Apr 25 2012

LTIFR, LTIIR and Severity Rates – Calculating Common Safety Indicators

Calculating LTIFRKnowing how to calculate LTIFR and other safety indicators is an important skill to have if you work in the health and safety field. Despite these not revealing a great deal of useful information, managers love them and will insist on knowing what they are. They will use them to measure internal health and safety performance and to compare your company’s performance with other companies.

Commonly used safety indicators such as the LTIFR are not difficult to calculate and this is even easier if you use a spread sheet.

Health and Safety Indicators

Broadly speaking, there are two types of common health and safety indicators – frequency rates such as the LTIFR and incidence rates – such as the LTIIR. So what’s the difference?

A frequency rate shows how many events happened over a given period by a standardised number of hours worked. An incidence rate is how many events happened over a given period time by a standardised number of employees (usually lower than the standardised number of hours). For example, the LTIFR which stands for Lost Time Injury Frequency Rate, is how many Lost Time Injuries (LTI) occurred over a specified period per 1 000 000 or 100 000 (or some other number) hours worked in that period. This could be over a month or a quarter or a year depending on the reporting requirements of your business. To convert this to an incidence rate just substitute the number of employees for the number of hours.

These formulas are used to calculate other safety indicators as well as LTIFR there are Medical Treatment Injuries (MTI), another is significant injuries which are often categorized as LTIs plus MTIs. A slight variation is the severity rate which is usually a measure of the amount of time lost due to work related injury divided by the number of LTIs to produce and average amount of lost time. This is often called the severity rate.

Calculating LTIFR Rates

The formula to calculate LTIFR is really very simple. Let’s say we want to know how many lost time injuries per 1 000 000 hours worked there were for the last year. You need to get two pieces of information – the number of LTIs that happened in the last year and the number of hours worked in the last year. You could probably get the number of LTIs from your workers compensation claims manager or insurance company and your payroll section should be able to tell you the number of hours worked over the period.

Multiply the number of LTIs by 1 000 000 and divide the result by the number of hours worked and there you have it – the LTIFR. To show it using numbers. Say there were 7 LTIs in the past year and 2 451 679 hours worked. So, 7 X 1 000 000 = 7 000 000. Divide that by 2 451 679 and you get 2.86 – go on, grab your calculator and try for yourself.

What does that mean? It means that this business experienced 2.86 LTIs for every 1 000 000 hours worked over the past year.

Calculating Incidence Rates

Now, to calculate the LTIIR (Lost Time Injury Incidence Rate) which is the number of LTIs per 100 (or whatever figure you want) employees we just substitute the number of employees for the number of hours and multiply the number of LTIs by a standardizing factor which is 100.

So say this mythical business had 791 employees, we get 7 X 100 = 700. Divide this by the number of employees (791) – and we get 0.88. So for every 100 employees this firm experienced 0.88 LTIs.

Calculating Severity Rates

Finally the severity rate. Depending on how this is expressed you will need at least the information from above and the number of work days lost over the year. Your claims Manager should be able to provide the information but let’s say its 73. Most often the severity rate is expressed as an average by simply dividing the number of days lost by the number of LTIs. So, using the figures we have we get 73 divided by 7 which gives 10.43. That is, on average each LTI will result in 10.5 days off work. This can be converted to a frequency or incidence rate by multiplying the result by a standardizing factor. This, of course will increase the result which is why you don’t see it very often – who wants a severity rate of 104 days off per 100 LTIs?

So there you have it. Not very hard and if you know even a bit about spreadsheets you can easily insert the formulas into specific cells to calculate these indicators automatically.


Skip to comment form

  1. RoyK

    Hi Bill the Safety Bloke,
    just a quick question about LTIFR and severity rates.
    Is there a problem with recording statistical data as 100,000 hours as opposed to 1,000,000 hours the company I am working for has very minimal hours worked per month. The company doesn’t have a great deal of incidents but when they do it looks drastic on the spread sheet. one lost time injury with 3006 hours worked for the month (including Office staff) gives a LTIFR of 332.7 admittedly this figure will come down as time passes and hours accumulate,
    appreciate any feedback you can give.
    Kind Regards RoyK

    1. Dave

      Roy, increasing or decreasing the standardised hours as you describe only moves the decimal point either to the left or right so it doesn’t really matter what you use for internal reporting so long as it’s consistent. There maybe some specific requirements for external reporting (eg OSHA require a 200000 standardising factor) that you may have to check out.



  2. a55cdp

    I have been provided with safety stats in the form of TRCF – these stats are based on 1,000,000 man hours and a 24 hour day. I need them as TRIF for 200,000 man hours at 12 hour days. Do you know the mathematical conversion to achieve this?

    1. Dave

      It would be nice to have a name to respond to but we’ll manage with what we’ve got.

      Total Recordable Case Frequency (TRCF) and Total Recordable Case Injury Frequency (TRIF) are calculated with dissimilar base data and one cannot be calculated from the other. Further, the base data is required to recalculate the indicator. If you only have access to the indicator values you will not be able discover the base data used in the calculation.



Leave a Reply

You must be logged in to post a comment.