Estimates of risk are compared to the risk criteria (risk evaluation) to estimate risks to workers’ health and to help prioritize hazard reduction actions. Note that this language may or may not actually be used in many MSD risk assessment tools and is frequently implicit.
Risk evaluation is a process that is used to compare measures of risk with risk criteria in order to determine whether or not a specified level of risk triggers the use of control or other measures.
Some MSD Assessment methods include implied risk criteria, sometimes with suggested actions. These are often seen in Observational or Comprehensive tools. An example is RULA where a score between 1 and 7 corresponds to recommended actions. Scores of 1or 2 mean that the posture is acceptable if it is not maintained or repeated for long periods, while scores of 7 means that investigation and changes are required immediately. Note that this is an intervention priority, not an injury risk score.
Other tools give the Risk Assessment team some latitude in setting scores at which action is triggered. For many tools, there are commonly accepted threshold scores. For example, the Strain Index computes a score. The original report used a threshold score of 5 to distinguish “safe” from “hazardous” single task jobs. More recent studies have proposed multiple thresholds. The LMMH Tables present tables for males and females separately as well as percentiles of workers who would find the load acceptable. A maximal weight that is acceptable to 75% of the population is a commonly accepted threshold.
The Risk Assessment team must examine the implicit and explicit risk criteria for the Assessment tools used or choose appropriate risk criteria for their environment.
ACGIH notes that nearly all workers may be repeatedly exposed below the TLV risk criteria without adverse health effects but emphasize that they are not fine lines between safe and dangerous exposures, …. The TLVs® … are not quantitative estimates of risk at different exposure levels…
Note also that the risk criteria may shift based upon new knowledge from users or researchers. Judgment may also be needed based upon the particular use of a tool, e.g., what adjustment, if any, is needed when using the NIOSH equation to assess a task in very hot and humid weather or for a very short worker? Again, as ACGIH notes, these methods must be used by persons with a strong knowledge of their development and interpretation.
CAN/CSA-Z1002-12 (R2017) Occupational health and safety - hazard identification and elimination and risk assessment and control.