Chemical Data Notebook Series: Sodium Hydroxide

Chemical Data Notebook Series: Sodium Hydroxide



Sodium hydroxide is an odorless and non-flammable white solid. A powerful corrosive, it is water-reactive to the degree that when it dissolves in water, enough heat is generated to ignite ordinary combustible materials.

Sodium hydroxide is soluble in water and has a specific gravity of 2.13. When it dissolves in water, a very corrosive solution is formed (depending upon the amount of sodium hydroxide that is dissolved in the water). The chemical formula for sodium hydroxide is NaOH and its molecular weight is 40.0.

Sodium hydroxide is an ionic compound formed by the electrostatic attraction of oppositely charged ions (here, the ions are the metallic sodium ion, NA+1, and the non-metallic hydroxide ion, OH-1). It is typical of metallic hydroxides in that it is corrosive (sometimes referred to as caustic), alkaline in nature (a pH of 7.1 to 14), and the chemical opposite of acids, which metallic hydroxides neutralize to form a salt and water. The metallic hydroxides are known chemically as bases. A typical chemical/neutralization reaction between sodium hydroxide and hydrochloric acid is as follows:

NaOH + HC1 — NaCL + HOH (or H2O)

Sodium hydroxide plus hydrochloric acid yield sodium chloride plus water.

With sulfuric acid, it is:

2NaOH + H2SO4

Na2SO4 + 2H2O

Sodium hydroxide plus sulfuric acid yields sodium sulfate plus water.


Synonyms for sodium hydroxide include caustic soda, Lewis-red devil lye, lye, soda lye, sodium hydrate, and white caustic. Its DOT (Department of Transportation) classification is corrosive, its UN/ NA designation is 1823 for the solid and 1824 for a solution, and its STCC (Standard Transportation Commodity Code) number is both 4935235 and 4935262 as solids, 4935240 as a liquid, and 4935243 as a solution. Sodium hydroxide’s RTECS (Registry of Toxic Effects of Chemical Substances) or NIOSH (National Institute for Occupational Safety and Health) number is WB4900000. Its IMO (International Maritime Organization) designation is 8, corrosive. Sodium hydroxide is shipped as flakes, beads, granules, pellets, or in a water solution.


Sodium hydroxide is a stable compound, but is very reactive and extremely corrosive to human tissue (and all other tissue). With certain metals, such as aluminum, brass, bronze, chromium, lead, magnesium, and zinc, solutions of sodium hydroxide (or dry sodium hydroxide plus wet metal) may generate explosive hydrogen gas. It will corrode some metals, plastics, rubber, and various coatings. Sodium hydroxide will react with the short chain aldehydes and alcohols, various nitro compounds, trichloroethylene, chloroform, phosphorus, organic peroxides, and some explosives.


Sodium hydroxide is used in the manufacture of dyes, explosives, paper, plastics, detergents, the refining of petroleum, metal cleaning, bleaching, the reclaiming of rubber, and in many kinds of chemical processing. Many people have small amounts of sodium hydroxide in their homes in the form of a very popular solid drain cleaner.

The use of this material to unclog a drain provides an excellent opportunity to experience its exothermic (heat-generating) properties firsthand. The instructions call for one or two tablespoons of the material to be added to the clogged drain with one half cup of cold water. Almost instantly the water begins to boil, and the heat generated will melt any grease in the trap. The corrosiveness of the solution will result in the dissolving of any other material in the drain and the effect is almost instantaneous. As much care must be practiced in using this material in the home as anyone else coming into contact with it in an incident, the big difference being the amount involved.


The corrosive action of sodium hydroxide dictates the kind of protection required for emergency responders. Contact with the pure material as a flake, granule, powder or dust, pellet, or in solution will cause severe burns to all body tissue. Needless to say, contact with the eyes will cause severe burns, scarring, and blindness. Therefore, faceshields and chemical-resistant goggles must be worn, including protection against fine powders and sprays or splashes of the water solution. All other clothing must be impervious to the solid material and water solutions.

Whenever circumstances of the incident allow for high concentrations of dusts, mists, and sprays of solution, total encapsulating suits of resistant material must be worn. Mists and sprays are obviously hazardous since they are just very fine forms of water solutions of the corrosive. Dusts, powders, flakes, granules, and pellets are hazardous because the material will dissolve in the moisture on the skin, liberating heat and its corrosiveness. If the finely divided material reaches the eyes, it will dissolve in the moisture there, causing severe burns and probable blindness.

