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.
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
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 solvents 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.
Robert H. Hill, Jr., Ph.D., Chair, ACS Committee on