200,000 (OSHA / 100 Employees)
1,000,000 (International Standard)
Accident Severity Rate (ASR)
0.00
function calculateSeverityRate() {
// Get input values
var lostDaysInput = document.getElementById('totalLostDays');
var manHoursInput = document.getElementById('totalManHours');
var baseSelect = document.getElementById('benchmarkBase');
var resultBox = document.getElementById('asrResult');
var resultValue = document.getElementById('asrValue');
var resultSummary = document.getElementById('asrSummary');
// Parse values
var lostDays = parseFloat(lostDaysInput.value);
var manHours = parseFloat(manHoursInput.value);
var baseConstant = parseFloat(baseSelect.value);
// Validation
if (isNaN(lostDays) || lostDays < 0) {
alert("Please enter a valid number for Total Lost Workdays.");
return;
}
if (isNaN(manHours) || manHours <= 0) {
alert("Please enter a valid number for Total Man-Hours Worked (must be greater than 0).");
return;
}
// Calculation Formula: (Lost Days * Constant) / Man Hours
var severityRate = (lostDays * baseConstant) / manHours;
// Formatting result
// If result is very small, show more decimals, otherwise standard 2
var displayRate = severityRate.toFixed(2);
// Determine context for summary
var baseText = (baseConstant === 200000) ? "200,000 hours (approx. 100 FTEs)" : "1,000,000 hours";
// Update DOM
resultBox.style.display = "block";
resultValue.innerHTML = displayRate;
resultSummary.innerHTML = "This score indicates that for every " + baseText + " worked, " + displayRate + " days were lost due to workplace incidents.";
}
How to Calculate Accident Severity Rate
The Accident Severity Rate (ASR) is a critical Key Performance Indicator (KPI) in Environmental, Health, and Safety (EHS) management. Unlike frequency rates, which tell you how often accidents happen, the severity rate tells you how serious those accidents are by measuring the amount of lost time they cause.
The Accident Severity Rate Formula
To calculate the severity rate, you need three specific data points: the total number of lost workdays, the total number of man-hours worked by all employees, and a multiplication constant (standardization factor).
The standard formula is:
ASR = (Total Lost Workdays × Constant) / Total Man-Hours Worked
Variables defined:
Total Lost Workdays: The sum of all days employees could not work due to work-related injuries or illnesses during the reporting period. Note: Some standards assign specific "chargeable days" for permanent disabilities or fatalities (e.g., ANSI standards).
Total Man-Hours Worked: The actual number of hours worked by all employees during the specific time period (excluding vacations, holidays, and sick leave).
Constant:
200,000: Used primarily by OSHA in the USA. It represents 100 employees working 40 hours a week for 50 weeks.
1,000,000: Often used in international standards to represent 500 full-time employees.
Why is Accident Severity Rate Important?
Calculating your ASR provides deeper insight into your safety culture than frequency rates alone. A company might have a low frequency of accidents (few incidents) but a high severity rate. This indicates that while accidents are rare, when they do occur, they are catastrophic.
Monitoring ASR helps safety managers:
Identify high-risk departments where severe injuries are occurring.
Justify budgets for safety equipment and training.
Compare safety performance against industry benchmarks.
Track the effectiveness of return-to-work programs.
Example Calculation
Let's assume a manufacturing plant has the following data for the year:
Total Lost Days: 45 days (due to 3 separate incidents)
Total Hours Worked: 500,000 hours
Constant: 200,000 (OSHA standard)
Calculation:
(45 × 200,000) / 500,000 = 18
This result means that for every 200,000 hours worked at the plant, 18 days are lost due to injury. By using the calculator above, you can quickly input your monthly or annual figures to track this trend over time.
Frequency Rate vs. Severity Rate
It is best practice to report ASR alongside the Lost Time Injury Frequency Rate (LTIFR). The Frequency Rate measures the probability of an accident, while the Severity Rate measures the consequence. A high frequency with low severity suggests minor process issues (slips/trips), while low frequency with high severity suggests critical hazard failures (machinery/chemical).