Different manufacturers list different resistances to caustic materials, so you must consult the chemical resistance charts that each manufacturer provides. Some materials from which total encapsulating suits are made that should be investigated are butyl rubber, chlorinated polyethylene, natural rubber, Neoprene, nitrile rubber, polyethylene, polyurethane, and polyvinyl chloride. If you investigate these or any other material, be careful to differentiate between those that offer protection from solutions of sodium hydroxide and those that can handle the solids and the solutions. Positive pressure self-contained breathing apparatus (SCBA) is required in every instance where dust is generated.


Fire situations

Sodium hydroxide will not burn and it does not support combustion. If a fire is burning in the area where sodium hydroxide is stored, or if the vehicle carrying it is burning, no additional combustion products will be produced by this material. However, it would be important for firefighters to be aware of its presence, since if wrater gets to the material, additional heat will be generated and some of the material will dissolve in the water, forming a very corrosive solution. In this situation, firefighters must protect themselves from the caustic solution and contain the run-off water. Where water is used, flooding amounts are necessary. This, of course, will cause a run-off problem.

It is also possible that a straight stream may produce dust, which is extremely hazardous (the TLVTWA for sodium hydroxide is 2 mg/m3). However in most cases, especially where the material is in a secure container, the sodium hydroxide will not be exposed to water. In any event, emergency responders must be made aware of its presence.

Contact with sodium hydroxide must be avoided at all times. In addition to tissue burns caused by direct contact of the solid or a concentrated solution, inhalation and ingestion may be fatal. Even inhalation of the absolute ceiling quantity (2 mg/m3) may cause irritation in many people, and can cause severe respiratory distress in others (including pneumonitis).


Alkali—Any substance which has a pH greater than 7.0 (neutral).

Alkaline—The property of being an alkali.

Base—A chemical compound that contains the hydroxide ion (OH*1), is the chemical opposite of an acid, and is very active chemically.

Caustic—Any strongly alkaline substance that has a corrosive effect on tissue; usually refers to bases.

Ion—An atom or group of atoms, bound chemically, that have gained or lost one or more electrons and are electrically charged according to how many electrons are gained or lost.

Corrosive—Any material that will attack and destroy, by chemical action, any living tissue with which it comes into contact.

Exothermic—The liberation of heat.

Metallic hydroxides—Ionic compounds that contain a metallic (or the ammonium) ion and the hydroxide ion.

Neutralization—A particular type of chemical reaction where an acid or base reacts with another material and the resulting pH is 7.0.

pH—Indication of the acidity or alkalinity of a solution of a substance. A pH of 1 to 6.9 is acidic, 7.0 is neutral, and 7.1 to 14 is alkaline.

Ingestion will cause severe burns of the mouth, esophagus, and stomach, at times severe enough to cause death. In some cases, cancer of the throat has been reported where the material had been swallowed several years before.

Accidental releases

Where solid sodium hydroxide has been released, no particular hazard exists if all contact with the product is avoided and conditions do not exist that will cause dust to be blown about (such as in a strong wind), or the product to become wet. The area should be isolated immediately, and all emergency personnel who enter the area should have proper personal protection.

The solid product may be covered with a resistant material to prevent it from being blown about or becoming wet. The sodium hydroxide should be removed as soon as possible by properly protected personnel using equipment compatible with sodium hydroxide. Many times the manufacturer or transportation company will provide containers into which the escaped product will be put. Several inches of soil may also have to be removed.



If the released sodium hydroxide is in solution, all techniques for liquid hazardous materials may be useful, particularly those techniques used for corrosive liquids such as acids. The first response should be one of containment, usually with dikes of soil, sand, or other sorbent material.

The spilled material may be captured in a containment pit dug for this purpose. Whether a dike or pit is used, contamination of the soil and sorbent material is a certainty, and this will have to be removed after the incident has been mitigated.

The liquid may be led to the diked area or the pit by digging trenches leading from the spill. This area will also become contaminated as the solution flows through.

Once the liquid has been contained, the material may be pumped into secure containers. The pump and all of its parts and peripheral accessories must be compatible with sodium hydroxide or corrosion will destroy the equipment. Remember that flammable (explosive) hydrogen gas is generated when sodium hydroxide contacts certain metals. Again, all metal surfaces must be compatible with the product; this means the containers as well as the pump and accessories.


The solution of sodium hydroxide may be absorbed safely by several materials, assuming there is enough sorbent present. Soil, sand, fly ash, cement powder, clay, and some commercial sorbents are compatible. Remember, after absorption, the contaminated material will have to be disposed of in accordance with federal, state, and local regulations, including all contaminated earth from the containment pond or the sides and bottom of the pit.

