PSFC Hydrofluoric Acid

PSFC Standard Operating Procedures for Hydrofluoric Acid Etching

Plasma Science and Fusion Center

Office of Environment, Safety, and Health

190 Albany Street, NW21 2nd floor
617-253-8440 (Catherine Fiore)
617-253-8917 (Matt Fulton)
617-253-5982 (Bill Byford)
617-258-5473 (Nancy Masley)
Fax 617-252-1808

Be Safe or Die

Reviewed and Approved By:

PSFC Supervisor

PSFC Supervisor

Catherine L. Fiore, PSFC Safety Officer

Standard Operating Procedures for Hydrofluoric Acid Etching

Author: K. Wenzel/A. Eckmann

Version: 1.5

Date: March 20, 1992. Revised 7/19/99 by C. Fiore

Persons Responsible: Pete Stahle - NW22-113

Bob Childs - NW21-109

Introduction

This document outlines the hazards involved with the use of hydrofluoric acid. It details procedures to be followed to minimize the risk of exposure of Plasma Science and Fusion Center employees to hydrofluoric acid during etching and cleaning procedures. Hydrofluoric acid is generally used in small quantities (i.e., a few ml) to etch glass surfaces.

Scope

This procedure covers employee safety during the handling, and use of hydrofluoric acid etching solutions.

Safety Analysis

Failure to follow this procedure could result in severe skin and eye irritation or burns, including eventual tissue death, from direct contact with hydrofluoric acid. In extreme cases of inhalation of hydrofluoric acid vapors, lung damage with pulmonary edema leading to subsequent death as well as respiratory arrest may occur.

Definitions:

Primary Irritant - Capable of causing tissue damage and burns resulting from direct contact.

Hazard Assessment

Hydrofluoric acid (HF) has unusual, and sometimes unrecognized harmful effects when it contacts human skin or mucous membranes. HF is a severe skin, eye, and respiratory irritant, which is unusual in that pain may not occur initially upon contact with the acid. Therefore, HF can penetrate deep into tissue without warning, causing delayed pulmonary edema or deep tissue burns requiring immediate medical attention. HF which penetrates into tissues may cause slow tissue death, resulting in very undesirable effects, such as the loss of a finger which came into contact with the acid! When hydrogen fluoride comes into contact with metals, it can generate hydrogen which can be a fire and explosion hazard. Metal containers used to contain HF-contaminated spill clean-up materials must be vented regularly to prevent accumulation of hydrogen. The Environmental Medical Service offers a first-aid gel to HF users. This gel should be obtained by all PSFC HF users. The gel is not intended to replace good prevention measures or medical department treatment in the event of HF accidents. The gel must be replaced through the medical department, (contact the Industrial Hygiene Office, 3-2596) at regular intervals and after each incident that causes opening of the storage container. The injured must seek immediate medical attention despite the use of the gel.

Responsibilities:

The supervisor or responsible person shall designate and train employees who are required to work with hydrofluoric acid, regarding its health and physical hazards and appropriate work procedures. The supervisor or responsible person shall ensure that necessary personal protective equipment and spill control supplies are available to employees. The supervisor or responsible person shall ensure that hydrofluoric etching operations are performed in accordance with good work practices in adequately ventilated areas.

Assumptions:

The hydrofluoric acid user shall be familiar with the hazards associated with hydrofluoric acid and appropriate spill and emergency procedures described in this document. The user shall be trained in the use of appropriate personal protective equipment. If respiratory protection is to be used, such protection has been obtained through the Industrial Hygiene Office and employees have received fit tests and appropriate medical examinations.

All hydrofluoric etching solutions used within the PSFC consist of small quantities. No immersion of the fingers or hands into the acid solution, regardless of the type of gloves used, is required.

Required Supplies and Personal Protective Equipment

Protective gloves.
Even pin-hole leaks through gloves may result in significant damage to the skin, especially if contact under the finger nails occurs. If hands are sweaty, leakage may not even be noticed. Gloves should be dedicated for HF use only, and should be discarded if any contact with the acid occurs. They should be inspected prior to use and changed frequently.
Glove breakthrough times vary with material, thickness,and manufacturer. Contact the glove manufacturer or EMS for information on specific gloves. In general, long gauntlet-type nitrile, neoprene, and natural rubber gloves should provide adequate protection against splashing and during the clean-up of small hydrofluoric acid spills.
Eye and Face Protection
Contact lenses may not be worn when handling HF. Splash-proof chemical goggles or safety glasses with side shields are required. In addition, face shields must be worn during HF use.
Protective Clothing.

