How to test a chair

(Heather) #1

I was browsing through Reddit recently and I saw a question “How to write test case for a chair”. It reminded me of a session that NI Testers had at the start of the year. We had a lot of non testers attend wanting to learn about testing. Once of the first challenges was to work as a team and write ideas for testing on to postits for how the team would test a chair.

It sounds simple on the surface but once you get a team from various different backgrounds working on ideas, you’d be amazed with what you can come up with.

So, how would you test a chair?

(Brian) #2

There is so much wrong with the post from the first link, I won’t even start.

So, what is the context for the chair?

(JC) #3

Never mind giving you extra information, how long will it take to test it? :expressionless:

(Chris) #4

Okay, let’s say we are seating manufacturer mainly for places of worship called “Sit On My Faith”. Our main earners are wooden pews with shelves in the back for bibles and hymn books and moulded plastic chairs with metal legs that you see at support group meetings. We need to ensure that the chairs are fit for purpose, stand up to frequent use, are easy to store where possible and above all don’t cause harm to their users. Comfort is a secondary concern but we don’t want to be liable for injury from their use - sermons can be lengthy.

(Brian) #5

And now, the correct answer.

I’m not sure yet, but I’m positive that it will be a pain in the ass.

(Heather) #6

I’m sensing a bit of negativity in this one :sweat_smile:

My intention was not to get answers to the original Reddit thread. I agree, when I opened it I was put off but it reminded me of a wonderful group session where some really unique ideas came out.

In that session, we had chairs similar to

Some ideas that came up in the session:

  • How much weight can the chair take?
  • What happens when the maximum weight is exceeded? Does it splinter with potential injury to someone or fall over gracefully?
  • Should we somehow automate a method to test prolonged weight on the chair to estimate it’s life time?
  • Is it stackable? If so, how many are safe to stack? If not, should it be stackable?
  • Does the chair have arms? Should it have arms?
  • Can it be used as a weapon? (This was a genuine response)

(Chris) #7

Well I actually do know a little about chair testing. Seating is designed and tested for quite a few things. With what I know and some research here’s some interesting facts about chairs:

  • Chairs should be stable and not easily fall over
  • Chairs should not have gaps or parts that a person can get their fingers caught in, especially if it has moving parts like in cinema seats. Also they must not have accessible sharp edges.
  • Pretty much all chairs in the UK and Europe must be tested for flammability and meet that country’s fire standards.
  • The maximum weight on a chair must be in sufficient excess to take the moving weight of a person (which is more than their static weight)
  • The standards by which you must test seating, in most countries (I believe), change depending on what the seating is used for (home, schools, theatres, camping, office, garden…). This can lead to changes in testing (outdoor furniture should reasonably last in the rain and freeze/thaw cycles, office chairs should resist 8 hour work days with a 110kg load and meet ergonomic standards for use with VDUs, public benches must be vandal-resistant and often have features to prevent people sleeping on them or skateboards sliding on them)
  • Chairs are tested for long-term durability, often with a robot that sits on them thousands of times. The frame must be durable as well as associated materials such as in the foam, padding, upholstery, etc.
  • Testers will test chairs for normal use, but also for misuse through accident or not-for-purpose use, such as standing on them.
  • Importers usually take responsibility for the safety of the chairs they import.
  • Chair testing standards can include velocity, force and load values.
  • The European standard for chair testing for domestic seating is EN 12520:2015
  • Because of the quality of engineering and measurement usually a designer in industry will know that their chair will pass standardised testing before it goes for testing.
  • Chairs are tested with the existing standards, so older chairs including antique chairs may not meet modern standards.

Some tests on chairs include:

  • A seat static load test, where a heavy weight is placed on the seat for a set period of time. Then the chair is examined for damage.
  • A leg strength test. If the chair has legs then the weakest one is the one that will cause injury. Weight is applied over each leg for extended periods of time.
  • Impact drop. Drop a weight on the chair from a set height.
  • Chair drop. Drop the chair at various angles so that different legs or parts of the standing mechanism hit the floor first.

Some types of chair include:

  • Office chairs
  • Dining room chairs
  • Dentist chairs
  • Beanbag chairs
  • Swing chairs
  • Picnic tables with bench seating
  • Public benches
  • Sofas
  • Armchairs
  • Bar stools
  • Massage chair
  • Beach chairs (adjustable sun loungers)
  • Deckchair (material hung on a frame)
  • Ceiling-suspended chairs
  • Inflatable chairs
  • High chairs
  • Cantilever chairs (no back legs)
  • Antique chairs
  • Rocking chair
  • Wheelchairs
  • Bath/shower chair
  • Chaise longue
  • An Electric Chair
  • Folding chairs
  • Gaming chairs
  • Pushchairs (prams)
  • A throne
  • Zaizu (a Japanese chair that has no legs)

Here’s a video from a furniture tester:

(Chris) #8

Also there some ambiguity as to what a “chair” really is. Some people define a chair by it being raised, while some “chairs” don’t have legs. Some people define a chair as having a back where one without a back is a stool. Some definitions have it that chairs are for one person only. Some words for chair-like objects include stool, seat, stall, perch, banquette and suite.

