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Author Topic: Are you sitting comfortably? (and can you quantify that?)  (Read 624 times)
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« on: August 14, 2019, 01:03:56 pm »

Last year RSSB started a study into seat comfort (done by Arup and FIRA). Well, actually they started back in 2016 with a literature search that showed there wasn't any accepted way of specifying the relevant factors of seat design, and after asking around started project T1140 to create a measurement method. T1140 is called "Defining the requirements of a seat comfort selection process", but don't worry - it's not quite that abstract: it is about the form of requirements used in choosing seats, not about the requirements the selection process must meet (though they did that, at the start).

Finding the right report is tricky, as there are several, each with its own web page,  but this is the final report on SPARK.* I imagine the bated breath is all for use on the matter of squidginess (not their term), and this is the relevant section:

Seat pad requirements summary

The compressible seat pad is an important factor when considering seat comfort. Paul Branton’s seminal report1 on seating behaviour, body mechanics and discomfort found that:

  • Based on 104 subjects, approximately 50% of the body weight is supported by 8% of the seat area (under the ischial tuberosities).
  • ‘The seat pan carries 65% of the user’s total weight’. This implies the seat cushion is an important factor in the offset of discomfort.
  • To further understand and define a workable minimum seat pad requirement, the Arup team met with a train seat foam manufacturing specialist and consulted with FIRA’s technical specialist on flammability and physical upholstery testing.

They concluded that recently, there has been a trend towards thinner seat pads (driven by fire, smoke and toxicity reduction requirements and the ever-reducing seat pitch needed to increase seat density and passenger capacity) but this has been at the expense of comfort. This is because most seats have a hard-backed seat structure to support the seated passenger and compressible seat pad. It therefore makes sense that a thicker seat pad can be softer or more compressive before it bottoms out. There is a balance however as a pad that is too thick will affect the seat height and angle and potentially cause discomfort under dynamic conditions. Seats with no hard backing structure and a flexible sling could result in a comfortable, compressible seat pad and a thinner pad thickness. There is potential for innovation in the design of thinner seat pads that achieve the minimum compression requirements.

1 Seating Behaviour, Body Mechanics and Discomfort, Medical Research Council, London, England. P. Branton, 1969.

So next time you are asked  "do my ischial tuberositie look big in this" you'll know how (or whether) to reply...

In the interim report, this was suggested as a follow-up task:
Use the results of project T1140 to inform DfT on the effect that high train capacity requirements are having on comfort? The benefit would be the DfT relax their focus on fitting in as many seats as possible and enable TOCs to produce trains with adequate space between seats (side by side and legroom) and therefore achieve appropriate comfort levels. 
The final report is less specific.

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« Last Edit: August 14, 2019, 07:34:57 pm by Red Squirrel » Logged
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« Reply #1 on: August 14, 2019, 07:22:58 pm »

How do I know when I have bottomed out?
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« Reply #2 on: August 14, 2019, 08:03:21 pm »

How do I know when I have bottomed out?

That'll be familiar to you, it's like riding a bike on a flat tyre.

My first trip in an IET also involved a 387, and I thought their seats similar. I didn't feel I could squash the pad flat however I sat on it in either, and I could barely do it with my thumb, which of course compresses a far smaller area than any of my ischiadic prominences.

Then I ended up on a 485, where the recent revision of the seating was an angle grinder job and the upholstery is now pretty old. The seat pad is much thicker than on an IET, but I could - with a little bit of bouncing up and down - squash that flat and feel the hard base underneath. I could also do that with my thumb quite easily.

The reports do go into the relationship between pad resistance and thickness, for obvious reasons -a pad that's too soft for its thickness leaves you sitting on a hard shelf.
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