Why is transformer oil boiling point important for thermal safety?

Boiling point relates to how the fluid behaves under extreme overheating. In normal operation transformer oil should never approach boiling, but during severe faults or cooling failure, local hot spots can generate gas, vapor, and pressure rise. Oils with better high temperature stability and higher characteristic temperatures reduce the chance of rapid vaporization that could worsen pressure events. Practical thermal safety is more often governed by flash point, fire point, and oxidation stability, but boiling behavior still matters for worst case scenarios such as internal arcing or runaway heating, especially in sealed designs with limited pressure relief margin.