An incident rate converts a raw count of injuries into a figure scaled to exposure, so that a 40-worker renovation firm and a 2,000-worker civil contractor can be compared fairly. The method you choose depends on who will read the number. US-style rates use 200,000 hours as the base, Singapore’s Ministry of Manpower (MOM) publishes frequency and severity rates per million man-hours, and its headline injury rate is expressed per 100,000 workers. This guide sets out each formula, a worked example, and the errors that most often distort the result.
TL;DR
- OSHA-style incident rate = (injuries and illnesses × 200,000) ÷ hours worked. The base equals 100 full-time workers over a year.
- Singapore’s Workplace Injury Rate = (injuries ÷ workers) × 100,000, while the accident frequency rate and severity rate use a base of 1,000,000 man-hours.
- Always divide by exposure. A higher injury count can coincide with better performance if hours worked grew faster.
- Keep the definition, period and denominator constant, or trend comparisons become meaningless.
- Rates are lagging indicators. Pair them with hazard identification, near-miss reporting and audits.
Table of Contents
- Why raw incident counts mislead
- The four formulas construction firms use
- A worked example
- Collecting clean inputs
- Common errors
- From rate to management: what the number cannot tell you
- Our perspective
- How MOSAIC supports measurement and improvement
- A practical monthly routine
- FAQ
- Sources
Why raw incident counts mislead
Two contractors each report five injuries in a year. One logged 150,000 hours, the other 900,000. Their counts are identical, but their risk profiles are not. Long-standing labor statistics guidance makes the same point: a rising injury count may reflect improved safety if exposure grew at a faster pace.
The US Bureau of Labor Statistics notes that incidence rates, because they share a common base and period, can show relative levels of injuries among industries, firms or operations within a single firm. That second use matters in construction, where one company may run a tower project, a fit-out and an infrastructure job at once, each with a different hazard profile.
The four formulas construction firms use
The OSHA-style total recordable incident rate
This is the formula most search results describe. As the BLS field definitions state, the calculation is (N ÷ EH) × 200,000, where N is the number of injuries and illnesses and EH is the total hours worked by all employees in the period. The constant of 200,000 represents 100 full-time employees working 40 hours a week for 50 weeks, so the result reads as injuries per 100 full-time workers per year.
The same structure produces variants by changing the numerator: count only lost-time cases for a lost workday case rate, or sum the days lost for a severity rate.
Singapore’s accident frequency rate and severity rate
MOM’s national statistics define the accident frequency rate (AFR) as the number of workplace accidents reported divided by man-hours worked, multiplied by 1,000,000. The accident severity rate (ASR) is man-days lost to workplace accidents divided by man-hours worked, also multiplied by 1,000,000. Both definitions appear in the Workplace Safety and Health Report 2018, which also reported 1.6 incidents per million man-hours for that year.
This answers a question readers often raise: whether the base is 200,000 or 1,000,000. Both are legitimate. The 200,000 base belongs to the OSHA convention, and the 1,000,000 base is used for AFR and LTIFR in Singapore and in many corporate reports. State your base beside every figure.
Singapore’s Workplace Injury Rate
Singapore’s headline measure uses workers, not hours. The WSH Performance Awards guidelines define it as (number of injuries ÷ number of workers) × 100,000. The same guidelines distinguish fatal, major (such as fractures and amputations) and minor injuries (any medical leave or light duties), so the numerator must be classified before it is counted.
Because the denominator is headcount, this rate cannot be compared directly with an hours-based rate. A firm using heavy overtime or many short-term workers will see the two diverge.
Quick comparison
| Measure | Formula | Base | Typical use |
|---|---|---|---|
| OSHA-style incident rate | Injuries × 200,000 ÷ hours | 200,000 hours | International clients, US-linked contracts |
| Accident frequency rate (AFR) | Accidents × 1,000,000 ÷ man-hours | 1,000,000 hours | Singapore national statistics, corporate reports |
| Accident severity rate (ASR) | Man-days lost × 1,000,000 ÷ man-hours | 1,000,000 hours | Measuring consequence, not just count |
| Workplace Injury Rate (WIR) | Injuries ÷ workers × 100,000 | 100,000 workers | MOM sector comparison, WSH award applications |
A worked example
The figures below are illustrative, not drawn from any real company. A contractor has 150 workers on its payroll and logs 310,000 hours across all sites in a year. It records four reportable injuries, which together cost 38 days of lost work.
- OSHA-style rate: 4 × 200,000 ÷ 310,000 = 2.58 injuries per 100 full-time workers.
- Accident frequency rate: 4 × 1,000,000 ÷ 310,000 = 12.90 per million man-hours.
- Accident severity rate: 38 × 1,000,000 ÷ 310,000 = 122.58 man-days lost per million man-hours.
- Workplace Injury Rate: 4 ÷ 150 × 100,000 = 2,666.7 injuries per 100,000 workers.
The four outputs look very different, yet all describe the same year. The lesson is that the figure is only meaningful with its formula. When a client’s prequalification form asks for “incident rate”, confirm which one it means before submitting.
How to interpret the result
An isolated figure has little value. Compare it against three references: your own prior periods, the same measure for your sector, and the rate across your individual projects. MOM reports that the construction sector’s fatal and major injury rate fell from 31.0 per 100,000 workers in 2024 to 26.3 in 2025. That benchmark is specific to fatal and major injuries. If your own rate includes minor injuries, it will be far higher and must not be set against that number.
Small firms should be especially cautious. With four injuries, one additional case changes the rate by 25 percent, so look at rolling twelve-month figures rather than reacting to a single quarter.
