Standard Operating Procedure
Laboratory Specific
Chemical: Piranha Solution (Piranha
Etch)
Please fill out the form completely. Print a copy and insert into your
Laboratory Safety Manual and Chemical Hygiene Plan.
Refer to instructions for assistance.
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Department:________________________
Date when SOP was written:_______
Date when SOP was approved by the lab supervisor: ___________________
Principal Investigator:___________________________________________________
Internal Laboratory Safety Coordinator/Lab Manager:___________________________________
Laboratory Phone:____________________ Office Phone:_____________________
Emergency Contact:____________________________________________________
(Name and Phone Number)
Location(s) covered by this SOP:__________________________________________
(Building/Room Number)
_____________________________________________________________________________
Type of SOP:
Process
Hazardous Chemical
Hazardous Class
Purpose
Piranha solution, also known as piranha etch, is a mixture of sulfuric acid (H2SO4) and hydrogen peroxide
(H2O2), used to clean organic residues off substrates. Because the mixture is a strong oxidizer, it will
remove most organic matter, and it will also hydroxylate most surfaces (add OH groups), making them
extremely hydrophilic (water compatible). Piranha solution is used frequently in the microelectronics
industry, e.g. to clean photoresist residue from silicon wafers.
Piranha solution is very dangerous, being both strongly acidic and a strong oxidizer. Before using
Piranha, a chemist should attempt more stable methods of removing stains, tars or clogs. Often,
glassware will "clean itself" if simply left with a rinse of a cleaning solution present. An immediate example
for a suitable substitute, prior to using Piranha, is 98% sulfuric acid.
Piranha solution can be an explosive. Mixing the solution is exothermic. The resultant heat can bring
solution temperatures up to 120°C. One must allow the solution to cool reasonably before applying any
heat. The sudden increase in temperature can also lead to violent boiling, or even splashing of the
extremely acidic solution. Also, explosions may occur if the peroxide solution concentration is more than
50%. 30% peroxide in water solution is more reasonable.
Many different mixture ratios are commonly used, and all are called piranha. A typical mixture is 3:1
concentrated sulfuric acid to 30% hydrogen peroxide solution; other protocols may use a 4:1 or even 7:1
mixture. A closely related mixture, sometimes called "base piranha", is a 3:1 mixture of ammonium
hydroxide (NH4OH) with hydrogen peroxide. Base piranha is also known under the name of TL1 cleaning.
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The traditional piranha solution is a 3:1 mixture of sulfuric acid and 30% hydrogen peroxide. The solution
may be mixed before application or directly applied to the material, applying the sulfuric acid first, followed
by the peroxide. Piranha solutions are extremely energetic and may result in explosion or skin burns if
not handled with extreme caution.
Physical & Chemical Properties/Definition of Chemical Group
Corrosive & oxidizer
Potential explosive
Potential Hazards/Toxicity
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Explosion hazards
Splash hazards
Container rupture/failure (due to pressure build-up)
Skin burns
Irritation of mucus membrane
Personal Protective Equipment (PPE)
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Chemical safety goggles and face shield must be used
Cotton based lab coat (fire resistant lab coats)
Chemically resistant gloves (Nitrile or Neoprene gloves)
Full length pants
Close toed shoes
Engineering Controls
Fume hood or chemical wet bench (depending on the process).
First Aid Procedures
In case of skin contact: May cause skin burns. Flush the skin with copious amounts of water for at least
15 minutes. Seek medical attention.
In case of eye contact: Piranha is corrosive and irritating to the eyes. Flush contaminated eye(s)
immediately with copious quantities of water for at least 15 minutes. Seek medical attention immediately.
In case of inhalation: May irritate the respiratory tract. Conscious persons should be assisted to an area
with fresh, uncontaminated air. Seek medical attention in the event of respiratory irritation, cough, or
tightness in the chest. Symptoms may be delayed.
In case of ingestion: Not a likely route of exposure.
