A Fairfax County judge said yesterday he struggled to understand why young people use drugs as he sentenced a man to 20 years in prison for a fatal accident that occurred while he was under the influence of laughing gas.

John Jeffrey Lisanick, 24, of Alexandria, made an emotional apology to the families of his two victims in Circuit Court.

"I'm truly sorry for what happened," Lisanick said, looking at the families of Elizabeth Robinson, 71, and Anne Fitchett-Rush, 59. "I have to live with this every day."

Lisanick said he wants to speak out on the dangers of nitrous oxide. He said he had no idea the gas could be so harmful or affect his driving.

Lisanick had inhaled six "whippits" of nitrous oxide, commonly known as laughing gas, as he was driving along busy Route 7 on Nov. 29. He blacked out, and his car ran a red light and hit two other cars. The women killed were longtime friends who had gone out for ice cream.

Judge Lewis Griffith sentenced Lisanick to consecutive 10-year prison terms on the two involuntary manslaughter convictions. Griffith also sentenced Lisanick to concurrent 10-year terms for possession of marijuana and possession of hallucinogenic mushrooms.

In addition, Lisanick also must serve a seven-year sentence, which had been suspended, for stealing checks when he was a student at Virginia Tech.