Severity Rate (SR) – Complete Guide for Safety Professionals
Measuring workplace safety isn’t just about knowing how often accidents happen — it’s also about understanding how serious those accidents are. That’s where the Severity Rate (SR) comes in.
The Severity Rate (SR) is a key performance indicator (KPI) used by safety professionals worldwide to measure the impact of accidents in terms of lost workdays. While Frequency Rate (FR) tells us how often injuries occur, SR tells us how severe they are.
This guide provides a comprehensive explanation of Severity Rate (SR) — including its definition, formula, calculation, importance, advantages, limitations, comparisons with FR and IR, case studies, and FAQs.
🔹 What is Severity Rate (SR)?
Severity Rate (SR) is a safety metric that indicates the number of workdays lost due to injuries per one million hours worked.
👉 In simple terms:
SR shows how much productive time is lost because of workplace accidents.
- ILO Definition: According to the International Labour Organization (ILO), severity rate represents the number of days lost due to disabling injuries per 1,000,000 hours worked.
- Industry Use: SR is used in construction, oil & gas, manufacturing, mining, and by regulatory authorities as a measure of accident seriousness.
🔹 Formula for Severity Rate (SR)
SR = (Lost Workdays × 1,000,000) ÷ Total Manhours Worked
Where:
- Lost Workdays = Total number of days lost due to occupational injuries.
- Total Manhours Worked = Combined hours worked by all employees, contractors, and inducted visitors.
- 1,000,000 = Standard multiplier chosen by ILO to standardize results.
🔹 Why 1,000,000?
Just like Frequency Rate (FR), the 1,000,000 multiplier is used to normalize data across different workforce sizes.
- One full-time worker works ≈ 2,000 hours/year (40 hrs/week × 50 weeks).
- For 500 workers, this equals:
500 × 2,000 = 1,000,000 hours
👉 So SR answers:
“How many workdays would be lost if 500 full-time workers worked for one year?”
🔹 Example of Severity Rate (SR) Calculation
Example 1:
- Lost days = 60
- Total manhours = 500,000
SR = (60 × 1,000,000) ÷ 500,000
SR = 120.0
✅ This means 120 lost days per 1 million hours worked.
Example 2:
- Lost days = 300
- Total manhours = 5,000,000
SR = (300 × 1,000,000) ÷ 5,000,000
SR = 60.0
✅ This means the project had a Severity Rate of 60.0.
🔹 Importance of Severity Rate (SR)
- Measures Impact of Accidents – Shows how much productive time is lost.
- Supports Safety Management – Helps prioritize corrective actions.
- Regulatory Reporting – Many industries require SR reporting.
- Benchmarking – Companies compare SR to industry averages.
- Decision-Making – A high SR signals that even if few accidents occur, their seriousness is high.
🔹 SR in Different Industries
- Construction: SR is used to assess contractor performance and accident consequences.
- Oil & Gas: Part of international safety reporting (IOGP).
- Manufacturing: Used to evaluate lost productivity from accidents.
- Government: Required by many labor and safety authorities.
🔹 Limitations of Severity Rate (SR)
- Does Not Show Frequency: A company may have very few accidents, but if one accident causes long absences, SR will be high.
- Lagging Indicator: It measures past performance, not future risks.
- Different Counting Rules: Some organizations count calendar days lost, others count working days.
- May Be Distorted: A single severe accident (e.g., fatality) can inflate SR dramatically.
🔹 Frequency Rate (FR) vs Severity Rate (SR)
| Aspect | Frequency Rate (FR) | Severity Rate (SR) |
|---|---|---|
| Definition | Number of injuries per 1,000,000 hours worked | Number of lost days per 1,000,000 hours worked |
| Focus | Accident frequency | Accident seriousness |
| Formula | FR = (Injuries × 1,000,000) ÷ Manhours | SR = (Lost Days × 1,000,000) ÷ Manhours |
| Use | Compare how often injuries occur | Compare how severe accidents are |
| Best Together | FR + SR = complete picture of safety performance |
👉 In short:
- FR tells you “how often” accidents happen.
- SR tells you “how bad” they are.
🔹 SR vs IR (OSHA Incident Rate)
- SR (ILO): Uses 1,000,000 hrs base, focuses on lost days.
- IR (OSHA): Uses 200,000 hrs base, focuses on recordable cases (not lost days).
So SR is about impact, while IR is about number of cases.
