When a fire broke out in a Fairfax County high school chemistry laboratory two weeks ago, it was the latest in a string of incidents in which well-intentioned instructional demonstrations — meant to captivate students while teaching them important chemistry lessons — went out of control, injuring students.

The fire at W.T. Woodson High School burned two students seriously, sent three others to the hospital and lit the teacher’s shirt on fire. The accident raised questions about the risks of certain kinds of chemistry demonstrations, particularly those that involve igniting flammable liquids in close proximity to observers.

[Six injured in chemistry fire at Woodson High School]

According to students who said they were in the class at Woodson, the teacher poured flammable liquid onto a desk and lit it with a Bunsen burner, passing metals through the flame to show how it altered the flame’s color. When the flame appeared to die down, the students said, the teacher poured on more of the liquid, causing a sudden “splash of fire” that burned students nearby.

Such chemistry class demonstrations are often called “rainbow flame.” Many chemistry teachers incorporate some form of it into their curricula, often using an alternative that involves passing metals through a controlled Bunsen burner flame using wooden sticks or by spraying chemicals into the flame, something that experts said is safer than using flammable liquids.

An image from Thoisoi2-Chemical Experiments!, a YouTube video that demonstrates the rainbow flame experiment.

The demonstration is extremely popular and common, even making it into pop culture: The pilot episode of AMC’s “Breaking Bad,” — in which the fictional protagonist, Walter White, is a meth-brewing high school chemistry teacher — features a version of the “rainbow flame” demonstration to students.

The Woodson fire is at least the fifth time since 2000 that a “rainbow flame”-type demonstration has burned students, not including school laboratory accidents involving other types of demonstrations. The demonstrations that resulted in accidents often involved igniting flammable liquids rather than passing the chemicals through the controlled flame of a Bunsen burner.

The Woodson high fire has prompted new safety warnings and a renewed call to ban the demonstration from classrooms. Filmmaker Bill Harris, whose documentary on burn victims included a young woman who was injured during a “rainbow flame” demonstration, started a Change.org petition to call attention to its dangers.

The woman, Calais Weber, said reading about the latest incident left her “wanting to scream from the rooftops just to make this stop.”

“It is so preventable,” Weber said.

Here are recent examples of chemistry demonstrations going awry in the nation’s classrooms:

  • Three students in an AP chemistry class in Tallahassee, Fla., were burned by a flash fire that resulted from a “rainbow flame” experiment five months ago, the Tallahassee Democrat reported. The students were burned despite wearing protective gear, and the experiment was overseen by a veteran teacher who had never had problems with the experiment before, the principal told the newspaper.
  • In New York, at Beacon High School in Manhattan, a teacher was performing the “rainbow flame” demonstration in January 2014, pouring methanol into dishes with various chemicals and then igniting the mixtures. The demonstration went awry, creating a “fireball” that burned two students, one severely, according to The New York Times. The school was later cited for improperly storing chemicals.
  • More than a dozen people — including several children — were injured when a tornado demonstration at a Reno science museum involving methyl alcohol and boric acid exploded because the chemicals were mixed in the wrong order in September 2014, according to the Reno Gazette-Journal.
  • A young teacher at a Denver charter school was charged with third-degree assault after his chemistry demonstration exploded, injuring four students in September 2014, according to the Denver Post. The teacher poured methanol on top of a small fire, causing an eruption of flames that burned those nearby. It prompted a safety bulletin from the U.S. Chemical Safety Board, which investigates and gives recommendations following chemical accidents.
    Daniel Horowitz, managing director of the U.S. Chemical Safety Board, said that the use of methanol in classroom and laboratory demonstrations should “definitely be avoided.”
  • The Dallas Morning News reported that two middle schoolers and a teacher were burned when a “controlled experiment” resulted in a flash fire in Frisco, Tex., in September 2013. The experiment involved strontium chloride, a stick lighter and methyl alcohol, a flammable liquid.
  • Four teenagers were burned at a Minnesota junior high school during a demonstration known as “Whoosh – Flash Bottle” that involves dropping a lit match into a jug of methanol in December 2011, television station KARE-11 reported. The school district later banned the demonstration and required safety training for all teachers.
  • A 13-year-old girl suffered “severe burns to the head” when a “flame test” demonstration burned out of control at a middle school in Oklahoma in September 2011, NewsOK.com reported.
  • Calais Weber and Cecilia Chen were sitting in their boarding school chemistry class when a teacher poured methanol atop a “rainbow flame” demonstration, igniting a devastating “whoosh” of flames that lit their clothing on fire in January 2006, the Cleveland Plain-Dealer reported. The teacher and her 11-year-old son, who was assisting with the demonstration, also were injured. The experience turned Weber, who is now training to be a nurse, into a crusader against the “rainbow flame” demonstration. Weber and the other student sued the boarding school, Western Reserve Academy, settling for $18.9 million, according to the Northeast Ohio Media Group.
  • A “rainbow flame” demonstration was the source of another fire at a high school south of Seattle in 2004, when 4-foot-high flames badly burned a teacher and two students. The teacher was performing the demonstration using methanol and had done the demonstration several times without any issues, the Seattle Times reported. The teacher had ignited methanol and — believing the flames had gone out — poured more of the liquid on top, causing the fire to go out of control. A district spokeswoman told the newspaper the teacher believed the demonstration was safe: “This was an experiment in a science book, so this is routine. She had been doing it (this experiment) all day in other classes.”
  • Two students at St. Albans School in Washington, D.C., were burned in 2000 when a “rainbow flame”-type experiment caused a small explosion. The students performing the experiment mistakenly ignited a beaker of methyl alcohol.