OHS026
Safe Work Procedure
Faculty/Division: Faculty of Science
DVC Research
Document number
SWP01.01
Initial Issue date
July 2008
School/Unit:
School of Physics, Optoelectronics Group
Biophotonics Laboratory
Current version
Current Version
Next review date
1.3
Issue date
August 2014
August 2013
The Writing Safe Work Procedures Guideline (OHS027) should be consulted to assist in the completion of this
form.
Safe Work Procedure Title and basic description
Title: Handling of hydrofluoric acid (HF)
Description: On the use of HF for the electrochemical etching of silicon for researchers in the
Optoelectronics Group.
Associated risk assessment title and location: RA01.01-05 Etching of Silicon with HF, K15:LG48A
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Safe Work Procedure SWP01.01
Date Effective: 01/07/2008
Uncontrolled document when printed
Current Version: 1.2, 15/08/2007
Describe the activity or process
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Safe Work Procedure SWP01.01
Date Effective: 01/07/2008
Uncontrolled document when printed
Current Version: 1.2, 15/08/2007
Scheme of activity:
The following document relates to the safe work procedure for electrochemical etching of silicon using
concentrated hydrofluoric (HF) acid. It covers all aspects of safe handling, storage, transportation and
disposal of hydrofluoric acid for this process.
1. Things to do before you start handling HF
1.1 Posting Signs
All stock solutions of hydrofluoric acid (50%) are stored in 500 mL bottles in the locked corrosives
cabinet in the School of Physics Biophotonics Lab, Old Main Building K15, Room LG48A. Before
handling HF, make sure you put the provided laminated signage (saying HF in use) on the fumehood
sash and on the laboratory door to warn people in and around the lab area.
1.2 Always inform Dr. Peter Reece ( via a text message or phone call) that you’re going to start using HF
in the lab. He will provide you the key required to open the corrosives cabinet where all the HF
solutions are stored. Only once you receive approval from him, you can start your HF handling and
use.
1.3 When handling sealed 500 mL containers of stock solution of HF acid (50%), a lab coat, safety
goggles and nitrile examination gloves must be worn.
2. Preparation of container for neutralising and storing low concentration HF acid waste.
Concentrated HF acid waste is neutralised with calcium carbonate after each process and stored as low
concentration HF acid (less than 1% vol) waste. HF acid reacts with calcium carbonate to form an inert
calcium fluoride precipitate. The main forms of waste are ethanol rinse, which contains trace amounts of
HF acid and concentrated etching solutions of no more than 100 mL.
2.1 Place a 10L waste container in a bund on the floor near the fume cupboard and label both container
and bund with appropriate signage for low concentration HF acid (< 1% vol).
2.2 Measure out 1.0 kg of calcium carbonate and add to the waste container. Ensure that the calcium
carbonate is spread evenly on the bottom of the container. The quantity of calcium carbonate has
been calculated to neutralize quantities of HF waste generated under normal working conditions, as
outlined in this safe working procedure.
2.3 Place marble chips in the bund around the base of the waste container.
2.4 Before discarding old concentrated HF solutions into the 10L waste container, neutralize the
concentrated acid in the small container provided inside the fumehood. For example, when discarding
a 50 mL HF solution, first add calcium carbonate (approximately 2 scoops) to the container followed
by ~300 mL of tap water. Carefully add the old acid solution to this solution, noting that there will
evolution of gas on HF addition. Once there is no gas produced, discard this neutralized solution into
the big 10 L waste container.
3. Preparation of HF etching solution by dilution of HF acid (50%) with absolute ethanol.
HF acid solutions are diluted with absolute ethanol to concentrations appropriate for the electrochemical
etching process (> 15% vol). The ethanolic HF acid solution is stored in a polyethylene bottle with welllined screw cap and appropriate warning labels. The final volume of the etching solution should be
restricted to 50 mL. The solution is recycled up to ten times and stored for no longer than 3 months before
being neutralised and discarded in the low concentration (< 1% vol) HF acid waste.
