Hermetic doors

For now, let's turn our attention to the sealed subway doors. Such thick-walled metal gates, usually located at the entrance to the station or in inter-station passages. They are different, but always half a meter thick.

On the left photo - a sealed door at the exit of the "Griboyedov Canal" station Gostiny Dvor. As you can see, it is of the vertical type ("guillotine").

In the center - a sealed door at the station Elektrosila, lifting type ("toilet lid").

On the right photo - a sealed door at the station exit Leninsky Prospect, sliding type ("compartment door").

Petersburg metro, Gostiny Dvor station, guillotine-type hermetic door

Petersburg metro, station Elektrosila, sealed door type toilet lid

Petersburg metro, Leninsky Prospekt station, a sealed compartment door

There are also swing doors, for example, in tunnels - there they are installed at least in areas under the Neva or quicksand:

Here is one of the doors on the stretch between the stations Gostiny Dvor and Vasileostrovskaya:

Petersburg metro, a sealed door in a tunnel under the Neva

And here is the sealed door on the stretch between the stations Chkalovskaya and Sportivnaya (upper hall):

But there are also tunnel-type hermetic doors of the "closet-compartment" type (leaving from the side):

Petersburg metro, wardrobe-type hermetic door in the tunnel

Also, before each line exits to the surface in the tunnel 2-3 sealed doors are placed in a row, after 30-40 meters. In all cases, the gates are controlled by an electric drive:

It would seem that from the flooding of the metro, if something happened, the pressurized doors at the stations would still not save, why are they needed?

To answer this question, let's turn to a couple of videos. Let's say right away - in all the videos we are talking about weak explosions within ten kilotons.

Ground explosion:

Underground explosion:

According to the standards of the USSR and now Russia, the metro was originally a dual-purpose structure:

When designing most underground subways (in Russia - all), the need to ensure the possibility of using them as a refuge for the population in emergency situations is taken into account. For this, as a rule, provision is made for equipping stations and stretches with emergency autonomous filtering, lighting and water supply systems, emergency exits, sealing systems for stations and ventilation shafts (including automatic ones, from the action of a blast wave, etc.). According to the standards in force in Russia, the metro must provide shelter to the population for two days: it is assumed that during this time the radiation level will drop to values at which it will be possible to evacuate the population outside the affected area. At the same time, in practice, the fulfillment of these requirements depends on the wishes of the customer, in connection with which the new stations of the Moscow metro are equipped with metal structures almost all, while in the Kazan metro civil defense systems for reasons of economy have been installed so far only at 4 out of 6 stations.

To protect the people inside, the station must withstand the explosion of a standard warhead at the head of the mine (well, or an escalator slope). The exact data is classified, but the parameters are not difficult to determine. The USA, like us, has several standard yields warheads, and if the average calibers coincide (100-159, 250-300, 450-500, 750-850 kilotons or so), then there is a significant difference for large ones - our maximum typical 25 megatons versus their maximum typical 9 megatons. It just so happened - we initially had an order of magnitude more powerful missiles, but problems with accuracy. Therefore, they took more, threw on. In the USA, on the contrary, everything was very good with accuracy, but with powerful missiles it was strained. By the end of the USSR, everything was roughly equal.

So. Shooting a megaton warhead at a metro station is economically profitable only if the President of All Russia himself is hiding inside the station. And even then it is questionable, because the cost of such a warhead is much higher than the cost of the entire metro station with construction, decoration and crew. It is difficult to hit (circular error probable even with the best warheads, both ours and the United States, is about one hundred and fifty meters). Therefore, we proceed from the fact that the probability of large megatons hitting directly into the mine is rather small.

Now let's see what will happen to our glorious Saint-Petersburg if we drop a one megaton warhead on it. By the way, in the early 90s, we were repeatedly taught, both at school and at the military department, that according to NATO military plans, 21 warheads are aimed at Saint-Petersburg, 20 medium (read - 500 kilotons) and one large (read - one and a half megatons), to the center, according to the principle "finish off everything that moves".

By the way - a video of the arrival of warheads at the Kura training ground. This is how the End of the World will look like for the unlucky, with one amendment - the block does not have to reach the ground, an explosion at a height of a kilometer or two or three may be more effective:

So, first, for an air explosion of one megaton at an altitude of one and a half kilometers (optimal altitude):

