Suggestions for Handling Hazardous Materials

All chemical, including many metals and oxides, pose some degree of danger to the human organism. This may come about by ingestion through the respiratory or digestive tracts or by external contact with the skin or eyes. Basically, the same precautions apply to the metallographic laboratory as to all chemical laboratories, except that certain specific areas are particularly critical. Some significant precautions are:

Clearly label all storage containers.

Dilute concentrated chemicals before disposal and observe all local waste-disposal regulations.

Critical substances (flammable, explosive, toxic, or corrosive) should be stored in approved containers in cool, fireproof, isolated areas.

Caustic materials, such as acids, bases, peroxides, and some salts should be handled only when wearing protective devices such as safety glasses, rubber gloves, and laboratory coats or aprons. Vapors of such materials are often harmful, too. Actual work should be carried out in an effective fume hood with an additional gas mask if evolution of toxic gases and vapors is suspected.

When preparing etchants containing aggresive chemicals such as sulfuric acid, the chemical should always be added to the solvent (water, alcohol, etc.) slowly with gentle stirring. External cooling may also be required if haet evolution is particularly strong.

Volatile, flammable and explosive materials, such as benzone, acetone, ether, perchlorate, nitrate, etc. should not be heated or kept near open flames.

When preparing microsections of toxic materials such as beryllium, and radioactive substances or alloys conrtaining uranium, thorium and plutonium, a glove box or hot cell must be used.

Perchloric acid in concentration exceeding 60 % is highly flammable and explosive. This danger is greatly increased by the presence of organic materials such bismuth, which oxides readily. Avoid the high concentration and heating of these solutions, particularly in electrolytic polishing and etching; never store high-concentration perhloric acid in plastic containers. When mixing perchloric acid and alcohol, highly explosive alkyl perchlorates may form. Perchloric acid should be added slowly under constant stirring. Keep the temperature of the solution below 35 degrees of Celsius and, if necessary, use a coolant bath. Wearing safety glasses is helpful, but working behind a safety shield is preferable.

Mixtures of alcohol and hydrochloric acid can react in various ways to produce aldehydes, fatty acids, explosive nitrogen compounds, etc. The tendency toward explosion increases with increasing molecule size. Hydrochloric acid content should not exceed 5 % in ethanol or 35 % in methanol. These mixtures should not be stored.

Mixtures of alcohol and phosphoric acid can result in the formation of esters, some of which are potent nerve poisons. If absorbed through the skin or inhaled, serve personal damage may result.

Mixtures of methanol and sulfuric acid may form dimethylene sulfate, an odorless, tasteless compound that may be fatal if absorbed in sufficient quantities into skin or respiratory tract. Even gas masks do not offer adequate protection. Sulfates of their higher alcohols, however, are not potentially dangerous poisons.

Mixtures of chromium (VI) oxide and organic materials are explosive. Mix with care and do not store.

Lead and lead salts are highly toxic, and the damage produced is cumulative. Care is also recommended when handling cadmium, thallium, nickel, mercury and other heavy metals.

All cyanide compounds (CN) are highly dangerous becaouse hydrocyanic acid (HCN) may easily form. They are fast-acting poisons taht can cause death, even in relatively low concentrations.

Hydrofluoric acid is a very strong skin and respiratory poison that is hard to control. It should be handled with extreme care, because sores resulting from its attack on skin do not heal readily. Hydrofluoric acid also attack glass, and fumes from specimen etched in HF solution could easily damage front element of microscope lenses. Specimen should be rinsed throughly and some cases placed in a vacuum desiccator for one or two hours before examination.

Picric acid anhydride is an explosive.

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