How to Calculate TRIR and DART (With the Actual Formula)

Your Total Recordable Incident Rate. Your DART rate. These two numbers appear in ISNetworld questionnaires, prequalification packages, and owner-client scorecards — and yet a surprising number of contractors calculate them wrong.

Sometimes the error works in their favor. Sometimes it doesn't. Either way, a miscalculated rate that doesn't match OSHA's records is a credibility problem with every hiring client who looks you up.

This page walks through both formulas with worked examples, industry benchmarks by NAICS code, and the six specific mistakes that inflate or deflate your numbers. Bookmark it — you'll need it at renewal time.

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The 200,000-Hour Baseline: Why That Number

Both TRIR and DART use 200,000 hours as a normalizing constant. It's not arbitrary.

200,000 hours represents the equivalent of 100 full-time employees working 40 hours a week for 50 weeks — 2,000 hours per employee per year, times 100 workers. It lets you compare incident rates across companies of different sizes on a level playing field.

A company with 8 employees and 2 incidents is not directly comparable to a company with 400 employees and 2 incidents. The formula corrects for that by expressing incidents per 100 full-time equivalent workers.

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TRIR: Total Recordable Incident Rate

The formula

TRIR = (Number of Recordable Incidents × 200,000) ÷ Total Hours Worked

A "recordable incident" is any work-related injury or illness that meets OSHA's criteria under 29 CFR 1904: medical treatment beyond first aid, days away from work, restricted duty or job transfer, loss of consciousness, or a significant injury or illness diagnosed by a healthcare professional.

Worked example — single year

Your company had 3 recordable incidents last year. Your employees worked a combined 85,000 hours.

TRIR = (3 × 200,000) ÷ 85,000
     = 600,000 ÷ 85,000
     = 7.06

A TRIR of 7.06 is above average for virtually every construction trade. Now see how one fewer incident changes the number:

TRIR = (2 × 200,000) ÷ 85,000
     = 400,000 ÷ 85,000
     = 4.71

And with one recordable incident:

TRIR = (1 × 200,000) ÷ 85,000
     = 200,000 ÷ 85,000
     = 2.35

This is why small companies feel every incident so acutely. At 85,000 annual hours, each recordable case adds roughly 2.35 points to your TRIR. A company running 500,000 annual hours adds only 0.40 per incident. Size is a natural stabilizer — small contractors are structurally disadvantaged in this metric.

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DART Rate: Days Away, Restricted, or Transferred

The formula

DART = (DART Cases × 200,000) ÷ Total Hours Worked

DART is a severity-weighted subset of TRIR. It counts only cases that resulted in days away from work, restricted duty, or job transfer. A recordable injury that was treated and the employee returned to full duty the same day counts in TRIR but not in DART.

Worked example

Of the 3 recordable incidents above, 2 resulted in days away from work or restricted duty assignments. The third was treated at urgent care and the employee returned to full duty the next morning.

DART = (2 × 200,000) ÷ 85,000
     = 400,000 ÷ 85,000
     = 4.71

What the TRIR–DART gap reveals

The spread between your TRIR and DART tells the story of your incident severity:

TRIR 5.0 / DART 4.8: Almost every incident involved significant time loss or restricted duty. High severity profile.

TRIR 5.0 / DART 0.8: Most incidents were minor — treated and back at full duty quickly. The TRIR is elevated but the severity is low. ISN clients read this gap.

A high DART relative to TRIR tends to trigger more scrutiny than the same TRIR with a low DART, because it suggests your incidents are causing real operational disruption.

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NAICS Industry Benchmarks

Your rates only matter relative to your industry. The Bureau of Labor Statistics publishes annual injury and illness incidence rates by NAICS code, and ISNetworld uses BLS data to benchmark your numbers. Here are representative figures from recent BLS reports for common contractor categories:

NAICS 2361 — Residential Building Construction: TRIR ~2.8, DART ~1.6

NAICS 2362 — Nonresidential Building Construction: TRIR ~2.5, DART ~1.4

NAICS 2371 — Utility System Construction: TRIR ~1.9, DART ~1.1

NAICS 2381 — Foundation, Structure, Building Exterior Contractors: TRIR ~3.1, DART ~1.9

NAICS 2382 — Building Equipment Contractors (MEP trades): TRIR ~2.1, DART ~1.2

NAICS 2383 — Building Finishing Contractors: TRIR ~2.6, DART ~1.5

NAICS 2389 — Other Specialty Trade Contractors: TRIR ~2.7, DART ~1.6

NAICS 2131 — Support Activities for Mining (oilfield services): TRIR ~1.5, DART ~0.9

These are approximate industry averages based on BLS data. Your specific ISNetworld clients may apply stricter thresholds — some oil and gas operators require TRIR below 1.0 as a hard qualification cutoff for certain work scopes.

