Precision Calculator
What TRIR is my system designed to produce?
Comparison Calculator
How do these two TRIR results compare?
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Understanding TRIR
TRIR (Total Recordable Incident Rate) measures how often a company experiences OSHA-recordable incidents, scaled per 200,000 worker-hours. That is the equivalent of 100 employees working 40 hours a week for 50 weeks. An incident counts as recordable if it requires medical treatment beyond first aid, or results in loss of consciousness, days away from work, restricted work, or transfer to another job.
Most organizations report TRIR as one precise-looking value, such as 1.84. But recordable incidents are rare, random events, so any observed TRIR is just one outcome from a range of results the same safety system could have produced.
That is why TRIR is best communicated as a confidence interval: the range of values likely to contain the true rate at a chosen level of confidence (for example 95%). A result below the lower bound would be unusually low for that system, and one above the upper bound unusually high. The Precision calculator above computes this interval for your numbers.
A company with 1 recordable injury in 200,000 worker-hours has an observed TRIR of 1.00. At 95% confidence, however, the true rate could be anywhere from 0.18 to 5.66.
If the next 200,000 worker-hours bring 2 recordables, TRIR appears to double to 2.00. Yet the new interval (0.55 to 7.29) overlaps heavily with the first, and a significance test shows no statistical difference between the two periods. You can run this test on your own numbers in the Comparison calculator above.
For the full statistical background, see The Statistical Invalidity of TRIR as a Measure of Safety Performance (Hallowell et al., 2021).