There are other dictionary definitions of “chair” as a noun, such as a person in charge of a meeting or organisation, a position of authority or state, a specific position of employment (as in the position of a member of an orchestra) or a professorship at an institution (as in a “university chair in biology”). The block that holds railway track in position is also called a chair.

(Jesper) #9

there is often a chair in a test conference programme committee - but does she want to be …“tested”? I wonder… Which personal, cultural, management… barriers will there be towards the testing of a chair (the object)?

Is this a chair?

(Brian) #10

I suppose now I could be a little bit more serious.

When I look at this lovely, blue, plastic chair, a few questions come to mind.

  1. How easy is it to clean this chair? As someone who tends to leave plastic furniture outside, the dirt and grime can reach epic proportions. If there are nooks and crannies on the chair, all manners of beasts can find a good home in these chairs. So prior to use, I want to clean them.
  2. Are they child-proof? As someone who might have children, could I leave my child and this chair alone in a room and expect the chair to survive the experience? To up the ante, I could even give the child a screwdriver. (What, OSHA? Never heard of it!)
  3. How weather-proof are the metal bits? Again, I tend to store plastic-and-metal things in a damp environment, such as a shed. Should I expect cracks and rust on the metal parts? (especially screws and joints, those are often overlooked in furniture)
  4. If I sit in this chair for several hours, will I hate my life? In my experience, this sort of chair is mostly used for gatherings in places where gatherings don’t often happen, such as town-halls in gyms. That means that someone will be sitting in it for long periods of times. If someone sits in this chair, will it be comfortable? What if they have back trouble? Knee trouble?

Then there are other questions, such as “How many of these chairs may I test?” If I get one chair, it will be a very short testing session. As a hardware tester, I frequently get one sample to test on, and if I break it, I have to fix it, which is often more expensive than getting a second sample. In the past, I have convinced management that prototypes and 0-series products to be ordered in “more than we think we need, usually by a factor of two”

Another potential question is “How are these chairs made?” Such as, if there are welds, then are these done by hand or by machine? The information may not affect what I test, but it does affect the conclusion.

(Chris) #11

Never be serious, unless you can be Batman. Then always be Batman.

(Beren) #12

Like all testing questions, this question is a very hard to answer in one definitive way.

I initially summed up about ten questions that popped in my mind, but deleted them.
This is an exercise of questioning and many good examples and proposed models have already been given.

What I rather lacked in this thread is the focus on:

Business value & Risk

While I did find it implicitly in some replies, testers need to make that focus more explicit. Especially when talking to non-testers.
I’d start with potential lawsuits, standards & regulations in the chair business, what our competitors are doing, Safety hazards, maybe research what other catastrophic chair-launches looked like,…

We’re pretty good at thinking out of the box, but usually not too great and explaining why we do so. :wink:

(Chris) #13

I think this happens less because chair manufacture carries with it a raft of contextual tacit knowledge.

For example it’s probably true that there are multiple types of testers in the chair industry. When it comes to physical safety standards then a manufacturer will create the chair and then pass it to a testing company with all of the lab equipment necessary to sign off on compliance for safety standards for that particular country. When it comes to physical properties then there will be material scientists who already know the suitable composition of their chair materials, and moreover that those materials have been successfully used for chairs in the past - most chairs are very much like the last lot of chairs that passed all the tests. When it comes to design there will be ergonomics experts and engineers who know about affordance and effect of colour and comfort and how to design a chair that doesn’t injure someone through bad posture. These all get tested by different people in different departments with different types of expertise and industry experience.

So the more genuine answer to “how would you test this chair” is “I wouldn’t, I’m not in the business of testing chairs. It’s very context-dependent and it’s a complex industry. But if I wanted to get into chair testing then step one would probably be getting up to speed with whatever company wanted my completely inexperienced services and how the chair industry works, and I’d want to know what the minimum requirements are to get a chair to market.”

(Heather) #14

A recent blog post & video by @tjmaher1 about this very topic :slight_smile:

(John) #15

Look, the only thing I’m interested in is, does a ripped off leg make an effective weapon in a fight?
Thinks - Perhaps I should think of other uses as well. :wink:

(Alexandre) #16

I was thinking that was what to be tested!! Those 80K USD seats are full of adjustements and yes, for the simulators we use those parts and we test them. However we rely on manufacturer to provide us documents showing compliance to G forces and fire resistant materials, electrical safety, RoHS …