What Is an OSHA Severity Rate?

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A severity rate is a calculation used to examine the safety performance of an organization, shift or department. Numbers used in the calculation come from a record-keeping device required by the Occupational Safety and Health Administration (OSHA). It is called the OSHA 300 log.

Lost Days

The most important number used to calculate a severity rate is the number of lost work days a company has. Lost work days occur when an occupational injury or illness prevents an employee from working his full, assigned work shift. Occupational injuries include those that go beyond basic first aid, such as injuries requiring sutures, prescription medications or repairing broken bones. Occupational illnesses may result from exposure to dust, heat, fumes or other work-related conditions.


The severity rate describes the number of lost work days experienced per 100 workers. The actual number of lost work days times 200,000 (a standardized estimate of the hours worked by 100 employees) divided by the actual, total number of hours worked by all employees results in the severity rate. So, a company with 85 lost work days over 750,000 hours worked would have a severity rate of 22.7.

What It Means

The severity rate is meant to show the extent of safety problems by exposing how critical each injury and illness is. The premise is that an employee who must miss time from work to heal and recover has a more severe problem than one who can immediately return to work.

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