CHEMICAL SAFETY TRAINING MODULES

PART VIII: CORROSIVE MATERIALS

The term `corrosive substances' was drawn up in 1956 by the United Nations Committee of Experts on the Transport of Dangerous Goods. It states: `These are substances which, by chemical action, will cause severe damage when in contact with living tissue or in case of leakage, will materially damage or even destroy other goods or the means of transport; they may also cause other hazards'.

Corrosive substances can be liquids, solids or gases. Some chemicals turn corrosive when they come into contact with water or humidity, for example on contact with sweat on the skin. This phenomena is present when handling substances such as chlorosilanes and benzyl chloride. Correspondingly, 1,2-dichloroethane attacks iron and some other metals in the presence of moisture at high temperatures.

Consequently, as the characteristics of corrosive materials are both general and specific, information on the properties of a given substance should be obtained before handling and taking decisions on safety measures.

Corrosive substances widely used in industry and agriculture may be grouped in the following general classes:

• Acids and anhydrides
• Alkalis (bases)
• Halogens and halogen salts
• Organic halides, organic acid halides, esters and salts
• Miscellaneous corrosive substances (substances that are widely used but do not fall into the above mentioned classes)

The USA which is responsible for 23% of the world's total chemical production, produces large amounts of corrosive chemicals. The first one of the Top 50 Chemicals (1992) is sulphuric acid, ammonia is 5th in production volume, phosphoric acid is 7th, sodium hydroxide (soda lye) 8th, nitric acid 13th and hydrochloric acid 25th; petroleum products are not included in this list. Large production implies large scale transport, storage for further processing and end use. The listed top ten chemicals involved in chemical accidents in USA (1988-92) include ammonia in second place followed by sulphuric acid, chlorine and hydrochloric acid. The reported immediate casualties or injuries in these accidents involved more than 1000 persons; chronic health and environmental effects are excluded from this figure.

ACIDS, ANHYDRIDES AND BASES

1. Properties

Acids and bases have a common property: they are corrosive. The corrosiveness is defined in contact with living tissue but acids and bases attack many other materials as well. They react with metals producing hydrogen gas which is highly flammable.

Acids and bases may have toxic properties and some are also flammable as such.

Acids and bases are often transported, used and disposed as water solutions.

Some acids, such as nitric acid and hydrochloric acid, release highly corrosive vapours at room temperature when in a concentrated form.

Anhydrides are compounds which have properties similar to those of acids, and they react with water forming the corresponding acids; for example acetic anhydride and water produce acetic acid.

When an acid and a base are mixed they neutralize each other producing a salt and water. Neutralization also produces heat. Mixing an acid or a base with water also involves a rise in the temperature of the solution. This may create hazards, such as splashes and formation of dangerous mists.

The pH is the scale used to compare the level of acidity and alkalinity of various acids and bases and their diluted solutions. The pH is related to the amount of hydrogen ions present in the solution. The pH of a neutral solution or substance is 7. Acids have a pH of <7 and bases of >7. To control and prevent adverse effects of acids and bases on health, several countries have set occupational exposure limits. These limits for acidity are: pH less than 2 (1.5 in some countries) and for alkalinity: pH 12-14 (11.5-14 for some countries).

Acids can be referred to as inorganic (mineral) acids or as organic acids. Examples of mineral acids are sulphuric acid, hydrochloric acid and nitric acid. Salicylic acid, ascorbic acid and acetic acid are organic acids.

2. Health effects

The health effects of acids and alkalis resemble those caused by heat. Effects of direct contact vary from irritation causing inflammation to a corrosive effect causing ulceration and, in severe cases, chemical burns.

Some acids and alkalis produce heat when they come into contact with water or moisture. These chemicals may cause both corrosive injuries and burns due to heat.

Occupational hazards due to contact with acids and alkalis mostly affect skin, eyes and the respiratory tract.

The tissues most susceptible to rapid, severe and often irreversible damage are those of the eyes.

Acid fumes may also corrode the teeth. For example long term exposure to low levels (10 ppm) of hydrochloric acid fumes can result in erosion of the incisor teeth.

The effect depends on the properties of the substance, on the concentration and time of contact with acids and alkalis. Even a dilute solution may cause irritation with prolonged or repeated contact, for example with skin.

The effect of strong acids and alkalis is experienced within moments of exposure. Depending on the substance and the concentration, the effect may also be delayed.