If personnel and equipment from other than emergency responders, qualified professionals, or governmental agencies are used (many times local contractors will volunteer their workers and equipment to help in an incident), they must be trained concerning the hazards of the material and how to protect themselves and their equipment. Care must be taken in the removal of solid material to prevent the formation of dust. In some cases, where a solution has been absorbed by solids, it is possible for dust to be created. Eye, skin, and respiratory protection is mandatory. Operators of removal equipment may need total encapsulating chemical suits and positive pressure SCBAs.


Neutralization is the technique utilized to convert the product to a less hazardous material. Unfortunately, those materials that are the best neutralizing agents are every bit as hazardous as sodium hydroxide, and, in some cases, more hazardous. Neutralization will be used only on a solution of the product, since the solid material may be scooped, shoveled, or bulldozed into containers.

Examples of the chemical reaction known as neutralization were given at the beginning of this article. When done in the laboratory using materials of known concentration and chemical composition, the neutralization of a powerful base such as sodium hydroxide (or of a concentrated acid) can be carried out precisely, producing a salt in a solution of water at a pH of 7.0.

But the real world is not the laboratory, and many things can go wrong (the incident itself is proof of that). Once the material is contaminated, as it will be in a spill, it may be difficult to determine how much neutralizer is needed. Test paper and other equipment should be available to test the pH of the solution after each addition of neutralizing agent.

The best neutralizers for sodium hydroxide would be strong inorganic acids such as sulfuric acid and hydrochloric acid, but these materials are extremely hazardous in their own right (see “Sulfuric Acid,” FIRE ENGINEERING, June 1986). Nitric acid probably would not be used, since it is also a powerful oxidizer (see “Nitric Acid,” FIRE ENGINEERING, October 1986), and there is no need to introduce additional hazards.

Other inorganic acids will also neutralize the hydroxides, but they are rarer and more expensive and many of them are very hazardous. It is not always advisable for emergency responders to correct a situation arising from the hazards of one substance by using an equally hazardous substance. However, if these powerful acids are available in the proper amounts and experts in handling these materials can overcome other problems caused by the use of these materials (the addition of concentrated sulfuric acid to a water solution of NaOH will cause an evolution of heat for a brief period of time)—in other words, everything has to be just right—then it may be advisable to use these acids to lessen the hazards of sodium hydroxide. Even then, it would be best to allow the handling of concentrated inorganic acids to be done by the experts, those people who work for the manufacturer or the user of the acid.

In the situation where a release or spill of sodium hydroxide has reached a waterway, action must be taken to protect downstream users. Environmental officials will be vitally interested in preventing damage to fish, animal, and bird life that use the waterway, but human concerns must be considered first.

If the spill can be contained by diking or damming the waterway and diverting the contaminated water to a holding area where it can be treated, this, of course, would be the preferred action. If this is not possible (and in most cases it isn’t), warnings must be issued to users or treatment plants downstream. Even though sodium hydroxide is a powerful corrosive, the sheer volume of water may be sufficient to dilute the caustic until the effects are negligible, in which case there is no need to intervene in the incident beyond issuing the proper warnings.

The solubility of sodium hydroxide in water notwithstanding, if the spilled product is in the shape of large pellets (the size of regular marshmallows), it may be possible to scoop them out of the water (by mechanical means) before they dissolve. If this is the case, be aware that a tremendous amount of heat will be generated by the undissolved material. All equipment should be decontaminated before corrosion affects the metal.

In any case, in any spill, all contaminated soil will have to be removed and disposed of in accordance with federal, state, and local regulations.


If anyone has inhaled sodium hydroxide dust or mist from a concentrated solution, the victim must be moved to fresh air and kept warm and quiet. Artificial respiration will be necessary if breathing difficulties develop.

The provider of the artificial respiration must be aware that he will be exposed to the material in the victim’s lungs. Immediate medical attention will be mandatory.

For contact with eyes or skin, 15 minutes of flushing with water is necessary (lifting the eyelids often). For skin contact, all contaminated clothing must be removed and medical attention provided immediately.

If the victim has swallowed sodium hydroxide, large amounts of water must be administered immediately while medical attention is being sought.


The primary hazard of sodium hydroxide is its corrosiveness to all living tissue, particularly humans. The corrosive action with certain metals may cause the evolution of explosive amounts of hydrogen gas. Additionally, tremendous amounts of heat will be generated.

Simple spills may be shoveled or scooped into secure containers, with all emergency responders fully protected. All contaminated product and soil or other sorbent must be disposed of properly. Only experts should attempt neutralization techniques with strong acids.

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