Tunnels

Posted by PITHOCRATES - January 22nd, 2014

Technology 101

A Bridge is a Fixed Structure that requires no Active Systems to Function

Bridges are dumb.  While tunnels are smart.  You can build a bridge and walk away from it.  And it will still work.  That is, you can still cross the bridge without anyone at the bridge doing anything.  It can even work in a power outage.  Even at night.  It may be dark.  But a car’s headlights will let a person cross safely.  Because a bridge doesn’t have to do much for people to use it.  All it has to do is stand there.  A tunnel, on the other hand, needs smart systems to make the tunnel passable and safe.

Bridges are high in the air.  Where there is plenty of fresh air to breathe.  If there is a car fire on the bridge all of that fresh air will allow other drivers to breathe as they drive around it.  And for first responders to breathe as they put that fire out.  They can use all the water they bring onto the bridge, too.  Even in a driving downpour.  For that water will just run off of that bridge without causing a drowning hazard.  Visibility doesn’t change driving onto or off of the bridge.  Unlike with tunnels.  Where you can go from bright daylight into a dark hole.  And from a dark hole into bright daylight.

A bridge is a fixed structure that requires no active systems to function.  Just some maintenance.  Painting and roadway lighting.  Maybe some traffic control signals.  But that’s about it.  Tunnels, on the other hand, need machinery.  Equipment.  Systems.  And people.  Because tunneling below grade causes a whole host of problems.  Problems that have to be addressed with machinery, equipment and systems.  And if they don’t work people can die in a tunnel.

Powerful fans at each end of the tunnel pull in fresh air and blow it through the duct under the roadway

Cars have internal combustion engines.  They exhaust carbon monoxide after combustion.  Which is poisonous if we breathe it.  A big problem in tunnels filled with cars with internal combustion engines.  Which is why if you look at a cross-sectional view of a tunnel you will see that the biggest section of these underground structures are used for moving air.

If you have driven through a tunnel you probably remember driving through a rectangular tube.  Little bigger than the vehicles driving through it.  What you don’t see is the air duct beneath the roadway.  And the air duct above the roadway.  Powerful fans at each end of the tunnel pull in fresh air from the atmosphere and blow it through the duct under the roadway.  It exits the duct at about exhaust pipe level.  This fresh air blows into the rectangular tube where cars are pumping in carbon monoxide.

Other powerful fans are also located at each end of the tunnel that pull air out of the tunnel.  Via the duct over the roadway.  Fresh air comes in from below.  Mixes with the poisonous carbon monoxide.  This gets sucked into openings overhead.  Into the duct over the roadway.  And vents to the atmosphere at either end of the tunnel.  Allowing these poison-making machines to travel underground in an enclosed space without killing people.

A Tunnel is a Complex Machine that requires Intelligent Programming not to put People in Danger

Tunnels through mountains go through porous rock that drip water into the tunnel.  Tunnels under bodies of water are low in the middle and high at the ends.  Making each tunnel portal a massive storm drain when it rains.  And water in a tunnel is a dangerous thing.  It can freeze.  It can get deep.  It can cause an accident.  It can drown people.  So when it enters the tunnel you need to pump it out.  Tunnels have storm drains that drain any water entering the tunnel to a sump at a low point.  And pumps move this water from the sump out of the tunnel.

Ever spend an hour or so shoveling snow on a bright day?  And then go inside only to temporarily lose your vision?  This is snow blindness.  Your pupils shrink down to a tiny dot outside to block much of the bright sun and the light reflecting from the snow and ice. And when you walk inside that tiny dot of a pupil won’t let enough light into your eye so you can see in the reduced lighting level.  After awhile your pupils begin to dilate.  And you can see.  Same thing happens when driving into a tunnel.  Of course, temporarily losing your vision while driving a car can be dangerous.  So they add a lot of lights at the entrance of a tunnel.  To replicate sunlight.  And as you drive through the tunnel the lighting levels fall as your eyes adjust.  At night they reduce the lighting levels to prevent blinding drives as they enter.  And prevent snow blindness when exiting the tunnel.

A bridge doesn’t need any of these systems.  But a tunnel won’t work without them.  As people could die in these tunnels.  Because it’s dangerous when people go below grade with machines that create poison.  So tunnels need computers and control systems.  To monitor existing conditions such as exterior lighting levels, carbon monoxide levels, smoke and fire detection, water levels and high water alarms, etc.  Based on these inputs a control system (or a person) turns lights on or off, increase or decrease supply and exhaust fan speeds, pump down the sump when it reaches a high water level, etc.  Only when these systems are on line and operating properly is driving through a tunnel as safe as driving over a bridge.  Because bridges are dumb things.  They only need to stand there to work.  While a tunnel is a complex machine.  That requires intelligent programming not to put people in danger.