A lab coat, in addition to long gauntlet-type gloves, is the minimum required protection for the small quantities of HF (i.e., a few ml) typically handled at the PSFC. Neoprene aprons with attached sleeves shall be worn while transferring quantities in excess of 10 ml of HF

Spill materials.
Lime may be used as a spill adsorbent. Commercial spill kits may be used, however, only HF specific kits may be used since some commercial spill materials are attacked by HF. Paper towels maybe used to wipe up a few drops. In any case, the spill area must be carefully rinsed with water.

Procedures:

Prior to initial assignment to the operation, read the Material Safety Data Sheet and become familiar with the hazards of HF.
HF work may only be performed inside a laboratory fume hood.
Do not use HF while wearing open-toe footwear, non-leather footwear, or shorts (these items of apparel are not appropriate for laboratory work at any time).
Locate spill control materials and ensure that an adequate supply is available. an appropriate container to hold any contaminated spill clean-up materials should also be available.
Ensure that an eyewash and safety shower are located nearby to flush the eyes or skin in the event of eye contact. If there is not an eyewash nearby, another employee who can escort the affected employee to an eyewash shall remain in the vicinity of the operation.
Place a protective sheet of paper on the table, counter, or cart where the HF is to be transferred.
Wear protective goggles and face shield.
Wear protective apron or lab coat and gloves.
Do not leave tongs, stirrers, etc., which have been contaminated with HF in fume hoods where other people may pick them up or otherwise come into contact with them.
Any unattended containers must be labelled. If it is not feasible to do this, and containers must be left in the laboratory fume hood unattended by the HF user, place a placard or sign in the fume hood indicating the HF hazard.
Always add acid to water, not the reverse.
When the work has been completed and personal protective equipment has been removed, wash hands thoroughly with soap and water.

Training:

The supervisor or responsible person shall supply this procedure to affected employees and verify that they understand it. Employees should understand the health and physical hazards of HF. The ability of HF to inflict damage without initial pain should be emphasized.

Solutions with concentrations > 50% may release hazardous concentrations of HF vapor under conditions of poor ventilation and require respirator use. If employees wish to use respirators when using HF, such respirators shall ONLY be obtained from the Industrial Hygiene Office (ext. 3-2596). The supervisor or responsible person shall ensure that only employees who have received respirator training and have received appropriate medical exams as determined by the Industrial Hygiene Office are allowed to wear respirators. Users must obtain training from a trainer designated by the Environmental Medical Services.

Spill Procedures:

Refer to the product Material Safety Data Sheet for proper spill clean-up procedures. Do not attempt to clean up any large spills, especially if the vapors from the spill result in noticeable eye or respiratory irritation. For large spills (>10 ml) restrict access to the spill area and dial 100.
Small spills of a few ml may be cleaned up by the person who caused the spill.
Do not attempt to clean up any spills without wearing gloves, an apron, eye, and face protection. Use of an appropriate respirator if the HF concentration of the spilled material is >50% is mandatory.
If there is any possibility of contamination of footwear while cleaning up the spill, do not proceed unless adequate shoe coverings or rubber boots can be obtained.
Absorb the spill with lime or another absorbent material designated for HF spills. Scoop the material into a suitable container. Note that HF may react with metal to form hydrogen.
Carefully rinse contaminated areas with water. Any paper towels or sponges used to absorb the rinse water should be added to the spill clean-up wastes.
Label the waste container and contact the Safety Office (ext. 3-4736) for pick up of the spill clean-up materials.

