The Dead Drop
New WTC Design Cont'd

This is one of my best designs.
Therefore, someone else must have thought of it before.
That's quite alright. I had a lot of fun designing "stuff".
If you happen to know of similar designs let me know.

his is a proposed egress plan, designed to allow 32,000 people to exit a 160 story building in under three minutes. It's a bit scary but not as much as watching those people jump to their deaths on September 11th.

It's not a joke ... it will most definitely work.

The problem is what we are willing to pay in a tall structure in exchange for peace of mind. Imagine working or living in a very tall structure knowing that you can get out in an emergency ... with relative safety ... in just minutes. That would make it much easier to sell office space wouldn't it?

Here's the gig

I propose using an 18" x 24" rectangular tube as a structural element doubling as an emergency mode of egress. Thus, the hollow tube runs all the way to the ground, slanting outward at the base, and delivering a person from the 160th floor (~2000 feet up) to the ground (about 100-200 yards distant from the base of the building) in about 25 seconds.

There could be as many as four tubes from each floor in a one building structure, but not less than two so that it is unlikely that both would become unusable at the same time.

Let's work with it ...

Dead Drop Schematic - 5kb You go to the main elevators. In a "dire" emergency, you go to the drop tube instead of the elevator or stairwell and "jump" in. You free fall and take the G's at the bend (and slow down some too). Continuing along you slow down much more and emerge at the end of the tube traveling at low speed. You get up immediately (you're lying down) and get out of the way.

Yes, some people might have a heart attack. No, no one will get any broken bones. Those who get up unscathed become the assistants for those who don't. The end of the tube is next to a subway platform. Those who are just getting in the way get on the subway and leave. Those who are messed up are put on the Medical Evacuation Subway train which goes to the nearest hospital.

Some math

If there are four tubes per floor and 200 people per floor (160 floors x 200 people = 32,000 people in the building) ... then ... each tube must drop 50 people on average to clear the floor. I estimate that one person could drop every 3 seconds. So 3 seconds times 50 people = about 150 seconds ... or ... about two and a half minutes to evacuate the entire structure ... all 32,000 at or below ground level and 200 yards away in less than 3 minutes.

In reality, people will loiter or refuse to "jump" and some will have to go back for that important document. So, I expect 95% to get out in five minutes or less and the rest will get burned up through their own stupidity. These people are "unwilling suicides" ... more or less.

deadrop2.gif - 3kb At the base of the building, the cross section of the tubes will look like this. The exact shape is not important here. Obviously, at its largest size, it can be a manageable, and realistic structural member. They will however flare out at the end to spread the evacuees out over a larger area.

Here's a bigger, nicer looking building

I didn't want to go higher than 160 stories because there's a minimum pixel problem, i.e. if I make too many stories and attempt to show them all, the picture will be just toooooo big for your screen. Actually I'd like to go as high as 3200 feet!

On top of the observation deck and below the radio tower is a U.S. Army base. Just a few soldiers ... and ... unknown offensive and defensive countermeasures (laser-guided missiles, etc.) to thwart "attacks". This is just to defend the building until the regular Air Force arrives. Such a small base might possibly defend the entire area around the building for several miles.

A New World Trade Center Building - 12kb

As we have seen, no matter how high a building is, with the drop chutes installed, the time required is that for one floor. And the single floor evacuation time is on the order of 2-5 minutes.

Let's back that up with some realistic details about the "dead drop".

By the way, I called it the dead drop because of the people who jumped out of the WTC. They preferred a dead drop to burning up in the building. They had the right idea, but had no cushion to land on. Let's give 'em one posthumously so that no one else will have to join their ranks.

Details, details, details ...

The drop chute is a smooth metal "clothes chute" deal about 18 x 24 inches (the exact dimensions are not too important to this discussion). They could be bigger or somewhat smaller depending on other considerations such as ... fat people, available space, etc.

Chute Bag - 6kb Now, if you just jump into the chute you might come out alive on the end but with multiple abrasions and clothes destroyed. So, to cover this aspect, I've designed a "chute bag". This is a canvas bag which you jump into and ride down the chute.

It also has a "parachute aspect".

It is sewn, as in the diagram, so that the air pressure from falling inflates the sack causing it to seal the sides of the chute preventing air from getting around the "hell-diver". Why? Well, remember the TransAmerica Building before it was finished? There was a dude, stoned on LSD, who fell down the elevator shaft all the way from the top to the bottom ... and he survived! ... because the air pressure in the confined space slowed his speed to survivable velocity. And, yes, he was messed up quite a bit from slamming the sides on the way down.

