Appendix B

Guidelines for Safe Use of Hydrofluoric Acid

PURPOSE: These guidelines establish safe work procedures for personnel working with hydrofluoric acid (HF), a highly hazardous chemical, and response in case of emergency to minimize health risks.

SCOPE:  These guidelines cover all of the Missouri University of Science and Technology campus.

APPLICABILITY:  These guidelines cover all users of Hydrofluoric Acid and other personnel present in the lab while it is being used, facilities workers, and first-responders to incidents involving HF releases.

INTRODUCTION to HF: Hydrofluoric Acid (HF) is one of the most corrosive of the inorganic acids.  It has the following properties:

  • Clear, colorless liquid with a strong irritating odor (pungent odor at < 1 ppm).
  • Nonflammable.
  • Volatile.
  • Very soluble in water.
  • Vapor Density = 0.7 (lighter than air).
  • Boiling Point = 19.5 °C.

HF is also available as gaseous material. All forms of HF can cause severe burns to tissue, which makes its handling and use especially hazardous. HF easily dissolves glass and can attack enamels, pottery, concrete, rubber, leather, many metals and organic compounds. Upon reaction with certain metals, explosive hydrogen gas may be formed. HF has many industrial applications but in an academic environment it is normally used in small quantities for fabrication of electronic components, etching glass, biological staining, mineral digestion, etc. 

HF, though a weak acid, is physiologically a very potent chemical due to fluoride ions, which can bind with calcium and magnesium ions in the tissue. Concentrated HF, liquid or vapor, may cause severe burns, electrolyte imbalance, pulmonary edema and/or life threatening cardiac arrhythmias. Even moderate exposure may rapidly progress to fatality if not treated promptly and properly. Symptoms of exposure may be delayed for several hours.  Therefore, immediate medical intervention, even in the absence of symptoms, is necessary.

PROCEDURE:

I.  Working safely with HF

  • Use the most dilute HF solution practicable; cap the container when not in use.
  • ALWAYS work in a chemical fume hood at least 6 inches inside the sash.  Before use, always check that the fume hood is working properly.
  • Eye protection:  wear approved splash goggles and a face shield.
  • Hand protection:  HF readily penetrates skin and becomes trapped under fingernails.  Heavy neoprene or nitrile rubber (HF attacks natural rubber) gloves are best for working with HF.  However, the increased thickness of the gloves reduces dexterity, increasing the possibility of spills.  Wear two pairs of nitrile exam gloves at a time, changing the outer pair often.  When working with larger quantities of HF in procedures that do not require as much dexterity, wear heavy nitrile or neoprene rubber gloves, with a nitrile exam glove worn under the outer glove.
  • Body protection:  Wear a long-sleeved shirt, long pants, and closed shoes.  Wear a lab coat over your clothes and consider wearing a chemical-resistant apron and sleeves.  Do not wear shorts and sandals in the laboratory.
  • Wash hands thoroughly with soap and water after handling HF. 

  • Make sure you have NON-EXPIRED 2.5% Calcium Gluconate in the lab.

  • Make sure you have a spill kit appropriate for HF acid.
  • Make sure you have a copy of the Safety Data Sheet (SDS) in the lab.

II. Limitations on the Use of HF

Hydrofluoric acid is an extremely hazardous material. Lab personnel should work using the buddy system and NO one be allowed to work alone.  Alert all others in the lab that you are using HF.  For safety reasons the use of hydrofluoric acid by the University staff or students should preferably be limited to office hours (You must discuss change in procedures with your supervisor). Only persons who have read and understood this document and who are suitably trained should be allowed to use this substance. Furthermore:

  • Inform any first responder called to deal with an incident involving HF about the hazards associated with this substance.
  • Provide a copy of these guidelines and a Safety Data Sheet (SDS) to the responder.  Be sure they know the concentration of the HF involved.

III. Storage of HF

  • Keep the amount on hand to a minimum.  Keep the concentration of the HF to minimum needed.
  • NEVER STORE HF IN GLASS CONTAINERS!  Hydrofluoric acid reacts with many materials, therefore avoid contact with glass, concrete, metals, water, oxidizers, reducers, alkalis, combustibles, organics and ceramics. HF must be stored in tightly closed containers made of polyethylene or fluorocarbon plastic, lead, or platinum
  • Use secondary containment.
  • Store away from incompatibles (bases, flammables, combustibles, etc.).
  • Store below eye level.
  • Be sure ALL containers, original and secondary, are LABELED.  Label must include concentration of the HF.
  • Containers of this material may be hazardous when empty since they retain product residues (vapors, liquid); observe all warnings and precautions listed for the product.

