Bomb disposal teams have conducted controlled explosions at seven schools across England after a warning over a lab chemical that is dangerous if stored incorrectly, The Guardian reports.

Some of the blasts prompted complaints online from local residents, who say they were not informed about what was happening.

At least seven schools are known to have summoned police and military bomb disposal teams to carry out controlled explosions in recent days. Speaking to BBC Radio 4’s Today Dr David Kinnison, a safety adviser said more were likely.

Schools received a note from the science advisory body, Cleapss last week, reminding them of the correct procedures for storing 2,4-dinitrophenylhydrazine, which is used in A-level chemistry classes. If the chemical, also known as 2,4-DNPH, is allowed to dry out it can become dangerous.

Cleapss warned schools to check how the chemical was stored and contact them immediately if they found safety concerns

Kinnison told Today:

“We have always known that this type of material if it’s not stored properly … can become potentially quite dangerous.”

If allowed to dry out 2,4-DNPH can become explosive, he said. Whilst it may seem extreme to call in explosive experts, Kinnison said the precaution was necessary, adding it was “best to be safe rather than sorry.”

A Department for Education spokesman said:

“It has been used for many, many years. As long as it’s stored correctly, it’s absolutely fine”

Declining to name the schools involved, he added that it was better to carry out the explosions on-site than to transport the chemicals elsewhere.

Local press reports are naming the affected schools as Nottingham academy, Ryde school with Upper Chine and the Isle of Wight college, both on the Isle of Wight, St Alban’sCatholic high school in Ipswich, Suffolk, Thomas Adams school in Wem, Shropshire, De Montfort school in Evesham, Worcestershire, and Turton school in Bolton.

Residents in the vicinity of the Thomas Adams school reportedly complained on Facebook about the explosion after stocks of the chemical were destroyed on 31st October, and a fire engine was dispatched.

The headteacher told the Guardian, she had been advised by Cleapss to contact the police immediately and had been left with no time to warn local residents. Describing the explosion as no louder than a firework, she said:

 “We were told the bomb squad were coming at quarter to six at night and they arrived by seven.

The school were following government and Cleapss advice and guidance. We were left with little time to warn neighbours but followed police and bomb squad disposal advice at every moment, and really people should be very very glad the school and police acted as quickly as they did.”