The CROSBY Group is a good source. The typical minimum factor of safety that should be used in rigging design is 5:1 or more.
Because of the nature of my work (guyed and self-supporting tower design), I am familiar with many industrial accidents in which workers have died as a result of rigging failures. The problem has most often been that the workmen, in effect, designed their own rigging. The failure most often occurred in the connections. Each of these deaths could have been prevented if a competent engineer had designed or at least reviewed the proposed rigging and reviewed the proposed lifting procedure.