Engineering Infrastructures For Humans

I’ve been lucky enough to have the chance to fly a lot over the past year or so. Working with Stephen Foskett and the rest of the Tech Field Day crew means that I’ve been to California almost every month. That’s a lot of flying.

One of the things that I’ve noticed on my flights is that they don’t want you to smoke. You actually used to be able to smoke on planes, which seems weird now that you can’t even smoke outside.

I’m not a smoker, so it doesn’t bother me. (As an adorable aside, when I was five years old, I literally glued hand-made no-smoking signs to the walls of my grandparents’ house. They were less than amused.) But the occasional legacy arm-rest with an ashtray harkens back to days of yore when every Joe Cool enjoyed the wonders of aviation while kicking back on a flight as smooth as a Laramie cigarette. He probably got a full meal as part of his ticket, too, the jerk.

Then the bleeding-heart liberals attacked in 1988, complaining about their “filthy air” and their “lung cancer”. The FAA banned smoking on flights less than 2 hours, presumably because any longer and the pilots would be having nic-fits.

This was, of course, the thin end of the wedge. In 2000, the FAA banned smoking on commercial planes altogether. Talk about a bunch of buzz-kills.

So now we’re flying without cigarettes, and they are not kidding around about this whole “no smoking” thing…all you have to do is open your eyes to see that they don’t want you smoking:

That light is never turned off. I have actually seen a few planes which were new enough that instead of a no-smoking sign say “Please turn off electronic devices”, under the assumption that everyone is already well-trained enough to not smoke, but those are comparatively rare. Nope, it’s mostly the “no smoking signs”. But in case you didn’t look up, here’s the safety information sheet on the airplane.

See if you can count the number of “No Smoking” warnings:

And on top of this, there’s a smoke detector in the bathroom (along with a heavy fine for disabling the smoke detector, too!)

No, planes are pretty much set up for not-smoking. Heck, there’s even a “No Smoking” sign on the ashtray in the bathroom:

Wait, what? Yes, you read me right. You’ve probably even seen them yourself. In airplane bathrooms, there is an ashtray (complete with No Smoking sticker) for the people who smoke in the bathroom, even though they shouldn’t.

When I first started bringing this up to people, I encountered the same reaction again and again. People would say, “oh, it just costs too much to replace the door or take out the ashtray”. This is absolutely not the reason, though.

Allow me to quote from the Code of Federal Regulations for airworthiness:

Regardless of whether smoking is allowed in any other part of the airplane, lavatories must have self-contained, removable ashtrays located conspicuously on or near the entry side of each lavatory door, except that one ashtray may serve more than one lavatory door if the ashtray can be seen readily from the cabin side of each lavatory served.

The plane can not leave the terminal if the bathrooms don’t have ashtrays. They’re non-optional.

That’s an awfully strange stance to take for a vehicle with such a stringent “no smoking” policy, but it really does make a lot of sense. Back in 1973, a flight crashed and killed 123 people, and the reason for the crash was attributed to a cigarette that was improperly disposed of.

The FAA has decided that some people (despite the policies against smoking, the warning placards, the smoke detector, and the flight attendants) will smoke anyway, and when they do, there had better be a good place to put that cigarette butt.

There’s a lot of wisdom in a decision like that. I think that it’s a lesson that we can put to use in a lot of the things that we do. There’s a really interesting book on a similar topic, called Nudge. The idea behind Nudge is that every design decision that you make, as an engineer, affects the way that people behave toward your creation, so you should tend toward design decisions that encourage positive behavior in users.

This is similar to the design consideration called affordance. If you’ve ever walked up to a door and pushed, then realized that the door was supposed to be pulled, even though it looked like it should have been pushed, then you’ve come up against someone who didn’t understand affordance.

Here’s a good image of handles which afford pushing or pulling by Yanko Design:

As the photo says, it’s a cross between form and function. We have “grippy” hands that open flat. We instinctively know how to use things like this handle because of how we are formed.

