Several organizations have drawn up recommendationsforthe safe handlingof perchloric acid, among them the Association of Official Agricultural Chemists, the Factory Mutual Engineering Division, and the Association of Casualty and Surety Companies. The recommendations from these and othersources are combined and summarized below.
Floors--Perchloric acid should be handled in a masonry building with concrete or tilefloors. Handling acid on wooden floors is dangerous, especially after the acid has dried.The wooden floor will then become sensitive to ignition by friction.
Note that since the original preparation of this article, commercial equipment specificallydesigned to be used with perchloric acid has become generally available-specifically hoods andejector ducts to exhaust perchloric fumes well above roof level.
For conventional wooden wall construction, which is [not] desirable, it is highly recom-mended that a 6-inch concrete curb be provided for the walls to rest on. In this way, acid seepage under the wall is minimized.
Concrete of course, is not resistant to acids, and thus should be covered. Epoxy paints in general are resistant to room temperature perchloric acid spills; however, epoxy paint will peel off concrete if pools of water stand for several days. Therefore, the floor should have a gentle slope to a drain and contain no low spots.
No equipment of any kind should ever be bolted to a floor by using bolts that screw into the floor. Perchlorates can enter and form hazardous metallic perchlorates that can be initiate a detonation when the bolt is removed. Studs, firmly and permanently set into the floor to which the equipment can be bolted, are far safer. The nuts can then be flushed with water and sawed off with a hacksaw under a constant water spray or remove that equipment.
Laboratory benches-Laboratory benches should be constructed of resistant materials
and not wood to prevent acid absorption, especially at the bottom surface which rests on the floor and would be subject to the greatest exposure from acid spills. Bench tops of resistant and nonabsorbent materials such as chemical stoneware, tile, epoxy composites, and polyethylene are recommended.
Shelves and cabinets-Shelves and cabinets of epoxy-painted steel are highly recommended over wood.
Heating source-Hot plates (electric), electrically or steam-heated sand baths, or a steam bath are recommended for heating perchloric acid. Direct flame heating or oil baths should not be used.
Vacuum source-Smith describes a simple apparatus, using a water aspirator or pump, for drawing fumes from a reaction vessel. The use of this apparatus is to be commended in that the contamination of the fume cupboard duct with a dust/perchloric acid layer is avoided and the vapors are drawn into water and discharged safely to the drain.* A similar apparatus is marketed for carrying out Kjeldahl digestions. Vacuum pumps from which all traces of petroleum lubricants have been flushed and refilled with halocarbon, Kel-F, or fluorolube are recommended.
Silverman and First have described a self-contained unit which has been developed and field tested for collecting and disposing of chemical fumes, mists, and gases.15 It is portable and compact and, when assembled, only requires connection to an electrical receptacle and water tap to be completely operational. Although originally designed for use in filter-type radiochemical laboratory hoods for safe disposal of perchloric acid fumes arising from acid digestions, it may be used as a substitute for a permanent hood in a variety of [low risk] locations. Collection and disposal of the acid at the source of emission is the guiding design principle.
The conventional vacuum pump has been used both in the laboratory and in a pilot plant
handling large quantities of 72% perchloric acid. The pumps were protected by the use of well-designed cold traps and desiccant columns as well as maintaining the practice of changing petroleum-based oil daily. The desiccant was also routinely changed, along with the frequent thawing and removal of the cold trap contents.
Glassware. The hazards that may ensue if an apparatus cracks or breaks due to thermal or mechanical shock are sufficient to make it desirable that quartz apparatus be considered, especially as it is necessary in many experiments to chill rapidly from the boiling point.
Glass-to-glass unions, lubricated with 72% perchloric acid, seal well and prevent joint freezing arising from the use of silicon lubricants. Rubber stoppers, tubes, or stopcocks should not be used with perchloric acid due to incompatibility.
Stirrers. Pneumatically driven stirrers are recommended rather than the electric motor type. Repeated exposure of the motor windings to perchloric acid vapor could result in a fire, unless the motor is an explosion-proof type, which would be unlikely.
Sundry items-The choice of tongs for handling hot flasks and beakers containing perchloric acid mixtures should be given due thought. Since the use of radioactive materi- als has become commonplace, much thought has been put into the design of indirect handling equipment. The cheap, commonly used crucible tongs are most unsuitable for picking up laboratory glassware. If possible, tongs with a modified jaw design should be used to ensure that a safe grip is obtained.
Handling 73 % or Less Perchloric Acid in the Laboratoty
1 .Use chemical splash and impact-rated goggles for eye protection whenever the acid is handled.
2. Always transfer acid over a sink in order to catch any spills and afford a ready means of disposal.
3. In wet combustions with perchloric acid, treat the sample first with nitric acid to destroy easily oxidizable matter.
4. Any procedure involving heating of perchloric acid must be conducted in a perchloric acid fume hood, with the sash
down.
5. No organic materials should be stored in the perchloric acid hood.
6. Do not allow perchloric acid to come into contact with strong dehydrating agents (concentrated sulfuric acid,
anhydrous phosphorous pentoxide, etc.).
7. Perchloric acid should be used only in standard analytical procedures from well- recognized analytical texts.
(This does not apply to analytical research workers.)
8. Keep the quantities of perchloric acid handled at the bare minimum for safety
Acid Disposal
Spills-Perchloric acid spilled on the floor or bench top represents a hazard. It should not be mopped up, nor should dry combustibles be used to soak up the acid. The spilled acid should first be neutralized and then soaked up with rags or paper towel. The contami- nated rags and paper towel must be kept wet to prevent combustion upon drying. They should be placed in a plastic bag and sealed and then placed in a flammable waste disposal can. If the spill can be rinsed down a chemical drain, neutralization of the wetted area is recommended followed by additional rinsing. Other recommendations in the literature include wearing a face shield and gloves while working on the spill. Cover the spill with a weak solution of sodium thiosulfate, and then transfer the slurry into a large container of water, where it should be neutralized with soda ash. After neutralization, it can be drained into the sewer, accompanied by abundant water.
Disposal-Stir the acid into cold water until the concentration is less than 5%; follow by neutralization with aqueous sodium hydroxide; then dispose of the resulting mixture in the sanitary system, accompanied by abundant water. Larger quantities in the original un- opened containers may be acceptable to a commercial hazardous waste vendor. If it is potentially explosive, the best option available is to hire a firm specializing in disposal of exceptionally hazardous materials. This will be expensive.
Conclusion
It is clear, however, that no one should attempt to use perchloric acid who is not fully conversant with the chemistry of the material, who has not made a careful appraisal of operating conditions and techniques, and who exhibits an unsafe attitude about his work.
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