Common cause failures (CCFs)Common cause failure are factors that cause failures in multiple components at the same time. CCFs are of crucial concern for risk analysts, as they often dominate the system dependability. Two important types of CCFs exist. External shocks are events that affect all or multiple components at the same time, for instance a fire, falling debris, or power outage. In the railroad example, nails on the road present a typical shock common cause. A second type is common mode failures, where the underlying condition shared by these components increases their failure probability or rate. Examples are production failures, harsh conditions, such as high-temperature or salted water, and maintenance errors.