Emergency Tower Evacuation

EMERGENCY TOWER EVACUATION

September 17th 2001

To get in touch with the author:
Jean-Pierre Petit, Astrophysicist, France

Translated by Benjamin Rottier

We have all seen how vulnerable skyscrapers are, as were the Twin Towers, the pride of Manhattan, an assembly of iron and concrete.

Note, 1/30/2008. I wrote these lines on 9/17/2001: When the terrorists crashed their airplanes into the towers, they had chosen planes full of fuel, knowing that its ignition would cause the towers to collapse. Without this use of heat, the towers would have been seriously damaged but would have stood. This phenomenon of successive floor collapse is inevitable. If such an event were to happen again, building occupants should be able to evacuate quickly, before the heat has its disastrous effects.

This shows how quickly we believed in the official theory. Things have changed since.

After the fire in San Francisco, Americans, traumatized by its effects, had made outside staircases the norm. But this solution could not be applied to very tall buildings. We propose another solution here, to be examined.

Below is the general evacuation plan of the tower, carried out outside, along cables. These cables are fixed on drums, placed at different heights depending on the number of people to evacuate. Thus, the central A cable would be assigned to the rescue of the residents on that side of the building. On the top left, the unwinding system. The drum is unlocked by activating a mechanism inside, near the corresponding evacuation post. The cable is pulled down by a shaped weight (to prevent it from getting caught on the building's facade), the speed being limited by an aerodynamic brake.

As noted by Canadian engineer Alexandre Berube, more cables would be needed for the upper floors. With all due respect to my Canadian friend Norman, the use of standard climbing devices and ascent ropes is not possible. Indeed, you have to zigzag the rope to attach the climbing device. This is impossible if the rope is being pulled by several people still descending below.

The "socks" evacuation system has been mentioned. It is very clever. Long nylon tubes are unrolled along the facade. People enter through the top. No one can suffocate because of their permeability. It is impossible to stop the descent, as there is no relief inside; this prevents lifeless bodies from getting stuck. The speed is limited by the friction of clothes on the inner surface of the tube. It is almost the same for everyone, regardless of height or build. Indeed, Norman said that a taller person would have a larger contact surface with the tube. The vertical speed is about 2 m/s. Since the tubes do not reach the ground, the evacuation is automatic. Of course, people can only enter the tube at one point, but increasing the number of tubes would solve this problem. These devices are also quite cheap and can be produced in large quantities. The only drawback: if people are wearing short-sleeved shirts or shorts and the building is very tall, the friction on the skin could cause burns. But suffering from minor burns is better than being buried under iron and concrete rubble, isn't it?

A remark: are buildings located in high seismic risk areas equipped with such evacuation systems? Remember a few things. When an earthquake occurs and if the building does not collapse, its deformation systematically jams all the doors in their frames, and it is absolutely impossible to open them. You will have to break them, if you can. Moreover, as in the case of a fire, stairwells are the first structures to be damaged. Remember also that there are often successive tremors. How many people would have been saved, even in buildings with just a few floors, if they could have evacuated as soon as the first signs appeared?

On the following drawing, an inside view of the evacuation post. Only these windows can be fully opened and lead to a small platform where a few people can stand without the risk of slipping. Stairs allow quick access to the evacuation platform. You can see the cable unrolled (diameter: about 5 mm). Below: the cable unwinding and a view of the rotating aerodynamic brake.

On the drawing below, a group of people (a couple with a child) about to jump. Each piece of equipment will be detailed later.

Below, the base of the mechanism. It is a descent brake, working on friction. In A, the flexible paddle system, derived from car centrifugal clutches, in its casing. The paddle system is shown outside its casing in D. The flexible steel paddles are connected to elements that rub on the inside of the E drum. In B, you can see the cable rubbing on one of the rollers, interdependent with a gear that increases the rotation. In C, a schematic: on the right, the roller and the gear; on the left, the braking paddles rotating in their housing. In G, a storage cupboard for two devices, different in the way they are connected to the descent brake. On the left, a simplified harness (similar to the harnesses used to hoist someone from a helicopter).

The following drawings: the complete descent brake. The paddles working on friction are no longer visible. They are enclosed in their casing. A image: the "cable-cover" is at the top, in the unlocked position. The device is stored in this configuration, hanging by the suspension hook. Below, a plate interdependent with the two casings (the second one containing the gear that increases the rotation, interdependent with the rubber roller you can see a part of, black-colored). The plate is equipped with a carabiner for people to hang on. The system has a groove in which the cable is placed. The cable is strongly tightened by the heavy weight that brought it down to the ground, it is connected by a tension spring (to prevent the cable from being moved by the wind). The cable then has to be enclosed in the groove by turning the cable-cover and the hand braking handle 180°. B drawing: system ready for descent. The triangular-shaped cable-cover hides the groove in which the cable has been inserted. Doing this, the cable is pressed against the first rubber roller. The hand braking control handle is downwards. In C, a side view of the device.