Special Handling and Storage Requirements
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Always use glass (preferably Pyrex) containers. Piranha will melt plastics.
Mix the solution in a fume hood with the sash between you and the solution. Wear gloves
and eye protection.
When preparing the piranha solution, always add the peroxide to the acid.
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Piranha solution is very energetic and potentially explosive. It is very likely to become hot,
more than 100 degrees C. Handle with care.
Leave the hot piranha solution in an open container until cool.
Never store piranha solutions for longer periods. Piranha stored in a closed container will
likely explode.
Adding any acids or bases to piranha or spraying it with water will accelerate the
reaction. This also includes Photoresist, which is a strong base.
Mixing hot piranha with organic compounds may cause an explosion. This includes acetone,
photoresist, isopropyl alcohol (other organic solvents), and nylon.
Piranha solution that is no longer being used should never be left unattended if hot. It should
not be stored in a closed container.
Adding anything to the piranha solution (such as a substrate that may have organic residue),
must be done slowly and carefully, giving the solution time to stabilize.
General handling & storage guidelines:
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Piranha solution may be prepared by adding the acid to the peroxide (following the usual rule
of adding acid to water) — although some authorities disagree. Once the mixture has
stabilized, it can be further heated to sustain its reactivity. The hot (often bubbling) solution
will clean organic compounds off substrates, and oxidize/hydroxylate most metal surfaces.
Cleaning usually requires about 10 to 40 minutes, after which time the substrates can be
removed from the solution.
The solution may be mixed before application or directly applied to the material, applying the
sulfuric acid first, followed by the peroxide.
Due to the self-decomposition of hydrogen peroxide, piranha solution should be used freshlyprepared. Piranha solution should not be stored. Waste piranha solution should be
neutralized and disposed in situ, instead of being accumulated in carboys. Oxygen given off
during the self-decomposition, as well as the oxidation products of organic compounds can
cause the container to rupture.
Immersing a substrate (such as a wafer) into the solution should be done slowly to prevent
thermal shock that may crack the substrate material.
It is important to remember that the solution, whilst susceptible to aging, will remain a
significant hazard as it drips off the item being cleaned.
NOTE: Do not store piranha. Mix fresh solution for each use. Excess solution should be disposed of as
hazardous waste with an online hazardous waste tag affixed. Note: The container used to store the
piranha waste should have a vented cap (tiny hole like a pin hole in the container cap on the top) to
prevent pressure build up in the container. VWR item no. 82013-170
Spill and Accident Procedure
Chemical Spill Dial 911 and x59797
Spill – Help contaminated or injured persons. Evacuate the spill area. Avoid breathing vapors.
Eliminate sources of ignition if the chemical is flammable. If possible, confine the spill to a small area
using a spill kit or absorbent material. Keep others from entering contaminated area (e.g., use caution
tape, barriers, etc.).
Small (<1 L) – If you have training, you may assist in the clean-up effort. Use appropriate personal
protective equipment and clean-up material for chemical spilled. Double bag spill waste in clear plastic
bags, label and take to the next chemical waste pick-up.
Large (>1 L) – Dial 911 (or 310-825-1491 from cell phone) and EH&S at x59797 for assistance.
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Chemical Spill on Body or Clothes – Remove clothing and rinse body thoroughly in emergency
shower for at least 15 minutes. Seek medical attention. Notify supervisor and EH&S at x59797
immediately.
Chemical Splash Into Eyes – Immediately rinse eyeball and inner surface of eyelid with water for
15 minutes by forcibly holding the eye open. Seek medical attention. Notify supervisor and EH&S at
x59797 immediately.
Medical Emergency Dial 911 or x52111
Life Threatening Emergency, After Hours, Weekends And Holidays – Dial 911 (or 310825-1491 from cell phone) or contact the Ronald Reagan UCLA Medical Center (emergency room)
directly at x52111 (located at 757 Westwood Plaza, enter from Gayley Avenue). Note: All serious injuries
must be reported to EH&S at x59797 within 8 hours.