For example, the effect of diluted hydrofluoric acid may vary from irritation to severe burns of the skin depending on the concentration and duration of exposure. Intense pain may be experienced hours after the initial contact with the acid. A white hard lump covers the damaged skin and the acid continues the destruction of the tissue under the damaged skin. This may be the case when a diluted solution of hydrofluoric acid has entered underneath the fingernails.

These effects continue until all the acid or the alkali has been removed, for example by washing the skin with plenty of water.

Direct contact of many organic anhydrides with skin, mucous membranes, eyes or the respiratory system causes irritation and sensitization.

The exposure may also increase the risk of cancer. Pickling operations in the metal industry produce mists of inorganic acids containing sulphuric acid; inhaling this mist involves an elevated risk of larynx and lung cancer of occupational origin.

3. Effects on the environment

Changes in the level of acidity and alkalinity affect the flora and fauna in soil and water. The change of pH from 7 (neutral water) has an adverse effect on aquatic life. At pH 6 crustaceans and mollusks start to disappear and moss increases. At pH 5.5, some fish such as salmon, trout and whitefish start to die and salamander eggs fail to hatch. Acidity of pH 4 has a lethal effect on crickets and frogs. On the alkaline side with higher pH levels (over 9) these adverse effects are equally present. Some alkalis such as ammonia also have an acute toxic effect on fish.

Soil may be classified as contaminated when, due to acidity, it has a pH value of 4-5 and heavily contaminated when the pH is 2-4. When soil has a pH value of 9-10 it is contaminated due to alkalinity and at pH 10-12 it may be classified as heavily contaminated.

Aerosols of solid or liquid corrosive substances are air pollutants, and so are corrosive gases. These gases may combine with water to form acids which precipitate with rain. Nitrogen oxides and sulphur oxides are well known causes of `acid rain'.

Acid gases and acid fumes damage plants. Effects may be specific, for example, acetic acid fumes harm trees with leaves.

Neutralization does not always remove the hazards to the environment as the salts produced in this reaction may also be harmful.

4. Occupational use

Inorganic acids, anhydrides and alkalis are very important in chemical and metal industries as raw materials used in the manufacture of a wide range of chemicals; in refining, electrolysis and cleaning of surfaces. Inorganic acids are widely used in pickling processes of electroplating, vehicle production plants and steel production plants.

Inorganic alkalis are produced in large amounts to be used in the production of fertilizers, pesticides, soaps, paper and pulp, textile and glass industry, food production, metal descaling and batteries.

Organic acids and anhydrides are used in the production of pharmaceuticals, detergents and soaps, dyes, and in the plastic industry.

Organic amines are alkaline substances.

5. Storage

The following aspects should be considered when planning or organizing a storage and handling area for acids and alkaline substances:

1. Total quantity and type of chemicals in area

• toxicity, flammability, corrosive properties of stored substances

2. Correct location

• distance from residential areas, schools, hospital, industrial storage activities
• distance from other buildings, equipment, incompatible chemicals
• the surrounding area: building, roads, ground water sources, access to the storage area

3. Containers, pipes, pumps, other equipment

• material choice, equipment and needs of maintenance
• total number and volume of the tanks

4. Safety precautions and practices

• minimizing the hazard to workers and to the surroundings: monitoring and alarm systems, dikes and reservoirs to collect spillage, ventilation
• sewage system with possibility to collect leakages
• exclusion area
• entry control

5. Emergency planning and training

• fire-fighting equipment, safety equipment
• personal protective equipment

5.1. Tank containers

Tanks for the storage of acids and alkaline substances are subject to many construction requirements and standards depending on the properties of the chemicals; the substance may be both acidic and flammable or alkaline and under pressure.

The construction materials must be able to resist corrosion from inside and outside. These materials must not react with the contents; impurities or changes in temperature may increase the corrosive effect of the substance to the tank.

Steel is the most common construction material for corrosion resistant tanks intended as containers for acids and alkalis. Some types of steel, such as carbon steel, are not resistant to strong acids and elevated temperatures.

The resistant properties of steel containers may be improved by coating, which may be a layer of glass, paint, plastic, ceramic or metallic materials.

Aluminum tank containers should not be used for acids or alkalis.

Reinforced plastic is light and chemically resistant to mineral acids. This material may be used at temperatures up to 80 ^oC. The corrosive effect of an organic acid should be checked before putting it into a reinforced plastic tank.

Thermoplastic materials, such as polyvinyl chloride, polyethylene, polypropylene and polytetrafluorine ethylene, are usually chemically resistant to acid and alkaline conditions.

