why does it work?

The Severity Adjusted Injury Frequency works by setting a benchmark injury, and adjusting the injury rate based on whether or not an injury is better or worse than the benchmark.

The benchmark injury for the SAIF Rate is an injury where someone is off work for two weeks (14 days lost time). If someone is off work for 2 weeks that injury becomes a 1 on both the injury rate, and the severity adjusted injury rate. All other injuries are adjusted based on whether or not they are more or less severe than 14 days lost.

Real-world severity is complex. What the benchmark does is allow for a quick and easy explaination of severity for people who are not particularly interested in the complex details behind severity, only the outcome.

If we want to explain safety measurement to average people we can now do so easily:

TRIF = the number of people we hurt, out of some hours

SAIF = the number of people with the equivalent of 2-week LTI, out of some hours