The former Beacon High School teacher accused of botching a chemistry experiment that left one of her students horribly burned broke down on the witness stand Tuesday while denying responsibility for the 2014 fireball.

Defendant Anna Poole — who conducted the “Rainbow Experiment” that engulfed pupil Alonzo Yanes in a fireball Jan. 2, 2014 — got emotional under cross-examination by Yanes’ lawyer, Ben Rubinowitz.

Yanes and his parents are suing Poole and the Department of Education for $27 million.

Poole was called as a defense witness to start the day and, on cross-examination, Rubinowitz pelted her with questions about Yanes’ injuries.

“You understood that Alonzo Yanes was terribly injured?” Rubinowitz said. “Yes,” she said.

“You understand that he suffered third-degree burns over 31 percent of his body?” the lawyer went on as Poole again, acknowledged, “Yes.”

“You understood that he would be scarred for life?” the lawyer asked.

“Every day for five years, every time I close my eyes,” an emotional Poole started to answer before Rubinowitz cut her off with an objection.

During the grilling, Poole maintained — contrary to Yanes’ and other students’ testimony in the Manhattan Supreme Court civil trial — that she didn’t pour a gallon jug of highly flammable methanol directly onto one of the ceramic dishes that held salts meant to demonstrate the different color of flames each produced.

“You don’t recall whether you poured [the methanol jug] into an evaporation dish?” Rubinowitz asked.

“I know I didn’t,” Poole said.

The former teacher — who is still employed at DOE headquarters as an administrator — denied that Yanes was 2 ½ feet from the demonstration table and said she didn’t see the fireball shoot toward him, as Yanes told jurors last week in gripping testimony.

“The flame shot away from you?” Rubinowitz asked, to which Poole answered, “No. I don’t know where they started.”

Rubinowitz pressed further, “Alonzo Yanes, you heard him testify he watched exactly what happened?”

“Yes.”

“Are you suggesting that he is telling anything less than the true?”

“No,” Poole answered shakily.

“Are you suggesting that he made up the story?” the lawyer pressed.

“I’m not suggesting that,” Poole said.

Earlier, under questioning by her own lawyer, Poole said she always put safety first.

“Did you have an expectation that the students in your class were required to wear goggles?” asked attorney Mark Mixson, who is representing the city and Poole.

“No,” she replied. “They were what I considered a reasonably safe distance [away] and they were not actually handling any equipment.”

“In your opinion did you perform the experiment appropriately?” Mixson asked.

Poole answered, “Yes.”

She appeared nervous as she testified — her hands would shake while taking swigs of water, and she sighed deeply before answering questions.

Earlier, she testified about struggling with obsessive compulsive disorder and having to drop out of medical school at the University of Pittsburgh because of it.

Additional reporting by Lia Eustachewich