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Corduroy Roads, Positive Buoyancy, Negative Buoyancy, Carbon Dioxide, Crush Depth, Pressurization, Rapid Decompression and Space

Posted by PITHOCRATES - May 9th, 2012

Technology 101

Early Submarines could not Stay Submerged for Long for the Carbon Dioxide the Crew Exhaled built up to Dangerous Levels

People can pretty much walk anywhere.  As long as the ground is fairly solid beneath our feet.  Ditto for horses.  Though they tend to sink a little deeper in the softer ground than people do.  Carts are another story.  And artillery trains.  For their narrow wheels and heavy weight distributed on them tend to sink when the earthen ground is wet.  Early armies needing to move cannon and wagons through swampy areas would first build roads through these areas.  Out of trees.  Called corduroy roads.  It was a bumpy ride.  But you could pull heavy loads with small footprints through otherwise impassable areas.  As armies mechanized trucks and jeeps with fatter rubber tires replaced the narrow wheels on wagons.  Then tracked vehicles came along.  Allowing the great weights of armored vehicles with large guns to move across open fields.  The long and wide footprints of these vehicles distributing that heavy weight over a larger area.  Still, nothing can beat the modern rubber tire on a paved road for a smooth ride.  And the lower resistance between tire and road increases gas mileage.  Which is why trucks like to use as few axles on their trailers as possible.  For the more tires on the road the more friction between truck and road.  And the higher fuel consumption to overcome that friction.  Which is why we have to weigh trucks for some try to cheat by pulling heavier loads with too few axles.  When they do the high weight distributed through too few wheels will cause great stresses on the roadway.  Causing them to break and crumble apart.   

Man and machine can move freely across pretty much anything.  If we don’t carry food and water with us we could even ‘live off the land’.  But one thing we can’t do is walk or drive on water.  We have to bridge streams and rivers.  Go around lakes.  Or move onto boats.  Which can drive on water.  If they are built right.  And are buoyant.  Because if a boat weighed less than the water it displaced it floated.  Much like a pair of light-weight, spongy flip-flops made out of foam rubber.  Throw a pair into the water and they will float.  Put them on your feet and step into the deep end of a pool and you’ll sink.  Because when worn on your feet the large weight of your body distributed to the light pair of flip-flops makes those flip-flops heavier than the water they displace.  And they, along with you, sink.  Unlike a boat.  Which is lighter than the water it displaces.  As long as it is not overloaded.  Even if it’s steel.  Or concrete.  You see, the weight of the boat includes all the air inside the hull.  So a large hull filled with cargo AND air will be lighter than the water it displaces.  Which is why boats float. 

Early sail ships had great range.  As long as the wind blew.  Their range only being limited by the amount of food and fresh water they carried.  Later steam engines and diesel-electric engines had greater freedom in navigation not having to depend on the prevailing winds.  But they had the same limitations of food and water.  And when we took boats under the water we had another limitation.  Fresh air.  Early submarines could not stay submerged for long.  For underwater they could not pull air into a diesel-electric engine.  So they had to run on batteries.  Which had a limited duration.  So early subs spent most of their time on the surface.  Where they could run their diesel engines to recharge their batteries.  And open their hatches to get fresh air into the boat.  For when submerged the carbon dioxide the crew exhaled built up.  If it built up too much you could become disoriented and pass out.  And die.  If a sub is under attack staying under water for too long and the levels of carbon dioxide build up to dangerous levels a captain has little choice but to surface and surrender.  So the crew can breathe again.

Rapid Decompression at Altitude can be Catastrophic and Violent

Being in a submarine has been historically one of the more dangerous places to be in any navy (second to being on the deck of an aircraft carrier).  Just breathing on a sub had been a challenge at times while trying to evade an enemy destroyer.  But there are other risks, too.  Some things float.  And some things sink.  A submarine is somewhere in between.  It will float on the surface when it has positive buoyancy.  And sink when it has negative buoyancy.  But submarines operate in the oceans.  Which are very deep.  And the deeper you go the greater the pressure of the water.  Because the deeper you go there is more ocean above you pressing down on you.  And oceans are heavy.  If a sub goes too deep this pressure will crush the steel hull like a beer can.  What we call crush depth.  Killing everyone on board.  So a sub cannot go too deep.  Which makes going below the surface a delicate and risky business.  To submerge they flood ballast tanks.  Replacing air within the hull with water.  Making it sink.  Other tanks fill with water as necessary to ‘trim’ the boat.  Make it level under water.  When under way they use forward propulsion to maintain depth and trim with control surfaces like on an airplane.  If everything goes well a submarine can sink.  Then stop at a depth below the surface.  And then resurface.  Modern nuclear submarines can make fresh water and clean air.  So they can stay submerged as long as they have food for the crew to eat.

An airplane has no such staying power like a sub.  For planes have nothing to keep them in air but forward propulsion.  So food and water are not as great an issue.  Fuel is.  And is the greatest limitation on a plane.  In the military they have special airplanes that fly on station to serve as gas stations in the air for fighters and bombers.  To extend their range.  And it is only fuel they take on.  For other than very long-range bombers a flight crew is rarely in the air for extended hours at a time.  Some bomber crews may be in the air for a day or more.  But there are few crew members.  So they can carry sufficient food and water for these longer missions.  As long as they can fly they are good.  And fairly comfortable.  Unlike the earlier bomber crews.  Who flew in unpressurized planes.  For it is very cold at high altitudes.  And there isn’t enough oxygen to breathe.  So these crew members had to wear Arctic gear to keep from freezing to death.  And breathe oxygen they carried with them in tanks.  Pressurizing aircraft removed these problems.  Which made being in a plane like being in a tall building on the ground.  Your ears may pop but that’s about all the discomfort you would feel.  If a plane lost its pressurization while flying, though, it got quite uncomfortable.  And dangerous. 

