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Prudent Practices in the Laboratory: Handling and Disposal of Chemicals
Flammability and Explosibility
Ammonia vapor is slightly flammable (NFPA rating = 1) and ignites only with difficulty. Ammonia forms explosive mixtures with air in the range 16 to 25%. Water, carbon dioxide, or dry chemical extinguishers should be used for ammonia fires.
Reactivity and Incompatibility
Ammonia vapors or solutions can react with compounds of silver, gold, and mercury to produce unstable and highly explosive products. Do not use a mercury manometer for measuring ammonia gas pressure. Highly explosive nitrogen halides can form in reactions of ammonia with halogens, hypohalites, and similar compounds. Violent reactions can occur with oxidizing agents such as chromium trioxide, hydrogen peroxide, nitric acid, sodium and potassium nitrate, chlorite, chlorate, and bromate salts.
Storage and Handling
Anhydrous ammonia should be handled in the laboratory using the ''basic prudent practices" described in Chapter 5.C, supplemented by the procedures for work with compressed gases discussed in Chapter 5.H. All work with ammonia should be conducted in a fume hood to prevent exposure by inhalation, and splash goggles and impermeable gloves should be worn at all times to prevent eye and skin contact. Cylinders of ammonia should be stored in locations appropriate for compressed gas storage and separated from incompatible compounds such as acids, halogens, and oxidizers. Only steel valves and fittings should be used on ammonia containers; copper, silver, and zinc should not be permitted to come into contact with ammonia.
Prompt medical attention is required in all cases of overexposure to ammonia. In the event of skin contact, immediately wash with soap and water and remove contaminated clothing. In case of eye contact, promptly wash with copious amounts of water for 15 min (lifting upper and lower lids occasionally) and obtain medical attention. If ammonia is ingested, obtain medical attention immediately. If large amounts of ammonia are inhaled, move the person to fresh air and seek medical attention at once.
In the event of a gaseous ammonia leak, shut down all ignition sources and ventilate the area at once to prevent flammable mixtures from forming. Carefully remove cylinders with slow leaks to a fume hood or remote outdoor location. Limit access to an affected area. Respiratory protection may be necessary in the event of a large release in a confined area.
Cylinders containing excess ammonia should be returned to the manufacturer. Ammonia gas may also be dissolved in water for neutralization and disposal. In some localities, aqueous ammonia may be disposed of down the drain after appropriate neutralization and dilution. If ammonia gas is directed into water, precautions should be taken to prevent the suckback of water into the ammonia-containing vessel or cylinder. Dissolution of ammonia in water is accompanied by heat evolution. In a fume hood, the diluted ammonia solution should be neutralized with a nonoxidizing strong acid such as HCl. The resulting solution can be discharged to the sanitary sewer. If drain disposal is not permitted, the aqueous ammonia should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines. For more information on disposal procedures, see Chapter 7 of this volume.