Caustic soda (excluding solutions containing not more than 5% caustic soda) is designated as a deleterious substance under Japanese laws, and is a strongly corrosive substance. Persons who handle caustic soda should learn about related laws and regulations (such as the Poisonous and
Deleterious Substance Control Law), its properties, and precautions on handling; and should observe them to ensure safety.
This leaflet compiles the information that dealers, transporters, and consumers handling caustic soda need to know as a guideline for the routine prevention of accidents.
I. Information about Caustic Soda
1. Commercial Caustic Soda
Commercial caustic soda is classified into solid types and liquid types according to its phases as well as into industrial, reagent, and Japanese
Pharmacopoeia grades according to its uses. Of the solid types of commercial caustic soda, flaked caustic soda is also a commercial product.
The types of solid caustic soda are as shown in the following table, and the qualities and testing methods are specified in JSIA (Japan Soda Industry
Association) Standards, JIS (Japanese Industrial Standards), the Japanese
Pharmacopoeia and the JSFA (Japanese Standards for Food Additives).
General Characteristics of Caustic Soda
Caustic soda is the most typical of the strong alkalis. Although there is no danger of it exploding or igniting, it reacts with various acids, such as hydrochloric acid, and is neutralized and generates considerable exothermic heat of neutralization.
It corrodes metals, such as aluminum, tin, and zinc. During this process, it generates hydrogen, which has the potential to behave as an explosive gas.
It is highly hygroscopic, and absorbs the moisture, carbon dioxide, or sulfur dioxide in the air. It is also highly deliquescent and absorbs moisture to form an aqueous solution.
When liquid caustic soda is diluted, it generates a considerable amount of heat of dilution. Since this rapidly generates strong heat and the resulting solution may spatter if the water is carelessly poured into it, care must be taken.
Caustic soda easily decomposes animal fibers. Although plant fibers are also decomposed, they have a higher resistance than animal fibers. Although materials resistant to corrosion by caustic soda include stainless steel, steel-epoxy resins, and fiber-reinforced plastics, steel and rubber-lined steel are the most frequently used.
2. Effects of Caustic Soda on the Human Body
Alkalis have a decomposing effect on proteins, which may gradually penetrate the deep tissues unless the adhered alkali is completely removed. In particular, if the eyes are exposed to an alkali, since eye tissue is rapidly affected causing a lowering or loss of vision, great care should be taken.
Even a dilute solution can affect the tissue of the skin if it repeatedly comes into contact with the skin, which may cause dermatitis or chronic eczema.
If the concentration of the solution is high, the affected tissue rapidly decomposes.
If the solution is swallowed by mistake, it causes inflammation in the mouth,
throat, esophagus, or stomach.
The inhalation of caustic soda dust or mist causes various degrees of injury in the respiratory tract. Thus, the allowable concentration of caustic soda dust or mist in the air in a working area is specified as 2 mg/m3 (upper limit).