Five school children were hospitalised on Wednesday after a hose burst, spraying them with hydraulic fluid.
The hose was part of drilling machinery being used by contractors involved in building work at the Noel Baker School in Bracknell Drive, Alvaston.
Emergency services treated 10 people including a teacher at the scene. A further five were taken to hospital with skin and eye irritation.
A Derbyshire Police statement confirmed they had informed the Health and Safety Executive, which will investigate.