More than 1,600 Laurel High School students were forced to evacuate their school yesterday when two seniors inadvertently created a "highly explosive" chemical experiment in a chemistry lab, school officials said.

The mixture of the chemical, called nitrogen tri-iodide, occured when the two 17-year-olds attempted to create a semiharmless explosive used in some fireworks, school officials said.

The two, who could be suspended and criminally charged, apparently entered the lab when they found it unlocked yesterday morning, said Thomas Ullrich, the school's vice principal.

The work done by the two students was discovered when the teacher came into the lab and made contact ewith some of the substance, causing a minor explosion or popping sound, officials said.

He questioned the two students about the proportions of chemicals they mixed and then advised the school's officials to call the county's bomb squad the officials said. When the fire department arrived school officials were told to evacuate the school.

County fire spokesman Capt. Burt Shaffner said the fire department neutralized the substance with water.

"That chemical substance is so sensitive that I remembered back in high school that a friend of mine put a drop on a sugar cub and it exploded when a fly landed on it . . . it killed the fly," Capt. Shaffner said.

The fire spokesman said the students mixed 50 grams of the substance enough to cause a large explosion and injuries. No one was injured in this incident.

School officials, who are still investigating the incident, said school rules prohibit students from using chemicals without the supervision of teachers and also specifically cite nitrogentri-iodide as an illegal substance in chemical labs.