Safety Instrumented Systems (SIS) have become increasingly important because of the dangerous substances handled in the industrial units requiring special reliable protection systems. Any SIS is characterized by an integrity level named Safety Integrity Level (SIL). Risk Graph is a qualitative method that can be used to determine the integrity level SIL that needs to be imposed to a SIS. This method takes into account the possible consequences of a dangerous event, the occupancy frequency of the dangerous affected area, the likelihood that an unwanted event to appear but also the probability that the personnel to avoid the danger. The consequences of the unwanted event can be from minor injuries to many deaths, the occupancy frequency can be from rarely to continuous, the probability to avoid the consequences can be from possible to almost impossible and the likelihood can be from very unlikely to a relatively high probability that the unwanted event to appear. Choosing a value for each Risk Graph parameter a Safety Integrity Level (SIL) results. This SIL must be accomplished by the Safety Instrumented System (SIS).