The formulas
Every rate here puts cases on the same scale: 200,000 hours is 100 full-time workers for a year, so a rate reads as cases per 100 full-time workers. Only the thing you count changes.
- TRIR = recordable cases × 200,000 ÷ hours worked. Count every case that meets the recording criteria in 29 CFR 1904.7.
- DART rate = DART cases × 200,000 ÷ hours worked. Count only the recordable cases with days away from work, restricted work or job transfer.
- Lost time rate (LTIR) = lost time cases × 200,000 ÷ hours worked. Employers usually count the cases with at least one day away from work. Part 1904 does not define LTIR, so use the definition your employer or client writes down.
- Severity rate = days lost × 200,000 ÷ hours worked. It measures how long cases keep people out, not how many there are. Use the same day count your employer uses, whether that is days away only or restricted days too.
All four are lagging indicators: they count what already happened. Read the OSHA recordkeeping (Part 1904) guide for what makes a case recordable, the forms and the reporting deadlines.
Why there is no EMR here
The experience modification rate (EMR) is set by your insurer or its rating bureau from claims history and payroll, not from hours worked. You cannot work it from the inputs above, so this tool leaves it out. Ask your insurer for the current figure.
Worked example 1: a small contractor
180,000 hours, 4 recordable cases, 2 of them DART cases, 1 with days away, and 18 days lost. TRIR = 4 × 200,000 ÷ 180,000 = 800,000 ÷ 180,000 = 4.44. DART rate = 2 × 200,000 ÷ 180,000 = 2.22. LTIR = 1 × 200,000 ÷ 180,000 = 1.11. Severity rate = 18 × 200,000 ÷ 180,000 = 20.00.
Worked example 2: a larger crew, one year
500,000 hours, 5 recordable cases, 3 DART cases, 2 lost time cases and 40 days lost. TRIR = 5 × 200,000 ÷ 500,000 = 2.00. DART rate = 3 × 200,000 ÷ 500,000 = 1.20. LTIR = 2 × 200,000 ÷ 500,000 = 0.80. Severity rate = 40 × 200,000 ÷ 500,000 = 16.00. Notice that 500,000 hours is 250 full-time workers at 2,000 hours each. The hours are invented, and so are the cases.
These are original arithmetic examples, not exam questions.
Incident rate questions
Is it 200,000 hours or 1,000,000 hours?
OSHA's incidence rate formula uses 200,000 hours, which is 100 full-time workers for a year. Some clients ask for rates per 1,000,000 hours. Multiply a 200,000-hour rate by 5 to convert it.
Is TRIR the same thing as DART?
No. TRIR counts every recordable case. DART counts only the cases with days away, restricted work or job transfer, so the DART rate is never higher than TRIR.
Where do I get my hours worked?
Use the hours your employees actually worked in the period. Form 300A asks for the same total next to your case counts, so the rate and the log agree.
The CHST blueprint lists recordkeeping and spotting trends in incidents under safety program development, so practice working a rate from hours and cases until it is automatic.