IV. Guidelines for Handling and Treatment of Exposed Persons

HF is a serious systemic poison, a true medical emergency.  On contact with live tissue in high concentrations exposed person will experience immediate necrosis and PAIN.  Burns may involve underlying bone. Personnel exposed to HF liquid solution or condensed vapors must be decontaminated with copious amount of water to avoid secondary contamination.  When working, pay close attention to the task at hand and do not allow yourself to become distracted.  Contact with dilute HF solutions (<50%) may not produce immediate pain, but may result in delayed health effects.

If a large amount is spilled, or if the HF is concentrated (>50%), contain the spill as much as possible, evacuate the area, and call 911.  Avoid exposure to the vapors.

Rescuers should don proper personal protective equipment (PPE) before coming in contact with contaminated individuals and clothing.

SKIN EXPOSURE

  • Immediately wash all affected areas with water for at least 15 minutes.  While flushing with water remove all clothing or jewelry that could trap HF.  Remove goggles last:  close eyes, face water flow and pull goggles over your head. Have someone else call for medical assistance during this time.  Rapid decontamination is critical to minimize/prevent injury.  HF binds to the calcium and magnesium in the body.  It is readily absorbed through the skin, so deep tissue penetration by the fluoride ion ensues.
  •  After washing the affected areas, apply 2.5% calcium gluconate first aid gel.  Affected area does not need to be dried prior to application.  Calcium gluconate binds HF and prevents it from penetrating deeper into tissues.  Note the time of initial application and reapply every 15 minutes until you receive further medical treatment.
  • Vapor burns to the skin are treated the same way as liquid HF burns.

EYE EXPOSURE

Immediately flush eyes for at least 15 minutes with copious amounts of water.  If 1% calcium gluconate solution is on hand flush eyes with water for 5 minutes then irrigate the eyes repeatedly with the solution.  Continue to irrigate with the 1% calcium gluconate solution or ice compresses while transporting the victim for medical attention, preferably to an eye specialist.

INHALATION

HF’s volatility makes it a high risk for inhalation injury. It is extremely destructive to the tissue of the mucous membranes and upper respiratory tract.  Severity can range from mild airway irritation to severe burning and dyspnea.  If inhalation occurs or is suspected, immediately remove victim to clean air until emergency personnel arrives on scene. Unlike external splashes, inhalation exposure is a serious medical emergency as it is more problematic because there are no immediate decontamination procedures. Keep person calm until medical help arrives.

INGESTION

  • Drink large amounts of water as quickly as possible to dilute the acid.  Do not induce vomiting.  Never give anything by mouth to an unconscious person.
  • Drink several glasses of milk or several ounces of Milk of Magnesia, Mylanta, Maalox or similar product, or eat up to 30 Tums, Caltrate or other antacid tablet.  The calcium or magnesium in these compounds may act as an antidote.

 

After decontamination, properly protected Emergency Responders (trained and attired) should remove the exposed person from the contaminated area, then transport the exposed person to the nearest Emergency Room.  Emergency Responders must be given a copy of these guidelines and a Safety Data Sheet, and must be informed on the concentration of the HF involved.

Contaminated clothing should be removed, double bagged and labeled as hazardous waste.

 

ALL HYDROFLUORIC ACID EXPOSURES ARE A MEDICAL EMERGENCY! IMMEDIATELY CALL 911 AND ARRANGE FOR MEDICAL TRANSPORT. A COPY OF THESE GUIDELINES and SAFETY DATA SHEET (SDS) MUST BE GIVEN TO THE MEDICAL PERSONNEL

V. Waste disposal procedures and accidental releases

Spent HF solutions are disposed of as hazardous waste through the Environmental Health & Safety (EHS) department.  Disposal down the drain is not allowed. You must consult EHS for disposal if you have any question.

VI. Spill Management

All areas where HF is used must have a proper spill control kit. Small spills can be neutralized by covering with acid neutralizer/calcium carbonate, and absorbed with spill control pads/absorbents. Once the spill is contained isolate the room and leave the area immediately. Call Environmental Health and Safety for help at (573)-341-4305.