Collecting clean inputs
The arithmetic is simple, and the data are not. Most distortions arise in four places.
Hours worked
Count actual hours on site, including overtime, for employees and for subcontractor workers under your control. Where timesheets are unavailable, a documented estimate (workers × days × shift length) is acceptable only if applied consistently. Do not use contracted hours when overtime is routine.
Case definition
Decide in writing which events enter the numerator: fatal, major, minor with medical leave, light duty, dangerous occurrences. In Singapore, MOM’s categories are the natural starting point, and the guide to reporting workplace accidents explains which incidents must be notified. The WSH Performance Awards guidelines also note that incident reports can be purchased from MOM’s WSH Incident Reporting eService to verify internal records, a useful check before any external submission.
Subcontractors and project-based work
Construction headcount fluctuates by phase. A research paper on a project-based incident rate was among the ranking results, but its method is not needed here. The practical rule is simpler: calculate per project as well as per company, then aggregate by summing injuries and hours, never by averaging project rates.
Time period
Use calendar or financial years consistently. For projects, report from mobilization to handover.
Common errors
- Averaging rates. Two project rates cannot be averaged without weighting by hours.
- Mixing bases. Quoting an AFR of 12.9 beside a sector figure per 100,000 workers.
- Excluding subcontractors. This lowers the numerator and the denominator unevenly and flatters the result.
- Reading low rates as proof of safety. Under-reporting produces an excellent rate and a dangerous site.
- Chasing the number. Pressure to hit a target can suppress reporting, which is the opposite of what the metric is for.
From rate to management: what the number cannot tell you
Incident rates are lagging indicators. They describe harm that has already occurred. ISO 45001 frames performance as monitoring incidents, near misses and performance indicators, with regular review and improvement of the system. A Plan-Do-Check-Act cycle is the underlying logic: check results, then act when they fall short.
In practice, add leading indicators beside the rate: the share of planned inspections completed, near-miss reports per 100,000 hours, closure time for corrective actions, and toolbox-talk attendance. A rising near-miss count with a falling injury rate usually signals a healthy reporting culture. The reverse deserves scrutiny.
Regulatory attention is also relevant. In its 2025 review, MOM reported that nine firms were issued stop-work orders because their safety management systems were found deficient, in its answer on construction fatalities in the second half of 2024. A rate on a dashboard does not substitute for a functioning system. Our guide to workplace safety and health management systems covers that structure, and the risk assessment guide for managers addresses the proactive side.
Our perspective
In our work with construction firms, the most frequent weakness is not the formula but the inputs and the use made of the output. Firms compute a rate once a year for a tender submission, with hours reconstructed from payroll and subcontractor data missing. The figure is then filed and forgotten.
We advise treating the rate as an audit trail. Define the case categories once, record hours monthly by project, reconcile injury records against statutory notifications, and review the trend at management level each quarter. When rate and system disagree, for example a very low rate and weak inspection records, we trust the inspection records and investigate reporting.
We also encourage design-stage thinking. A rate improves most durably when hazards are removed before work begins, which is the purpose of Design for Safety, rather than controlled by supervision after the fact.
— Aman
How MOSAIC supports measurement and improvement
MOSAIC Ecoconstruction Solutions provides Quality, Environment and Safety consultancy for the construction sector. For firms that want their incident data validated and acted on, the WSH audit and inspection service examines records, site conditions and the management system behind the numbers. Companies pursuing certification can also review our bizSAFE Level 3, 4 and Star support, where consistent performance monitoring is part of the evidence base. To discuss your own reporting framework, contact us through the consultancy page. Pricing is not published, and scope is agreed per engagement. See also our safety audit examples.
A practical monthly routine
- Collect hours from timesheets by project and by employer (own staff and subcontractors).
- Log every incident with its category and days lost.
- Reconcile against notifications made to MOM.
- Calculate AFR, ASR and, if clients request it, the OSHA-style rate. Record the formula used.
- Compute the rolling twelve-month figure and compare with the prior year.
- Review leading indicators next to the rates, and assign owners to corrective actions.
A spreadsheet is sufficient. Consistency matters more than tooling.
FAQ
Is an incident rate a percentage?
No. It is a ratio scaled to a standard base, such as injuries per 200,000 hours or per 100,000 workers. Reading it as a percentage is a common mistake. An OSHA-style rate of 2.58 means roughly 2.58 injuries per 100 full-time workers per year.
Is LTIFR calculated per 200,000 or 1,000,000 hours?
Both conventions exist. The OSHA tradition uses 200,000, while many corporate and Singapore-style frequency measures use 1,000,000. Neither is wrong, but the two cannot be compared, so always state the base alongside the figure.
Which rate should a Singapore contractor use?
Use MOM’s definitions for anything compared with national or sector statistics: the Workplace Injury Rate per 100,000 workers, and AFR and ASR per million man-hours. Use the 200,000-hour formula only when a client or foreign parent company requests it. Reporting both, clearly labeled, is the safest approach.
Should subcontractor hours be included?
Generally yes, for workers under your control on your sites, because they are exposed to the same hazards. Document the rule you apply and keep it constant between periods.
Sources
- BLS: How to compute your firm’s incidence rate
- BLS: Occupational safety and health field definitions
- Accident Record Manual for Industrial Plants (FRASER)
- MOM: Workplace Safety and Health Report 2018
- WSH Performance Awards 2026 application guidelines
- MOM: WSH Report 2025 press release
- MOM: Oral answer on construction fatalities in 2H 2024
- ISO 45001 explained
- BSI: Health and Safety, the little book
