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.


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  1. Damien

    Thanks for all of this … why haven’t I discovered your site before? I couldn’t agree more when you question the use of LTIFR’s … why do Companies choose to measure performance by failure and not success? It’s easier … and is driven by laziness … also driven by an expectation to fail in Duty of Care.

    1. Dave

      Damien, thanks for the compliment, they’re always welcome :)

      I think another thing is that if safety performance was measured using positive indicators then the management group would have to demonstrate that they’d actually done something rather than just passing responsibility onto the safety people.

  2. Jaaas0n

    Hi there, I am looking at calculating the frequency rate over a year(monthly). If I have, for example, 7,6,9,4,3,7,5,5,9,11,5,8 LTI and 100 workers working 2000 hours each for the year. How do I calculate it, so I can have a monthly frequency rate.
    Hope this makes sense.


    1. Dave

      Jason, from the data you’ve presented you can’t calculate an accurate monthly frequency rate. One can be estimated by dividing the annual number of hours by 12 to provide a monthly average number of hours worked. The accuracy of this figure depends on the working arrangements in place.

  3. Jaaas0n

    Thank you Dave. The frequency rate based on this formula seems really excessive. For example, 6×1,000,000/ 16666.66667(hours worked in a month x 100) = 360. But I guess I’ll go with this.

    1. Dave

      Jason, Your calculations are correct. If these are actual data and not hypothetical I think your business has some serious problems. 79 LTI’s per year for a workforce of only 100 working only 2000 hours per annum would have to be one of the worst accident rates I have ever seen. Even extremely high risk industries such as construction and mining don’t have accident rates anywhere near this.

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