Our data on 11,000+ unit sized hazard reviews to date (using HAZOP, What-if, and variations) show that using a risk matrix detracts from brainstorming and does not improve the risk judgment of a multiple discipline team of process and operations with good to excellent expertise. If you don’t have such a team, then you will miss most of the scenarios of importance; there is NO WAY to compensate for poor team composition; no way. If you do have a good team (which is minimum needed), then risk matrices are an unnecessary encumbrance for 95% to perhaps even 99% of the risk judgments. For the other 1-5% of the risk judgments, a risk matrix or LOPA can help. So, the best approach is to make the use of a risk matrix (qualitative scoring) or LOPA (order of magnitude scoring of discrete factors) optional… then you will not be slowing the team down on risk judgments unnecessarily (which otherwise will hurt brainstorming).
IF the client forces us to use a risk matrix, then we will use it. But we still try to reach a team consensus on the risk of the scenario (by simply asking the team members if the risk is acceptable or not) before using the matrix (since risk matrices have also been shown to hurt risk judgment as much as they help, since the matrix is an artificial construct). We normally can convince a company to stop requiring use of risk matrices in PHA, HAZOPs, etc., after a day or so of showing them how well the teams function without it. Again, this is based on experience with hundreds of leaders/facilitators, with hundreds of client companies, over about a 25 year period.
Case Study from Argentina: I was “auditing” a meeting in progress in Argentina in 2013 at the request of a client and they forced the team to use a risk matrix. They also forced the team to go to causes first instead of consequences first. Both of these approaches add to long discussion of low risk scenarios and many unnecessary discussions of the categories on a risk matrix. I pointed these issues out several times (lunch and at the end) and then summarized the savings on an alternative approach. I doubt the client in Argentina will continue to require use of a risk matrix in the meetings; they likely will also discard other “rules” that detract from brainstorming.
Final comments: Be careful on the answer you get from a question like “what are my peers doing”… many times the peer may be partially blind and you will be following them down the same path. It is best for a company to ask “what is the best way to maximize brainstorming and ensure I have sufficient layers of protection for all scenarios” … too many companies seem too interested in “what are my peers doing” … what if your peers haven’t tried different approaches? What if they have been trained wrongly? To deviate from the “risk matrix” example for a moment to illustrate the point just made: Note that a majority of companies are not really analyzing for scenarios during non-routine modes of operation (such as what happens if the operator skips a step or what if they do a step a wrong, during say startup)… this is because their peer group is not… and it likely all started with someone being poorly trained in the beginning… this likely explains why 80% of major process safety accidents continue to occur during non-routine modes of operation. That is not a good trend to be following… we believe the same thing is now happening with the overuse of risk matrices in brainstorming meetings.