While school officials have not confirmed what experiment was being performed when a high school chemistry lab caught fire, there are some experiments that aren't considered safe for classrooms.
Friday's fire at W.T. Woodson High School in Fairfax County left five students and a teacher injured. Two of the students had to be airlifted to area burn centers; one of those students remains hospitalized.
The fire occurred as a teacher was conducting a demonstration for students about the different colors of fire, Fairfax County Fire Chief Richard Bowers said.
"It was a demonstration of fire in the different colors," Bowers said. "The students were observing the experiment when the explosion occurred."
An exercise often known as "the rainbow experiment" has previously left students with serious injuries and should not be performed in classrooms, according to the U.S. Chemical Safety Board and the American Chemical Society.
"These demonstrations present an unacceptable risk of flash fires and deflagrations that can cause serious injuries to students and teachers," the ACS said.
In New York City, a botched rainbow experiment -- which shows how various mineral salts produce flames in different colors when mixed with highly flammable methanol -- left a 16-year-old high school student with serious injuries in January 2014. In Hudson, Ohio, the same experiment left a 15-year-old prep school student and model with devastating burns in January 2006.
It's not clear whether the Fairfax teacher was performing this particular experiment. John Torre, a spokesman for Fairfax County Public Schools, said he could not comment on what experiment was being done.
But "the rainbow experiment" isn't the only classroom activity that the ACS has issued an explicit warning against.
Last September, the ACS issued a safety alert about an activity known as "the tornado experiment." The alert came days after a chemical incident at a Nevada science museum left several people injured.
Mary Kirchhoff, the director of education for the ACS, says both experiments are dangerous because they involve using methanol and an open flame.
Kirchhoff says other experiments can be dangerous, but the vast majority can be conducted safely with proper training and conditions.
"We need to make sure teachers and student are aware of the potential dangers,' Kirchhoff said.
But she adds the fire at Woodson High School shouldn't lead to calls against hands-on experimentation.
"Experimenting is vital," Kirchhoff said. "I think the essential thing is teachers have the right safety training and that they've been properly educated."
On Monday, Fairfax County Public Schools (FCPS) suspended the use of open flames in science classes, said Superintendent Karen Garza.
Federal investigators with the U.S. Chemical Safety Board are also looking into the fire.