Risk factors are used in some codes to allow for the
 higher than normal consequences of the failure of essential
or important structures. A classification of high-risk structures is given, based on different reasons for high importance. Risk factors are then related to reliability factors, defined as the increases in reliability required compared with that for a normal building. By assuming reasonable values for reliability factors, a set of risk
 factors is derived. Some of these correspond closely to those specified in the New Zealand code, while others differ markedly.