A YOUTH was cleared yesterday of starting a blaze which left a teacher engulfed in thick black smoke after she was trapped in her office.

The 16-year-old, who cannot be named, was accused of setting fire to a chair outside the year head's office, trapping her inside.

But a jury of eight women and four men took 50 minutes to find him not guilty of starting the fire.

Newcastle Crown Court heard that 1,300 pupils were inside the County Durham school building when an arsonist struck.

Staff and pupils escaped unscathed, but the court heard how the trapped teacher was left frightened by her ordeal.

Graham Duff, prosecuting, said that the teacher was in the middle of a telephone call when she noticed smoke billowing around her door.

He said: "She was in a dilemma. She thought if she opened the door there might be flames but could not get out through the window. She started to panic and she was extremely upset, so she decided to open the door slightly and she was immediately engulfed in thick black smoke."

The fire caused £24,000 damage to classrooms and corridors in the school.

The court was told that the pupil was caught on CCTV lingering around the area of the fire at about the time it was started.

He was said to have bragged to fellow pupils about how he managed to start the fire, but was yesterday cleared of arson with intent to endanger life.

Mr Duff told the court that the school had reviewed its fire system in the school and had disposed of all similar chairs after the blaze