Although injury and illness rates are trailing indicators, they can be useful as a measure in evaluating your organization's safety management system. Trailing indicators do not measure the most direct effects of a safety management system as do leading indicators (employee thoughts and behaviors, and workplace conditions).

To evaluate your firm’s injury-and-illness experience over time or to compare your firm’s experience with that of your industry as a whole, you need to compute your incidence rate. Incidence rates can help you identify problems in your workplace or progress made toward preventing work-related injuries and illnesses. This is also the information used by OSHA to calculate potential penalty reductions.

What is an incidence rate?

An incidence rate is the number of recordable injuries and illnesses occurring among a given number of full-time workers (usually 100 full-time workers) over a given period of time (usually one year).

How do I calculate an incidence rate? You can quickly and easily compute an occupational injury and illness incidence rate for all recordable cases or for cases that involved days away from work and days of restricted work using the following steps:

• Calculate total recordable injuries and illnesses. To find out the total number of recordable injuries and illnesses that occurred during the year — count the number of line entries on your OSHA Form 300 or refer to the OSHA Form 300A and sum the entries for columns (G), (H), (I), and (J).
• Calculate total workhours. The number of hours all employees actually worked during the year — refer to OSHA Form 300A and optional worksheet to calculate this number.
• Calculate the DART Rate. The "DART" (Days Away, Restricted, or Job Transferred) is used to express the incident rate. To determine the DART Rate, count the number of line entries on your OSHA Form 300 that received a check mark in columns (H) and (I), or refer to the entry in columns (H) and (I) on the OSHA Form 300A.

You can compute the incidence rate for all recordable cases of injuries and illnesses using the following formula:

Total number of injuries and illnesses (N) ÷ number of hours worked by all employees (EH) x 200,000 hours = total recordable case rate.

(The 200,000 figure in the formula represents the number of hours 100 employees working 40 hours per week, 50 weeks per year would work and provides the standard base for calculating incidence rates.)

You can compute the incidence rate for recordable cases involving days away from work, days of restricted work activity, or job transfer using the following formula:

For instance, if you have 50 employees who work a total of 100,000 hours during the year and have experienced 10 recordable injuries, the DART rate would be (10 ÷ 100,000) x 200,000 = 20. The number of employees doesn't matter. The total number of injuries and the total number of hours the employees work during the year are the two important figures entered into the formula.

You can use the same formula to calculate incidence rates for other variables such as cases involving restricted work activity (column (I) on OSHA Form 300A), cases involving skin disorders (column (M-2) on OSHA Form 300A), etc. Just substitute the appropriate total for these cases, from OSHA Form 300A, into the formula in place of the total number of injuries and illnesses.

What can I compare my incidence rate to?

The Bureau of Labor Statistics (BLS) conducts a survey of occupational injuries and illnesses each year and publishes incidence-rate data by various classifications (e.g., by industry, by employer size, etc.). You can get the data at www.bls.gov or by calling a BLS regional office, or by visiting www.cbs.state.or.us/imd to look at OSHA reports.

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