What we want here is the same thing but in a controlled fashion. We don't want to slow the decent too much ... just enough so that the human body can easily handle it.

Now, when you exit the chute, after a drop of perhaps 25 seconds (in the present case), you emerge lying down in a padded shallow trench which provides the necessary friction to bring you to a complete stop.

You extricate yourself from the bag and assume a position on the "off ramp" to assist others coming down. When there are too many assistants on the off ramp ... you leave via the nearest subway or walking.

The room you emerge in must necessarily be airtight so as to avoid sucking air into the drop chute from the floor from which it came ... which may be on fire ... and more importantly ... There must not be a downdraft created in the chute. The terminal velocity from a height of 2000 feet in a vacuum would be about 240 miles per hour. So that's the fastest you could fall down and the fastest downdraft that could occur in the chute ... if ... the end room was open and unpressurized. You exit this room through revolving doors which let the air out but put in about as much as they let out. We should note here that a powerful fan could increase the air pressure in the room and slow the decent even further. In fact, since the chute here is 432 square inches, an increase in air pressure of about one half pound per square inch could actually blow a 216 pound occupant up the chute! Perhaps this fact could be useful for delivering emergency personnel to any given floor PDQ (though I think the elevators will always be preferable).

Note here that, as many people come down the chutes, they will push air ahead of them and there will be others coming behind them. At any time there might be 7 people in the same chute. So letting the air get back to the top is a potential problem. To resolve this we must allow some air from the end room to return up the chute by passing around the divers coming down. We can't have the drop bag to completely seal the chute.

As the first person goes down the chute there is a negative pressure behind him and a positive pressure in front. The next man down is going into a somewhat lesser pressure zone and so will fall somewhat faster than the first guy and so on with each successive person ... up to a point where air backs up from the end room fast enough to fill the low pressure at the top. Controlling the size of the bag skirts, insures that a proper fall velocity is maintained. One can then discover the right amount of time to wait to drop the next man so that he doesn't "catch up" to the previous diver.

No Bag Drop

It might happen that someone will have to do the drop without a chute bag. This is OK. You will probably arrive not very damaged. One should go feet first. Discard all loose items. Women with skirts should reach between their legs and pull the back of their skirt up to the front and hold it ... otherwise the skirt or dress will be blown over their heads and they may arrive "buck naked" in the end room.

A nude diver will arrive severely "scraped". Skin does not slide too well on metal.

Animals will arrive with their own excrement. Send them last.

Chute Bag Deployment

A quick exit requires the smooth operation of an army parachute drop. But unlike a para-trooper, we won't have our chutes strapped to our backs. Nor can we waste precious minutes putting on a gizmo.Bag Deployment Spring - 2kb It must be there waiting for the next man to jump into with no fixin' or fussin' on the part of the jumper. My solution is a spring loaded drop chute. Here's the setup.

Spring-loaded Bag Deployment - 94kb

Note that four spring steel clips (attached to the bag) slide down on inclined chrome plated rods. Only one can deploy at a time since the rear clips of the first one block the front clips of the next one. This, I believe, will work pretty well.

You just kneel in front of the "hole" and tumble over the entrance falling in head first. Jump in! - 18kb The reason for going head first is speed, simplicity and you won't catch a shoe on the side of the bag breaking it loose prematurely. Remember, this is not a water park ride ... it's a life or death emergency. Anyway there is no water in the end room and there is no sudden stop to worry about.

Kneel and Keel (over) ... that's all there is to it.

You'll note the "helmet" on the guy's head. I thought it would be prudent to don one before entering such a "laundry chute". The Helmet - 3kb So I designed a quick fit, one size fits all. It's to be made of foam rubber (heavy duty) and must lie flat in a case by the drop chute so that a couple hundred can be readily available. Packing is a problem.
< < Here is my solution.

The End Room

This room should be long and small ... containing as little volume of air as is reasonably possible. That way, when the diver is coming down it will pressurize faster.
The End Room - 4kb
At the end of the room is a revolving door to facilitate exit without losing air pressure which is what slows the diver down to safe speeds. There is some form of "final arrest" just in case something "gets away".

The slanted area (red) is where you are slowed to a stop. If the person behind the last diver is faster, he may crash into the first. The slant causes the slower person to drop lower sooner. The faster person then goes over him and collision is avoided.

