Updated: Thursday, January 24 - 1:45 PM Home --> Training --> HazMat Studies --> 1996 --> Article

E-Mail This Page Discuss HazMat

ROBERT BURKE
Published: March 1996

Class 8 materials are liquids and solids that are corrosive. There are no subclasses of corrosives. There are however, two types of corrosive materials found in hazard class 8, they are acids and bases. Acids and bases are actually different types of chemicals that are sometimes used to neutralize each other in a spill. They are grouped together in Class 8 because the corrosive affects they have on tissue and metals, if contacted, are much the same. It should be noted that the correct terminology for acids is that they are considered to be corrosive and bases are considered to be caustic. The Department of Transportation (DOT) however does not differentiate between the two. The (DOT) definition of corrosive is "a liquid or solid that causes visible destruction or irreversible alterations in human skin tissue at the site of contact, or a liquid that has a severe corrosion rate on steel or aluminum. This corrosive rate on steel and aluminum is .246 inches per year at a test temperature of 131F".

pH Scale Of Common Materials ACID 0-6 NUETRAL 7 BASE 8-14 Hydrachloric Acid 1.1 Sulfuric Acid 1.2 Acetic 2.9 Soda 3.0 Skin 3.6-5.5 Beer 5 Milk 7 Pure Water 7 Blood 7 Sodium Bicarbonate 8.4 Magnesium Hydroxide 10.4 Ammonia 11.0 Tri-Sodium Phosphate 12.0 Sodium Hydroxide 13.0 Potassium Hydroxide 14.0

A chemical definition for an acid from the Condensed Chemical Dictionary is "a large class of chemical substances whose water solutions have one or more of the following properties: sour taste, ability to make litmus dye turn red and to cause other indicator dyes to change to characteristic colors, ability to react with and dissolve certain metals to form salts and the ability to react with bases or alkalies to for to form salts".

There are two basic types of acids, organic and inorganic(Figure 1.1). Inorganic acids are sometimes referred to as mineral acids. Organic acids as a group are generally not as strong as the inorganic acids. The main difference between the two is the presence of carbon in the compound. Inorganic acids do not have carbon in the compound. Inorganic acids are corrosive but they do not burn. They may be oxidizers and support combustion or may react with organic materials and spontaneously combust the organic material. Inorganic acids begin with hydrogen in the formula such as H2SO4 for sulfuric acid, HCl for hydrochloric acid, and HNO3 for nitric acid. Organic acids are hydrocarbon derivatives. Therefore organic acids have carbon in the formula. Organic acids are corrosive, may polymerize and some of them may burn. Organic acids will have a carbon in the compound and the name will begin with the prefix indicating the number of carbons. For example the prefix for a 1 carbon compound with the organic acids is form- so a one carbon acid would be called formic acid. Two carbons would be acetic acid, three carbons propionic acid and so on.

Most acids are produced by the dissolving of a gas or a liquid in water. For example hydrochloric acid is derived from dissolving hydrogen chloride gas in water. All acids contain hydrogen. This hydrogen is an ion (+H) and can be measured by using the pH scale(Figure 1.2), which in simple terms, measures the hydrogen ion concentration of a solution. Acids as a group have high hydrogen ion concentration. Bases have very low hydrogen ion concentrations and high hydroxyl (OH-) concentrations. The strength or weakness of an acid or base is the amount of hydrogen ions or hydroxyl ions that are produced as the acid or base is produced. If the hydrogen ion concentration in an acid is high then the acid is a strong acid. If the hydroxyl concentration is high then it is a strong base. In both cases there is almost total ionization of the material dissolved in water to make the strong acid and base. For example, hydrochloric acid is a strong acid with a pH of 1.1, almost all of the hydrogen chloride gas is ionized in the water. If the hydrogen ion concentration is low then the acid is a weak acid. Acetic acid is a weak acid with a pH of 3, only about 2% ionization has occurred in producing the compound.

MC/DOT 312/412 Corrosive Tanker Truck

Another term associated with corrosives is concentration. Concentration, unlike strength, has to do with the amount of acid that is mixed with water. This is often expressed in terms of percentages. A 98% concentration of sulfuric acid would be 98% sulfuric acid and 2% water. A solution of 50% nitric acid would be 50% nitric acid and 50% water. In the 50% concentration the solution would have only half of the H+ ions that the 100% concentration would have. A 50% concentration of nitric acid would be a solution diluted to 50% of the original acid.

