Safer Demos Through Safety Data Sheets
On September 15, 2014, a high school chemistry teacher in Colorado intended to demonstrate the characteristic emission spectra of metal ions with a flame test large enough for the entire classroom to watch. The different colored flames produce the so-called rainbow effect, which would certainly impress the students. Unfortunately, in this instance, four students were injured. All four suffered burns, one seriously.
Traditionally, the “Rainbow Demonstration” is performed by placing 5–7 grams of a metal chloride in a glass Petri dish and then adding 7–10 milliliters (mL) of methanol. The lights are dimmed, the mixture is ignited, and the audience observes the flame test color. But demonstrators are cautioned not to add more methanol to the Petri dish after starting the demonstration — the mistake this teacher made.
The flame quickly traveled back up into the bottle and ignited the rest of the alcohol. Pressure built up within the bottle, as the temperature of the gases produced in this chemical reaction quickly increased, and the bottle spewed a fiery stream of alcohol at a distance of 12 feet (3.6 meters), hitting a student in the chest.
In September and October 2014, a total of 22 students and two adults were injured throughout the United States in four separate incidents involving methanol used in rainbow demonstrations.
These accidents could have been prevented by using methanol’s Safety Data Sheet (SDS). Formerly known as Material Safety Data Sheets (MSDS), SDSs contain a wealth of information in a simple, easy-to-read format. Each chemical has its own SDS, and learning to read them can help you handle the chemical appropriately and address any potential health hazards.
Understanding the hazards of chemicals
If you ever read the labels of chemical products, you may have noticed a lot of symbols. The use of these symbols is a direct result of recent efforts to modernize and standardize the way chemicals’ potential hazards are labeled. One update is the adoption of a uniform set of pictograms developed by the United Nations, which is used throughout the world.
An SDS meets the requirements of the Occupational Safety and Health Administration (OSHA), a U.S. federal agency created to ensure a safe work environment for all employees. OSHA mandates that all workers exposed to chemicals have the right to know about the potential hazards of these chemicals. Although OSHA regulations were developed to protect employees, state laws typically extend similar protections to students. So when you or your professor order chemicals, each chemical will come shipped with an SDS, either in written or electronic form. Having an SDS on hand for each chemical you use is not just a good idea — it’s the law.
The SDS for any particular chemical is written by the supplier or manufacturer of that chemical. There is a great deal of motivation for these companies to be thorough and accurate, as any incomplete or false information could lead to serious harm by the user, not to mention a lawsuit. (Note that an SDS does not address the possible hazards that could occur as a chemical reaction moves takes place, so it’s a good idea to look up SDSs for the products and by-products of your reactions, too.).
Using an SDS
An SDS can seem like a flurry of cautions and warnings. Learning how to sift through the information is the key to dealing with dangers and using chemicals safely. Consider an example of an SDS for methanol.
SDS for Methanlol
A typical listing for methanol in the “Hazards Identification” section of the SDS (section 2) may read as follows:
- Highly flammable liquid and vapor
- Keep away from heat, sparks, open flames, hot surfaces — No smoking
- Toxic if swallowed, in contact with skin or if inhaled
- Causes damage to organs
- Use only non-sparking tools
- Take precautionary measures against static discharge
The Hazards Identification section documents the highly flammable nature of methanol. It is so flammable that there is a direct warning to avoid open flames and even sparks.
Although the label says that both the liquid and vapor are flammable, liquids themselves do not actually burn. When a liquid is ignited, it is the vapors on top of the liquid that actually burn. For a liquid to be considered flammable, it needs to evaporate so quickly that the vapors above the surface of the liquid concentrated enough to combust. If enough heat is applied, these vapors will ignite.
Even though most people know better than to pour a flammable liquid, such as methanol, onto an open flame sometimes even trained professionals make this mistake, with disastrous consequences.
Read through the “Fire-Fighting Measures” section (section 5) to see if you can figure out why this mistake may occur.
- Highly flammable liquid and vapor
- Sealed containers exposed to excessive heat may explode
- Vapors may travel back to ignition source
- Flame may be invisible during the day
- Use dry chemical, CO2, or foam to extinguish
- Avoid using water to extinguish — water may not cool the fire to a temperature below methanol’s flash point. Water will cause fire to spread if not contained
- Water and methanol mixtures still flammable at concentrations above 20% methanol
Because methanol burns with a clear, clean flame, it is often difficult to see this flame in the daytime. As stated in the SDS, the flame may appear invisible during the day. If you are performing a demonstration where a methanol flame is produced and then the flame dies down, you might be tempted to add more, thinking that the fire has gone out. This could be a tragic mistake.
