By Noel Kelsch, RDHAP
We have a rustic cabin canopied by cotton woods 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 thinking. There is a shed at the edge of the forest that contains the riminates of my grandfather’s life. This man was the first recycler that I have ever known. He practiced being green before it was a concept. He could turn a garden house into a tire for a wheel barrel and recycle old canning jars into an organization system that contain recycled bits of piping, nails and nuts and bolts. Cans of suave and unlabeled solvents still line the shelves of that shed. I have used this stash of treasures to patch and repair for many years. I seldom delve into the solvents because to be honest I simply do not know what they contain and 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 involved in the chemicals we are exposed to simply by reading the Materials and Data Sheet. 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 are we going to find the required information? It is right on the Materials Safety Data Sheet that each office is required to keep.
What is a MSDS?
It is an information sheet that is prepared by the product’s manufacture. It gives you all of the health effects of the chemical and the chemicals physical properties. Details on using, storing, hazards and handling are included. Though these are not always complete they a good source of guidance in the use of a product.
OSHA provides a great guidance tool in understanding what you are reading on the sheet, which can be found here.
The most commonly used categories that we as healthcare workers need to be aware of are:
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.
Synonym. Another name for the material. Methyl alcohol, for example, is also known as methanol or wood alcohol.
Section 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 8-hour workday. The PEL (Permissible Exposure Limit) is the exposure limit set by the Occupational Safety and Health Administration; 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.
TLV. Threshold Limit Value: a term used by the American Conference of Government Industrial Hygienists to describe the amount of a material that almost anyone can be exposed to day after day without harmful effects. The TLV can be described in three different ways:
- TLV-TWA. The Time Weighted Average amount allowed for a normal 8-hour workday or 40-hour work week. If only "TLV" is listed, it usually refers to this value.
- TLV-STEL. The Short-Term Exposure Limit, or maximum amount for a 15-minute exposure period. (At the most, only four such 15-minute periods are allowed per day, with at least 60 minutes between exposure periods. And, these four 15-minute periods should not add up to more than the daily TLV-TWA, described above).
- TLV-C. The Ceiling Exposure Limit. This is the amount that exposures should never rise above, even for an instant.
- PEL. The amount of a substance in the air that any employee may be exposed to over an 8-hour work shift. This number can be an average or maximum exposure limit. The PEL is enforceable by OSHA and is believed to protect workers from damaging health effects.
- "Skin" or "S". A notation sometimes used with PEL or TLV; it indicates that the substance may be absorbed through unbroken skin, or through mucous membranes and eyes, by direct or airborne contact-and that this additional exposure must be added into the total exposure to avoid going over the PEL or TLV.
- mg/m3. Milligrams of substance per cubic meter of air; a unit for measuring concentrations of dusts, gases or mists in air.
- mg/kg. Milligrams of substance per kilogram of body weight; used generally for solids or liquids taken in by mouth rather than inhaled substances.
- ppm. Parts per million; a unit for measuring the concentration of a gas or vapor in air, i.e. the number of parts (by volume) of a gas or vapor in a million parts of air. Also used at other times to indicate the amount of a liquid or solid.
Section 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). Carbon monoxide has a boiling point of -310°F, so it is normally a gas. Water has a boiling point of 212°F. Ethylene oxide has a boiling point of 53.6°F; above this it is a gas, below it is a liquid. 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, 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.
Solubility in Water. The quantity of a substance, by weight, that will dissolve in water at room temperature. Expressed as a percentage or by one of the following terms: negligible-less than 0.1%; slight-0.1 to 1%; moderate-1 to 10%; appreciable-greater than 10%; complete-100%. This is useful for determining spill cleanup procedures and how a material will act in the environment. Gases with low or medium-range water solubility, such as nitrogen dioxide or chlorine, are more likely to reach the deep tissues of the lungs, and highly soluble gases will dissolve in the moist mucous membranes of the upper airways.
Specific Gravity. The ratio of the weight of a volume of the substance to the weight of an equal volume of water. A specific gravity greater than one means the substance will sink in water; if specific gravity is less than one, it will float on water.
Appearance and Odor. May help identify the material. However, odor is not a reliable indicator of the concentration of the substance in air. Gasoline, for example, has a detectable odor at very low concentrations; carbon monoxide, on the other hand, has no odor even at lethal concentrations.
Section 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. Materials with narrow flammable limits may burn only near the ignition source. In terms of evaluating explosion hazards, the LEL value is considered the most important. The lower the LEL, the less of the substance needed in the air before it can ignite. Upper Explosive Limit is the UEL.
Unusual Fire and Explosion Hazards. May cover factors such as release of toxic or irritant gases in a fire. Fire conditions vary widely, and for this reason, it is difficult to predict the exact composition of combustion products that would result from a fire.
Extinguishing Media. What to use to put out a fire. The usual materials are water, fog, foam, alcohol foam, carbon dioxide and dry chemicals.
Special Fire-Fighting Procedures. Special protective equipment or measures may be recommended.
Section 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-term 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.
Section 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.
Hazardous Decomposition Products. Includes hazardous materials released during fires and created by aging of the product.
Hazardous Polymerization. Polymerization is a chemical reaction in which small molecules combine to form larger molecules. If this reaction occurs with an uncontrolled release of energy, it is a hazardous polymerization. This section should list storage procedures and the shelf life of the chemical.
Section VII - Spill And Disposal Procedures
This section indicates methods for cleanup and disposal of hazardous materials. Precautions to protect workers may be listed.
Section 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.
Section 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.
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 the time to continually check the risks involved in the products we are using. The MSDS is the key.