3.1 When handling and decanting from open 500 mL containers of stock HF acid (50%), a lab coat, apron,
full face shield, nitrile examination gloves and medium weight Viton or nitrile over-gloves must be
worn. All steps must be carried out inside a fume cupboard rated for HF acid use, and the sash of the
fume-hood should be pulled down as low as possible throughout the process.
3.2 Measure an appropriate amount of ethanol into a polyethylene bottle with Teflon lined screw cap.
3.3 Using a polyethylene measuring cylinder, measure the corresponding amount of HF acid to achieve
the desired concentration and pour into the bottle.
3.4 Put the cap on and agitate gently until well mixed.
3.5 Rinse the measuring cylinder twice with ethanol, discarding the rinse waste at each stage into a
beaker marked HF waste. Finally rinse the cylinder with deionised water and discard the rinse waste
into the chemical/solvents waste beaker.
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3.6 Discard the contents of the HF waste beaker to the container marked low concentration (< 1% vol) HF
acid waste.
3.7 Label the polyethylene bottle with the following;
Contents (p% HF: ethanol)
Date of preparation
Name of user
HF safety label
3.8 Return the stock solution of HF acid (50% w/w) and the ethanolic HF acid etching solution to the
corrosives cabinet.
4. Electrochemical etching of silicon using concentrated ethanolic hydrofluoric acid.
The following section outlines the main procedure for electrochemical etching silicon using ethanolic HF
etching solution. Someone who is fully conversant in the proper usage of the electrochemical cell may
only carry out this procedure. Appropriate training will be provided before inducted users are signed off for
this process.
4.1
When handling and decanting from concentrated HF etching solutions inside the fume cupboard, a
lab coat, safety goggles, nitrile examination gloves and medium weight Viton or nitrile over-gloves
must be worn. Throughout the etching and detachment process the sash of the fume-hood should be
pulled down enough to eliminate the potential risk of splashes induced by pipette tip flicks.
4.2
Cleave silicon wafer pieces to an appropriate size for the electrochemical cell to be used.
4.3
Ultrasonically clean the wafer pieces in 10mL of acetone followed by 10mL of ethanol; rinse in
deionised water (milli Q) and then dry in nitrogen gas flow. Discard the acetone and ethanol to the
solvents waste.
4.4
Mount the silicon into the recess at the back of the upper chamber of the electrochemical cell using a
Viton o-ring to make a liquid-tight seal between the polished face of the silicon and upper chamber of
the cell (which will contain the etching solution).
4.5
Place the stainless steel electrode in contact with unpolished back surface of the wafer and screw in
the outer Teflon shell to ensure proper electrical and mechanical connection. Invert the cell and place
inside the fume cupboard. Connect the bottom stainless steel electrode to the programmable power
supply.
4.6
Pour approximately 50ml of HF etching solution into the top chamber of the electrochemical cell and
insert the Teflon lid containing the top platinum electrode; the electrode ring will be immersed in the
etching solution.
4.7
Connect the top electrode to the programmable power supply and perform the etching sequence.
4.8
Remove the Teflon lid and rinse any residue from the top electrode using ethanol; place rinse waste
into a beaker marked HF waste.
4.9
Return the HF etching solution to its original container using a pipette (PTFE or polyethylene).
4.10 OPTIONAL: If electrochemical detachment of the porous silicon layer is required, pour in
approximately 50 mL 15% ethanolic HF acid solution into the cell; return the Teflon lid and apply the
appropriate etching sequence. Remove the Teflon lid and rinse any residue from the top electrode
using ethanol; place rinse waste into a beaker marked HF waste.
4.11 Rinse the top chamber of the electrochemical cell thrice with ethanol, discarding the waste at after
each rinse (via a pipette) into a beaker marked HF waste.
4.12 Release the etched wafer from the electrochemical cell with tweezers and immerse in approximately
10 mL of pentane. Remove from pentane and dry the sample in nitrogen gas flow.
4.13 Discard the contents of the HF waste beaker to the container marked low concentration HF waste.
4.14 Return ethanolic HF acid etching solution to the corrosives cabinet.
4.15 Discard the pentane to the solvents waste.
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5. Disposal of recycled concentrated ethanolic hydrofluoric acid.
