Acid Safety and Drinking Water

There seems to be a need for clarification about the safe practices to be used when working with some of the most hazardous chemicals in the dental laboratory ñ acids.  As most of you are aware, OSHA’s Hazard Communication Program 29 CFR 1910.1200 requires employers to identify the hazardous chemicals, notify employees of their existence, and train employees on safe handling.  Acids definitely fall into this category with some of the most commonly used acids in the dental laboratory being hydrofluoric, sulfuric, phosphoric, and boric acid.  The first resource, of course, to be used to determine health risks involved with working with acids is one of our favorite tools - the Material Safety Data Sheet.  In the case of acids, the MSDS really comes in handy for you as it contains information to indicate the health risks, first aid procedures, personal protective equipment to be used, proper storage and disposal of the acid.  Here’s a review of some of the safety precautions that you can share with workers:  

Health Risks:

These risks can range from burns to inflammation of the upper respiratory tract.  The most common entry route in the dental lab is skin contact.

To avoid inhalation of acid fumes they should be used only in a well-ventilated area.

First Aid Procedures:

Ensure that you have the appropriate first aid supplies on hand to use in the event of an emergency.  For eye injury have availability of an eyewash station for quick drenching.  In the event of ingestion, most MSDSs indicate that you should not induce vomiting, but give water, milk, or milk of magnesia.  For skin contact rinse thoroughly with running water (15 minutes) and then seek medical attention.

Various strengths of hydrofluoric acid are used in the dental lab.  Skin exposure to diluted hydrofluoric acid may not be felt immediately, but exposure of less than 10% of the body to it can be fatal even with immediate medical treatment.  Hydrofluoric acid should be handled with extreme care beyond that given to hydrochloric, sulfuric, or other mineral acids.  When hydrofluoric acid comes into direct contact with the fingers it can severely damage or destroy the tissue underneath the nail without causing any damage to the nail itself.  This lack of initial pain often delays treatment, which can then lead to extreme pain and further complications.

Keep calcium gluconate gel on hand for initial treatment of hydrofluoric acid exposure.  In all cases, hydrofluoric acid exposure requires immediate professional medical attention. If coming in contact with human skin or bone the acid can severely burn and then decompose the bone, potentially necessitating amputation of the affected limbs.

Protection:

The personal protective equipment required when working with acids is neoprene gloves, neoprene apron, goggles, and a mask if fumes or spray are generated by the acid.

Eye protection in the form of safety glasses or goggles and a face shield should be used. Stanzoil Neoprene or Stanzoil Nitrile (22mil) gloves or other HF resistant gloves should be worn. It is also recommended that an acid resistant suit or apron be used (Some clothing is able to absorb the toxic material and maintain it close to the skin).

Other Precautions:

Acid must be stored and/or used in an appropriate container such as polyethylene or Teflon.  Glass is not advisable because it dissolves glass by reacting with silicon dioxide, the major component of most glass. Check the MSDS for this information.

Disposal:

Unfortunately, the one item that isn’t always detailed on the MSDS is the proper disposal of the acid.  The manufacturer advises you to check your local or state hazardous waste laws regarding disposal.  Typically after the acid is neutralized, it can be disposed of in the sewer system.

Scientists use something called the pH scale to measure how acidic or basic a liquid is. The scale goes from values very close to 0 through 14. Distilled water is 7 (right in the middle). Acids are found between a number very close to 0 and 7. Bases are from 7 to 14. Most of the liquids you find every day have a pH near 7. Battery acid is a strong acid with a pH value of less than 1.

The other factor to take into consideration in regard to disposal is what the resulting end-product is after use.  For instance, sulfuric acid used for electro-polishing partial frameworks will contain deposits of the alloy that is placed in the chemical.  Alloys that contain chromium are of particular concern in regard to disposal.  The Safe Drinking Water Act was passed by Congress in 1974.  It requires EPA to determine the safe levels of chemicals in drinking water.

Chromium is a metal found in natural deposits as ores containing other elements. The greatest use of chromium is in metal alloys such as stainless steel; protective coatings on metal; magnetic tapes; and pigments for paints, cement, paper, rubber, composition floor covering and other materials. The regulation for chromium became effective in 1992. Between 1993 and 1995, EPA required your water supplier to collect water samples once and analyze them to find out if chromium is present above 0.1 ppm. If it is present above this level, the system must continue to monitor this contaminant every 3 months.

EPA strongly encourages people to learn more about their drinking water, and to support local efforts to protect and upgrade the supply of safe drinking water.   See the list of contacts below for more information on how to protect our drinking water.

For proper disposal of acids and the end-product as described above, you should contact the EPA or a local waste management company for their advice.  It may be necessary to pay a hazardous waste company to pick up and properly dispose of the waste.

Here are some links to websites that will provide you additional information about storage of acids:

http://www.cdc.gov/od/ohs/ENVIRONM/khemstore.htm

http://www.mcg.edu/services/ehs/chemsafe/chemstor.htm

http://www.ehs.cornell.edu/lrs/chemInfo/01.Chem.Stor.Guide.htm

Storage:

Another consideration with acids is storage.  They should not be stored with solvents so ensure that you have these types of products separated during storage such as under cabinets and/or in your supply room.  If you have sufficient volumes of these acids, you may need to store them in a corrosives cabinet.  The same holds true for flammable items.

(Check on storage of corrosives).  For small quantities such as one or two bottles, you can store them in a container with an absorbent material so that if it should leak out of the bottle it will be absorbed and not leak into other chemicals or work areas. Use and store hydrofluoric acid in polyethylene, polypropylene, Teflon, wax, lead or platinum containers.

Learn more about your drinking water!

Your local water supplier can give you a list of the chemicals they test for in your water, as well as how your water is treated.

Your state Department of Health/Environment is also a valuable source of information.

For help in locating these agencies or for information on drinking water in general, call: EPAs Safe Drinking Water Hotline: (800) 426-4791.

For additional information on the uses and releases of chemicals in your state, contact the: Community Right-to-Know Hotline: (800) 424-9346.