The project includes £16m capital funding from CBC, which was approved by its executive last April.
But planning documents on the council’s website, at the early stages of the process, include an objection from the HSE.
“There are sufficient reasons on safety grounds for advising against the granting of planning permission in this case,” according to the HSE.
“As the proposed development is within the consultation distance of a major hazard pipeline, you should consider contacting the pipeline operator (Cadent Gas Limited) before deciding the case,” it warned.
“There are two particular reasons for this. The operator may have a legal interest in the vicinity of the pipeline, which may limit some developments within a certain proximity of the pipeline.
“The standards to which the pipeline is designed and operated may restrict occupied buildings or major traffic routes within that same distance.
“Consequently there may be a need for the operator to modify the pipeline, or its operation, if the development proceeds.”
The local authority said: “A planning application has been registered with CBC for changes to remodel and refurbish Sandy Secondary School.
“This is because, while the premises is recognised by the Department for Education as a school of more than eight forms of entry, it doesn’t have the capacity to accommodate the current level of students.
“The number has increased in five years from 535 to just over 1,000 on the 17-and-a-half acre site.
“These plans are for a two-storey detached teaching block, a single-storey special educational needs and disabilities (SEND) block, remodelling and improvements to the school buildings, and a new all-weather artificial pitch. The renovation will also include work on the front of the school.”
The planning consultation closes on May 6 and the target date for a decision on the application is July 1, added CBC.
“If planning permission is granted, the council will appoint a contractor and a build programme will be produced.
“Feedback is welcomed on these proposed changes for Sandy Secondary School, which are aimed at helping improve the education of young people in the area.
“This will be achieved by offering more facilities for the students, while increasing specialist learning spaces to meet the changing demands of the curriculum.”
Sandy Upper School converted to a secondary in September 2018, along with the lower schools in the cluster, which became primaries, the executive was told last April.
Conservative Cranfield and Marston Moretaine councillor and executive member for families, education and children Sue Clark said at that time: “There was no funding made available to make that change.
“The school was built in 1975 for three year groups with 22 students in each class, so much smaller than the current requirements.”