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Why ISNetworld Clients Care About These Numbers

Hiring clients use TRIR and DART as filters, not just data points. Here's how they typically apply them:

• Hard cutoffs: Some clients set an absolute TRIR threshold — anything above it disqualifies a contractor from certain work scopes regardless of grade letter. These rules are often built into ISN's contractor management system automatically, so you may not even know you've been filtered out.
• Grade weighting: ISN's scoring algorithm uses your safety statistics as a significant input. An above-average TRIR can pull your overall score down enough to drop your grade letter — sometimes triggering the grade change notification email before you've filed any new documents.
• Three-year rolling average: Most clients evaluate your three-year average, not just the current year. One bad year is survivable with context. Three years above the industry average is a pattern that raises questions.
• Trend direction: A TRIR declining from 4.0 to 3.0 to 2.0 tells a different story than 2.0 to 3.0 to 4.0, even when the current year number is identical. ISN clients and safety managers read the trend.

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Six Common Mistakes Contractors Make in the Math

1. Using payroll hours instead of actual hours worked

Payroll hours — what gets reported for compensation purposes — frequently differ from actual exposure hours. If your crews work consistent overtime that payroll records at straight time, your hours-worked denominator is understated, which overstates your incident rate. Use actual timesheet records.

2. Excluding salaried employees and office staff

The total hours worked figure must include all employees who could generate a recordable case — salaried project managers, estimators, administrative staff, part-time workers, and temporary employees on your payroll. Counting only field crew hours understates your denominator and inflates your rate.

3. Including non-recordable cases in the incident count

First-aid-only cases are not OSHA recordable. If a case resulted only in first aid treatment, it does not go on Form 300 and does not go into your TRIR calculation. Adding it inflates your numerator.

4. Misclassifying restricted-duty cases as non-DART

If an injured employee was placed on any form of light duty — even informally — that case is a DART case if the restriction was related to the injury. "He just did phone calls for a week" counts if there was a physician recommendation or a company decision to restrict duties because of the injury. Informal restrictions are still restrictions.

5. Annualizing hours for a partial year

If your company was formed mid-year or you're reporting for a partial operating period, do not multiply partial-year hours to a full-year equivalent. Your rate reflects the actual period your employees worked. Annualizing would artificially deflate your rate for the startup year.

6. Inconsistent rounding

Report your rates to two decimal places. The difference between 1.99 and 2.01 can be the difference between passing and failing a client threshold. Rounding to one decimal place before submission obscures this. Use the unrounded calculation result, then round the final figure consistently.

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Bonus Metric: LTIR (Lost Time Incident Rate)

Some ISNetworld clients — particularly in upstream oil and gas and utilities — also ask for LTIR, the Lost Time Incident Rate. It counts only cases with actual days away from work, excluding restricted duty and job transfer cases.

LTIR = (Lost Time Cases × 200,000) ÷ Total Hours Worked

Using the example above with 1 lost-time case out of 3 total recordables:

LTIR = (1 × 200,000) ÷ 85,000
     = 200,000 ÷ 85,000
     = 2.35

LTIR is a narrower, higher-severity measure than DART. It's less commonly required in ISNetworld than TRIR and DART, but worth understanding if you work in industries where operators use all four metrics.

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Quick Reference: The Three Formulas

TRIR = (All Recordable Cases × 200,000) ÷ Total Hours Worked

DART = (Days Away + Restricted + Transferred Cases × 200,000) ÷ Total Hours Worked

LTIR = (Days Away from Work Cases × 200,000) ÷ Total Hours Worked

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Getting the Inputs Right Is the Hard Part

The formulas are simple division. The difficulty is accuracy in the inputs — correct incident classification, accurate hours-worked totals, and consistent methodology year over year. A single miscounted incident or a misreported hour total can move your rate by half a point, which is often the difference between being within a client's acceptable range and getting flagged.

ISNetworld stores three years of your reported rates. If your current-year submission looks inconsistent with prior years — a sudden large change in hours worked, or a DART rate that exceeds your TRIR — it raises questions with reviewers even if the math is technically correct.

If you want to verify your TRIR and DART calculations before submitting to ISNetworld, PrequalPilot calculates your rates automatically from the incident data you enter and flags inconsistencies with your historical numbers before your next renewal window opens.