A controlled explosion was carried out a North Tyneside school.
The bomb disposal squad from Northumbria Police was called to St Thomas More RC Academy, in North Shields, last Thursday.
The school is among a number of schools around the country that have called their local force out.
Schools have been given fresh advice from CLEAPSS – the Government’s science and technology advisory service – about the storage of the chemical 2,4-dinitrophenylhydrazine, known as ‘DNP’.
Concerns have been raised over the safety of the chemical, used as a reactive agent in lab tests, if it gets dry.
The bomb disposal squad carried out a controlled explosion on the school field after pupils head left for the day.
Headteacher David Watson said: “The advice received was that if the external appearance of the chemical looked like it could be dry, we weren’t to investigate it further.
“We were reassured there was no immediate concern and the only reason bomb disposal teams come into school as there is a risk if there was an accident in transporting the chemical.
“We contacted the police, we were the seventh school in the region they visited that day, and they came out after school and carried out the controlled explosion in the field.
“We told our neighbours what was happening, if they heard a loud bang then that was what it was. When it was all done we told the parents what had happened. We followed all the procedures. Nobody was in any danger at any point.”
A police spokesperson said: “Police were called to St Thomas More School in North Shields on Thursday, November 3, at 2.22pm regarding the chemical 2,4 DNP at the school.
“It was safely disposed of via a controlled explosion.”
A Department for Education spokeswoman said: “We have contacted schools to remind them of the importance of storing chemicals for practical science activities carefully.”