Volcanic hazards assessments for critical facilities, such as nuclear power plants, often must consider the potential effects from phenomena that have very low likelihoods of occurrence. The International Atomic Energy Agency recently released a Technical Document that provides detailed guidance on conducting practical volcanic hazards assessments that include rare phenomena, using both deterministic and probabilistic approaches. This guidance develops a graded approach to the analysis, and provides a range of model complexities for assessing hazardous volcanic phenomena. Although this guidance focuses on the safety of nuclear installations, it is applicable to other sites that warrant consideration of low likelihood volcanic hazards that have potentially high consequences.