All tanks and containers must have a clear, updated marking. Dangerous substances must be labelled according to their classification.

The life cycle and the use of a tank container should be documented in a folder containing technical data, testing, maintenance and inspection data.

Tanks are tested before operational use and they are regularly inspected. The documents to be kept for each tank should include:

• structure drawings
• production documents with information of

• used materials
• welder's certificates

• documents stating preheating procedures and materials used in welding

• producer's warranty

• protocol and results of tests
• documents related to the construction of the mounting
• maintenance plan of interior and exterior inspections; minutes of the inspections
• changes made to the original structure; repairs

5.2 Installation

There are national and international regulations and standards on how to build storage for acid and alkaline materials. The tanks (volume over 15 m³) are placed in a entrenched area able to resist the corrosive effect in case of spillage. This entrenchment should be large enough to hold the content of the largest tank if the substance is toxic, very toxic, corrosive or flammable. In case of harmful chemicals, the entrenchment should be able to withhold at least a fifth of the content of the largest tank. The placement of tanks should allow free access to and from them in case of emergency, and during normal operations.

The diked area should not have any other installations, pumps should be placed outside or on an elevated platform. The area should be equipped with controllable rain water drainage. Substances which may react dangerously when they come into contact with each other should not be in the same dike.

If several pipes are in the same supporting structure, the pipes containing acid should be placed under other pipes.

5.3 Storage of barrels and receptacles

Barrels and receptacles containing the same type of substance should be placed in groups.

Resume:

CORROSIVE MATERIAL MAY BE IN FORM OF

• GAS chlorine; nitrogen oxides; ammonia
• LIQUID sulphuric acid; hypochlorite solutions
• SOLID sodium hydroxide; aluminium chloride

GROUPS OF SUBSTANCES WITH CORROSIVE PROPERTIES

• ACIDS AND ANHYDRIDES

• Examples: Acetic acid and acetic anhydride
• Phosphoric acid and phosphorous trioxide

• ALKALIS (BASES)

• Examples: Sodium hydroxide
• Organic amines such as ethanolamine

• HALOGENS; ACID HALIDES; HALOGENATED SUBSTANCES

• Examples: Chlorine gas; iron (ferric) chloride;
• Chlorite solutions; acetyl iodide

• OTHER COMPOUNDS

• Examples: Mercury; Ammonium polysulphide;
• Hydrazine; Peroxides

ANNEX 1.

USE OF SOME RESINS IN PROCESS EQUIPMENT IN CONTACT WITH ACIDS AND ALKALINES

ANNEX 2.

ACIDS, ALKALIS AND EFFECTS ON COMMON CONSTRUCTION METALS

Corrosion resistance assessed at 20 ^oC if no other temperature indicated

Reference: Corrosion Tables, Jernkontoret, Stockholm 1979

ANNEX 3.

EFFECT OF SOME CORROSIVE SUBSTANCES ON CONCRETE

ANNEX 4.

EXAMPLES OF INCOMPATIBLE SUBSTANCES

related to corrosive chemicals

ANNEX 5.

SOME COMMON CORROSIVE SUBSTANCES

and their classification in European Union

ANNEX 6.

FIRST AID ADVICE

related to acids and alkalis

Check the Chemical Safety Data Sheet (See the Cards by CAS Number, in alphabetical order or by risk phrases.) and the label for first aid advice. If not available follow the general first aid procedure:

• Remove the patient from sources of exposure to fresh air
• Apply artificial respiration if the victim is not breathing and check that the heart is beating
• Remove contaminated clothing and shoes preferably under a shower
• Wash the damaged skin or eyes for several minutes (at least 15 minutes) with large amount of pure water and cover affected areas with clean bandage
• Turn unconscious patient so that he lies on his side to avoid suffocation due to vomiting
• Wash the damaged eye with running water for several minutes and cover it with a clean cloth
• If acids or alkaline substances have been swallowed wash the mouth with water. If the swallowed substance is a strong acid or alkali do not induce vomiting. If the pain allows the patient to swallow and he is conscious, give water to drink (2 dl) to dilute the swallowed substance. Do not give substance which could neutralize the acid or alkali as the heat of neutralizing reaction may cause burns.
• Keep the victim warm and resting
• Obtain medical care in all cases except if the skin irritation is light. Injuries to eyes, respiratory system, and if the acid or alkali has been swallowed need always medical attention.
• Skin injuries caused by hydrogen fluoride need immediate treatment. Work places should have available necessary emergency equipment, including calcium gluconate gel.

Continue to Part IX: Polymers