NC State University
Perchloric Acid Safety
Section II. Guidelines for Perchloric Acid Use and Storage
NC State University, Environmental Health and Safety Center (EH&S) requires
that all process using perchloric acid to be performed in an exclusively designed and
designated perchloric acid hood. This is required to prevent perchloric acid vapors to
form shock sensitive perchlorates in ventilation system. All conventional (non- perchloric
acid) chemical hoods are posted, indicating that no perchloric acid use is allowed.
Any perchloric acid use in a conventional chemical hood requires EH&S approval.
1. What is Perchloric Acid?
Perchloric acid (HClO4) is a clear, colorless, odorless, and strong mineral acid
used as laboratory reagent for digestions and other chemical process. At concentrations
above 72% or when heated (at any concentrations), perchloric acid becomes a strong
oxidizer. Metal and non-organic salts formed from oxidization are shock sensitive and
pose a great fire and explosion hazard. These guidelines present information on how to
handle and store perchloric acid safely. Please contact EH&S at 513-1282 if you have
any concern about using perchloric acid in your laboratory.
2. Hazards
Perchloric acid is a corrosive acid and destructive to human tissue. Perchloric acid
can be a health hazard if inhaled, ingested or splashed on skin or eyes. Once heated above
room temperature or used at concentrations above 72% (any temperature), perchloric acid
becomes a strong oxidizing acid. Organic materials are especially susceptible to
spontaneous combustion if mixed or contacted with perchloric acid. Perchloric acid
vapors may form shock sensitive perchlorates in ventilation system ductwork. Process
involving perchloric acid, particularly concentrations above 72% or when heated above
ambient temperature shall only be used in a laboratory hood specially designed and
designated for perchloric acid operations (perchloric acid hood)
3. Perchloric acid hood
Perchloric acid hood is a specifically designed local exhaust system with material
(hood, ductwork, fan, gaskets, sealants, …) resistant and non-reactive to perchloric acid
and a shatterproof sash. Perchloric acid hood is equipped with a manual water spray
system to wash down perchlorate residues on the hood interior behind the baffle and the
entire exhaust system.. Perchloric acid hoods shall not be manifolded with other exhaust
systems. It is necessary to wash down the perchloric acid hood before and after each use.
Perchloric acid hoods are subject to ‘exhaust Ventilation for Hazardous Materials’
requirements as described in the EH&S home page at:
http://www.ncsu.edu/ehs/www99/right/handsMan/lab/exhmpg2.html
Procedures for purchasing chemical hood, including perchloric acid hood are also
outlined on this website. Perchloric acid hood purchasing, installation, use, and
maintenance shall be in accordance to EH&S and construction management guidelines
(section 9)
4. Examples of perchloric acid incompatible material:
4.1 Plastics such as polyamide (nylon) and polyester (Dacron)
4.2 Metals such as copper and copper alloys, aluminum, and nickel alloys
4.3 Glycerin-lead oxide (letharge)
4.4 Strong dehydrating agents such as concentrated sulfuric acid and anhydrous
phosphorous pentoxide
4.5 Organic material such as cotton, wool, grease, and wood
5. Perchloric Acid Safety Requirements
Before using perchloric acid, it is necessary to consult EH&S to determine if a
substitute material/procedure may be used. All new procedures involving the use of both
cold and hot perchloric acid work, in any amounts, will be reviewed by EH&S for
approval.
To prevent injury, goggles and face shield, protective gloves, shoes, and an apron
over lab coat shall be worn when handling perchloric acid. The lab area shall be
equipped with an approved emergency eyewash and safety shower. Labs shall develop a
safety plan, including written SOPs (standard operating procedures) for safe handling of
perchloric acid in lab (and how to operate a perchloric acid hood).
Because of its' reactivity hazard, perchloric use of any size above room
temperature must be performed in a special perchloric acid hood that is equipped with a
wash down system and posted as “Perchloric Acid Hood”. Organic Chemicals must never
be used or stored in a designated perchloric acid hood.
