Police, fire and ambulance crews were called to the Noel Baker School in Alvaston, Derbyshire after teachers raised the alarm.
The hose was part of drilling machinery being used by contractors involved in building work at the school.
As a result of the incident hydraulic fluid sprayed out over a number of students. Five people were taken to hospital to be treated for skin and eye irritation.
Ten others, including a teacher were treated at the scene and given further advice.
The scene of the incident was cordoned off and initial details taken.
Derbyshire police have now informed the Health and Safety Executive who are carrying out an investigation.