Rapid decompression at altitude can be catastrophic.  And violent.  The higher the altitude the lower the air pressure.  And the faster the air pressure inside the airplane equals the air pressure outside the airplane.  The air will get suck out so fast that it’ll take every last piece of dust with it.  And breathable air.  Oxygen masks will drop in the passenger compartment.  The flight attendants will scramble to make sure all passengers get on oxygen.  As does the flight crew.  Who call in an emergency.  And make an emergency descent to get below 10 thousand feet.  Almost free falling out of the sky while air traffic control clears all traffic from beneath them.  Once below 10 thousand feet they can level off and breathe normally.  But it will be very, very cold.

Man’s Desire is to Go where no Man has Gone before and where no Human Body should Be

Space flight shares some things in common with both submarines and airplanes.  Like airplanes they can’t fly without fuel.  The greatest distance we’ve ever flown in space was to the moon and back.  The Saturn V rocket of the Apollo program was mostly fuel.   The rocket was 354 feet tall.  And about 75% of it was a fuel tank.  In 3 stages.  The first stage burned for about 150 seconds.  The second stage burned for about 360 seconds.  The third stage burned for about 500 seconds (in two burns, the first to get into earth orbit and the second to escape earth orbit).  Add that up and it comes to approximately 16 minutes.  After that the astronauts were then coasting at about 25,000 miles per hour towards the moon.  Or where the moon would be when they get there.  The pull of earth’s gravity slowed it down until the pull of the moon’s gravity sped it back up.  So that’s a lot of fuel burned at one time to hurl the spacecraft towards the moon.  The remaining fuel on board used for minor course corrections.  And to escape lunar orbit.  For the coast back home.  There was no refueling available in space.  So if something went wrong there was a good chance that the spacecraft would just float forever through the universe with no way of returning home.  Much like a submarine that can’t keep from falling in the ocean.  If it falls too deep it, too, will be unable to return home.

Also like in a submarine food and fresh water are critical supplies.  They brought food with them.  And made their own water in space with fuel cells.  It had to last for the entire trip.  About 8 days.  For in space there were no ports or supply ships.  You were truly on your own.  And if something happened to your food and water supply you didn’t eat or drink.  If the failure was early in the mission you could abort and return home.  If you were already in lunar orbit it would make for a long trip home.  The lack of food and hydration placing greater stresses on the astronauts making the easiest of tasks difficult.  And the critical ones that got you through reentry nearly impossible.  Also like on a submarine fresh air to breathe is critical.  Even more so because of the smaller volume of the spacecraft.  Which can fill up with carbon dioxide very quickly.  And unlike a sub a spacecraft can’t open a hatch for fresh air.  All they can do is rely on a scrubber system to remove the carbon dioxide from their cramped quarters.

While a submarine has a thick hull to protect it from the crushing pressures of the ocean an airplane has a thin aluminum skin to keep a pressurized atmosphere inside the aircraft.  Just like a spacecraft.  But unlike an aircraft, a spacecraft can’t drop below 10,000 feet to a breathable atmosphere in the event of a catastrophic depressurization.  Worse, in the vacuum of space losing your breathable atmosphere is the least of your troubles.  The human body cannot function in a vacuum.  The gases in the lungs will expand in a vacuum and rupture the lungs.  Bubbles will enter the bloodstream.  Water will boil away (turn into a gas).  The mouth and eyes will dry out and lose their body heat through this evaporation.  The water in muscle and soft tissue will boil away, too.  Causing swelling.  And pain.  Dissolved nitrogen in the blood will reform into a gas.  Causing the bends.  And pain.  Anything exposed to the sun’s ultraviolet radiation will get a severe sunburn.  Causing pain.  You will be conscious at first.  Feeling all of this pain.  And you will know what is coming next.  Powerless to do anything about it.  Brain asphyxiation will then set in.  Hypoxia.  The body will be bloated, blue and unresponsive.  But the brain and heart would continue on.  Finally the blood boils.  And the heat stops.  In all about a minute and half to suffer and die.

Man is an adventurer.  From the first time we walked away from our home.  Rode the first horse.  Harnessed the power of steam.  Then conquered the third dimension in submarines, airplanes and spacecraft.  We are adventurers.  It’s why we crossed oceans and discovered the new world.  Why we climbed the highest mountains.  And descended to the oceans’ lowest depth.  Why we fly in airplanes.  And travelled to the moon and back.  When things worked well these were great adventures.  When they did not they were horrible nightmares.  While a few seek this adventure most of us are content to walk the surface of the earth.  To feel the sand through our toes.   Or walk to the poolside bar in our flip-flops.  To enjoy an adult beverage on a summer’s day.  While adventurers are still seeking out something new.  And waiting on technology to allow them to go where no man has gone before.  Especially if it’s a place no human body should be.

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