Office of Research

Appendix K

Use of Perchloric Acid

Perchloric acid (HCl04) is a colorless, odorless, fuming liquid that is miscible with water and extremely corrosive. Perchloric acid is noncombustible, however the anhydrous acid and certain perchlorate salts of organic, organometallic, and inorganic cations present a serious explosion hazard and have been set off by either heat or shock. Because of perchloric acid’s extremely corrosive physical properties and it tendency to react violently with many oxidizable substances, it is among the most hazardous substances found in the laboratory and should be used and stored with extreme care.

Perchloric acid is very corrosive to all living tissue. It can cause severe burns on contact with eyes, skin, and mucous membranes and is a severe irritant. Its acute toxicity is moderate. Perchloric acid has not been shown to be carcinogenic nor or reproductive or developmental toxin in humans.

Although perchloric acid is not combustible, the anhydrous form is a serious explosion hazard due to its unstable nature and ability to react violently with many organic materials (e.g. wood, paper, cotton, etc.). Perchloric acid can cause violent explosions if it is misused, or if it is in concentrations greater than normal commercial grade strength (72%). At concentrations less than 72%, aqueous perchloric acid will not decompose spontaneously nor explode on standing. Many heavy metal perchlorates and organic perchlorate salts are very sensitive explosives. Mixtures of perchlorates with many oxidizable are explosive. When used cold, 70% perchloric acid acts as a strong acid, but is not considered to be a strong oxidizing agent; however, when heated it acts as a strong oxidizing agent. More concentrated solutions are strong oxidizers and increases in temperature increase the oxidizing power of perchloric acid. Hot concentrated solutions are very, very dangerous and should not be taken lightly.

Perchloric acid is a strong inorganic acid used for complete digestions of organic material. It is normally supplied in bottles of up to one gallon capacity at 70-72% strength. In many respects, its hazards are similar to those of nitric acid, as both are strong oxidizers. Perchloric acid presents an additional hazard in that perchloric acid mist and fumes can condense in ventilation systems to form metallic perchlorates which can be explosive.

All perchlorates are potentially hazardous when in contact with reducing agents. Oxidizable organic compounds including alcohols, ketones, aldehydes, ethers, and dialkyl sulfoxides can react violently with concentrated perchloric acid.

 

Perchloric Acid Hood:

Perchloric acid should be used only in hood designed/designated for perchloric acid use. Perchloric hoods should be constructed with an integral liner of a single piece of 316 stainless with welded seams (and as few seams as possible). The liner should have coved corners. Ductwork should also be stainless steel or PVC (must be properly fire-rated). At a minimum, the blades and any other portion of the exhaust fan coming into contact with the perchloric fumes should be coated with PVC, Teflon, or another approved material that will resist the effects of the perchloric acid. In order to avoid buildup of perchloric precipitates in the hood and the duct system, the hood must be equipped with a washdown system that will rinse the system thoroughly at the end of each work session involving the use of perchloric acid. The washdown mechanism should be capable of cleaning the entire duct from the point of exhaust all the way back to the hood.

Personal Protective Equipment: The following PPE should be worn when handling perchloric acid.

 

Splash/Impact Goggles

Face shield

8 mil Nitrile, PVC, or neoprene gloves

Lab coat

Chemically-resistant apron

 

Researchers using or anticipating using perchloric acid in their experiments should keep the following in mind:

All use of perchloric acid must be approved by the Institutional Biosafety Committee (IBC). Contact Research Compliance (656-6460) to obtain protocol submittal forms.

1.     Perchloric acid digestions of any size must be performed only in a perchloric hood.  

      No open bench top digestions should be performed. All perchloric acid digestions

      performed above ambient temperature require a special perchloric acid hood with a

      washdown system. These hoods used for hot digestion should be posted with a label

      stating "Perchloric Acid Hood Only-- Organic Chemicals Prohibited.”

 

2.     Regardless of the size of the digestion, no organic solvents should be in the hood

      during the digestion. Solvents must never be stored or used in a designated perchloric

      acid hood at any time.

 

3.     Keep concise records of who uses the hood, with what agents and amounts, as well as  

      the washdown frequency.

 

4.     Perchloric acid will attack human tissues as easily as it will attack samples of organic

      material. To prevent injury, goggles or face shield, gloves, and apron should be worn

      when handling perchloric acid.

 

5.     Because of the potential for explosion, no repair or maintenance should be done on a

      hood used for perchloric acid digestions until it has been thoroughly washed.

 

6.     Perchloric acid waste must not be mixed with any other waste. It should be put into

      acid-resistant bottles (preferably the original acid container), clearly labeled, and

      treated as hazardous chemical waste. You can submit your waste pick up request on

      line from the EH&S web site hazardous waste page.

 

7.     Perchloric acid should be stored segregated from all other chemicals. If this is not

       possible, it may be stored in the same cabinet with other inorganic acids such as

      hydrochloric, sulfuric or nitric acid, provided that secondary containment (such as a

      Pyrex baking dish or plastic dish pan large enough to capture the contents of the

      container(s)) is provided). Secondary containment should also be provided for sulfuric

      and nitric acid.  Perchloric acid must not be stored near organic acids such as acetic

      acid, near bases, or near any other organic or flammable material. Perchloric must not

      be stored on wood shelves unless secondary containment is provided.

 

8.     In the event of a spill contact the University Fire Department at 911.

 

9.     Any use of perchloric acid must be approved by RS. An IBC protocol must be

      submitted and approved prior to use of perchloric.

 

10.  Do not store or use organic materials in a perchloric acid hood.

 

11.   If a vacuum is needed for perchloric acid work, use a water aspirator rather than a

       mechanical pump. Perchloric acid contact with hydrocarbon based oils or greases in a

       conventional mechanical pump may result in an explosion.

 

12.  Purchase the smallest quantity of perchloric acid possible. When possible, use

       alternative chemicals/techniques.

 

13.  Only experienced research workers should handle anhydrous perchloric acid. These

Workers must be thoroughly familiar with the literature on the acid.

 

14.  If a laboratory hood or exhaust system was used for perchloric acid heated above ambient temperature, you must inform maintenance personnel and RS personnel before any inspection, maintenance, cleaning, or any other work is done on any part of the exhaust system or hood interior.

 

If you have any questions about safe use and handling of perchloric acid, or wish to have a chemical hood approved for use with perchloric acid, please contact the Chemical/Lab Safety Manager at 650-8155 or nkelly@clemson.edu.

  

Record of Use

 

Date

User

Chemicals Used

Washdown Completed Yes/No

Comments