Once the shelf life of the etching solution has been reached the solution is neutralised and disposed of in
the low concentration (< 1% vol) HF acid waste. The solution is recycled up to ten times and stored for no
longer than 3 months.
5.1 When handling open containers of ethanolic HF acid etching solution outside of the fume cupboard, a
lab coat, full face shield, nitrile examination gloves and medium weight Viton or nitrile over-gloves
must be worn.
5.2 Open the polyethylene bottle containing the etching solution only when you are next to the HF waste
container.
5.3 Open the waste container and carefully pour the etching solution into the low concentration (< 1% vol)
HF acid waste.
5.4 A small quantity of carbon dioxide gas will evolve when the acid reacts with the neutralising agent. To
prevent the build-up of gas in the waste container, wait until the reaction has completed before
replacing the lid.
5.5 If the low concentration (< 1% vol) HF acid waste container is three quarters full, arrange to have the
waste removed through the university waste management system and replace with a new waste
container (see section 2).
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Safe Work Procedure SWP01.01
Date Effective: 01/07/2008
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Current Version: 1.2, 15/08/2007
List all resources required including plant,
chemicals, personal protective clothing and
equipment, etc
Safety precautions for HF use:
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Researchers Information and Training: HF is a colorless liquid with a strong irritating odor at
low concentrations (3ppm). Employees who handle HF must receive documented training on the
hazards of HF and on what to do in the event of an exposure or a spill. A Material Safety Data
Sheet (MSDS) on HF should always be kept in the immediate work area where HF is used
Ventilation: HF should be used with adequate ventilation to minimize inhalation of vapor.
Concentrations greater than 5% should always be handled inside a properly functioning chemical
fume hood with the sash pulled down as far as possible (while not obstructing the task to be
carried out).
Eye protection: Wear chemical safety goggles for all experiments involving HF. Use a face shield
in addition to the goggles when handling large quantities of concentrated HF.
Body protection: Wear a laboratory coat for all experiments involving HF. Never wear shorts or
open-toed shoes when handling HF.
Gloves: Typically, nitrile exam gloves must be worn. When handling large quantities of
concentrated HF wear medium weight Viton or nitrile gloves over an uncontaminated pair of nitrile
exam gloves. If gloves become contaminated with HF, remove them immediately, thoroughly
wash your hands and check your hand for any sign of contamination. Contaminated gloves must
be disposed of in a contaminated waste container.
Sink/Shower/Eyewash: Since HF is corrosive and rapidly damages skin tissue, rinse the
exposed area for 15 minutes, and then treatment of skin with calcium gluconate gel should be
initiated. In the case of eye contact, undertake eyewash for at least 5 minutes (do not use calcium
gluconate gel).
Calcium Gluconate Gel: Calcium gluconate gel is a topical antidote for HF skin exposure. It
works by combining with HF to form insoluble calcium fluoride, thus preventing the extraction of
calcium from tissues and bones. Keep calcium gluconate gel nearby whenever you’re working
with HF. It has a limited shelf life and should be stored in a fridge if possible and replaced with a
fresh supply after its expiration date has passed. Use disposable exam gloves to apply the gel.
Even after applying calcium gluconate, it is essential that a medical evaluation be made.
Safe work Practices: Never work alone when using HF. Wash hands thoroughly after handling
HF.
General handling:
Before commencing any procedure involving hydrofluoric acid, another “trained” user must be present
within the Old Main Building and available at short notice.
The following protective clothing must be worn at all times when working with HF:
- Lab coat.
- Nitrile gloves.
- Safety glasses.
Further protective equipment is required for specific procedures as outlined in the activity description.
All experiments involving HF must be carried out in HF certified fume hood with the sash pulled down as
far as possible while not obstructing the task to be carried out.
Only use beakers, measuring cylinders, containers, etc that are chemically compatible with HF (e.g.
polyethylene or Teflon). Glass, metal and ceramics are not compatible with HF.
