Use and Handling of Perchloric Acid (HClO₄)

Policy:

   Perchloric acid is a highly volatile acid and requires special precautions when being handled. Every precaution should be taken to insure safe handling, including the use of eye protection and full protective clothing. Persons who use this acid, should inform their supervisor and other persons who might be in the immediate area.

Hazards:

1. Contact of perchloric acid with combustible materials such as wood, paper, cotton waste, grease, oil, and most organic compounds make such materials highly flammable and dangerous. Such materials may explode on heating by impact, friction, or spontaneous ignition.
   
   
2. Perchloric acid solutions in contact with dehydrating materials may result in the formation of anhydrous perchloric acid which is unstable even at room temperature and ultimately undergoes spontaneous decomposition with a violent explosion.
   
   
3. Perchloric acid reaction with metallic bismuth produces a spontaneously explosive compound.
   
   
4. Combustible materials, previously wet with perchloric acid solution and allowed to dry, will burn with great intensity. Ordinary fire extinguishers are not effective on such fires and personnel should be warned against entering a perchloric acid storage area involved in a fire because of the rapid propagation of flame and the possibility of the accompanying explosion. Only large quantities of water delivered in a solid stream are effective in controlling such fires.
   
   

Safety Procedures:

1. All laboratory use of perchloric acid should be restricted to a specially designed perchloric acid hood constructed of stainless steel and provided with a water scrubber and stack wash ring.
   
   
2. Solutions containing perchloric acid that are to be evaporated to the fuming point should, preferably, be exhausted through the use of a water aspirator to serve the dual purpose of providing localized ventilation and to scrub out perchloric acid from the fumes.
   
   
3. Heating of perchloric acid should be by means of hot plates, electric mantle, steam baths, or electric or steam-heated sand baths. Gas flames or oil baths should not be used for heating such solutions.
   
   
4. Laboratory set-ups containing perchloric and solution should have all glass-to-glass unions. Rubber tube stoppers or stop cocks should never be used. Grease, including silicon types, should not be used.
   
   
5. Accidental spills of perchloric acid solution should be cleaned up immediately using large quantities of water. Repeated moppings and thorough final rinsing is necessary if the acid is spilled on wooden floors or shelves. Thorough rinsing of the material and equipment used for cleanup with large amounts of water should follow.
   
   
6. Persons handling perchloric acid should be provided with and required to wear gloves, sleeves, and aprons, or a coat of rubber or a similar impervious non-combustible material, face shields or goggles, and should work in an area provided with an emergency deluge shower and eye wash fountain.
   
   
7. Laboratory quantities of perchloric acid should be limited to a one pound reagent bottle per hood. The reagent bottle should be kept in the hood and in a deep glass or ceramic tray with sufficient capacity to hold entire contents in case of breakage. The tray and outside of the bottle should be rinsed daily.
   
   
8. All glass apparatus, used for perchloric acid work, should be rinsed immediately after use. The reagent bottle should be rinsed with water after each use before returning to the glass tray.
   
   
9. The diluted, or partially exhausted, samples from digestion or reaction flasks containing perchloric acid should be collected and disposed of as hazardous waste in accordance with Hazardous Chemical Waste Management Guidebook 5th Edition.
   
   
10. Reagent bottles not in active use should be isolated in a non-combustible cabinet away from combustible materials and other chemicals.
    
    
11. When maintenance is required and perchloric acid contamination is suspected, such as use of perchloric acid in a standard fume hood, all surfaces should be checked by the application, using a medicine dropper, of a solution of diphenylamine sulfate (1 gram in 100 ml of 1 to 1 H₂SO₄). The liquid turns black upon contact with a perchlorate. The solution also reacts with nitrates, but turns blue. Contaminated areas must be thoroughly washed and flushed with water (up to 24 hours of flooding may be required) and then rechecked.