Non-Life Threatening Emergency– Go to the Occupational Health Facility (OHF), x56771, CHS
room 67-120 (This is on the 6th floor, 7th corridor, room 120. Enter through the School of Dentistry on
Tiverton Drive and proceed to the “O” elevator to the 6th floor.)Hours: M - F, 7:30 a.m. to 4:30 p.m. At all
other times report to Ronald Regan UCLA Medical Center (emergency room) at x52111. Note: All serious
injuries must be reported to EH&S at x59797 within 8 hours.
Needle stick/puncture exposure (as applicable to chemical handling procedure)– Wash the
affected area with antiseptic soap and warm water for 15 minutes. For mucous membrane exposure,
flush the affected area for 15 minutes using an eyewash station. Page the needle stick nurse by dialing
231 from a campus phone, enter 93333 when prompted and then enter your extension. Hours: M – F,
8:00 a.m. to 4:00 p.m. At all other times report to Ronald Regan UCLA Medical Center (emergency room)
at x52111. Note: All needle stick/puncture exposures must be reported to EH&S at x59797 within 8 hours.
Decontamination/Waste Disposal Procedure
The gases from the piranha solution must be allowed to dissipate, and the solution must be allowed to
cool. Spent piranha solution is mainly concentrated sulfuric acid. Care must be taken not to allow the
solution to be mixed with organic solvents (e.g. in waste solvent carboys), as this will cause a violent
reaction and might even cause a substantial explosion.
Never mix piranha solution waste with other chemical wastes.
NOTE: Just before taking the piranha solution waste (i.e., container affixed with an on-line hazardous
waste tag) to the routine EH&S waste pick-up, replace the vented cap with a non-vented cap. Please let
the EH&S waste pick-up personnel know about this.
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Label Waste
o Affix an on-line hazardous waste tag on all waste containers using the Online Tag
Program http://otp.ucop.edu/ as soon as the first drop of waste is added to the container
Store Waste
o Store hazardous waste in containers with a vented cap, in secondary containment and in
a designated location
o Double-bag dry waste (if generated during spill clean-up. Example: Sorbent pads, gloves
etc.) by using transparent bags http://map.ais.ucla.edu/go/1002774
o Waste must be under the control of the person generating & disposing of it
Dispose of Waste
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Dispose of regularly generated chemical waste within 90 days
Call EH&S at x61887 for questions
Empty Containers
 General Note (not applicable for Piranha solution): Dispose as hazardous waste
if the containers once held extremely hazardous waste (irrespective of the
container size) http://ehs.ucla.edu/Pub/ExtremelyHazardousWaste.pdf
Consult waste pick-up schedule
http://ehs.ucla.edu/pub/HazWaste%20Pickup%20Schedule.pdf
Prepare for transport to pick-up location
 Check on-line waste tag
 Close the piranha solution waste container with a non-vented cap just before
transporting the waste to the pick-up location.
 Mark the date of pick-up on the waste tag
 Use secondary containment
 Wear eye protection & closed toe shoes; bring gloves
Material Safety Data Sheet (MSDS) Location
(State the location of MSDS)
Hardcopy or electronic copy MSDS from the same manufacturer must be available for Sulfuric acid and
Hydrogen peroxide.
Online MSDS can be accessed at http://msds.ehs.ucla.edu.
Protocol/Procedure
(Add specific description of procedure)
NOTE: Any deviation from this SOP requires written approval from PI.
Documentation of Training (signature of all users is required)
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Prior to conducting any work with Piranha solution, designated personnel must provide training to
his/her laboratory personnel specific to the hazards involved in working with this substance, work
area decontamination, and emergency procedures.
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The Principal Investigator must provide his/her laboratory personnel with a copy of this SOP and a
copy of the Piranha solution chemicals MSDS provided by the manufacturer.
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The Principal Investigator must ensure that his/her laboratory personnel have attended appropriate
laboratory safety training or refresher training within the last two years.
I have read and understand the content of this SOP:
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