Corrosives

Corrosives consist of four major classes: Strong acids, strong bases, dehydrating agents and oxidizing agents. Inhalation of the vapors of these substances can cause severe bronchial irritation. These chemicals erode the skin and the respiratory epithelium, and are particularly damaging to the eyes. Acids and alkalis should be stored separately in a cool ventilated area, away from metals, flammables, and oxidizing materials. The storage area should be checked regularly for spills and leaks, and there should be suitable spill cleanup materials available. Protective clothing should be worn whenever acids or alkalis are handled.

Always pour acids into water, never the reverse. Cap bottles securely and store them securely, but do not store acids and alkalis together. Clean up spills promptly. Do not leave residues on a bottle or lab bench where another person may come in contact with them. Wear protective garb when handling acids or alkalis. This includes rubber gloves, apron, and eye protection.

Four acids deserve special attention because of the hazards they pose. These are: nitric acid, perchloric acid, picric acid, and hydrofluoric acid.

Nitric acid
is corrosive and its oxides are highly toxic. Because nitric acid is also an oxidizing agent, it may form flammable and explosive compounds with many materials (e.g., ethers, acetone and combustible materials). Paper used to wipe up nitric acid may ignite spontaneously when dry. Nitric acid should be used only in a hood, and should be stored away from combustible materials.

Perchloric acid
(HClO4) forms highly explosive and unstable compounds with many organic compound and even with metals. Unstable perchlorate compounds may collect in the duct work of fume hoods and cause fire or violent explosions. Therefore, perchloric acid should be used with extreme caution and only in a fume hood designed for its use-a perchloric acid hood having corrosion-resistant duct work and washdown facilities. We have no such facilities in our school. Minimum quantities of perchloric acid should be kept on hand, and the container stored in a perchloric acid hood on a glass tray that is deep enough to hold the contents of the bottle. Perchloric acid should not be kept for more than one year since explosive crystals may form. A number of graduate students at universities have had their fingers blown off when unscrewing the cap from perchloric acid. Liquid residue forms a crust on the bottle and cap threads, which explode when the next user attempts to open the bottle. Similar explosions occurred when attempting to clean non-perchloric acid fume hoods, where vapors formed crystals in the crevices in the hood and duct work. Perchloric acid should be stored in an explosion proof refrigerator since it may become unstable at room temperature.

Picric acid
can form explosive compounds with many combustible materials. When the moisture content decreases, picric acid may become unstable and may explode from being shaken. Picric acid should be dated, stored away from combustible materials, and not kept for extend periods (i.e., longer than one year).
Hydrofluoric acid
is extremely corrosive and will even attack glass. All forms-dilute, concentrated solutions or the vapor-can cause serious burns. HF does not produce overt tissue burns like most acids; instead, it diffuses through tissue and will dissolve bone. Burns from hydrofluoric acid heal slowly and with great difficulty. Therefore, hydrofluoric acid should be used in suitable fume hood while gloves, safety glass and lab coat are being worn. Inhalation of HF mists or vapor will cause serious respiratory tract irritation that may be fatal. Care should taken to avoid contacting hydrofluoric acid with metals or ammonia since toxic fumes may result.