The "trench" is of indeterminate length and is where you would be slowed to manageable speeds while under control of the trench. This entire apparatus needs computer simulation to determine optimum lengths, durations, pressures, etc. I'm here giving only the basics and a few major details.

Air Valve - 3kb I think we will need also an emergency air valve to keep the air pressure from getting too high. This design will work well since it requires no maintenance whatsoever. The weight keeps the valve shut until sufficient pressure is able to pick it up. Also, it must be big enough to allow lots of air out quickly should the need arise.

( I didn't draw it too well because
I'm in a hurry and I'm using MS Paint ;o)

Some Math

Suppose the end room is 8'x10'x100' ... then there are 8000 cubic feet of air in the room. If the length of the longest chute is 2000 feet and it is 18"x24" (3 square feet), it will contain about 6000 cubic feet of air. If all that air were forced into the end room, it would cause the pressure to go from 14 psi (sea level) to about 24 psi. This would be ridiculous and would blow up the end room ;o).

Since it would only take about 14.5 psi to force a man UP the chute ... if everything were perfectly sealed a diver would only go a hundred yards or so till the air pressure in the chute would support his weight and he would be suspended there ... no longer falling ... bobbing up and down like a cork. We want the air pressure in the end room to be just slightly greater than normal air pressure to lower our man at a respectable rate, say, 60 mph. Any slower, and the evacuation is going to get held up. At that speed, you would experience a G-force about the same as in a typical roller coaster on the first hill. This would be acceptable in an emergency situation.

One might expect younger employees to take the chute as their normal commute from work. It's fast, fun, and safe. They should be encouraged to do so in order to make this method of egress more acceptable to all in an actual emergency.

The Drop Room

Here is my floor plan for the elevator and drop room. Drop Room - 5kb There is an outside walkway on either side so that in the event of smoke, you could take the leeward smokefree walkway. The droproom is behind the elevator bank, accessible from the inside or outside. The outside walkway is covered by heavy wire mesh to prevent suicides and thrown objects while allowing fresh air in. The stairwells are here as well to prevent smoke from filling them. An inside hall around the main building should prevent people having to jump from windows.

Concluding ...

I think everyone can get the picture now. This is a viable system but will add to the cost of construction. How much? I don't know. But since the WTC disaster, I think a really tall building will need a quick exit plan in order to get tenants. I sure wouldn't want to work in another "target".

For those interested, there is also another design on this page - CableDown - for a cheaper drop scheme.

Addendum: 09-25-02

I've added a topic for this page to my Bulletin Board - EBTeXt
if anyone wishes to post a comment. It's a topic under "Physics & Mechanics". Thanks for your input.

Addendum 12-18-01:

My thanks to Art Bell's Site for the early Christmas present of a link to this page (12/14/01) which resulted in an incredible spike in my daily stats.

Although it makes little difference in the long run (these visitors generally did not go to any other pages), it gave me the opportunity to see how much power a popular web site has to drive traffic. I got about 4000-5000 extra visitors to my site in only three days. My data transfer rate went ballistic from about 28 megabytes per day to ... on the first day ... 485 megs!! Wow! The most I've ever used in a month was last October (594 megs). I guess I'll do 1.5 gigs this month at least.

Also, I got "discussed" on a D-Board at:

For the most part these people didn't understand the design. Some did and pointed out the obvious. I did not participate since a registration was required and the discussion was mostly over when I got there.

One reader said it was impossible to evacuate a whole building in 3 minutes, failing to recognize the simple math of the situation.
Others thought that an inflatable bag on the ground would be better.
or ...
it couldn't be made because of the Americans with Disabilities Act.
or ...
didn't understand the idea of air pressure.
or ...
thought it was amusing, etc.

No one said anything about the "outriggered" elevator/stairwells which is probably the single most important thing that architects could incorporate into the design of tall buildings.

This experience has got me to look for the checkbox on my web site control panel which says "Suspend my site if file transfers exceed 7.5 gigabytes" (my limit). An excess would result in me having to pay about $80 per gigabyte. Now, I don't expect it to ever happen ... but ... if some extremely prominent person ever mentioned one of my pages ... Verio's servers would just keep churning away ... emptying my wallet and my next several paychecks. I could be wiped out financially in a single day and all I would get would be "memories".

Phewwww! . . . . :_o(

Addendum 12-18-04:

wtc-lotd.gif - 8kb Same date as last addendum three years ago. This page was link of the day from generating another 300 megabytes of traffic with an extra 1000 visitors. Their site is cluttered and hard to navigate but Thanks anyway for the link so here's one for you.


Ebtx Home Page