What this clause does
When a husband and wife die in the same car accident, or when a parent and adult child die within hours of each other, the order of death has cascading consequences. Under the default rules, a beneficiary who outlives the testator by a single second can inherit. The estate then passes through that beneficiary's own plan to a different set of people. A common disaster clause replaces those default rules with a chosen outcome — usually a 30-, 60-, or 120-hour survival requirement.