How to Calculate Severity Rate in Safety

Safety Severity Rate Calculator

The total number of days lost due to work-related injuries or illnesses in the period.

Total hours worked by all employees during the specific period.

OSHA Standard (200,000 hrs / 100 Employees) Mining/International (1,000,000 hrs)

OSHA uses 200,000 hours. Some international standards use 1,000,000.

function calculateSeverityRate() { var lostDaysInput = document.getElementById("lostDays"); var totalHoursInput = document.getElementById("totalHours"); var baseRateInput = document.getElementById("baseRate"); var resultBox = document.getElementById("resultBox"); var severityRateValue = document.getElementById("severityRateValue"); var severityExplanation = document.getElementById("severityExplanation"); var lostDays = parseFloat(lostDaysInput.value); var totalHours = parseFloat(totalHoursInput.value); var base = parseFloat(baseRateInput.value); // Validation if (isNaN(lostDays) || lostDays < 0) { alert("Please enter a valid number of lost workdays."); return; } if (isNaN(totalHours) || totalHours <= 0) { alert("Please enter a valid number of total hours worked (must be greater than 0)."); return; } // Calculation // Formula: (Lost Days * Base) / Total Hours var severityRate = (lostDays * base) / totalHours; // Formatting severityRateValue.innerHTML = severityRate.toFixed(2); resultBox.style.display = "block"; // Interpretation Logic var explanationText = ""; var multiplierLabel = base === 200000 ? "100 full-time employees" : "500 full-time employees"; explanationText += "This means that for every " + multiplierLabel + ", "; explanationText += "your organization loses " + severityRate.toFixed(2) + " days due to work-related injuries."; if (severityRate === 0) { explanationText += "Great Job! A zero severity rate indicates no lost time due to injuries."; } else if (severityRate > 0 && severityRate < 10) { explanationText += "Status: Your severity rate is relatively low, but aim for zero."; } else { explanationText += "Attention: A higher severity rate indicates that injuries occurring are resulting in significant time off. Review your high-risk areas immediately."; } severityExplanation.innerHTML = explanationText; }

In the field of Environmental, Health, and Safety (EHS), tracking performance metrics is essential for maintaining a safe workplace. While the frequency of accidents tells you how often incidents happen, the Severity Rate tells you how serious those incidents are.

This guide explains exactly how to calculate the severity rate, why it matters, and how to interpret the numbers using the standard OSHA formulas.

What is the Safety Severity Rate?

The Severity Rate (often called the Lost Time Severity Rate) is a calculation used to measure the average number of lost days per recordable incident or per a specific number of hours worked. It provides insight into the impact of injuries on the workforce and productivity.

Unlike the Incident Rate, which counts the number of accidents, the Severity Rate focuses on the consequences (time lost) of those accidents.

The Severity Rate Formula

The most common formula used, particularly under OSHA (Occupational Safety and Health Administration) guidelines, is based on 200,000 working hours. This number represents the equivalent of 100 employees working 40 hours a week for 50 weeks a year.

Severity Rate = (Total Lost Workdays × 200,000) / Total Employee Hours Worked

Variables defined:

• Total Lost Workdays: The sum of days employees were away from work due to work-related injury or illness.
• Total Employee Hours Worked: The actual hours worked by all employees (including overtime, minus vacation/leave) during the reporting period.
• 200,000: The standard base for 100 full-time equivalent (FTE) workers. Note: Some international or mining standards use 1,000,000 hours.

Example Calculation

Let's look at a practical example for a manufacturing plant.

• Scenario: In the year 2023, a company had 3 incidents resulting in lost time.
• Incident A: 5 days lost.
• Incident B: 12 days lost.
• Incident C: 3 days lost.
• Total Lost Workdays: 5 + 12 + 3 = 20 days.
• Total Hours Worked: The company has 150 employees who worked a total of 300,000 hours.

Calculation:

(20 × 200,000) / 300,000 = 13.33

This means for every 100 full-time employees, the company lost approximately 13.33 days of work due to injury.

Why Calculate Severity Rate?

Calculating the severity rate is vital for several reasons:

1. Identify High-Risk Areas: A high frequency rate with a low severity rate implies minor accidents. However, a high severity rate suggests that when accidents do happen, they are dangerous and costly.
2. Insurance and Costs: High severity rates often correlate with higher Workers' Compensation premiums.
3. Trend Analysis: Tracking this metric year-over-year helps EHS managers determine if safety interventions are effectively reducing the seriousness of injuries.

Severity Rate vs. Frequency Rate

It is important not to confuse Severity Rate with Frequency Rate (TRIR – Total Recordable Incident Rate):

• Frequency Rate: How often accidents happen.
• Severity Rate: How bad the accidents are (based on time lost).

A complete safety profile requires analyzing both metrics together. A company might have zero accidents for months (Low Frequency) but one major accident resulting in months of lost time (High Severity).

How to Improve Your Severity Rate

Reducing your severity rate requires a focus on hazard elimination and risk management:

• Conduct thorough Job Hazard Analyses (JHA) for tasks associated with severe injuries.
• Implement Return-to-Work programs to help injured employees reintegrate safely and sooner, reducing lost days.
• Focus on Leading Indicators (near-miss reporting, safety audits) rather than just reacting to Lagging Indicators (injury rates).