Guide to Caustic Soda
“Caustic soda” is a term that might be unfamiliar to those who haven’t worked with industrial chemicals. However, it is a substance used either as an ingredient or in the process of manufacturing dozens of household products (such as body soap, detergents and drain cleaners). Often referred to by its household name of “lye,” which literally means “wash stuff” in Old English, caustic soda has probably been used since the time of the ancient Babylonians and Egyptians, who used it in saponification (the soap-making process).
If you’ve ever been involved in producing, transporting or dispensing caustic soda, you should have received extensive training in safe handling and packaging of this potentially dangerous, corrosive chemical. This guide can serve as a refresher or as a supplement to your previous training. If you’ve discovered a new use around your home for caustic soda and want to familiarize yourself with the safe handling of this potentially dangerous and corrosive chemical, you’ll want to pay attention to the Hazardous Material Classifications and Warnings, Cleaning a Caustic Soda Spill and Skin or Eye Contact with Caustic Soda sections below.
Please note this article is not a safety manual. If you require chemical safety training for caustic soda or any other hazardous material, contact the organization that regulates chemicals in your area for certified safety instructors.
What is Caustic Soda?
Caustic soda is a relatively simple man-made chemical compound. It is comprised of one sodium (Na), one oxygen (O) and one hydrogen (H) atom, which is why it’s also referred to as sodium hydroxide bearing the chemical symbol “NaOH." Caustic soda is probably the lesser-known product of the Chloralkali process, which is the electrolysis procedure used to free chlorine (Cl) from the sodium chloride (NaCl) found in salt brine. When chemical manufacturers produce chlorine, they also end up producing a comparable amount of caustic soda, which is in many ways as useful as its chemical counterpart.
It is important to recognize that the terms “caustic soda,” “sodium hydroxide” and “lye” all refer to the same chemical compound of NaOH. These terms are used interchangeably throughout the industry and throughout this guide.
Caustic soda is a highly corrosive base or alkaline chemical widely utilized in several different industries. Some common uses include:
|Organic Chemical Production||Cosmetic Production||Soaps & Detergent Production|
|Paint Manufacturing||Paper & Cellulose||Textile Bleaching|
|Glass & Ceramic Manufacturing||Food Processing||Manufacturing Rayon|
|Fuel Cell Production||Water Treatment||Plumbing (drain cleaners often contain lye)|
Caustic soda can cause severe burns to the skin, so it may seem counterintuitive to use lye for making soap. However, sodium hydroxide is one of the few inorganic materials allowed by the USDA in the manufacture of organic soaps. The United States Department of Agriculture (USDA) maintains strict rules over many products grown, raised and produced for human consumption.
The regulations are even more rigorous when the USDA allows a product to bear the distinctive green and white USDA Certified Organic seal on its packaging. Although caustic soda is in no way organic (it’s a man-made chemical product that results from the breaking up of salt molecules), the USDA makes an exception in the production of organic soap. This is because sodium hydroxide is necessary to the chemical reaction that produces soap.
When combined with oils or fats in the saponification process, the caustic soda compound is transformed during the reaction to make the soap safe to use. While the soap acquires some of the atoms once existing in the caustic soda molecule, they are no longer part of the sodium hydroxide compound: the sodium hydroxide and its corrosive properties are gone.
Why Is Caustic Soda Useful as a Chemical?
In its natural room-temperature state, caustic soda is a solid, but since it readily dissolves in water, it is often sold and transported as a solution of varying concentrations. When caustic soda is mixed with water or an acid, there is a strong exothermic reaction where heat is released, which can be used as a source of energy to trigger other chemical processes. In many lye-related chemical reactions (as was mentioned with soap) caustic soda gives up its sodium, hydrogen and oxygen atoms to help form new chemical compounds. In situations where a corrosive substance is required, like for a drain blockage, caustic soda will work to dissolve the organic materials but will leave the PVC pipes intact. Sodium hydroxide is also used in the production of soft drinks, ice cream and food dye. The corrosive and toxic properties of caustic soda disappear in these processes such as the case with soap above.
It’s important to note that sodium hydroxide is not safe for direct consumption. It should never be ingested and can cause severe injury or death. Food companies rigorously train their employees in the safe use of sodium hydroxide in chemical food preparation processes, and the end products are tested before being placed on the market.
Transporting Caustic Soda
The transportation of hazardous materials including caustic soda, is subject to overlapping federal, state and local laws and regulations, as well as international regulations. In addition to the legal requirements for transportation of hazardous materials, the laws of nature also place numerous de facto restrictions on the way sodium hydroxide can be safely packaged for transport.
For instance, caustic soda can corrode or react with aluminum and shed hydrogen atoms which becomes an explosive hydrogen gas. Caustic soda should never be stored in aluminum containers for transport or storage. Other metals that interact with sodium hydroxide to produce hydrogen include magnesium, zinc, tin and chromium; caustic soda should never be kept in containers constructed of any of these materials.
Caustic soda doesn’t react with stainless steel making stainless steel drums, tanks and pipelines the standard in the industry. However, caustic soda does interact with some plastics and can corrode the walls of containers or bags constructed of plastic causing dangerous leaks or spills. For this reason, high-density polyethylene (HDPE) barrels and containers are used for packaging.
As was previously mentioned, caustic soda releases thermal energy when mixed with water. For this reason, dry caustic soda should be in airtight containers to prevent moisture from reaching the material. Caustic soda should not be packaged in paper or cardboard, as those materials tend to be both porous and susceptible to combustion.
Liquid sodium hydroxide can be transported in tanks, drums or through pipelines. The same restrictions regarding packaging and container materials apply when caustic soda is being transported in its solid state.