All items used inside the fume hood should be treated as potentially contaminated with HF and should be
rinsed with ethanol and water into a beaker containing water and enough sodium bicarbonate to quench
the remaining HF. After handling items inside the fume hood, the nitrile exam gloves must be discarded in
an appropriately marked waste bin and a fresh pair must be used to handle equipment outside the fume
hood to avoid contamination.
All users should have a container of calcium gluconate at home in case of delayed symptoms
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Safe Work Procedure SWP01.01
Date Effective: 01/07/2008
Uncontrolled document when printed
Current Version: 1.2, 15/08/2007
List potential hazards and risk controls including
specific precautions required
Health Hazards:
- Eyes and skin exposure: HF is corrosive and readily destroys skin tissue. Exposure of the eyes
to HF may results in blindness or permanent eye damage. HF readily penetrates human skin,
allowing it to destroy soft tissues and decalcify bone. Chemical burns from HF are typically very
painful and slow to heal. Skin exposure to concentrated HF (49% or greater) immediately results
in serious and painful destruction of tissue. Not only can skin contact cause burns but systemic
fluoride poisoning may also result. One of HF’s more insidious properties is that skin contact at
lower concentrations may not produce pain or burning sensations until hours after the exposure.
Because of the ability of HF to produce severe delayed tissue damage without necessarily
producing pain, all skin, eye or tissue contact with HF should receive immediate first aid and
medical evaluation, even if the injury appears minor or no pain is felt.
- Inhalation of HF vapours: Inhaling HF vapours can seriously damage the lungs. Delayed
reactions up to and including fatal pulmonary oedema (flooding of the lungs with body fluids) may
not apparent for hours after the initial exposure. Airborne concentrations of 10 to 15 ppm will
irritate the eyes, skin and respiratory tract. Thirty ppm is considered immediately dangerous to life
and health and may have irreversible effects. At airborne concentrations above 50 ppm, even brief
exposure may be fatal.
- Chronic HF exposure: Long-term chronic exposure to HF may result in fluorosis, a syndrome
characterized by weight loss, bone embrittlement, anaemia and general ill health.
Spill Kit (for small spills only, call 56666 for large spills):
Additional safety measures:
- Face shield.
- Medium thickness gloves to be worn over a fresh pair of nitrile gloves.
Open the doors and windows for ventilation. Alert other researchers in the area of the spills.
Surround the spill with Chemisorb and neutralize with sodium bicarbonate. Then pour more Chemisorb
onto the neutralized spill to soak up the liquid. Scoop the contaminated solid into the heavy duty plastic
bag using the dust pan. Re-sprinkle more sodium bicarbonate onto the area to ensure neutralizing and
scoop up. Close the bag tightly and arrange for disposal through the UNSW chemical waste disposal
system. Wash the area with excess water clean up and dry. Report to supervisor.
Spill, storage and waste issues:
- HF spills:
o If a large volume of HF is spilled outside a chemical hood, evacuate the area and call
56666 for emergency assistance. If possible, open the window for ventilation before
evacuating the lab, close the doors behind you (to avoid vapours from entering other
areas) and post the area with a sign to prevent others from entering.
o Small spills of HF can be cleaned up by lab staff if they have the correct equipment,
understand the hazards and know how to clean up the spill safely and dispose of the
waste properly. Lime soda, ash, sodium bicarbonate or a spill absorbent specified for HF
should be used for clean up.
- Storage:
o Store all HF and HF waste in labelled chemically compatible containers (e.g. polyethylene
or Teflon). Glass, metal and ceramic containers are not compatible with HF. HF should
never be stored with incompatible chemicals such as ammonia or other alkaline materials
or with other chemicals stored in glass. Always place HF on a low, protected storage
cupboard where it will not be accidentally spilled or knocked over and keep the cupboard
properly locked.
- Waste:
o HF waste should be placed in a chemically compatible container with a sealed lid and
clearly labelled.
o All HF waste generated through this process is neutralised with calcium carbonate during
disposal. Calcium binds strongly with fluoride to produce an inert CaF precipitate.
o The maximum volume of neutralised HF waste (concentration < 1% vol) stored in the
laboratory (Room LG48A) is 10L. Dispose of all the waste liquid, gloves, wipes and empty
bottles through the UNSW chemical waste disposal system.