5.1 Process using perchloric acid at room temperature (≤72%):
At room temperature, perchloric acid up to concentrations of 72% has properties
similar to other strong mineral acids. It is a highly corrosive substance and causes
severe burns on contact with the eyes, skin, and mucous membranes. The
following precautions should be taken when using perchloric acid at or below
72% at room temperature:
5.1.1 Substitute with less hazardous chemicals when appropriate. Use dilute
solutions (<60%) whenever possible.
5.1.2 Only after EH&S approval, conduct operations involving cold
perchloric acid in a properly functioning laboratory (chemical) hood with a
current test sticker. If there is a major change in frequency, volume, or
concentration of the acid used in the lab, or when process change requires
heating the acid above the room temperature, contact EH&S in advance to
determine if specially designed hood dedicated to perchloric acid use is
required.
5.13 Always use impact-resistant chemical goggles, a face shield, protective
gloves, shoes, and a rubber apron when handling perchloric acid.
5.1.4 When using or storing even dilute perchloric acid solutions avoid
contact with strong dehydrating agents (concentrated sulfuric acid,
anhydrous phosphorous pentoxide, etc.). These chemicals may concentrate
the perchloric acid and make it unstable.
5.1.5 Always transfer perchloric acid over suitable containment in order to
catch any spills and afford a ready means of cleanup and disposal.
5.1.6 Perform all operations on chemically resistant surfaces. Avoid contact
with cellulose materials such as wood, paper and cotton, which could result
in a fire or explosion.
5.2 Process involving heating perchloric acid (any concentrations) or using
highly concentrated (73 –85 %)
When heated above room temperature or at high concentrations, perchloric
acid becomes a strong oxidizer and unstable chemical. Concentrated solutions are
very dangerous and can react violently with many oxidizable substances, such as
paper and wood, and can detonate. Vapors may also contaminate work surfaces or
ventilation equipment with perchlorate residues, which may form highly unstable
compounds, such as metallic perchlorates. These compounds may ignite or
detonate under certain conditions. The following additional precautions should
be followed when heating perchloric acid:
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
5.2.6
5.2.7
Experiments shall only be performed in a laboratory chemical
hood, specifically designed and posted for perchloric acid
operations only. Contact EH&S if you have been performing
perchloric acid digestion in a laboratory hood not designed for
perchloric acid use.
Use chemical hood sash or a safety shield to provide
splash/splinter
Explosion proof electrical equipment such as hot plates, electronic
or steam –heated sand baths, heating mantles, or steam baths are
preferred methods of heating perchloric acid. Oil bath or open
flames shall not be used to heat acid.
Avoid storing or using other material in a perchloric acid hood,
including incompatible material such as paper, wood, and
incompatible grease or hose.
Be sure you understand the reaction(s) that can occur when using
perchloric acid. Perchloric acid may react violently with many
chemicals, including acetic anhydride, organic material, alcohol,
reducing agents, and many metals.
In wet digestions with perchloric acid, treat the sample first with
nitric acid to destroy easily oxidizable matter.
Do not distill perchloric acid in a vacuum, because the unstable
anhydride may be formed and cause a spontaneous explosion.
5.2.8
5.2.9
5.2.10
5.2.11
5.2.12
Protect vacuum sources from perchloric acid/perchlorate
contamination. Vacuum pumps should be thoroughly flushed and
refilled with Kel-F or Fluorolube.
Wash down perchloric acid hoods before and after each use,
following operating instructions provided by the manufacturer of
the perchloric acid hood.
All apparatus should have glass-to-glass joints. Use silicon-based
lubricants for glass-to-glass joints. Do not use rubber stoppers,
tubes or stopcocks.
If an apparatus cracks or breaks due to thermal or mechanical
shock, the hazards are sufficient to make it desirable to consider
using quartz apparatus since it is necessary in many experiments to
chill perchloric acid rapidly from the boiling point.
When handling beakers of hot acid use properly designed tongs or
other remote-handling devices.
