Total Recordable Incident Rate was developed in the US as a measure of occupational safety. Some recordable incidents lead to an employee being unavailable for normal work duties for one or more days, and these incidents are counted in both TRIR and Lost Time Incident Rate (LTIR). Both metrics, are calculated as the equivalent number of incidents if 100 people working full time for one year had been monitored.
Some organizations outside the US (for example, the International Marine Contractors Association, IMCA) normalize the rate to ‘per one million hours worked’ rather than the two hundred thousand hours implied by the US definition (40 hours for 50 weeks for 100 people). In the US specification, if local first aid allows immediate return to work, then the injury will be noted in safety logs, but not classified as a recordable incident.