A prototype hazard identification system, qualitative hazard identifier (QHI) works by exhaustively positing possible faults, automatically building qualitative process models, simulating them, and checking for hazards. QHI matches a library of general faults such as leaks, broken filters, blocked pipes, and controller failures against the physical description of the plant to determine all specific instances of faults that can occur in the plant. Faults may perturb variables in the original design model or may require building a new model. Fault models are automatically generated using the qualitative process compiler and simulated using QSIM. Hazards including overpressure, overtemperature, controller saturation, and explosion are identified in the reactor section of a nitric acid plant using QHI.