For Flit: What Was Your Answer?

>> Monday, July 6, 2009

Flit asked: What sort of system did YOU design ...and did he recognize your brilliance and give you a decent mark for it?
OK, I was hoping someone would ask me. :)

So, we come in with our projects. Now, this was an upper level class and had a prerequisite (which no one told me about) so it was my first design project. It was not the first one for the other students.

The project which I described yesterday was a "personal fire escape device" for high rise buildings (~10 floors), with a 300 pound limit, a minimum and maximum speed, cost per unit, etc. It was pretty clear, although not said out loud, that the teacher was looking for a braking system for a cable/harness system. Ostensibly this was in response to tragedies like the MGM Grand Hotel fire and to reduce insurance liability. In case of fire, the hotel guest would strap on diaper attached to a cable in a black box and leap from the window, confident that the device would save him.

I went into the reasons why the proposal as written didn't work for me on yesterday's post. Feel free to check it out. So, if I didn't like the proposal, what did I do instead?

Well, I completely scrapped the "personal" fire escape device. I couldn't see a way for it to be flexible enough to work for families, be inaccessible for nonemergencies but reliably available for emergencies and be maintainable. So, if I, the scaredy cat, wouldn't want to jump out the window tied to a harness, I thought, what would work for me?

So, I came up with a notion of a rotating net on each side of the building, which one could reach out,grab, and ride right down. Hooks could be provided to help you stay on. You could move out of the way if there was fire directly beneath you. It was not inherently limited to weight. It was easily maintained (four winches on the roof with a backup generator in case power was discontinued), and the net, nominally rolled around it's rotor was only released in case of emergency. It addressed most of the issues I had with the original premise. As an added bonus, a fireman could actually ride the net up and over (or the net could be reversed if necessary) to help rescue people who are trapped or too afraid to come down. See my quick sketch from memory.

The winches were sized appropriately. The net was made of Kevlar (fire resistant) with a wire core to help it hold it's shape if it were exposed to direct flame.

The response to my idea was not what I expected. "That isn't what we asked for." The teacher was confused. The other students were confused. No one had any idea why I chose something different.

"I know," I said, "the other idea wouldn't work and here's why." (I had sketches demonstrating the problems). When I questioned those that provided solutions where they hadn't accounted for the issues, I got a lot of perplexed looks. No one had thought of them. No one understood why I was asking those questions (although those questions - gasp! - get asked in the real world).

Now, I mentioned that say 36/40 students did the cable/braking design, but there were a few that did something a little different. I remember three of them.

One involved jumping into "some sort of panty-hose" like material that would slow one down. The person who proposed it had no understanding that the forces required to slow a person don't just disappear - it's friction and that creates heat. Falling ten stories, it creates a lot of heat. Also, how do you size it? If you get a fat person, you can plug the whole thing up (he had them on every corner of the building as opposed to each room so multiple people would use them). Someone too skinny could slam into the ground (or someone below them). Nor could I think of any pantyhose-like material that could withstand fire or heat. The designer couldn't either.

Another involved a winch in every room that would allow escapees to walk backwards down the side of a building at 4 mph (because Boy Scouts can walk 4 mph), a building covered with windows. Asking if that wasn't a bit challenging got me a blank look and the designer had given no thought to the maintenance (or cost) of a winch in every room.

But I have to give top laurels to the parachute material design though. One individual (who deserves credit for originality) proposed tubes made of parachute material pleated into a tube kept in the ceiling that would shoot out the window at 45 degrees so that people could slide down. There would be a trickle of water to help with friction, but we were missing a method for entering said tube. But more than that, again the physics weren't fully thought out. What happens if the tube gets water (or a person) but the end isn't weighed down? So much for the 45 degree angle. A little water and the tube will end up flat against the building unless you weight the ends. Why not weight the ends? Imagine if you will, tubes shooting out of the building in every direction, heavily weighted.

So, now you know. I got a C, but I think I surprised everyone. Also, I was apparently missing pieces of the project I didn't know about. If it makes you feel better, I ended up with an A in the class and the respect of the professor. And I learned a valuable lesson that I have seen played out a hundred times.

Now I play to my strong suit and professionally ask the hard questions so that our designs end up better than they might have otherwise. So, it's all good.


  • Shakespeare

    WOW. I like your system better... although if someone is reluctant to endure heights (I think of my husband as well as you), this someone might not so readily climb into a net. Would the net wait on people? If you didn't catch it the first time around, would you just push a button on the wall and wait for it to come back?

    FASCINATING, to say the least. Stupid of your advisor to put you in a class with a prerequisite, though. That person wasn't doing his job (I speak from an educational perspective). Thank goodness you had the natural intelligence to succeed anyway.

  • Aron Sora

    Wow, that is a great design. You should get a patent on it. It may be useful in some buildings.

    But, what stops a designer from using an external elevator that can be used in a fire and has backup systems.

    I'm glad to see your not risk aversive. I feel high school trains people to give the teacher what he wants and to mindlessly do work. By designing this and raising these questions, you where giving up an easy A, but you are a better engineer because of that.

  • Stephanie B

    Actually, Shakespeare, all of my electives in junior/senior years in engineering had prerequisites I didn't know about. Engineering Physics was really geared for the electrical engineering side except for some core classes (thermodynamics, fluid mechanics, etc) - except I didn't like electricity and magnetism, so I went with solar engineering and orbital mechanics and other aerospace and mechanical engineering courses - which assumed you were coming down the ASME route. Since 100% of my engineering electives had to be upper division courses, I could only have taken the prerequisite by taking extra courses. I don't think my counselor knew what to do with me since I broke the mold. Apparently, no one did what I did.

    By the way, the entire loop was net. If you missed one "rung", there was another one right after it. You could catch it any time.

    Aron, nothing. I don't for one second assume this was the only solution. I don't even know that it was the best solution, but I felt (strongly) it was a better design than the assignment and that it addressed shortcomings that had gone unnoticed.

  • flit

    It definitely sounds like you are in exactly the right job for you.

    Your description of the net being a loop made me think of those old style towels in public washrooms - the ones you pulled, hoping there was more clean in there.

  • Stephanie B

    You're good, flit. That's what made me think of that style for the net.

  • The Mother

    The outside of the box thinkers are not always rewarded. At least not at first.

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