drain cleaners and oven cleaners can contain high concentrations of caustic. It is important to read and follow the instructions for use on the container because these instructions help prevent injury. It is also important to keep all chemical products out of the reach of children.
  • Environmental releases – In the event of a spill, the focus is on containing the spill to prevent contamination of soil, surface or ground water. If caustic does reach soil and water nearby, it can increase the pH (decrease the acidity) of the aquatic or terrestrial environment.
  • Large release – Industrial spills or releases are infrequent and are generally contained. If a large spill does occur, the material is captured, collected and re-processed, or disposed of according to applicable governmental requirements. Small, residual amounts can be neutralized with dilute acid, such as acetic acid. (Vinegar is dilute acetic acid.) Emergency personnel should wear proper protective equipment and follow emergency procedures carefully.

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Health Information4

Skin and eye exposures to caustic soda in industrial and home environments can cause injury. Read and follow all instructions on the product label to avoid hazards associated with caustic soda.

50% caustic soda solution is corrosive to the skin, and may cause a severe burn, even with a short exposure. Solutions or mists of caustic soda may also be damaging to the eyes, resulting in vision impairment, even blindness. Ingestion of caustic soda can cause chemical burns to the mouth and throat with possible ulceration to the gastrointestinal tract.

If there is a potential exposure to caustic soda solution, immediate first aid is required, including flushing the area with running water, having the exposed person drink plenty of water or milk (do NOT induce vomiting) and contacting a local medical facility or emergency response center for continued treatment.

After extensive testing and more than 100 years of industrial experience with caustic soda, there is no evidence that caustic is a skin sensitizer or is readily absorbed through the skin. It is not a known carcinogen, mutagen, developmental toxicant or reproductive toxicant.

For more information on the health hazards of caustic soda and recommended protective equipment, view the Safety Data Sheet.

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Environmental Information

Sodium hydroxide does not bioaccumulate due to its high solubility in water. It is considered slightly toxic to aquatic organisms unless there is a significant pH shift outside the range of 5 – 10; this change may be toxic to aquatic organisms.

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Physical Hazard Information

Caustic soda, as a 50% solution, is an odorless and colorless liquid that is highly corrosive and reactive.

Caustic soda solution is a chemically stable product. It will pick up carbon dioxide (CO2) from the air to form sodium carbonate (Na2CO3) which can impact product quality over time. In addition, iron pick-up is common in carbon steel storage vessels or in lined carbon steel storage vessels where the liner has been damaged. To extend the storage life of caustic soda solution, minimize its exposure to air and its direct contact with iron-containing metals.

Consider the materials of construction carefully for caustic soda storage containers and processing equipment. Caustic soda solution reacts readily with metals such as aluminum, magnesium, zinc, tin, chromium, bronze, brass, copper, tantalum and galvanized (zinc-coated) materials.

Use care when diluting concentrated solutions of caustic soda. In addition to using proper personal protective equipment, ALWAYS add caustic soda to tempered water with constant agitation to minimize a rapid temperature increase and the potential for the solution to boil, splatter or violently erupt.

Additional physical property information for caustic soda is available at on the Caustic Soda Web site.

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Regulatory Information

Regulations may exist that govern the manufacture, sale, transportation, use and/or disposal of Caustic Soda. These regulations may vary by city, state, country or geographic region. Information may be found by consulting the relevant Safety Data Sheet or Contact Us.

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Additional Information

For more business information about caustic soda, visit Dow’s Caustic Soda Solution web site.

Last Updated: May 2, 2006

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References

1 Caustic Soda Solution Web site (www.dowcaustic.com).
2 Sodium Hydroxide OECD SIDS Initial Assessment Report, UNEP Publications, SIAM 14, Paris, March 26-28, 2002, pages 3-4.
3 Caustic Soda Solution Applications (www.dow.com/causticsoda/prod/app.htm).
4 Sodium Hydroxide OECD SIDS Initial Assessment Report, UNEP Publications, SIAM 14, Paris, March 26-28, 2002, page 8.

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