110 meters from the point of explosion, 6 microseconds before the arrival of the shock wave. A seismic shift destroys metro tunnels with various types of attachment at depths of 10 and 20 m, animals in tunnels at depths of 10, 20 and 30 m die.
215 meters, 9 microseconds. Destruction of the head of the trunks leading to the metro tunnels under the epicenter. Each head was a powerful reinforced concrete casemate on the foundation of a large supporting area to keep the head from being pressed into the barrel; from above it is covered with a small earth embankment. The fragments of the heads fell into the trunks, the latter then crushed by the seismic wave.
240 meters, 0.015 seconds. Strong destruction of rocks (50-200 MPa). The speed of the shock wave is higher than the speed of sound in the metal: theoretical ultimate strength of the entrance door to the shelter; the tank is flattened and burned.
About 300 meters - the limit of guaranteed defeat of the modern silo launcher of the Soviet "Satan" (apparently, and other modern missiles of the Russian Federation).
320 meters, 0.028 seconds. The person is dispersed by the flow of plasma (the speed of the shock wave = the speed of sound in the bones, the body collapses into dust and immediately burns up). Complete destruction of the most durable ground structures (speed of sound in concrete).
About 435 meters - the limit of guaranteed destruction of a modern silo launcher of US and French ballistic missiles.
Between 435 and 530 meters, from 0.06 to 0.1 seconds. A subway-type shelter, lined with cast-iron tubing and monolithic reinforced concrete and buried 18 meters, received minor deformations and damage. The entrance to the building is not an ordinary pavilion, but a reinforced concrete casemate with massive doors.
Up to 530 meters, up to 0.1 seconds. An unprotected person does not have time to see the explosion and dies without suffering (a person's visual reaction time is 0.1-0.3 s, a reaction time to a burn is 0.15-0.2 s).
630 meters, 0.25 seconds. The person turns into charred wreckage: the shock wave causes traumatic amputations, and the fiery sphere that overtook the discarded body charred the remains. Complete destruction of the tank. Complete destruction of underground cable lines, water pipes, gas pipelines, sewerage systems, inspection wells. Destruction of underground reinforced concrete pipes with a diameter of 1.5 m, with a wall thickness of 0.2 m. Severe destruction of long-term reinforced concrete forts. Severe deformation and damage to buried vaulted concrete defenses. Minor damage to underground metro structures.
800 meters, 0.4 seconds. Heating up to 3000°C. Complete destruction of all protective structures of civil defense (shelters), destruction of protective devices of entrances to the metro. Cracking in buried vaulted concrete structures, possible damage to entrance doors.
1100 meters, 0.5 seconds. In one and a half seconds, there will be the border of the fiery sphere of a nuclear explosion.
1500 meters, 1.15 seconds. The conditions for the shock wave are close to those in the area of the epicenter of the explosion in Hiroshima (~ 20 kt). Estimated pressure of the shock wave for the design of structures and protective devices for underground structures of deep underground lines. Severe deformation of ground vaulted steel defenses in the form of bulging inward. A man in a standing position - with an explosion of 0.5 Mt (i.e., twice as weak), is thrown by a shock wave (not at the epicenter, the wave goes parallel to the ground) at a distance of over 300 m with an initial speed of over 575 km/h, of which 100–150m (0.3–0.5 track) free flight, and the rest of the distance - numerous ricochets against the ground; in the prone position, the rejection is over 190m at a speed of 216 km/h.
1600 meters, 1.4 seconds. A person in a concrete shelter with a ceiling thickness of 73 cm will receive fatal radiation damage. The tank is thrown about 10 m and damaged. Damage to ventilation and entrance doors at ground vaulted steel defenses.
1750 meters, 1.6 seconds. Complete destruction of concrete, reinforced concrete monolithic (low-rise) and earthquake-resistant buildings, built-in and detached shelters, shelters in the basements of high-rise buildings.
2100 meters, 2.4 seconds. All urban development turns into solid rubble (separate rubble merges into one solid one), the height of rubble can be 3-4 m.
2230 meters, 2.6 seconds. Design pressure of the shock wave for the design of structures and protective devices for underground structures of shallow metro lines.
2550 meters, 3.2 seconds. At an explosion height of ~1.5km, a joint direct and reflected bow shock wave appears at the surface. At this time, within a radius of more than 1.5 km from the center, the pressure drops to 0.8 atm and remains for several seconds; in case of a ground or low air explosion, this effect can squeeze and open a protective door to a shelter and even raise a 0.9 m thick concrete ceiling. Complete destruction of reinforced concrete buildings with a large glazing area.

Well, further it is no longer so interesting - fires, destruction, but you can already survive, just standing right under the nuclear mushroom on the street. If you're lucky. Interesting:

Up to 5 kilometers and 10 seconds. A person will not hear the roar of an explosion due to hearing damage and shock wave concussion.
32 kilometers, one and a half minutes. The maximum radius of damage to unprotected sensitive electrical equipment by an electromagnetic pulse. Almost all the usual ones are broken and some of the reinforced glass in the windows is actually a frosty winter, plus the possibility of cuts by flying fragments. 160 dB - the sound of a shot from a gun near (not close) to the ear. "Mushroom" climbed to 10 km, the ascent speed ~ 220 km / h.
48 kilometers, 3 minutes. The border of massive glass knockouts in windows. Sound 140-150 dB - noise next to an aircraft taking off, 140 dB - maximum volume at a rock concert.
85 kilometers, 4 minutes. From this distance, the fireball looks like a large unnaturally bright Sun near the horizon, and at the time of the first maximum of 0.001 s, a flash many times brighter than the midday luminary can cause a retinal burn, a rush of heat to the face. The approaching shock wave can still knock down a person and break individual glass in the windows. Further, it finally loses its deafening and destructive power and degenerates into a thunderous sound. "Mushroom" climbed over 16 km, ascent speed ~ 140 km/h.