Flash point and auto-ignition temperature
Methanol does not have to be poured directly onto a flame to produce unintended results. On September 3, 2014, a demonstrator at a science museum in Reno, Nev., attempted to conduct a flame tornado demonstration on a rotating platform that makes a vortex composed of flames. He poured some additional methanol onto cotton balls in a dish after the flames had apparently gone out, but the cotton balls were still smoldering and instantly re-ignited when the methanol was added. The flame traveled up into the bottle (as described in the SDS), spraying the flaming liquid into the audience. Thirteen people were injured, mostly children.
How is it possible to ignite methanol without an actual flame? To answer that question, we need to look at the “Physical Data” of the SDS (section 9) for methanol:
- Melting point : -97.8 °C
- Freezing point : -97.6 °C
- Boiling point : 64.7 °C
- Flash point : 11 °C
- Auto-ignition temperature : 464 °C
If you examine the data above (which is only a small portion of what is contained in the SDS for this section), you will notice the terms “flash point” and “auto-ignition temperature.” The flash point is the temperature at which the vapors above a liquid ignite if an outside ignition source, such as a spark or flame, comes near.
For example, if a beaker of methanol is at a temperature below its flash point, you cannot set it afire, even if you put an open flame to it. So, at 10 °C and below, methanol will not catch on fire. But once it reaches 11 °C—its flash point—you can set it on fire if you light it.
As a liquid warms, the average kinetic energy of its molecules increases. Because more molecules have enough kinetic energy to escape the attractive forces holding them together in the liquid phase, its evaporation rate increases, producing more vapor. The flash point occurs when a sufficient concentration of vapor has accumulated above the liquid, which, in combination with oxygen, will burn if ignited. Remember: only vapors burn, not liquids.
When the flash point is reached, the vapors will ignite, but the fire will not be sustained, because there is not enough vapor present to sustain combustion. This ignition is still very dangerous, as a quick burst of flame can produce severe burns, and if other combustible substances are nearby, they can also catch on fire.
A more useful value is the fire point, which is the point at which a flammable liquid will not only catch on fire if lit but will also keep burning for five seconds. The fire point is typically only a few degrees higher than the flash point. Under most ambient conditions, methanol will be above its fire point, so when lit, it will continue to burn. Although the fire point is not included on the SDS, it is important to know how it differs from the flash point.
The auto-ignition temperature is the temperature at which a substance will burst into flames without an outside ignition source, such as a spark or a flame. At the auto-ignition temperature, spontaneous combustion occurs. According to the SDS for methanol, the auto ignition temperature is 464 °C. So, when the methanol was poured onto the smoldering cotton balls, if they were at a temperature above 464 °C, the methanol would instantly burst into flames on contact. Substances do not need flames to catch on fire—they only need a sufficient amount of heat along with air.
Considering the number of students who take chemistry or see chemistry demonstrations, the number of students who are involved in such accidents is relatively small, and of the accidents that occur, most are relatively minor.
The number of students injured in science labs is smaller than those injured in sports. This good safety record is due to vigilance about enforcing safety. So, the next time you do a chemistry demonstration, make sure you follow all safety protocols— use well-established procedures, make sure you and your audience are wearing googles and any other appropriate protection, and read up on all the hazards associated with your chemicals and equipment. You can find recommendations and other information for demos at www.acs.org/safety.
The recent incidents with methanol likely could have been avoided, had the experimenters used the information in the SDSs appropriately. Anytime chemicals are used, there are risks involved, but these risks can be minimized by understanding the chemicals involved. By keeping your demos safe, you and your audience can focus on the excitement and fun of chemistry, not the fear of injuries!
Understanding Fire Extinguisher Labels in Case of a Lab Fire
If a fire occurs in a lab, it is important to know that different types of fire extinguishers are used for different types of fires. In the United States, fires are classified depending on the materials that catch fire. Methanol combustion is an example of a Class B fire. Most classroom fire extinguishers should be able to extinguish this kind of fire, but to make sure, read the label on the fire extinguisher.
- CLASS A: Wood, paper, cloth, trash, and other ordinary liquids
- CLASS B: Gasoline, oil, paint, and other flammable liquids
- CLASS C: Wiring, live electrical equipment, computers, and other electrical sources
- CLASS D: Combustible metals and combustible metal alloys