🔹 Factors Affecting Severity Rate
- Nature of Work – High-risk jobs (heights, confined space) have more severe injuries.
- Type of Accidents – Falls and electrical shocks cause more lost days than minor cuts.
- Medical Care Quality – Faster recovery reduces lost days.
- Reporting Practices – Different rules for counting lost days.
- Workforce Size – Smaller projects may show fluctuating SR values.
🔹 How to Reduce Severity Rate
- Improve emergency preparedness to reduce recovery times.
- Enforce strict safety rules for high-risk activities.
- Provide PPE and ensure compliance.
- Conduct regular training and mock drills.
- Establish return-to-work programs to minimize lost days.
- Investigate accidents thoroughly and prevent recurrence.
🔹 Severity Rate in Safety Reports
- Monthly Reports: SR is presented alongside FR.
- Annual HSE Reports: Companies highlight low SR as proof of effective safety systems.
- Client Evaluations: SR is often part of contractor performance scoring.
- On-Site Boards: Displayed along with Safe Manhours and FR.
🔹 Case Study Example
A petrochemical plant logged 3,000,000 manhours in one year. During this period:
- 12 injuries occurred.
- 400 workdays were lost.
Calculations:
FR = (12 × 1,000,000) ÷ 3,000,000 = 4.0
SR = (400 × 1,000,000) ÷ 3,000,000 = 133.3
👉 Interpretation:
- FR = 4.0 (moderate frequency).
- SR = 133.3 (high severity → indicates accidents caused serious downtime).
🔹 How to Calculate Severity Rate Using Online Tools
Manually calculating Severity Rate (SR) can sometimes be confusing, especially when dealing with large projects with thousands of workers and millions of manhours. To make this process easier, we’ve built a free online Severity Rate Calculator Tool at our second website The HSE Tools.
✅ Steps to Use the Severity Rate Tool
- Go to The HSE Tools → Severity Rate Calculator.
- Enter the following values in the tool:
- Total Lost Workdays
- Total Manhours Worked
- Click Calculate.
- The tool will instantly show the Severity Rate (SR) result.
- You can also download a PDF report of the calculation for documentation, audits, or monthly HSE reporting.
👉 Example:
- Lost Workdays = 300
- Total Manhours Worked = 5,000,000
Enter these into the tool, and the calculator will display:
SR = (300 × 1,000,000) ÷ 5,000,000 = 60.0
And you can download this result as a professional PDF directly.
🔹 Why Use The HSE Tools?
- ✅ Accurate & Instant Results – No manual calculation errors.
- ✅ Free PDF Downloads – Professional reports for audits & client submissions.
- ✅ Mobile-Friendly – Use directly on-site from your phone.
- ✅ Multiple Safety Tools Available – Not just Severity Rate, but also Frequency Rate (FR), Incident Rate (IR), Safe Manhours, Job Safety Analysis (JSA), and more.
🔗 Try it now: Severity Rate Calculator – The HSE Tools
🔹 FAQs on Severity Rate (SR)
Q1. Is Severity Rate mandatory?
Yes, in most industries it’s required for monthly/annual reporting.
Q2. Do fatalities affect SR?
Yes. Many organizations assign 6,000 lost days for each fatality, which heavily impacts SR.
Q3. What is a good Severity Rate?
A low SR indicates safer workplaces with fewer lost days.
Q4. Does SR include first aid cases?
No, SR only counts lost workdays.
Q5. Can SR be zero?
Yes, if no workdays were lost during the reporting period.
🔹 Conclusion
Severity Rate (SR) is a vital safety metric that shows how serious accidents are in terms of lost workdays. By normalizing results per 1,000,000 hours worked, SR enables fair comparisons across projects and industries.
When used alongside Frequency Rate (FR) and Incident Rate (IR), it provides a complete picture of workplace safety performance.
👉 Key takeaway:
- FR = How often accidents happen.
- SR = How severe accidents are.
- IR = OSHA’s case-based rate.
For safety professionals and students (NEBOSH, OSHA, Fire & Safety), mastering SR is crucial for both reporting and career growth.
🔗 External Reference
For further reading: International Labour Organization (ILO) – Safety and Health Statistics
Frequency Rate (FR) – Complete Guide for Safety Professionals
How to Calculate the Safe Working Load (SWL) of a Lifting Sling
Crane Safety: How to Calculate Capacity?