Now let's imagine that the explosion is ground. In general, with ground explosions, everything is more interesting. They are just designed to destroy ballistic missile silos and underground command posts.

Also, a ground contact explosion digs out a large pit - a funnel (reminiscent of a meteorite crater), scattering radioactive soil around and generating powerful seismic explosive waves in the soil mass, not far from the epicenter many orders of magnitude stronger than during ordinary earthquakes. The action of seismic vibrations makes shelters of increased security ineffective, since people in them can die or be damaged even if the shelter retains its protective properties from other damaging factors, and not far from the crater there is no chance for such protected objects as tunnels and metro stations to survive deep-laid and even especially important shelters and command posts. Unless they are built at a depth of several hundred meters - kilometers and preferably in continental rock (Yamantau, command post NORAD). So, for example, the B53 nuclear bomb (the same charge - the W-53 warhead of the Titan-2 rocket, taken out of service) with a capacity of 9 megatons, according to American experts, was capable of destroying the most durable Soviet underground bunkers in a surface explosion. Only buried warheads, in which a much larger percentage of energy is spent on the formation of seismic waves, have a greater destructive ability to protected targets: a 300-kiloton B61 aerial bomb in an explosion after impact penetration to a depth of several meters, in terms of seismic effect, it can turn out to be equivalent to 9-megaton in an explosion at surfaces (theoretically).

Consider the sequence of effects of a ground explosion on a silo launcher, designed for a shock wave with a pressure of ~ 6-7 MPa and falling into these most difficult conditions for it. An explosion occurred, radiation almost instantly reaches (mainly neutron, in total about 10⁵ - 10⁶ Gray or 10⁷ - 10⁸ R), after ~0.05-0.1 s, an air shock wave hits the protective cover and immediately rolls the shaft of a fiery hemisphere. The shock wave generates a seismic shock in the soil, which almost simultaneously with the air wave rolls over the entire mine and displaces it along with the rocks downward, gradually weakening with depth; and after it in a split second come seismic vibrations, formed by the explosion itself during funnel formation, as well as reflected waves from a layer of rocky continental rocks and layers of inhomogeneous density. The mine shakes for about 3 seconds and several times throws it down, up, to the sides, the maximum vibration amplitudes can reach up to half a meter or more, with accelerations up to several hundred g; the missile is saved from destruction by a special damping system. At the same time, from above on the roof of the mine for 3-10 seconds (the time depends on the power of the explosion) a temperature of 5-6 thousand, and in the first half-second up to 30 thousand degrees, then falling rather quickly with the rise of a fiery cloud and the rush of cold outside air towards the epicenter... The head and protective cover creak and crack due to temperature effects, their surface melts and is partially carried away by the plasma flow. In 2-3 seconds after the explosion, the plasma pressure in the area of the mine drops to 80% of the atmospheric pressure, and for several seconds the lid tries to tear off the lifting force up to 2 tons per square meter. To top it off, soil and stones are falling down, thrown out of the funnel and continuing to fall for about a minute. The radioactive soil, heated to stickiness, forms a thin, but solid bulk (in some places with the formation of lakes from molten slag), and large stones can damage the lid. Particularly large debris, like meteorites, can dig up small craters when falling, but they are relatively few and the probability of falling into the mine is small. Not a single ground structure will survive such impacts, and even such strong structures as powerful reinforced concrete casemates are partially or completely destroyed and can be thrown out of their place by a high-speed air pressure. If the bunker is strong enough to resist destruction, people in it will still suffer injuries from vibrations with vibrations, hearing damage, contusions and fatal radiation injuries, and hot plasma can penetrate through embrasures and open passages.

So, we explode one megaton on the surface of the Earth:

100 meters to the point of explosion, 0.0015 seconds before the arrival of the shock wave in the ground. Here there will be a crater border in a rock up to 40 m deep. At a depth of 40 m, the rock is shifted to the side by ~ 5 m with an acceleration of thousands of g. Particularly durable underground structures (uninhabited) in granite rock at the limit of conservation.
160 meters. Complete destruction or severe displacement of a heavy shelter.
220 meters, 0.01 seconds. The security limit of a silo launcher in rocky ground.
250 meters, 0.015 seconds. Damage to the internal equipment of a heavy shelter, minor deformations, sometimes pipeline ruptures.
350 meters. The security limit of a silo launcher in normal soil.
400 meters. US silo launchers security limit.
470 meters, 0.09 seconds. The protection limit of a subway-type shelter is at a depth of 18 m, but the entrances to it will be completely destroyed and blocked.

Further uninteresting:

85 kilometers. A bright flash-hemisphere at this distance is almost all over the horizon, it becomes fully visible already at the stage of the dome and cloud. "Mushroom" over 16 km.
165 kilometers. A flash far beyond the horizon, glow and cloud visible. The "mushroom" has grown to its maximum size.

That is, in fact, why such massive sealed doors are needed in the metro. If you pass by - take a look, appreciate what it is - when the entire metro station, together with people, located at a depth of 60 meters, within a split second, several times shifts FULLY to and fro with an amplitude of several meters.