What the rates mean
Each rate is the number of cases you'd expect per 100 full-time workers in a year. The 200,000 in the formula is 100 workers at 40 hours a week for 50 weeks. That's what lets a 12-person sub and a 900-person GC compare numbers.
- TRIR counts every OSHA recordable case.
- DART counts the recordable cases with days away from work, restricted duty or a job transfer.
- Lost-time rate here counts days-away cases only. Some owners define it differently, so check their prequalification form.
Which cases count
Use the cases on your OSHA 300 log for the same period as the hours. A first-aid case isn't recordable. A case is recordable when it involves days away, restricted work or a transfer, medical treatment beyond first aid, loss of consciousness, or a significant diagnosed injury or illness. The full rule is in 29 CFR 1904.7.
An example
A crew of 50 works 10-hour days for 200 days: 100,000 hours. Two recordables in that time gives a TRIR of 2 × 200,000 ÷ 100,000 = 4.00. If one of them had restricted duty, the DART rate is 2.00.
Hours are where it goes wrong
Use the hours actually worked, from payroll or timekeeping, not hours paid. Leave out vacation, holidays and sick leave. When you can't get exact hours, the estimate above is fine for planning, but say it's an estimate if the number goes on a prequalification form.