1. It may be that the boiler operator failed to operate according to the operating procedures and left his post without authorization; 2. The boiler may be seriously short of water, causing instantaneous vaporization during the water replenishment process, and the vaporized steam in the boiler expands instantaneously!

3. The boiler operates at overpressure and the safety valve fails!

It cannot be discharged safely after causing overpressure!

4. The boiler failed to undergo annual internal and external inspections as scheduled.