The pH scale measures the acidity or alkalinity of a solution. Acids are acidic and bases are alkaline. Acids will have a value on the pH scale of 1 to 6.9. Materials with a value of 7 are considered to be neutral, they are neither acidic or basic. Bases have values on the scale from 7.1 to 14. It is not important that emergency responders know how the pH scale measures corrositivity or the specific values of any given acid or base. It is important however for responders to know that numerical values less then 7 are acids and higher then 7 are bases. The acidic side of the scale is a reverse ratio. Usually the higher the number the greater the amount that is being measured. With the pH scale on the acidic side it is reversed. The lower the pH number the more acidic an acid is. So an acid with a pH of 1 would be much more acidic than an acid with a pH of 2 and so on. This difference in acidity is much greater then the numbers of 1 through 6.9 may represent(Figure 1.3). The ratio and the intervals between the numbers are exponential. For example an acid with a pH of 6 is 10 times more acidic than an acid with a pH of 6.9. A pH of 5 is 10 times more acidic than a pH of 6 and so on. The result of this exponential ratio is that an acid with a pH of 1 is 1,000,000 times more acidic than an acid with a pH of 6.9. So the difference between individual values on the pH scale is very great and one of the reasons that dilution and neutralization are not as simple as they might sound. Those terms will be discussed further later in the article.

If the chemical name of a hazardous material is known and it is determined to be a corrosive, looking up the chemical name in reference sources will identify if the material is an acid or a base. It will not be necessary for responders to get a pH measurement of the material unless it is to verify the reference information. The use of pH measurements can be useful when a material hasn't been positively identified. The pH measurement can be used to narrow the chemical family possibilities in the identification process. There are a number of ways for emergency responders to measure the pH of a corrosive material. First of all, the proper chemical protective clothing must be worn when working around the corrosive material. The simplest and least expensive method of determining pH is the use of pH paper. pH paper changes color based upon the type and strength of corrosive material that is present. The colored paper is then compared to a chart on the container the paper was purchased in. The chart will indicate numerical pH values much the same as the pH scale. Although not as accurate as a pH meter, the numbers will give a "ballpark" measure of the pH of the material. There are also commercially available pH meters from hand held to sophisticated laboratory instruments. This equipment can be expensive and pH paper will be accurate enough for emergency response. If the only determination needed is whether a material is an acid or a base, litmus paper can be used. Litmus paper turns blue if the corrosive material is a base. If the litmus paper turns red the corrosive is an acid. The litmus paper will not give actuall pH numerical values.

The chemical definition of a base from the Condensed Chemical Dictionary is "a large class of compounds with one or more of the following properties: bitter taste, slippery feeling in solution, ability to turn litmus blue and to cause other indicators to take on characteristic colors, and the ability to react with (neutralize) acids to form salts". It is important to note, while the definition of acids and bases mention the taste and feeling of the materials, these are dangerous chemicals and can cause damage to tissues upon contact. Therefore, it is NOT recommended that responders come in contact with these materials! Ionization occurs with the bases just as with the acids as they are made. Most bases are produced by dissolving a solid, usually a salt, in water. However, with the bases the ion produced is the hydroxyl ion (0H-). The base is considered strong or weak depending on the numbers of hydroxyl ions produced as a material is dissolved in water. A large OH- concentration produces a strong base, a small OH- concentration produces a weak base. Sodium and potassium hydroxide are strong bases, and calcium hydroxide(hydrated lime) is a weak base. Bases will have a pH from 7.1 to 14 on the scale. The ratio is increasing from 7.1 to 14 with 7.1 being the least basic and 14 the most basic. The amount of basicness between the numerical values on the pH scale is exponential just as with the acids. A base with a pH of 8 is 10 times more basic then one with a pH of 7.1.