You don’t engineer your systems with the belief that none of your computers will ever break. That’s insane; you KNOW they’re going to break. So don’t assume that your users will never break the rules. Build in graceful failure as often as possible, whether you’re designing a user interface or a security policy.

Likewise, when you are designing your infrastructure (or security policies), keep in mind the idea of affordance, and nudge people into making the “right” decision each time. The cynical Hanlon’s Razor says

Never attribute to malice that which can adequately be ascribed to stupidity

Instead of stupidity, maybe people are trying to push on the door that’s supposed to be pulled.

  • See: “The Design of Everyday Things” by Donald Norman, 1988

  • I don’t normally say I enjoyed a blog post, especially a technical-minded one. This is one of those.

  • Jeff: I’ve seen that, and it’s awesome. I don’t have a copy, sadly. I should pick one up.

    Fred: Thanks! (I think) ;-)

  • This might surprise you, but true.
    Am always flying taken long 15, 16 hours flights to and from asia and back to California. The one thing I noticed is the “Smoking areas” IN SIDE THE AIRPORTS Yup, you have smoking areas in-between terminals in airports i.e. kuwait, Qatar, and U.A.E. I was shocked a little due to the whole “no smoking” inside any commercial land! Nevertheless, people are being delayed and late for show-up at their terminals due to taken that last smoke before boarding.

  • allan

    Those handles don’t strike me as perfect affordances: Fingers don’t generally open flat, they crease at the joints. The “push” handle looks like it will fit curled fingers while pulling.

    There’s no good push handle in this case, because pushing isn’t a natural fit for a handle, it’s better to use a pad to get the largest possible pushing surface.

  • It’s terribly a good post! People often take it for granted that the systems/mechanism will work or users would or should definitely follow. But it’s indeed the affordance that is out of consideration by many engineers, designers and policy makers…It should be a well accepted philosophy and principle but unfortunately not everyone realises and buys it. I have to admit I often ignore it myself.

  • Jeff, that book is a must. If I remember correctly they also have door handle push/pull examples in the book.

  • Stephen Coolidge

    It is safe to smoke in the toilet. The trick is to put a wet paper towel over the smoke detector before lighting up, and ensuring that you throw the cigarette but into the toilet bowl after you are finished your business.

  • SD

    This is absolutely new learning for me..thanks for this and this is indeed very informative.

  • Alex Fenn

    Good job Matt, that was actually worth reading. Bro don’t ever post opinion like so many bloggers do. If I were you? I would make more articles like this. The everyday questions we have articles. These are actually enjoyable to read. Instead of all the political drama and so on :p You don’t see many articles like these today, and I would think most people would enjoy this over who has what in hollywood. Thanks for reading my long comment :p Duces matt

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  • John M


    There are airports in the US that have designated smoking areas also. If I remember correctly, Minniapolis, Denver, and Atlanta(?) have them.

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  • Those handles are horrible. I would pull both handles. That’s why they are HANDLES — so you can pull them. For something you push, put something you can’t pull.

    But moreover, if you told me that one of them was for pushing, I would pick the wrong one. I want the ‘wedge’ on the side I’m grabbing. If I grab the flat side and pull towards me, the edges will dig into my fingers. Granted, it won’t kill me. But it will be slightly uncomfortable compared to the other one.

  • Dougal Scott

    Nice blog post. Something I see a lot (and which leads to those doh moments) is the words “Push” or “Pull” on glass doors as a stencil which can be seen in reverse from the other side, and our human brain is quite happy to read and interpret subconsciously, so we do exactly the wrong thing. If the label had a solid background so it can’t be read from the reverse side you would at least have a 50-50 chance.

  • Steve

    If that’s true (and it’s not just an oversight that they haven’t removed it from the regs, which would have been my bet), why is it on the *entry* side of the door? Eg. out in the cabin, where everyone can see you sneaking a smoke? It seems as if it should be inside the lav if you were trying to accomodate people sneaking a smoke…

  • smilr`

    The last image with the push/pull handle design doesn’t make much sense to me. The handles don’t look like I should be pushing OR pulling with either one. They both look like they should TURN.

