In engineering insurance explosion means the sudden and violent rendering of the plant by force of internal steam or other fluid pressure (other than pressure of ignited flue gases) causing bodily displacement of any part of the plant, together with forcible ejectment of the contents. The risk is insured by using the term explosion or collapse as a way of specifying the insured perils. They are the prinicipal risks covered in respect of boilers and steam pressure vessels under the control of the insured.