Corrosiveness is not the only hazard of Class 8 materials. In addition to being corrosive they may have other hazards, they may be poisons, oxidizers or flammables. Many corrosives, especially acids, can be violently water reactive. Contact with water may cause splattering of the acid, produce toxic vapors, and produce heat that may ignite near by combustible materials. Some of the water may be turned to steam. Overpressurization of the corrosives container is possible from contact with water. Many corrosives may also be unstable and reactive. They may explode, polymerize, decompose and produce poisons. Picric acid, C6H2(NO2)3OH, for example becomes a high explosive when dried out and is sensitive to shock and heat. The slightest movement may cause an explosion. Picric acid when shipped in transportation is mixed with 12-20% water to keep it stable. It is when this water evaporates in storage, over time, that the material becomes unstable. Perchloric acid, HClO4 is a colorless, fuming, liquid that is unstable in its concentrated form. It is a strong oxidizing agent and will spontaneously ignite when in contact with organic materials. Contact with water produces heat, when shocked or heated it may detonate. Perchloric acid it toxic by ingestion and inhalation. It is used in the manufacture of explosives, esters, electro-polishing, as a catalyst and in analytical chemistry. Hydrocyanic acid, HCN, is a very toxic material. It is also a dangerous fire and explosion risk. It has a wide flammable range of 6% - 41% in air. It is toxic by inhalation, ingestion and through skin absorption. The TLV of hydrocyanic acid is 10 ppm in air. It is used in the manufacture of acrylonitrile, acrylates, cyanide salts, dyes, rodenticides and other pesticides.

Organic acids may polymerize by exposure to heat or sudden shock. For example, acrylic acid, C2H3COOH, has a double bond between the carbons that can come apart in a polymerization reaction. Generally, materials that have double bonds are reactive in some manner. If polymerization occurs inside a container an explosion may occur that can produce heat, light, fragments and a shockwave. Formic acid, HCOOH, is a colorless, fuming liquid with a penetrating odor. It is soluble in water. As with many of the organic acids formic acid may burn. It has a flash point of 156F, and a flammable range of 18% to 57%. Formic acid has a TLV of 5 ppm in air. It is used in dyeing and finishing of textile, treatment of leather, making of esters, fumigants, insecticides, refrigerants and others. Propionic acid, C2H5C00H, is a colorless, oily liquid with a rancid odor. It is flammable with a flash point of 130F, and a flammable range of 2.9% to 12.1%. It is toxic with a TLV of 10 ppm in air. It is used as a mold inhibitor in bread and as a fungicide, herbicide, a preservative for grains, in artificial fruit flavors, pharmaceuticals and others.

Corrosive Rail Car

Corrosives may also contact poison materials and produce poison gases as the poisons decompose. The poison vapors could be much more toxic than the corrosive vapors. When acids come in contact with cyanide hydrogen cyanide gas is produced. Hydrogen cyanide gas is very toxic with a TLV of 10 ppm in air.

When strong corrosives contact flammable liquids the chemical reaction that occurs may produce heat. The heat produced will cause more vapor to be present and if an ignition source is present, combustion may occur. Corrosives may be strong oxidizers. If they come in contact with particulate combustible solids, spontaneous combustion may occur. Once ignition has occurred, the corrosive will act as an oxidizer and accelerate the rate of combustion taking place. Nitric acid in contact with combustible organic materials containing cellulose will produce a chemical reaction. This reaction will produce nitrocellulose which is a dangerous fire and explosion risk. Toxic vapors may also be produced when the cellulose burns.