    Also, they appear to be mounted to a slab of polished granite. Which doesn’t look like it is going anywhere despite whatever I do with the handle.

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  • will langford

    Also don’t forget most airplanes are older than the law and the interiors are only refreshed, so the ash tray stays.

    Also in some airliners second life as it becomes too old for use in the US but will be sold to a 3rd world country that still allows smoking. The FAA is only for the USA.. not the world.

  • TeMc

    @allan: I agree, The shape of the pull and push handle isn’t a good example in my opinion. Our hand is the same either way. Although I personally prefer the grep to be like a pipe (round from both sides), if anything the ideal shape would probably work best for both pull and push. I think we’ll have to stick with textual signs or arrows to make the clue obvious in casual passing.

    @Dougal: So true, I’ve had that on numerous occasions. Didn’t think about it at the time, but you’re right. I did read the reversed text and interpreted without really thinking about it.

  • Dougal Scott

    Reminds me of “School for the gifted” Gary Larson cartoon. Maybe a short strip of barbed wire along the appropriate inner or outer edge of those handles would provide the visual indication of correct use. :) A solid push handle (no hole for fingers) would also work I think, although might not have as effective behaviour re-enforcement. :)

  • Dougal Scott

    To prevent pushing the pull handle, might I suggest a big sign saying “DANGER: do not push this door under any circumstances”. Obviously you will also need a siren connected to a push sensor to stop those people who just can’t help pushing big red buttons.
    (And what’s with these captchas, needed a calculator for the last one)

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  • Subha Ray

    I had actually lighted up in a transpacific flight – toilet. They sealed off the toilet and made an announcement over the PA system. I hope they will not arrest me now that I am confessing – it was 10 to 12 years ago. And yes there are smoking areas in Tokyo/HKG – where even the chain smokers choke.

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  • Pär Björklund

    If people designed for what people do and not the rules you set up then we could’ve avoided a whole lot of security issues. “what do you mean view source? Who would ever do such a thing? That’s where we store secrets!”

  • IPv6Freely

    I cracked up at “bleeding-heart liberals”. Damn liberals, always trying to do sane and logical things!!!

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  • Flemming Jacobsen

    Another point worth noting is that when smoking was allowed on airplanes, the air inside was actually replaced more frequently and thus “ultimately” a better air circulation inside the airplane.

    With no smoking inside the airlines has reduced the level of which the air is refreshed inside the fuselage and thus the air inside has actually gotten a lot worse.

    Another question tho, is there no way for people to register for this blog so I can have a screen name and what not?

  • Ryan

    This seems less of a human interface design consideration than a legacy policy issue that no one will dare propose changing because a cigarette once led to the death of 123 people aboard a plane 40 years ago when smoking was legal in planes.

  • Captain Fuqalott

    I remember smoking on planes (and buses, hydrofoils, trains and hovercrafts, such were the times). I also remember being herded to the back of the plane as a smoker although I doubt that kept the fog out of the front section. Indeed, Iberia used to have the smoking section in front but back then it was merely a suggestion as is often the case with third world countries. I would request a clarification on the calim made by Flemming Jacobsen though. The concept that a plane that allowed smoking would somehow have better air quality due to an unexplained faster refresh rate seems absurd. Do you hae a source for the benefits you list and the reduced refresh rate, no doubt a few folks would like to see the data.

  • Flemming Jacobsen

    Captain Fuqalott:

    I have no official source for this as such. But I am an avid watcher of the british tv show called QI which stands for Quite Interesting. Which revolves around interesting and odd facts and is hosted by Stephen Fry.

    During one of those shows they had some aviation related questions, and as a responce to one of the participants comment he said that since people didn’t smoke anymore they had actually reduced the refresh rate since there was no reason for the higher refresh rate when people didn’t smoke. Which also at the same time made it a bit cheaper for the airlines to run their flights.

    But I could go and look for an official source if you really want me to, but generally I take more or less “everything” that comes out of that show as somewhat factural.

  • Where can I buy this book ?

  • Engineering is for human being and it has helped Science in its own way.

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