Next drawing: storage. A: the descent brake hanging, hand brake upwards, in the unlocked position. You can see the groove in which the cable runs. In B, a nylon harness looking like pants so that lifeless people or people prone to panic can be evacuated. Being hoisted up from a helicopter or jumping from a height of 400 meters may not give the same sensations. Elderly people, people with limited mobility or children should not be forgotten. In C, someone pulling on the pants-harness. In D, he tightens the suspenders. Near him, a person equipped with a simplified harness (similar to the one used for hoisting). The suspension is done by a sewn nylon strap, ending with a carabiner.

Below, a man ready to jump. His descent brake is in position. The cable-cover is closed, thus ensuring the contact of the cable with the rollers. He has tightened his suspenders and is attached to the brake. He holds his suspension strap in his right hand and is about to grab the hand brake with his left one. None of these grips is essential for safety, the device being able to descend automatically to the ground.

On this aerial view, someone descending. His left hand is on the hand brake, which he will use theoretically only near the ground to avoid hitting a person who has already reached their destination but has not yet left or been removed. A person of normal weight could descend at about 2 m/s. The friction being proportional to the square of the descent speed, this would not increase much if several people were hanging from the same brake or if the people were heavier. When I jumped with old hemispherical parachutes, the usual vertical speed at the time of impact was 6 m/s.

Next view: several people on the same climbing device. Anyway, a person in charge of the evacuation post would stand at each platform. He would fix the descent brake to the cable and the carabiner to the people arriving. He would show them the hand brake, remind them of its use, and check that everything is in order before allowing the jump.

Finally, people must be received. To make the evacuation as quick as possible, people would be spaced only a few feet apart on the same cable. It is up to them to control their descent speed using the manual brake, and to maintain a distance from the person below, without ever reducing the vertical flow. Two people would play a major role in the evacuation operations (there should be periodic training): the first one would use the cable to wait on the ground for the "loads". He would quickly remove the climbing devices, lifting the cable-cover, thus allowing the cable to exit the groove. Above, someone has used his brake and is waiting, in order not to disrupt the operation (B). In the foreground, someone is moving away quickly (D).

If such a system had been installed on each of the four sides of the New York towers, thousands of human lives could have been saved. But who could have foreseen such horror?

Today, we know.

September 17th, 2001

The unwinding of the cables remains problematic, especially from several hundred meters, due to the effect of crosswinds. The cables must not tangle due to a gust of wind, otherwise people would collide with each other. We had simply considered a heavy weight. But no weight could tighten the cable if it is two, three or even four hundred meters long. The solution would therefore be to lock the cable at the bottom. To do this, the weights could be shaped as shells (B) and drop (A) quite quickly (minimal aerodynamic braking) into shafts blocked by plastic manhole covers, strong enough to support a person's weight but fragile enough to explode upon impact. The shells would align in cone-shaped guides. The locking could be automatic.

In D, the person who triggered the cable's drop could tighten it using a simple lever (M). If, as mentioned above, the cables were assigned to the evacuation of a finite number of floors, the unwinding and tightening of the cable could be done from several operating and evacuation posts (as one of them could be inaccessible).

We have here spoken about a friction brake, derived from car clutches. A system derived from the classic James Watt's fly-ball governor could ensure a constant descent speed, regardless of the load (because this system has a very "non-linear" response).

Fly-ball governor

Under these conditions, the manual brakes could be removed, which would probably be better. Indeed, there is a risk that someone panicking or becoming dizzy might grip the brake too tightly, thus blocking the entire evacuation chain. If people descend at very similar speeds, spacing the jumps from the platform would give the person on the ground enough time to free the arriving people.

All of the above is only ideas I have written down as they came to me. But they seem to show that it is possible, without modifying existing buildings, to equip them with an effective evacuation system. No one had foreseen the effects of such terrorist attacks on the building structures. No firefighter, no architect, no security expert could have imagined that the structure could be attacked in a very short time due to the presence of thousands of liters of kerosene softening the steel reinforcements, leading to the collapse of floors like dominoes. In the future, even the most incredible ideas must be considered.

One more word:

This text will not be followed by a patent filing. I believe some things are more urgent than trying to make money in the security business. Above all, human lives must be saved. Thus, these ideas are completely free for anyone wishing to apply them. When your house is on fire, you don't waste time cleaning the living room.

**From November 15th, 2001, number of connections: ** ---