by Noel Kelsch, RDHAP
We have a rustic cabin canopied by cottonwoods in the middle of nowhere that my great–grandfather homesteaded. I think the middle of nowhere is one of the best destinations on earth. There is no electricity and, therefore, no TV to interfere with my thoughts.
There is a shed at the edge of the forest that contains the remnants of my grandfather's life. This man was the first recycler I ever knew. He practiced being green before it was a concept. He could turn a garden hose into a tire for a wheelbarrow and recycle old canning jars into an organization system with recycled bits of piping, nails, nuts, and bolts. Cans of salve and unlabeled solvents still line the shelves of that shed. I have used this stash of treasures to patch and repair other things for many years. I seldom delve into the solvents though, because to be honest, I don't know what they contain or the risks involved in their use.
Knowing the risks involved in the use of a chemical is vital. In dentistry we are given great information on the risks inherent in the chemicals we are exposed to simply by reading the material safety data sheets (MSDS).
Last month, we learned about the time weight average (TWA) and how important it is to know how long you can be exposed to a chemical before it can harm you. Where do we find this information? It is right on the MSDS that each office is required to keep.
What is an MSDS?
Material safety data sheets are information sheets prepared by the product's manufacturer. They give you all of the health effects of the chemical and the chemical's physical properties. Details on usage, storage, hazards, and handling are included. Though these are not always complete, MSDS are a good source of guidance in the use of products.
OSHA offers a great guidance tool to help you understand what you are reading on the sheet: This can be found at http://www.osha–slc.gov/Publications/MSDS/msdsform.html. In addition, the complete version of this article is available at DentistryIQ.com.
The most commonly used categories that we as health–care workers need to be aware of are divided into nine sections.
I — Product Identification
This information identifies the manufacturer and product. The substance may be listed by its formal chemical name or by its trade name. If the product is a mixture of several chemicals, only the trade name will be listed. Methyl alcohol, for example, is also known as methanol or wood alcohol.
II — Hazardous Ingredients
This section identifies hazardous ingredients and exposure limits. Product ingredients are listed by percentage of total weight. Information should be given on what amount of the ingredient causes ill effects; this amount may be stated as a TLV, PEL, or LD50. The TLV (Threshold Limit Value) is a recommended maximum average concentration over an eight–hour workday. The PEL (Permissible Exposure Limit) is the exposure limit set by OSHA. Unlike the TLV, it can be enforced by law. The LD50 is the lethal dose concentration that, in experiments, kills 50% of the test animals. Remember that this information is only for the individual ingredient, not for the entire mixture. Visit the OSHA Web site for a better understanding of TLV, PEL, or LD50.
III — Physical Data
The physical properties of a substance give clues to the type of hazard it may present, meaning whether it is liquid, solid, or gas at room temperature, how much vapor it forms, whether the vapor rises or settles, and whether it dissolves in water.
Boiling point. The temperature at which the liquid boils at sea level. Ranges are presented for mixtures. In general, a low boiling point means the substance will be in gas form at room temperature (unless it is pressurized). Materials that can catch fire and also have a low boiling point generally present greater fire hazards.
Vapor pressure. Measured in millimeters of mercury and indicates how easily a liquid will evaporate. Solids have no vapor pressure and don't evaporate. Liquids that evaporate easily have higher vapor pressures and the amounts in the air can build up quickly. Good ventilation is necessary to prevent breathing in materials like solvents that have high vapor pressures.
Vapor density. The weight of vapor or gas compared with an equal volume of air. Air has been assigned a value of one. Vapors that are heavier than air, such as gasoline or hydrogen sulfide, have a vapor density greater than one and accumulate in low places, such as along floors, in sewers, tank bottoms, manholes, and elevator shafts where they may create fire or health hazards.
Percent volatile. The percent of a liquid or a solid (by volume) that will evaporate at an ambient temperature of 70°F (unless some other temperature is stated). Examples: butane, gasoline, and mineral spirits are 100% volatile; their individual evaporation rates vary, but over a period of time each will evaporate completely.
Evaporation rate. The rate at which a particular material will vaporize (evaporate) when compared with the rate of vaporization of a known material. Usually normal butyl acetate (n–BuAc), with a vaporization rate designated as 1.0, is used for comparison. The evaporation rate can be useful in evaluating the health and fire hazards of a material. Fast–evaporating solvents can quickly release hazardous amounts of vapors into the air.
IV — Fire and Explosion Hazard
Flash point. The lowest temperature at which enough vapor is formed by a liquid so that the air/vapor mixture will burst into flames when exposed to an ignition source such as a spark from static electricity or a burning cigarette. A flash point near or below room temperature (77°F) indicates that the material is especially dangerous because explosive vapors can form without additional heating.
Flammable limits. The lowest and highest concentrations of vapor or gas in the air (by percent volume) that will burst into flames when exposed to a spark or flame. The Lower Explosive Limit is the LEL (below this the air/substance mix is too lean to burn). Substances with a wide range of flammable concentrations, such as ether, may burst into flames near or far from the ignition source.
Extinguishing media. What to use to put out a fire. The usual materials are water, fog, foam, alcohol foam, carbon dioxide, and dry chemicals.
V — Health Hazards
This section provides a combined estimate of the total hazard of the product, including the ways that exposure may occur, effects of short–term (acute) and long–term (chronic) overexposure (such as signs, symptoms, and disease that would result from short– or long–term exposure), the acceptable air concentration of the substance, and emergency and first–aid procedures. The workplace standard may be stated as a TLV or PEL, or it may be an LD50, which does not indicate the amount that is safe, but how toxic the substance is (the lower the LD50, the more toxic the substance). Acute exposure data are usually more detailed and accurate than chronic exposure data. In fact, chronic data are often not listed at all.
VI — Reactivity
This section describes how the substance will react under particular circumstances.
Stability. Indicates whether the substance may decompose (disintegrate) over time. It is used to help decide how and where the material is stored.
Incompatibility. Indicates chemicals that should not come into contact with this substance. Mixing may result in fire, release of toxic gases, or buildup of pressure in a container.
VII — Spill and Disposal Procedures
This section indicates methods for cleanup and disposal of hazardous materials. Precautions to protect workers may be listed.
VIII — Protective Measures
This section describes the equipment and ventilation procedures that should be used when working with the substance. Respirators, eye protection, garments, gloves, boots, and other protective equipment should be specified by type and material of construction.
IX — Special Precautions
Precautions not listed elsewhere in the MSDS are described in this section. It may include cleaning or disposing of contaminated clothes, handling procedures, storage information, label statements, etc.
A great Web site for obtaining free MSDS sheets is the Environmental Health and Safety Online. http://www.ehso.com/msds.php
My grandfather left me a patchwork of things I cannot identify and therefore cannot weigh the risks involved in use, so they will stay on the self. Each of us must take time to continually check the risks involved in the products we use. The material safety data sheet is the key.
A special thanks to the Organization for Safety and Asepsis Procedures (OSAP.org) and OSHA for the information in this article.
About the Author
Noel Brandon Kelsch, RDH, is a freelance cartoonist, writer, and speaker. She has received many national awards including Colgate Bright Smiles Bright Futures and Sunstar/RDH Award of Distinction. Her family lives in Moorpark, Calif.