First Aid Procedures

Any splash or exposure, even if initially painless, requires attention. Personnel rendering first aid or assistance should avoid contact with contaminated surfaces or clothing.
Skin contact requires flushing the affected area with cool water for 5-15 minutes. Do not allow contaminated clothing to remain in contact with the skin. Large exposures require the removal of contaminated clothing under the shower. Exposure affecting the face, and especially the skin under nails, require special medical treatment no matter how small. In ALL cases where skin contact with HF occurs the Medical Department shall be contacted and the affected individual shall be immediately taken to the Medical Department for examination.
For pinhole-size exposures, HF gel may be applied at the lab before follow-up in the Medical Department.
HF gel should be applied to all skin exposures as long as this does not delay emergency medical treatment.
Dilute HF solutions (<40%) may cause delayed pain as long as 24 hours from the initial contact. In the event that exposure is not recognized until after contact, immediate medical examination is still required.
In the event of eye contact, the eye should immediately be flushed with water. If the eye is very irritated, it is likely that the affected individual will require assistance to hold the eye open during the flushing. The Medical Department (3-4481) shall be contacted immediately. Apply ice water compresses to the affected area during transport.
In the unlikely event that an individual ingests HF, immediately call the Medical Department. Do not induce vomiting or give baking soda. Drink several glasses of milk or milk of magnesia, or water if milk is not available, until medical assistance arrives.
When HF solutions with concentrations > 50% are used without adequate ventilation, problems may occur. If inhalation occurs, evacuate the exposure area and call the Medical Department (3-4481) for assistance. Inhalation of high concentrations may cause respiratory arrest.

Waste Disposal Procedures

Regardless of the concentration of HF, it may not be put down the drain. It may also not be neutralized and put down the drain.
Collect waste HF in a clearly labelled, appropriate container with a screw cap. The original container is suitable if one is available. Glass and metal are unsuitable containers. Do not mix different kinds of acids together unless instructed to do so by the supervisor. Red hazardous waste labels are available from the Chemical Hygiene Officer and from the Safety Office. When the waste container is sufficiently full or when the experiment using HF is complete, contact the Safety Office (ext. 3-4736) for pick up.

References

• MIT Industrial Hygiene Office, Memorandum on Safety Procedures for Handling Hydrofluoric Acid

• Discussions with Kevin Wenzel

SPECIFIC PROCEDURES: CLEANING THE COCKCROFT-WALTON ION SOURCE BOTTLE AND INSULATOR SLEEVE

Review and follow steps outlined above for the handling, use, and disposal of hydrofluoric acid. This work must be done in a fume hood.

Ion Source Bottle

Pour about 5 ml of 50% hydrofluoric acid solution into the source bottle.
Use a small cork to seal the end of the bottle. Hold the bottle horizontally and swirl it so that the acid covers the entire inner surface.
When the discoloration of the bottle is gone, pour the acid into a 500 ml beaker half-filled with water. Drain as much acid as possible into the beaker.
Fill the source bottle with distilled water and pour it into the beaker.
Repeat step 4. two more times.
Rinse the source bottle two times with methyl alcohol, pouring the waste into a separate beaker (see Standard Operating Procedures for Flammable Liquids).
Discard the contents of the beaker containing hydrofluoric acid wastes into the hydrofluoric waste container. Rinse the beaker 2 times with approximately 20 ml of water and add the rinse into the waste container. Rinse the beaker several more times in the sink.

Insulator Sleeve

Pour 25 ml of distilled water into beaker then add 5 ml of 50 % HF into a 50 ml beaker.
Place the sleeve in the beaker and gently agitate by swirling until the discoloration has disappeared (approximately 5 minutes).
Place the sleeve in a 250 ml beaker containing distilled water and gently agitate by swirling to rinse thoroughly.
Using a pair of tongs, pick up the sleeve and rinse with methyl alcohol dispensed from a squirt bottle. Perform the rinsing step over a separate beaker to contain the methyl alcohol rinse waste (see Standard Operating Procedures for Flammable Liquids).
Discard the contents of the 50 ml beaker and the 250 ml beaker into the HF waste container.
Rinse the 50 ml beaker two times with approximately 15 ml of water and add the rinse into the HF waste container. Rinse the 250 ml beaker with approximately 20 ml of water and add the rinse into the HF waste container. Continue to thoroughly rinse the beakers in the sink.

This page maintained by Catherine L. Fiore FIORE@PSFC.MIT.EDU