A casual teacher who wanted to demonstrate a scientific principle by inviting students to hold on to dry ice thought it would be a good learning experience, a NSW court has heard.

‘‘Some students obviously took the game too seriously and [held on] too long to the dry ice,’’ Damien Hilton wrote in an incident report after eight of the students suffered  blisters and severe burns at Terrigal High School, in the NSW Hunter, last February.

Mr Hilton, 49, of Wyong, previously pleaded not guilty to 10 charges, including eight counts of assaulting a student occasioning actual bodily harm.

He was also charged with negligently inflicting grievous bodily harm and recklessly inflicting grievous bodily harm.

The evidence concluded at Toronto Local Court on Tuesday with a burns expert from Concord Repatriation Hospital telling the court contact with dry ice for at least one minute could cause scarring, while contact for more than two minutes could cause burns so severe that they could require surgery.

At least one of the students held the solid carbon dioxide for more than two minutes, the court previously heard.

In the incident report, which was filed after a number of students were taken to Gosford and Wyong hospitals, Mr Hilton wrote: ‘‘I thought it would be a good learning experience for the students to experience sublimation of dry ice.’’

Sublimation is the transition of a substance from a solid state to gas.

‘‘I had volunteers from the class come out and hold dry ice whilst another student timed them as a sort of game,’’ the report continued.

Photos tendered to the court showed a range of injuries from redness and swelling to large blisters and skin completely burnt from the students’ palms.

At the conclusion of yesterday’s evidence, defence barrister Stuart Bouveng said he would argue that the prosecution had not provided evidence that was capable of proving the assault charges.

Magistrate Jennifer Atkinson adjourned the case to April.