Hazardous Material Classifications and Warnings
In the United States, the Pipeline and Hazardous Materials Safety Administration (PHSMA) creates rules and issues permits for the transportation of hazardous materials:
According to the Federal Motor Carrier Safety Administration (FMCSA), sodium hydroxide is a Class 8 (corrosive) hazardous material, meaning vehicles and railcars transporting the substance are required to bear the appropriate placard. The United Nations (UN) number for sodium hydroxide is 1823 for its solid form and 1824 for the liquid caustic soda solution should also be used on the placard. The placard for both forms of caustic soda is a black-and-white standard diamond shape with an image representing a material dissolving a solid mass and burning a hand.
The National Fire Protection Association (NFPA) ranks hazardous materials on a scale of 0 – 4 in three categories. The placards are diamond-shaped and color-coded. Both solid and liquid forms of caustic soda share the following rankings:
- Health Risk (Blue): 3 – “Materials that can affect health or cause serious injury, during periods of short exposure, even though prompt medical treatment is give [sic].”
- Flammability (Red): 0 – “Materials that will not burn.”
- Reactivity (Yellow): 1 – “Materials that are normally stable, but become explosive at elevated temperatures and pressure.”
While NFPA rankings are useful as a quick reference to assess the threats posed by various hazardous materials, they provide less than a complete picture for sodium hydroxide. While caustic acid isn’t flammable under normal conditions when interacting with other materials, it can give off heat or flood the area with volatile hydrogen gas. Either situation can substantially increase the risk of fire or an explosion. Therefore, it is essential for those in the chemical transportation field to be familiar with the properties of each type of hazardous material they carry.
Cleaning a Caustic Soda Spill
Despite the heavy regulation governing chemical manufacturers and transporters along with the extraordinary care they take in handling hazardous materials like caustic soda, spills and other accidents can occasionally occur. As corrosive to biological materials as sodium hydroxide is (coupled with the fact that there are several substances it reacts with) it is essential to know how to properly clean a caustic soda spill.
If you haven’t been trained to handle a caustic soda accident, clear the area and contact emergency responders to inform them of the size of the spill, the location and other potential hazards in the area. If you have been trained to clean up caustic soda spills, you can follow this clean-up checklist:
- Evacuate and Seal – Evacuate the area of the spill and close off the area if possible. If you can smell the substance, you are inhaling it and should move farther away.
- Safety Equipment and Clothing – Avoid any skin contact with caustic soda. Particles in the air can be inhaled and will burn mucous membranes inside the mouth and the throat. Wear gloves made from a non-reactive substance like Butyl, Nitrile, Neoprene or PVC and wear a face shield or wrap around safety glasses for protection. To prevent inhalation of caustic soda particles, a respiratory mask with a filter rated for sodium hydrochloride is required. For smaller spills, a surgical-type facemask that is rated for caustic soda should prevent accidental inhalation. If available, wear a protective HAZMAT suit to prevent the chemical from interacting with your skin.
- For Liquids – Use an absorbent substance such as sand to allow the liquid to soak up, and then shovel the saturated absorbent material into bags for disposal.
- For Solids – Sweep or shovel the caustic soda into bags or appropriate disposal containers. Do not use water or any liquid cleaning solution that could potentially interact with the caustic soda and trigger a reaction.
- Ventilate and Wash – Once all the caustic soda is cleaned up, it should be safe to wash down the area with water and complete the cleaning process. Allow the area to ventilate and use a copious amount of water. Remember to only use commercial cleaners after all traces of caustic soda are gone.
Skin or Eye Contact With Caustic Soda
Wearing the proper safety equipment should significantly reduce the occurrence of skin or eye contact. Because of the extremely corrosive nature of caustic soda, it’s essential to have a plan in place to deal with this contingency:
- Dry caustic soda on skin – Remove as much of the substance as you can with a brush or dry rag. Remove any contaminated clothing or jewelry and wash the affected area for 30 minutes. Remember, mixing caustic soda with water can trigger a thermal reaction and can create a corrosive solution. Ensure all the material is off your skin and do not initially use a wet rag.
- Liquid sodium hydroxide solution on skin – Use a dry towel to absorb as much of the material as possible. Remove contaminated clothing or jewelry. Wash the affected area for 20 minutes once it is completely removed.
- Dry or liquid caustic soda in the eyes – Flush the eyes at an eye-flushing station or under a tap or in the shower if an eye-flushing station isn’t available. Do not bother removing your clothing before getting into the shower. Flush for 30 minutes, keeping your eyes open for as much time as possible before taking any other action.
- Ingesting dry or liquid caustic soda – First call paramedics and then Poison Control at 1-800-222-1222 for anywhere in the United States. Do not induce vomiting or give the person milk or water unless advised by rescue personnel or Poison Control.
Time is of the essence when it comes to mitigating caustic soda injuries. It is best to contact emergency rescue personnel immediately after the chemical is removed but not before attempting to remove the chemical first.
Do not use vinegar to neutralize the effects of human contact with caustic soda. The acid in vinegar will interact with caustic soda creating a harmful chemical reaction.
Purchasing Caustic Soda
Depending on your requirements, you can buy small quantities of caustic soda or products containing sodium hydroxide at most hardware stores. For larger quantities of caustic soda or sodium hydroxide solution, Brenntag stands out among chemical distributors for both the quality of its products and reliability of service. We offer sodium hydroxide solution in concentrations from 20 – 50 percent and in quantities from 25 – 1,200 kg. We also offer 25-kg units of caustic soda flakes and pearls.
We adhere to the highest standards of safety and guarantee the purity of our chemical products. Headquartered in Germany, Brenntag delivers chemical products to customers around the globe and has an unparalleled reputation in the industry. For more information about purchasing caustic soda or the other chemicals we offer, contact one of our representatives.