Injury Severity Rate

Injury severity rate, abbreviated as ISR, is used to measure the severity of workplace injuries and illnesses within a specific period.  Unlike the injury frequency rate (IFR), which focuses on the frequency of injuries, the ISR considers the seriousness or severity of those injuries.

The formula to calculate the ISR varies depending on the methodology used by different organizations.  However, a common approach is to assign a severity rating to each injury or illness based on factors such as medical treatment required, days away from work, or lost workdays, and then calculate a rate based on these severity ratings.

Like the IFR, the ISR provides organizations with valuable insights into the effectiveness of their safety programs and helps identify areas for improvement in preventing and managing workplace injuries and illnesses.  A lower ISR indicates lower severity of injuries relative to the number of hours worked, which suggests better safety outcomes.  Conversely, a higher ISR suggests more severe injuries and may indicate the need for enhanced safety measures and intervention strategies

 

Injury Severity Rate formula The constant 200,000 - Used to normalize the rate to the number of lost workdays that would occur if 100 employees worked full time for a year (200,000 hours).

\( ISR =  TNDL \; 200,000 \;/\; THW \)

Symbol

\( ISR \) = injury severity rate

\( TNDL \) = total number of days lost due to work injuries

\( THW \) = total hours worked