See http://www.hr.unsw.edu.au/ohswc/ohs/ohs_forms_checklists.html).
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Safe Work Procedure SWP01.01
Date Effective: 01/07/2008
Uncontrolled document when printed
Current Version: 1.2, 15/08/2007
List emergency shutdown instructions
Emergency Procedures for HF exposure:
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CALL 56666 FOR EMERGENCY MEDICAL ASSISTANCE. CLEARLY STATE THAT THERE
HAS BEEN A HYDROFLUORIC ACID EXPOSURE.
All exposure to or contact with HF should receive immediate first aid and medical
evaluation, even if the injury appears minor or no pain is felt. HF can produce delayed
affects and serious tissue damage without necessarily producing pain.
First aid for skin contact:
o Immediately (within seconds) proceed to the nearest shower station and wash affected
area for a minimum of 5 minutes before applying calcium gluconate gel.
o While washing the affected area, have someone call 56666 for emergency medical
assistance.
o Remove all contaminated clothing while in the shower.
o Check other parts of the body for contamination.
o Massage calcium gluconate gel into the affected area. Be sure to wear nitrile gloves on
the hand spreading the gel.
o Reapply calcium gluconate gel and massage it into affected area every 15 minutes until
assistance arrives or pain completely stops.
o Send the MSDS and medical treatment information with the person to hospital or give it to
the paramedics if applicable. Ensure the paramedics understand that this is not an
ordinary acid burn.
First aid for eye contact:
o Immediately (within seconds) proceed to the nearest eyewash station and thoroughly
wash for at least 15 minutes while holding eyelids open.
o Do not apply calcium gluconate gel to eyes.
o While washing eyes, have someone call 56666 for emergency medical assistance.
o Remove to hospital by ambulance accompanied by the Material Safety Data Sheet.
Continue eye irrigation during transport to hospital.
First aid for ingestion:
o Do not induce vomiting.
o Dilute the acid by drinking large quantities of milk (preferable) or water.
o Call 56666 for emergency medical assistance.
First aid for inhalation:
o Immediately move to area with fresh air. Call 56666 for emergency medical assistance.
List clean up and waste disposal requirements
Disposal:
HF waste should be placed in a chemically compatible container with a sealed lid inside a bund and
clearly labelled.
All HF waste generated through this process is neutralised with calcium carbonate during disposal.
Calcium binds strongly with fluoride ions to produce an inert calcium fluoride precipitate. A predetermined
quantity of calcium carbonate is included in the waste container before it is used for HF waste.
Leave the HF waste container on the floor (never attempt to lift it in the fume hood), place it in front of the
fume hood. Remove the screw top from the HF waste container and slowly pour the HF waste from the
waste beaker into the container. When disposing of etching solution, do not open the bottle until you are at
the waste container.
Dispose of gloves, wipes, empty bottles and any contaminated materials into the contaminated waste bin
provided. Thoroughly rinse all HF containers (and other contaminated items) before disposal.
The maximum volume of neutralised HF waste (concentration < 1% vol) stored in the laboratory (Room
LG48A) is 10L. When either the HF waste container is three quarters full or the contaminated waste bin is
full, dispose through the UNSW chemical waste disposal system. The appropriate form will need be
completed.
See http://www.hr.unsw.edu.au/ohswc/ohs/ohs_forms_checklists.html).
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Safe Work Procedure SWP01.01
Date Effective: 01/07/2008
Uncontrolled document when printed
Current Version: 1.2, 15/08/2007
List legislation, standards and codes of practice used
in the development of the SWP
Office of environment, Health and Safety, University of California, Berkeley (http://www.ehs.berkeley.edu)
Section B2.15 of AS 2243.2:1997
Supervisory approval, training, and review
Supervisor:
Signature:
Plant custodian:
Signature
List competency required – qualifications, certificates, licencing, training - eg course or instruction:
HF training session ‘working safely with HF’
SWP review date:
Responsibility for SWP review:
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Safe Work Procedure SWP01.01
Date Effective: 01/07/2008
Uncontrolled document when printed
Current Version: 1.2, 15/08/2007