Emergency crews outside W.T. Woodson High School in Fairfax County, Va., after a chemistry lab fire that injured five on Oct. 30, 2015. (Dayna Smith/For The Washington Post)

A popular chemistry lab demonstration that went awry and burned five students at a Fairfax County high school in October was performed without a ventilation hood, safety goggles or guidelines from the school system on how to conduct it, according to a safety investigation.

The fire at W.T. Woodson High School on the Friday before Halloween prompted the school system to rewrite its safety protocols and ban the demonstration — known as a “rainbow flame” — which involves igniting a pool of ethyl alcohol on a lab table and adding salts to change the color of the flames. The district also temporarily suspended all activities involving open flames in classrooms while teachers were retrained.

The school system, which said little about the incident in the fall, confirmed this week that the teacher, who was also hurt, violated safety protocols because neither she nor her students were wearing safety goggles during the demonstration. It created what one student described as a “splash of fire” that burned students who were nearby.

Although a ventilation hood would not have been required, an expert said it should have been used and could have prevented or mitigated the fireball. Two students with serious burns had to be flown to hospitals.

Burned items in a chemistry lab at W.T. Woodson High School in Fairfax County, Va. (Virginia Department of Labor and Industry)

The teacher remains on paid administrative leave, according to Fairfax schools spokesman John Torre, who declined to disclose the reason, citing personnel privacy.

The district has concluded an internal investigation of the incident, but Torre said the school system is not planning to share its findings publicly.

The teacher did not respond to a request for comment this week.

Ken Roy, safety adviser for the National Science Teachers Association, said that a ventilation or fume hood, which sucks air out of a laboratory, might have prevented the spread of the ethyl alcohol vapors that ignited and burned students.

“It would help prevent this type of accident,” Roy said. “She should have done it under a fume hood, which would have contained any issues she had with a fireball.”

But the broader problem, Roy said, is that many science teachers receive little to no training on lab safety procedures. Even university labs, where many future science teachers train, are plagued with accidents. He believes school districts should do a better job to ensure science teachers are properly trained in safety protocols.

“It’s up to the school districts, the boards of education, to provide the training,” Roy said.

Torre said the district provided safety protocols to teachers before the incident and had conducted in-service safety training. He would not comment on the specific training the teacher had received, but he said the way the teacher performed the demonstration was not outlined in the curriculum.

Fairfax schools mandated more training for science teachers after the incident and strengthened its safety protocols, Torre said. Teachers are no longer allowed to have bulk containers — like the jug of ethyl alcohol was used in the demonstration — in classrooms when there are open flames.

Science teachers got another in-depth safety training course in January. The same course will be provided to all new science teachers and long-term substitutes teaching science, Torre said.After the fire at Woodson, the association issued a letter to its 68,000 members, saying they should “halt the use of methanol-based flame tests on an open laboratory desk.” Methanol is a cousin of ethyl alcohol, and both are considered highly flammable. The Chemical Safety Board counted 25 incidents in school science labs since 2010, seven involving methanol or ethyl alcohol.

The fire was the one of the most recent of many mishaps involving the “rainbow flame” demonstration. The captivating display is a vivid way to teach about a chemical’s atomic structure.

Experts and educators have warned against performing the demonstration with flammable liquids because of the risk that the vapors could ignite and explode. They advise that teachers and students perform a safer version of the demonstration using a controlled flame from a Bunsen burner and wooden splints soaked in salts.

Severe student injuries have resulted from some demonstrations, prompting warnings from the U.S. Chemical Safety Board and the National Science Teacher’s Association.

Virginia Occupational Safety and Health found no workplace safety violations at Woodson during an investigation that concluded in December. WJLA first reported on that agency’s findings last week.

According to the investigative report obtained by The Washington Post through the Freedom of Information Act, the teacher told investigators that she poured ethyl alcohol from a beaker onto a demonstration table and ignited it. She then introduced different kinds of salts to the flame.

When the flames began to die down, according to the report, she lifted a large jug of the flammable liquid by its midsection and dumped it onto the table. The bottle compressed, creating what officials called a “bellows effect” that shot a plume of flammable vapor out of the bottle. A burst of air from an HVAC vent might also have propelled the vapors.

The vapor ignited, generating a large fireball that led to the burns. The blaze melted plastic chairs and charred a backpack, according to investigative photos.

The report notes that the classroom had an array of safety equipment, including lab gloves, aprons, safety goggles and a ventilation hood. Although the safety equipment was not in use, investigators concluded that no citations were warranted because of a lack of classroom guidelines.

“The school curriculum for this demonstration does not provide any detailed instructions on how a teacher should perform the demonstration,” investigators wrote.