Safety Alert – Stop Using the Rainbow Demonstration: The American Chemical Society Committee on Chemical Safety recommends that the "Rainbow" demonstration on open benches involving the use of flammable solvents such as methanol be discontinued immediately. When carried out on open benches (outside of a chemical hood) these demonstrations present an unacceptable risk of flash fires and deflagrations that can cause serious injuries to students and teachers. On an open bench, invisible flammable vapors can flow across and off of the bench to the floor where they can be ignited by a flame, a spark (even static electricity), or even a hot surface. Even carrying out this demonstration in a hood poses risks if solvents are not adequately controlled. If you are considering this "Rainbow" demonstration or have used it in the past, we urge you to stop using this demonstration. There are alternatives available that demonstrate the same rainbow colors but don't use flammable solvent s on an open bench. These alternate demonstrations involve soaking wooden splints in salt solutions and then placing the splints in a Bunsen burner to observe the salt's characteristic color. We have listed some of these alternatives at www.acs.org/safety.
We – the American Chemical Society (ACS) Committee on Chemical Safety – need your help in getting a message out to high school science teachers and university teachers to prevent further injuries from this Rainbow Demonstration. The ACS alone simply cannot reach all of our nation's science teachers without your help. We are asking you to pass on the following message to your local science-chemistry teachers in high schools or colleges – please do not assume that they have gotten this message.
On January 2, 2014 a demonstration known as the "Rainbow" experiment using a flammable solvent on an open bench resulted in a tragic incident with two high school students from New York being burned. In early December 2013 the U.S. Chemical Safety and Investigation Board (CSB) released a video that featured Calais Weber, a burn victim of a similar demonstration in 2006 (www.csb.gov/videos/after-the-rainbow). The video emphasized that the incident was preventable – safer practices were not followed.
The "Rainbow" demonstration performed on an open bench using a flammable solvent is a high risk operation. When this "Rainbow" is carried out on an open bench, the conditions for a flash fire or deflagration are easily met – a fuel, oxygen, and a source of ignition. Highly flammable solvents, such as methanol, can produce heavier-than-air vapors that move across surfaces and down toward the floor where they spread undetected among unsuspecting viewers of the demonstration. A flame, spark, or even very hot surfaces can ignite the vapors resulting in a sudden flash fire or worse if a nearby open container of solvent is located. Laboratory operations involving flammable solvents should be carried out in a properly functioning chemical hood – not on an open bench. Even carrying out this demonstration in a chemical hood poses risks if fuel sources are not controlled, but doing this in a hood is surely safer than an open bench. Teachers, having an inadequate understanding of the hazards and risks presented by this demonstration, put themselves and their students at unnecessary risk during the conduct of this demonstration.
We chemists all love chemistry and we know the great satisfaction and reward that chemistry has provided to us and we want to share it with our younger generation. Many of us have seen the joy of students with great demonstrations that thrill and grab their interests in chemistry and science. However, this demonstration presents a conundrum for teachers – it offers the "wow" factor that interests and delights students, but this demonstration carries with it, a "whoa" factor of very significant risk to students and teachers. The "whoa" factor clearly outweighs the "wow" factor for this demonstration.
Robert H. Hill, Jr., Ph.D., Chair, ACS Committee on Chemical Safety