These risks can be covered as an extension to a boiler and pressure plant policy but the insurance is limited to self-damage. The risks apply to plant of cast-iron construction and items with welded or brazed seams. Plant such as heating boilers, ironing machines and air-heating batteries would require the extension. The cause can be internal pressure, low water, water hammer, frost, etc. A valid claim only arises when the crack or weld failure gives rise to leakage of the contents.