Next to flammable liquids and gases, corrosives are the next most common hazardous material encountered by emergency responders. There are seven corrosive materials in Chemical and Engineering Magazines Top 50 Industrial Chemicals for 1994. Combined these seven account for over 171 billion pounds produced annually. The corrosives in the Top 50 include sulfuric acid #1, sodium hydroxide #8, phosphoric acid #9, nitric acid #13, hydrochloric acid #28, acetic acid #34, and potash #38. Sulfuric acid, is an inorganic acid, and is the most heavily produced and widely used industrial chemical in existence. Sulfuric acid is used in batteries for cars and other vehicles. It is a strong corrosive material. It has a pH of 1.2. It is a dense oily liquid, colorless to dark brown depending on purity. The vapors are toxic at 1 ppm in air. It is used in the manufacture of fertilizers, chemicals, dyes, pigments as an enchant, a catlyst, in electroplating baths, explosives and many other uses. Fuming sulfuric acid is called oleum. Fuming sulfuric acid is a solution of sulfur trioxide in sulfuric acid. The sulfur trioxide if forced into solution with the sulfuric acid to the point that the solution cannot hold anymore. As soon as the solution is exposed to air the fuming begins forming dense vapor clouds. It is violently water reactive as are most acids. Sodium hydroxide, NaOH, is a strong base. It has a pH of 13.0. It is the most important industrial caustic material. It is used in the manufacture of chemicals, as a neutralizer in petroleum refining, in metal etching, electroplating, and as a food additive. Sodium hydroxide is a white deliquescent solid in the form of pellets or beads. It may absorb water and carbon dioxide from the air. It is water soluble and is found in 50% and 73% solutions. Phosphoric acid, H3PO4 an inorganic acid, is a white or yellowish, crystalline mass. It is water soluble and absorbs oxygen very readily. Its primary use is in chemical analysis and as a reducing agent. Nitric acid, an inorganic acid, is a colorless, transparent, or yellowish, fuming , suffocating, corrosive liquid. Nitric acid will attack almost all metals. The yellow color results from the exposure of the nitric acid to light. Nitric acid is a strong oxidizer, and is soluble in water. It may be found in solutions of 36, 38, 40, 42, degrees B`e and concentrations of 58-63%, and 95%. Nitric acid is a dangerous fire risk when in contact with organic materials. It is toxic by inhalation, and is corrosive to tissue and mucous membranes, the TLV is 2 ppm in air. Nitric acid is used in the manufacture of ammonium nitrate fertilizer and explosives, in etching of steel, reprocessing spent nuclear fuel and others. There are two types of fuming nitric acid. White fuming nitric acid is concentrated with 97.5% nitric acid and less than 2% water. It is a colorless to pale yellow liquid which fumes strongly. It is decomposed by heat and exposure to light and becomes red in color from nitrogen dioxide. Red fuming nitric acid contains more than 85% nitric acid, 6 to 15% nitrogen dioxide and 5% water. Both are toxic by inhalation, strong corrosives, they are dangerous fire risks and may explode in contact with reducing agents. They are used in the production of nitro-compounds, rocket fuels and as a laboratory reagent. Hydrochloric acid, an inorganic acid is a colorless or slightly yellow , fuming pungent liquid. It has a pH of 1.1. It is water soluble, a strong corrosive and toxic by ingestion and inhalation. Hydrochloric acid is used in food processing, pickling and metal cleaning , alcohol denaturant, and a laboratory reagent. Acetic acid, CH3COOH, an organic acid, is a clear, colorless corrosive liquid, with a pungent odor. It has a pH of 2.9. The glacial form is the pure form without water, it is 99.8% pure. It is flammable with a flashpoint of 110F and a flammable range of 4.0 to 19.9. Acetic acid is water soluble. It is toxic by inhalation and ingestion, with a TLV of 10 ppm in air. It is a food additive at lower concentrations, it is used in the production of plastics, pharmaceuticals, dyes insecticides and photographic chemicals. Caustic potash, also known as potassium hydroxide KOH, and lye. It is a white solid found as pieces, lumps, sticks, pellets or flakes. It is water soluble and may absorb water and carbon dioxide from the air. It is a strong base and is toxic by ingestion and inhalation. It is used in soap manufacture, bleaching , it is an electrolyte in alkaline storage batteries and some fuel cells, it is an absorbent for carbon dioxide and hydrogen sulfide and is used in fertilizers and herbicides.

Dilution vs neutralization, often tactics considered when dealing with corrosive materials. Dilution is placing water into the acid to reduce the pH level. The addition of water to a corrosive can create a very dangerous chemical reaction. Acids are very water reactive creating vapors, heat, and splattering. First of all with dilution you must consider the exponential values of the numbers on the pH scale. Just moving the pH from 1 to 2 on the scale will take an enormous amount of water. Dilution may not be a practical approach for large volume spills. For example if a 2000 gallon spill of concentrated hydrochloric acid occurs. In order to have enough water to dilute the material to a pH of 6, would require the following efforts:

One 1000 gpm pumper, pumping 1000 gpm, 24 hours per day, 7 days per week, 365 days per year, for 64 years! (The pump operator would be given all of the 29th days of February off). This would produce 1,440,000 million gallons of water per day! As the process proceeds it would become necessary to stir the mixture of water and acid to ensure uniformity in the dilution process.

