General Safety of Skyscrapers
**Note dated January 30, 2008. **
I wrote this sentence on September 17, 2001 :
We recently saw (September 2001) the extreme vulnerability of the huge skyscrapers, like the twin towers, the pride of Manhattan, assemblies of iron and concrete. When the terrorists crashed their two planes into these towers, they deliberately chose fully fueled aircraft that had just taken off, knowing that the combustion of the fuel would cause a drastic weakening of the structure and, eventually, its collapse like a house of cards. Without this use of heat, the towers would have suffered significant damage, but would have remained standing. This phenomenon of successive floor collapses, like dominoes, is unstoppable. If such an event were to happen again, it would be important that the building's occupants could evacuate in record time, before the heat effect could take place.
This shows how we all believed in the official theory, without asking questions, immediately after the event
...After the San Francisco fire, Americans, traumatized by the effects of fire in that city, generalized the installation of external staircases. But this solution could not be implemented for large buildings. We propose here a solution, to be studied.
...Below is the general evacuation plan of the tower, which takes place outside, along cables. These cables are fixed on drums that start at different floors, depending on the population to be evacuated. Thus, the central cable A would be assigned to the rescue of residents on the floors in the range a, for this face of the building, which, if isolated, could have four. At the top and to the left, the drum system. When the activation order is given, inside the building, near the corresponding evacuation post, the drum is unlocked. Drawn by a shaped counterweight (to avoid catching on any possible relief of the facade), the cable unwinds at a high speed, but limited by an aerodynamic braking system (using rotating paddles, coupled by a gear train).
...As highlighted by Canadian engineer Alexandre Berube, a greater number of cables would be needed for the upper floors. Despite what my Canadian friend Norman might say, the use of traditional descenders and climbing ropes would not work. Indeed, to install such a descender, it is necessary for the rope to make a zigzag. Impossible, if this rope is already under tension by several people using it below.
...The "sock" evacuation system has also been mentioned. It is very clever. Long nylon tubes are deployed on the facade. People just have to enter through their upper opening. Their permeability makes it impossible to suffocate. It is also impossible to resist the descent once it has begun: there is no internal relief, which also makes it impossible to get stuck with the bodies of unconscious people. The speed is limited by the friction of the clothes on the tube wall. It is approximately constant for all individuals, regardless of their size and build. Indeed, as Norman points out, a larger person will have a larger contact surface with the tube fabric. Speeds are around 2m/s. As the tubes do not touch the ground, the evacuation of people is automatic. Obviously, these tubes can only be accessed through one point. But by multiplying them, this problem could be circumvented. These are relatively inexpensive devices, which can be mass-produced. The only drawback is that if people using these tubes are wearing short-sleeved shirts or shorts, and if the buildings are tall, the friction on the skin could cause some burns. But are slight burns not preferable to being trapped in a tangle of iron and concrete after the building's collapse?
...A remark: are buildings located in high seismic risk areas equipped with such evacuation systems? One must remember several things. In the case of an earthquake, if the buildings do not collapse, their deformation will systematically jam all doors in their frames, making it absolutely impossible to open them. They must be forced open, if one is able to do so. Moreover, as in fires, the first structures to be affected are the stairwells. One must also remember that earthquakes sometimes occur in successive shocks, not through a single wave. How many people could have been saved, even from a low-rise building, if they could have evacuated at the first signs of the event?
...In the following drawing, an evacuation post seen from the inside. Only these windows can open fully and lead to a small platform where several people can stand without the risk of slipping. The other windows have an opening possibility as a ventilation system, not as an escape route. An staircase allows quick access to the evacuation platform. Visible: the unwound cable (diameter: about 5 mm). Bottom image: the unwinding of a rescue cable in progress, with a view of the rotating aerodynamic brake.
...In the image below, a group of people (a couple with a child) in the evacuation position. The equipment of each will be specified later.
...Below is the basic mechanism. It is a descent reducer, which works by friction. In A, in its casing, the flexible paddle system derived from centrifugal clutches (2 CV Citroën). The paddle system is removed from its casing in D. The flexible steel blades are connected to pads that rub against the inner part of the bowl E. In B, you can see the cable rubbing against one of the rollers, which is connected to a gear train, multiplying the rotation. In C, a schematic view. On the right, the roller-gear assembly. On the left, the braking paddles rotating in their bowl. In G, a storage cabinet for two different coupling devices for the descent reducer. On the left, a simplified harness (similar to those used for helicopter rescues from helicopters).
...Next drawings: the complete descent reducer. The friction-based paddles are no longer visible. They are enclosed in their casing. Image A: the cable cover is raised, unlocked. This is also the configuration in which the system is stored, in a closet, hanging by the suspension hook visible at the top. At the bottom, a soldered plate of the two casings (in the second, the gear multiplier turns, connected to the rubber roller, operating by friction, of which a small part is visible in black). The plate is equipped with a carabiner for attachment. The system has a groove into which the cable is inserted, which is strongly tensioned by the heavy weight that brought it into contact with the ground, and is held there by a tension spring (this to prevent the cables from being moved by the wind). It remains to trap the cable in this groove, by rotating 180° the entire "cable cover" plus manual braking handle. Drawing B, the system ready for descent. The triangular cable cover has hidden the groove into which the cable was inserted. This action pressed the cable against the first rubber roller, visible here in transparency. The manual braking handle is at the bottom. In C a side view of the device.
