Risk Evaluation

When a HAZOP team follows the methodology of Figure 1, it uses the guidewords to identify causes of potential problems. When the team finds a problem cause, it goes on to brainstorm the potential consequences of that scenario. The team is now in a position to carry out a simple risk evaluation, and the steps of this are shown in Figure 2.

The first step of this process considers the consequences of the scenario. Traditionally this is done ignoring all safety measures in place. Thus the team would assume an operator was not wearing personal protection, and that any emergency trip or shutdown system would not function. If the consequence is not significant under these circumstances, no additional measures are required and the risk is under control. If it is significant we must go on to consider likelihood, and here we take into account all existing safety measures, work practices etc. Again, if the risk is not considered significant, bearing in mind the likelihood with existing safety measures, we need take no further action.

If at this point the risk is not acceptable, we must seek appropriate additional control measures to reduce the risk to an acceptable level. The choice of these measures falls within the remit of the team in most cases, although often the final decision is left to the responsible manager. The team should ensure that, if their recommendation is followed, the risk will be adequately controlled.