The government has been accused of having a “shockingly cavalier” attitude to fire safety, as schools continue to be built without sprinkler systems.

Unions have raised concerns about an announcement that Selsey Academy in West Sussex, which was almost completely destroyed by a fire in 2016, is set to be rebuilt without sprinklers because the original building did not have them.

In an open letter to education secretary Damian Hinds, leaders from the National Education Union (NEU) and Fire Brigades Union (FBU) described the decision as “incomprehensible” and warned: “If all decisions were made on this basis sprinklers would never be fitted for rebuilds, because no school fitted with a sprinkler system has ever burned down.”

The letter also condemns the decision to build 32 new schools in Northamptonshire without sprinkler systems, and adds that none of the new schools built in Croydon or Kensington Aldridge Academy, the school at the base of Grenfell Tower, have sprinklers fitted.

In 2007, the Building Bulletin 100: Design for Fire Safety in Schools guidance specified that all schools should have sprinklers apart from “a few low risk schools”. However, the unions warned that only 35 per cent of new schools have been fitted with sprinklers since 2010.

Unions successfully campaigned last year to stop the government weakening fire protection arrangements for schools and remove the “expectation” for sprinklers to be fitted in new schools.

In Scotland and Wales, it is a legal requirement for all new schools to be built with sprinkler systems installed.

The NEU’s joint general secretary, Kevin Courtney, called for sprinklers in new school buildings to become a “legal requirement” to stop the policy being “flouted”.

He added: “Grenfell Tower should have been a defining moment in the way we view safety in public buildings, but it seems that health and safety is still seen as an opportunity to cut corners and save money.”

The FBU’s assistant general secretary, Andy Dark, accused the government of being “shockingly cavalier” in its attitude to fire safety in schools.

“The cost of fitting sprinklers represents a very low investment when weighed against the potential threat to life, the damage to buildings and the disruption of children’s education if there is a fire in a school.

“It is essential that the government act immediately to make it a legal requirement for sprinklers to be fitted in all new school buildings,” he added.