...Next drawing: the storage elements. A: the descent reducer fixed, manual brake on top, unlocked configuration. Visible: the groove where the cable is inserted. In B a nylon harness that looks like pants. This way, unconscious people or those prone to panic could be evacuated. Being hoisted by a helicopter or swinging from a height of 400 meters are certainly not the same experiences. One must also think about elderly people, or those with mobility issues, or children. In C a person is putting on this pant-shaped harness. In D he tightens the straps. Beside him, a person equipped with a simpler harness (helicopter rescue style). The suspension of people is ensured by a simple nylon strap sewn, ending in a carabiner.
...Below, a person ready for the big jump. His descent reducer has been positioned. The cable cover is lowered, thus ensuring the contact between the rollers and the cable. He has tightened his straps and attached himself to the descent reducer. He holds his suspension strap in his right hand and is about to grab the brake handle with his left hand. None of these grips are essential for his safety, as the device can deposit its load on the ground completely autonomously.
...In this overhead view, an individual in the process of descending. His left hand is on the manual brake, which he would normally only activate near the ground, to avoid colliding with a person already arrived at the destination and not yet cleared, or not yet cleared. A person of "normal weight" could descend at about 2m/s. The friction being proportional to the square of the descent speed, it would not be much increased if several people were to hang from the same descent reducer or if the person's weight was greater. In the old hemispherical parachutes I used, the normal speed at impact was 6m/s.
...Next view: the theme of using a single descender by multiple people. In any case, during these maneuvers, a post evacuation supervisor would be stationed at each platform, on the ground with the window. He would attach the descent reducers to the cable, then the carabiners of the people who arrived. He would indicate the brake handle, remind them of its purpose, ensure everything is in order before giving them the green light for the jump.
...Finally, it is necessary to ensure the reception of people who, in order for the evacuation of the tower to be as fast as possible, will follow each other closely on the same cable. It is up to them, with their manual brake (of the "climbing descender" type), to control their descent speed and thus maintain their distance from the person below, without slowing the vertical flow. In the evacuation maneuvers, which should be the subject of periodic exercises for the resident staff and training for new employees, two people would play a key role. The first would use the cable to position himself at the bottom, at the reception of the "packages". He would be quick to perform the disengagement maneuver of the "cable covers" by turning the lever, thus allowing the cable to be freed from its groove. Above, a person who has activated his manual brake to wait and not interfere with the maneuver. In the foreground, another person quickly leaves the area.
...If such a system had been in place on all four sides of each of the twin towers in New York, it would have saved thousands of human lives. But who could have predicted such horror?
...Now, we know.
September 17, 2001.
...The deployment of cables, especially from today's towers reaching several hundred meters, remains problematic due to the effect of possible lateral wind. It should not be that, under the effect of strong gusts, these cables become entangled and people get caught on each other. We had simply considered a heavy weight. But with a cable deployed over two hundred, three hundred or even four hundred meters, no weight would be able to keep a cable under tension subjected to lateral wind. The solution would therefore be to lock this weight at the bottom. For this, these cable weights could be shaped like shells (B) and descend (A), quite quickly (minimal aerodynamic braking) into shafts sealed by plastic covers, strong enough to withstand the weight of a person, but fragile enough to burst upon impact of the shell. The shell would center itself in a conical entrance housing (C). The locking could be automatic.
...In D, an operator who, after triggering the vertical deployment of the cable, can maintain its tension with a simple crank. If, as mentioned at the beginning of the document, sets of cables would be assigned to the evacuation of a limited number of floors, the deployment and tensioning of the cable could be carried out from several evacuation and maneuver posts (just because one of them could be inaccessible for any reason).
...A friction-based reducer, inspired by car clutches, was considered. It is possible that a system inspired by the classic "Watt's governor", by James Watt:
**Ball governor. **
could ensure a constant descent speed, regardless of the load (given the device's very "non-linear" response). In these conditions, and this would probably be preferable, manual brakes could be eliminated. There would indeed be a risk that one of the people, completely panicking or seized by vertigo, would grip this brake, thus blocking the entire evacuation chain. If people can descend at very similar speeds, then it would be sufficient to space out the departures from the platform so that the person in charge of reception at the bottom has time to clear those who arrive.
...These are just random ideas. But they seem to indicate that by modifying existing buildings, one can equip them with an efficient evacuation system. No one had actually thought about the terrible impact of such attacks on the structure. No firefighter, no architect, no safety specialist in the world would have imagined that the structure could be attacked in a very short time by the introduction of several tens of thousands of liters of kerosene, which would ignite upon impact, softening the steel structures in a matter of minutes, then causing the floors to collapse "like dominoes", a catastrophe which, as a seismic specialist pointed out, leaves even fewer chances for humans caught in such a trap. All fire scenarios have been considered in these "infernal towers", including the effect of explosives brought on site. But no one had imagined "that one could bring so quickly tens of thousands of extremely flammable fluids". In the future, the most insane ideas must be taken into consideration, in the style of the worst scenarios of James Bond movies, reviewing the entire available technological palette. The way the commander Massoud was killed recently (explosives placed in television cameras brought by kamikaze cameramen) represents a new variant of this new weapon: suicide terrorism.
....................................................................................................................................**.**J.P.Petit 18 sept 2001
A clarification :
...This text is not the preface to a patent filing. I believe there is more urgent than trying to get rich with the "security industry". It is above all to save lives. Thus, these ideas, if they can be useful to anyone who can implement them, are obviously free. When the house is on fire, one does not have time to paint the living room.
Sommaire "Dangers" Sommaire
"Géopolitique"
Counter initialized on September 18, 2001
