In the field of Occupational Health and Safety (OHS), the Severity Rate (often referred to as the Lost Workday Rate) is a critical Key Performance Indicator (KPI). Unlike the Frequency Rate, which counts how many accidents happened, the Severity Rate measures how serious those accidents were by calculating the amount of time lost.
This calculator helps safety managers, HR professionals, and site supervisors quickly determine the severity rate of workplace incidents based on OSHA or international standards.
Severity Rate Calculator
Total number of days employees could not work due to injury.
Total hours worked by all employees during the period.
OSHA Standard (200,000 hours)
International / Million Hours (1,000,000 hours)
200,000 represents 100 employees working 40hrs/week for 50 weeks.
Calculated Severity Rate:
0.00
function calculateSeverity() {
// Get input values
var daysLostInput = document.getElementById('daysLost').value;
var totalHoursInput = document.getElementById('totalHours').value;
var baseConstant = parseFloat(document.getElementById('baseConstant').value);
// Parse values
var daysLost = parseFloat(daysLostInput);
var totalHours = parseFloat(totalHoursInput);
// Validation
if (isNaN(daysLost) || isNaN(totalHours) || totalHours <= 0) {
alert("Please enter valid positive numbers for Days Lost and Total Hours.");
return;
}
// Calculation Logic
// Formula: (Days Lost * Constant) / Total Hours
var severityRate = (daysLost * baseConstant) / totalHours;
// Formatting logic: round to 2 decimal places
var formattedRate = severityRate.toFixed(2);
// Display Result
var resultBox = document.getElementById('severity-result-box');
var resultValue = document.getElementById('finalResult');
var explanation = document.getElementById('result-explanation');
resultBox.style.display = 'block';
resultValue.innerText = formattedRate;
// Dynamic explanation based on the constant used
var standardText = baseConstant === 200000 ? "per 100 full-time employees" : "per 1,000,000 hours worked";
explanation.innerHTML = "This indicates that for every " + baseConstant.toLocaleString() + " hours worked, " + formattedRate + " days were lost due to injury.";
}
How to Calculate Severity Rate
The severity rate is calculated using a standard formula that normalizes the data, allowing companies of different sizes to compare their safety performance. The formula determines the number of lost days experienced per a set number of working hours.
Severity Rate = (Total Days Lost × 200,000) ÷ Total Hours Worked
Understanding the Variables
Total Days Lost: The aggregate sum of all days that employees were unable to work due to work-related injuries or illnesses during the reporting period.
Total Hours Worked: The sum of all actual hours worked by all employees. This should exclude vacation, sick leave, and holidays.
The Constant (200,000 vs. 1,000,000):
200,000: This is the OSHA standard base. It represents the equivalent of 100 employees working 40 hours a week for 50 weeks a year ($100 \times 40 \times 50 = 200,000$).
1,000,000: Used in some international contexts to measure the rate per million hours worked.
Severity Rate Calculation Example
To better understand the calculation, let's look at a realistic scenario for a mid-sized manufacturing plant.
Scenario:
A company has 500 employees.
In one year, they worked a total of 1,000,000 hours.
During that year, there were 3 accidents resulting in lost time:
Accident A: 5 days lost
Accident B: 20 days lost
Accident C: 2 days lost
Step 1: Sum the Lost Days
$5 + 20 + 2 = 27 \text{ Total Days Lost}$
Step 2: Apply the Formula (OSHA Standard)
$$ \text{Severity Rate} = \frac{27 \times 200,000}{1,000,000} $$
Result: The Severity Rate is 5.4. This means that for every 100 full-time equivalent workers, 5.4 days of work were lost due to injury that year.
Why is Severity Rate Important?
While the Frequency Rate tells you how often accidents happen, it treats a minor cut requiring a bandage the same as a major fracture requiring months of recovery (if both result in lost time). The Severity Rate gives weight to the incident. A low frequency but high severity rate indicates that accidents are rare, but when they do occur, they are catastrophic.
Interpretating Your Results
High Severity Rate: Indicates serious risks in the workplace that result in long recovery times. Immediate investigation into high-risk machinery or processes is needed.
Low Severity Rate: Indicates that while accidents may occur, they are generally minor in nature.