Failure and Hazard Rate

Abstract

Chris and Fred discuss the similarities and differences between two terms that many people think mean the same thing.

Key Points

Join Chris and Fred as they discuss the idea that a failure rate and hazard rate are the same, or are they?

Topics include:

• What is the ‘hazard rate’? The rate at which functional products, systems or items fail. Think of human beings. There aren’t many people who are 100 years or older. But even though there aren’t many of them, the chances of them dying in the ‘short term’ is very high. So the ‘hazard rate’ is analogous to the frequency of something failing if it is still working.
• What is the ‘failure rate’? Depends who you ask … because some will tell you that the failure rate is the rate at which products, systems or items fail (without the word ‘functional’). Let’s go back to human beings. The frequency of people who are 100 years or older dying on any given day is relatively low, at least compared to the rest of us who are dying. And the reason for this is that even though really old people are more likely to die, there are fewer of them around.
• So the ‘failure rate’ can be seen as the height of the Probability Density Curve. Like the height of the bell curve.
• … and the ‘hazard rate’ can be seen as the height of the Probability Density Curve divided by reliability. To take into consideration that it only applies to functional products, systems or items fail.
• But … there are ‘repairable’ systems. If you replace or repair products, systems or items that ail, then there will always be replenishment. Meaning every system is always functional, so the hazard rate and failure rate become the same.
• And some people just think the failure rate is exactly the same as the hazard rate.
• … so use the definitions that best works for you, your organization, and limits confusion!

Enjoy an episode of Speaking of Reliability. Where you can join friends as they discuss reliability topics. Join us as we discuss topics ranging from design for reliability techniques to field data analysis approaches.

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Show Notes

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