If it is a large spill call 911 and immediately evacuate all persons in the area and close all doors. Any type of spill/accidental release of HF must be reported to Environmental Health & Safety during working hours at (573) 341-4305 or University Police after hours at (573) 341-4300.

Any Department working with HF must keep 2.5% Calcium Gluconate gel on-site.  It is the responsibility of the Principle Investigator (PI)  to maintain a non-expired stock.  PI  must inform employees about the presence and location of the gel and advise on its use, and present these guidelines before allowing work with HF.

DELAY IN FIRST AID OR MEDICAL TREATMENT OR IMPROPER MEDICAL TREATMENT WILL LIKELY RESULT IN GREATER DAMAGE OR MAY, IN SOME CASES, RESULT IN FATALITY.

VII. INFORMATION AND TRAINING

  • The Principle Investigator shall train employees who handle hydrofluoric acid on the hazards of HF and what to do in the event of an exposure or a spill or other emergency.
  • The SDS together with these guidelines shall be used to train employees on the hazards of HF.
  • A Safety Data Sheet (SDS) on HF and copy of these guidelines must always be kept in the immediate work area where HF is used.

VIII. RESPONSIBILITIES

Principle Investigatory (PI):

  • Must ensure personnel are trained in the safe use of HF and these guidelines.
  • Ensure stocks of non-expired 2.5% calcium gluconate are on hand in case of emergency.
  • Ensure HF spill kit is present and workers know how to use in case of a spill.
  • Require employees to work in a buddy system.

Environmental Health & Safety (EHS):

  • Provide annual velometer test of fume hood.  Tag hoods that have deficient air flow and notify Facilities on these hoods and any others that need repair.
  • Follow up on exposure or spill incidents.
  • Review and update these guidelines, as necessary.

 

IX.  Attachments

Attachment A: Toxicological Properties of Hydrogen Fluoride/Hydrofluoric Acid
Attachment B: Links to more information about HF.

ATTACHMENT A

Toxicological Properties of Hydrogen Fluoride/Hydrofluoric Acid

I.  Properties of hydrogen fluoride

 Hydrogen fluoride gas and hydrofluoric acid have nearly the same toxicological properties in living tissues/systems, and can be considered interchangeable.  For the purposes of this section of the guidelines, the term “HF” will be used to denote either the gas or the liquid acid. 

In aqueous solution, hydrofluoric acid is only a weak acid, having a pKa = 3 (in contrast, HCl has a pKa = -8, and perchloric acid has a pKa = -10).  In terms of acid strength (i.e., degree of dissociation in water), HF is similar to formic acid.  HF does not dissociate strongly in water because HF molecules form hydrogen bonds with water molecules and because there is a large negative change in entropy when HF molecules react with water (less entropy = more order).  Other hydrogen-halide molecules form only weak van der Waals forces with water molecules.

HF interacts corrosively with a wide variety of materials. This property makes HF both useful and hazardous.  HF dissolves most metals, natural rubber, concrete, glass, fiberglass, ceramics and glazes.  HF does not attack metallic lead or platinum, polyethylene, polypropylene, Teflon, Plexiglas (= acrylic), and wax.

Airborne concentrations of HF are difficult to detect precisely using direct-reading electronic instrumentation, and HF-specific test strips tend to have a large margin of error.  However, HF has good warning properties, detectable by humans at concentrations as low as 0.04 ppm (the OSHA Permissible Exposure Limit (PEL) for HF is 3 ppm)

II. Toxicology of hydrogen fluoride

In the body, HF readily penetrates skin, corroding soft tissue and bone.  Inhaled HF vapor/gas is corrosive to the respiratory system and can cause delayed pulmonary edema.  Systemic HF poisoning removes Ca2+ from soft tissues and bones, creating a disturbance of Ca2+ concentrations (hypocalcaemia).  Ca2+ regulation is critical for normal cell function, neural transmission, bone integrity, blood coagulation and intracellular signaling.  Sudden death following acute HF exposure is common.

Use the utmost care in preventing exposure to even the most dilute HF solutions.  Although exposure to concentrated HF solutions (>50%) will cause immediate pain, more dilute solutions (20% - 50%) may not cause any pain on contact and may go undetected for hours.  Delays in first aid/treatment of HF exposure result in painful, slow-to-heal burns and systemic HF poisoning.

ATTACHMENT B

For more general information about Hydrofluoric Acid (or hydrogen fluoride) see:

 

(Missouri S&T’s Environmental Health & Safety Office, June 2013)