The idea of dilution may work on small spills, but it will not work well on large spills. Neutralization involves a chemical reaction that works very well under laboratory conditions using small amounts of acids and bases. However, when you are in the field facing a large spill of a corrosive material neutralization may not be feasible. The neutralization reaction first of all will require a large amount of neutralizing agent. For the same spill of 2000 gallons of concentrated hydrochloric acid it would take 8.7 tons of sodium bicarbonate, or 5.5 tons of sodium carbonate, or 4.15 tons of sodium hydroxide. The latter would not be recommended because sodium hydroxide is a strong base and would be dangerous to work with by itself without trying to add it to a concentrated acid. There would be a need for a method to apply the neutralizing agent. The reaction that occurs will be a violent one producing heat, vapor, and splattering of product. Neutralization may not work well at the scene of an incident with a large spill. The method of choice may turn out to be one of cleaning up the product by a hazardous waste contractor. They may use vacuum trucks, absorbent or jelling materials to accomplish the task.

Stainless Steel Nitric Acid Containers

The main danger of corrosive materials to responders is the contact of these materials to the human body. Corrosive materials destroy living tissue. The destruction begins immediately upon contact with the corrosive material. Many of the strong acids and bases will cause severe damage upon contact with the skin. Other materials may not cause any damage for several hours after the exposure. A chemical burn is nine times more damaging than a thermal burn. There are four basic methods of interfering with the chemical action of corrosives on the skin. They are : physical removal, neutralization, dilution and flushing. Flushing is the method of choice for corrosive materials. Removal of the material is difficult to accomplish and may leave a residue behind. Neutralization is a chemical reaction that may be violent and produce heat. This type of reaction on body tissues may cause more damage then they prevent. Neutralization should not be attempted on personnel wearing chemical suits either, for the same reason as mentioned above. The layer of chemical protection is very thin and the heat from the neutralization may melt the suit or cause burns to the skin below the suit. Dilution takes a large amount of water to lower the pH to a neutral position. While dilution may be similiar to flushing the intended outcome is different. With dilution the goal is to reduce the pH number as near neutral as possible. With flushing the goal is to remove as much of the material as possible with a large volume of water. Flushing is by far the method of choice and should be started as soon as possible to reduce the amount of chemical damage. Flushing should continue for a minimum of 15 minutes. Most corrosives are very water soluble in water. This also applies to the eyes. Contact lenses should not be worn at hazmat incident scenes. Contact with acids can "weld" the contact to the eye, which almost always produces blindness. The person being treated may be in a great deal of pain and may have to be restrained during the flushing operation. Treatment after flushing involves standard first aid for burns.

Corrosives are transported in MC/DOT 312/412 tanker trucks. These trucks have a small diameter tank with heavy reinforcing rings around the circumference of the tank from front to rear. The tank diameter is small because most corrosives are very heavy. No other type of hazardous material is carried in this type of tanker. The 312/412 is a corrosive tanker regardless of how it is placarded. The placard may be poison, oxidizer or flammable but don't forget the "hidden hazard", the tank identifies corrosives. Lighter corrosives may also be found in MC/DOT 307 tankers and may be placarded corrosive, flammable, poison and oxidizer. Corrosives may also be found in rail tank cars, intermodal containers, and varying sizes of portable containers. Portable containers may range from pint and gallon glass bottles to stainless steel carboys and 55 gallon drums. Some are also shipped in plastic containers.

Emergency responders should have a thorough knowledge of corrosive materials. Next to flammable liquids and gases corrosives are the next most frequently encountered hazardous materials. Responders should have proper chemical protective equipment and SCBA to deal safely with corrosive materials. Firefighter turnouts will not provide protection from corrosives. The most common places of exposure to responders occur with the hands and feet. The next is inhalation of the vapors. Make sure that the chemical suits chosen to wear are compatible with the corrosive material. No suit will protect you from chemicals forever. They all have breakthrough times. Make sure personnel are rotated to avoid prolonged exposure and make sure they do not contact the material unless absolutely necessary. Safety should be your number one concern.

Related:

• HazMat Studies Archives
  
• The Street Chemist