Construction safety rate and exposure guide
Incidence rates put case counts on a common exposure basis: 200,000 hours, representing 100 full-time workers at 40 hours per week for 50 weeks. This supports comparison across periods or establishments with different work hours.
A rate is a lagging indicator, not a safety verdict. Correct classification of recordable and DART cases must come from OSHA recordkeeping rules and the establishment’s records.
How to calculate OSHA-style safety rates
- Set one reporting scope: Use one establishment and a consistent calendar or analysis period.
- Enter exposure: Copy total employee hours worked and average employment from reliable payroll or Form 300A records.
- Enter classified cases: Use case counts already classified under current OSHA recordkeeping criteria.
- Enter days: Add recorded days away and restricted or transfer days for the same scope.
- Review trends and events: Compare like periods, then investigate the hazards and events behind any change.
Formula and variables
Use the applicable case count for each rate. The combined day-severity indicator applies the same exposure factor to days away plus restricted or transfer days; it is an analytical measure rather than a substitute for required OSHA forms.
Rate = cases × 200,000 ÷ employee hours worked- N — Applicable cases or days
- Recordable cases, DART cases, days-away cases, or combined days for the selected metric.
- EH — Employee hours
- Total hours worked by all employees during the reporting period.
- 200,000 — Standard exposure base
- Hours for 100 employees working 40 hours per week for 50 weeks.
Worked example: annual safety rates
An establishment reports 400,000 hours, four recordable cases, two DART cases, one days-away case, and 30 combined days.
- Hours worked
- 400,000
- Recordable cases
- 4
- DART cases
- 2
- Combined days
- 30
- TRIR = 4 × 200,000 ÷ 400,000.
- DART = 2 × 200,000 ÷ 400,000.
- Day indicator = 30 × 200,000 ÷ 400,000.
Result: TRIR is 2.00, DART is 1.00, and the combined day-severity rate is 15.00.
These values normalize exposure; they do not by themselves identify cause, compliance, or future risk.
Understanding your results
TRIR
Total recordable cases per 100 full-time-equivalent workers on the 200,000-hour basis.
DART rate
Cases involving days away, restricted work activity, or job transfer on the same exposure basis.
Day severity indicator
Days away plus restricted or transfer days normalized by exposure. Use it consistently as an internal trend measure.
Assumptions
- All values cover the same establishment and reporting period.
- Hours include all employees whose cases are represented.
- Case classifications and recorded day counts are already correct.
- The 200,000-hour exposure base is used for each incidence rate.
Limitations
- Rates do not measure hazards, near misses, leading indicators or safety-culture quality.
- Small workforces can show large rate swings from one case.
- The calculator cannot determine whether an event is work-related or recordable.
- Results do not replace OSHA forms, required reporting, posting, retention or electronic submission.
Common mistakes
- Mixing case data and hours from different scopes or periods.
- Counting days instead of cases in TRIR or DART.
- Treating all incidents as OSHA-recordable without applying the criteria.
- Including vacation, sick leave or other non-worked hours in the exposure total.
- Comparing partial-year and full-year rates without context.
Practical use cases
Annual establishment review
Normalize completed Form 300A values for year-over-year discussion.
Contractor trend review
Compare a contractor’s own consistent periods while retaining case-level context.
Management dashboard
Pair lagging rates with corrective actions, observations, training and hazard-control leading indicators.
Planning and decision guide
Start with authoritative records
OSHA states that covered employers use Forms 300, 300A and 301 or equivalent forms. Reconcile entries before calculating rates.
Keep DART categories distinct
DART counts cases involving days away, restriction, or job transfer; do not add days to the case count.
Avoid ranking by one number
Interpret rates with workforce size, work mix, reporting maturity, event severity and exposure changes. Investigate individual cases and controls.
Frequently asked questions
What does 200,000 represent?
It represents 100 employees working 40 hours per week for 50 weeks, providing a standard exposure basis.
Is DART a count of days?
No. DART uses the number of cases involving days away, restriction or job transfer.
Are TRIR and DART enough to prove a site is safe?
No. They are lagging incidence measures and do not establish current conditions or compliance.
Can this calculator decide if a case is recordable?
No. Apply current OSHA recordkeeping criteria and seek qualified guidance for classification questions.
Why did the rate change sharply?
With low hours or few cases, a single added case can materially change a normalized rate. Review raw counts and exposure alongside the rate.
Sources and review
- OSHA Field Operations Manual, Chapter 3 — Manual DART Rate Calculation — Occupational Safety and Health Administration. Accessed 2026-07-18.
- Injury and Illness Recordkeeping Forms — Occupational Safety and Health Administration. Accessed 2026-07-18.
- Recording Work-Related Injuries and Illnesses — Occupational Safety and Health Administration. Accessed 2026-07-18.
Reviewed 2026-07-18.