What is the Chance of a Drinking Glass Breaking?

Its Reliability is, ‘The chance it will hold water next time you use it’

If "reliability" is the chance that a thing will work properly, we can ask what will stop the glass from "working properly".?There are numerous reasons why glass will break; "failure mechanisms"; most are listed in the table in Fig 1.?Each cause of failure can happen to glass if particular circumstances arise.?This means the "chance" of the glass breaking depends on the frequency, or how often "bad" circumstances arise.?But before the glass breaks, it needs to be both put in danger (the opportunity) AND enough force applied (the failure mechanism) to break it.

Most often people say ‘failure modes’ rather than ‘mechanisms’.

There are 15 causes of drinking glass breakage shown in the list.?I’m sure that you can come up with more causes.?We can estimate the chance of breaking glass in a year, i.e. the failure rate, by analysing the history of the glass.?Let’s say it came from a manufacturing run of a million drinking glasses sold through shops worldwide in carrier packs of twelve glasses.?Each pack went to a household; one was your place, and another was mine.?That means 83,333 households had a set of glasses and put them on their shelf to use.

How many times a year does the glass get broken in your place??People have told me from one a year in their place and others up to five a year at their place.?In my house about two glasses, a year get broken.?Primarily by me, because I wash the plates and glasses after meals.

In the beginning, only a few of the many causes of glass breakage can happen. When a new drinking glass is taken out of the glass carrier and put on a shelf it is possible to drop it. The glass can hit something else when it is first moved onto the shelf. So the chance of the glass being broken at the start of its ‘working’ life is not zero because in some of the 83,333 households a glass will be broken when first stored. Over time more opportunities for failure arise. As the glass is used for different functions, such as family get-togethers, celebrations, special occasions, etc., opportunities constantly arise for an accident or problem that results in broken glass. With enough time the causes repeat endlessly.

You can see in Fig 1 how the annual failure rate of 0.167 was calculated for the group of 1,000,000 glasses.?The failure rate for 12 glasses at my home is 0.167 ÷ 83,333 = 0.000002, or two in a million.

What can you do if you want to reduce the number of drinking glasses broken in a year?

Once the causes of failure are known they can be targeted with solutions to prevent them.?Glass breakages can be stopped by a design change, such as replacing the glass with plastic, changing the glass design to one that is stronger, or using a glass of a design that prevents a failure cause arising.?Procedural changes can be made such as carrying glasses in locating trays.?Improved instructions with training can be used to up-skill people and give them specialised knowledge and techniques.

Once failure causes are removed, there are fewer failures, and the failure rate curve falls.?With fewer failures, less money is lost to DAFTC/s (Defect & Failure True Cost).?The maintenance costs fall, the operating profit improves, and people win back time to spend on improving the operation further.

Waseem Rehman CMRP is an Australian chartered mechanical engineer specializing in maintenance management, data analytics, digitalisation, and cyber security. He provides asset management & reliability solutions to the Libyan Oil & Gas sector under a license of LRS (Lifetime Reliability Solutions)?