Using /maintaining perchloric acid hoods requires specialized
training
5.3 : Using anhydrous perchloric acid (> 85%)
Anhydrous perchloric acid (> 85% concentration) is very unstable and will
usually explode when it comes in contact with organic materials. Follow these
additional precautions when working with anhydrous perchloric acid.
5.3.1
5.3.2
5.3.3
5.3.4
5.3.5
5.3.6
Allow only experienced researches to handle anhydrous
perchloric acid. These researchers shall be thoroughly familiar
with the perchloric acid use SOPs. Assure that a second person in
lab is informed of the intended use of the anhydrous perchloric
acid.
Use a safety shield to protect against the effects of a possible
explosion
Use thick gauntlet in addition to PPE previously recommended
Use only freshly prepared acid. Do not make any more anhydrous
perchloric acid than is needed for a day/shift.
Dispose of any unused acid at the end of each day (no storage)
Use the acid in a designated, perchloric acid hood with a minimum
of equipment present. No other chemicals shall be kept/used in this
hood
6. Storage
6.1 Minimize the storage quantities and the bottle size
6.2 Keep bottles in labeled original bottles, preferably with a compatible secondary
container (e.g. glass). Do not use rubber stoppers, tubes, or stopcocks due to
incompatibility with acid (use glass to glass unions)
6.3 Store in a compatible corrosive cabinet or a perchloric acid hood (limited
quantity). Avoid storage in wood cabinets
6.4 Sore separate from organic chemicals /solvents, flammables / combustibles,
strong dehydrating agents such as sulfuric acid and anhydrous phosphorous
pentoxide
6.5 Expired/used chemical should be preferably collected in the original bottle and
discarded as hazardous waste.
6.6 Prolonged storage of perchloric acid may result in shock sensitive perchlorate
salts, particularly around the bottle’s neck (white explosive crystals). DO NOT
touch or move the bottle. Contact EH&S immediately.
7. Accidents and Spills
7.1 Spill clean up needs to be done immediately and only by trained and authorized
people, wearing appropriate PPE
7.2 For large spills, evacuate the area, close the door behind and immediately contact
campus police at 911 (form a land phone)
7.3 For small spills, neutralize the acid spill with sodium carbonate. Any spill can be
hazardous if allowed to dry
7.4 Do not use organic material such as kim-wipes or paper towels (possible
spontaneous ignition)
7.5 Soaked organic material may ignite spontaneously. Wet them with water and
place them in a sealed compatible container for immediate disposal.
7.6 Contain and label waste in a compatible container and contact EH&S for
immediate waste pickup
7.7 In case of eye/skin exposure, wash the effected area for at least 15 minutes, using
the safety shower/eyewash stations. Seek medical attention, even for a minor
exposure.
7.8 Consult MSDS for spill and exposure information.
http://www.actiocms.com/displaycode/searchdetail.cfm?msds_id=251838&Language=1&noprint_la
bel_fax_ema
8. Perchloric acid hood label
All perchloric acid hoods need to be posted with the following label:
(Contact EH&S if your hood perchloric acid
Hood is not poster)
PERCHLORIC
ACID HOOD
When perchloric acid is
used in this hood:
*The hood must be
thoroughly washed down
before and after perchloric
acid use
* The hood must be
devoted exclusively to
perchloric acid work
Specialized training is
required for anyone who
uses or maintains this hood
9. Relevant standards and references
1. Exhaust Ventilation for Hazardous Materials (EH&S home page):
http://www.ncsu.edu/ehs/www99/right/handsMan/lab/exhmpg2.html
2. NFPA 45, Standards on Fire Protection for Laboratories Using Chemicals
3. CRC Handbook of Laboratory Safety
4. NC State Construction Guidelines (decommissioning - decontamination):
5. Recommended Chemical Hood Use Procedure:
http://www.ncsu.edu/ehs/hood/recommended_hood_proc.pdf
6. NC State University Supervisor’s Safety Self Assessment Checklist (#59 & 60):
http://www.ncsu.edu/ehs/www99/right/super/NCSUSafetySelfAssesment.pdf