Risk matrix is a team based tool to aid decision analysis. It is a two dimensional graphical representation of consequences scale and likelihood scale. It is presented as an array of cells. AS4360 and associated notes provide general explanations on risk matrix. The smallest risk matrix used is 2*2 matrix consisting of 4 cells. Largest risk matrix used is 10*10mosaic. Risk matrices commonly used in industrial studies ranged from 4*4 to 7*7 arrays.

Many risk assessment studies used a normalised risk matrix which included wide ranging consequence scales and likelihood scales. Allocation of risk levels within the risk matrix also varied across these studies.

Consequence scale covered personnel safety, property damage, business interruption, service quality, reputational issues, public relations, environmental damage, regulatory matters etc. In many cases, there were inconsistencies in increments, range of scales and mismatches between various scales. As a result, there was significant potential for error especially in evaluation and treatment of mid level (proximate to ALARP - As Low As Resonablty Practicable) risks.

Hence it is important to develop a risk matrix fit for purpose. Salient features of risk matrix types and array dimensions will be discussed in this paper. Based on the review of various risk matrices and experience in developing / calibrating risk matrices, an attempt is made here to identify the steps for development of a risk matrix fit for purpose. Some generic examples to highlight the broad differences across sectors and industries (including government utilities) will also be presented.