question: When underwater tunnels are built, why does a crack in the ceiling of the tunnel cause a powerful vacuum effect or a “blowout”?
comment: Neither. An underwater tunnel has high pressure water on the outside and atmospheric pressure air on the inside. If there is a crack, water squirts in, but in no sense is there a vacuum. Some crack geometries might let water in at the bottom and air out at the top, but only in very shallow water.
passages: Section::::Test facilities.:Cavitation tunnel.
   Additionally, many water tunnels are sealed and can reduce or increase the internal static pressure, to perform cavitation studies. These are referred to as cavitation tunnels.
  
  Section::::Methods.
   Work by Smith in 2007 confirmed prior forensic work by Faulkner in 1998 and determined that the MV "Derbyshire" was exposed to a hydrostatic pressure of a "static head" of water of about with a resultant static pressure of . This is in effect of green water (possibly a "super rogue wave") flowing over the vessel. The deck cargo hatches on the "Derbyshire" were determined to be the key point of failure when the rogue wave washed over the ship. The design of the hatches only allowed for a static pressure of less than of water or , in other words the typhoon load on the hatches was more than ten times the design load. The forensic structural analysis of the wreck of the "Derbyshire" is now widely regarded as irrefutable.
   Section::::Application Characteristics.:Air leakage in UFAD plenums.
   Section::::Shock instability or buzz.
  
  Under certain conditions, the shock wave in front or within a duct may be unstable, and oscillate upstream and downstream. This phenomenon is known as buzz. Stronger shock waves interacting with low momentum fluid or boundary layer tend to be unsteady and cause buzz. Buzz conditions can cause structural dynamics-induced failure if adequate margins are not incorporated into design.
   In the hydrostatic test, a vessel is filled with a nearly incompressible liquid – usually water or oil – and examined for leaks or permanent changes in shape. The test pressure is always considerably higher than the operating pressure to give a margin for safety, typically 150% of the operating pressure.
  
  Section::::Test mechanisms.:Burst test.
  
  In the burst test, a vessel is filled with a gas and tested for leaks. The test pressure is always considerably more than the operating pressure to give a margin for safety, typically 200% or more of the operating pressure.
  
  Section::::Test mechanisms.:Helium leak test.
   Würsig and several colleagues developed and tested a bubble curtain system to reduce underwater industrial noises, and this technique has more recently received much engineering and environmental attention.
  
  Section::::Major Publications.
   Spalling can also occur as an effect of cavitation, where fluids are subjected to localized low pressures that cause vapor bubbles to form, typically in pumps, water turbines, vessel propellers, and even piping under some conditions. When such bubbles collapse, a localized high pressure can cause spalling on adjacent surfaces.
  
  Section::::Mechanical spalling.:Antitank warfare.
   BULLET::::- high work of breathing.
  
  The arterial bubble assumption is also consistent with the accidental production of arterial bubbles. One scenario considers a shunt at the heart or lung level that passes bubbles from the venous to the arterial side. A patent foramen ovale (PFO) is thought to only open in certain conditions. A PFO conveniently explains neurological accidents after recreational air diving without any procedure violation, but it does not explain vestibular hits in deep diving. Vestibular symptoms can appear very early in the decompression, long before the massive bubble production required to overload the system.
   BULLET::::- Time taken to pass through the Arch may be underestimated. The tunnel appears shorter than it actually is because of the clarity of the water, the light at the outside end and the lack of reference points; divers report that the tunnel appears to be less than 10 m long but has been measured as 26 m. Moreover, there is frequently a current flowing inward through the arch into the Blue Hole, increasing the time it takes to swim through and increasing gas consumption.
   In addition fast moving waves are now known to "also" exert extremely high dynamic pressure. It is known that plunging or breaking waves can cause short-lived impulse pressure spikes called Gifle peaks. These can reach pressures of (or more) for milliseconds, which is sufficient pressure to lead to brittle fracture of mild steel. Evidence of failure by this mechanism was also found on the "Derbyshire". Smith has documented scenarios where hydrodynamic pressure of up to or over 500 metric tonnes per could occur.
  
  Section::::Ship failure mechanism.
   BULLET::::- Deceptive entry to the Arch is not easy to find because of the indirect line between the Blue Hole and open water. Divers who miss the entry may inadvertently continue to descend past it, while the floor continues on down to well over 100 m providing no visual depth reference.
   The Baengnyeong incident, in which the ROKS "Cheonan" broke in half and sank off the coast South Korea in 2010, was caused by the bubble jet effect, according to an international investigation.
  
  Section::::Damage.:Shock effect.
   A water tunnel is an experimental facility used for testing the hydrodynamic behavior of submerged bodies in flowing water. It is very similar to a recirculating wind tunnel but with water as the working fluid, and related phenomena are investigated, such as measuring the forces on scale models of submarines or lift and drag on hydrofoils. Water tunnels are sometimes used in place of wind tunnels to perform measurements because techniques like particle image velocimetry (PIV) are easier to implement in water. For many cases as long as the Reynolds number is equivalent, the results are valid, whether a submerged water vehicle model is tested in air or an aerial vehicle is tested in water. For low Reynolds number flows, tunnels can be made to run oil instead of water. The advantage is that the increased kinematic viscosity will allow the flow to be a faster speed (and thus easier to maintain stably) for a lower Reynolds number.
   Tunnel boom can disturb residents near the mouth of the tunnel, and it is exacerbated in mountain valleys where the sound can echo. Reducing these disturbances is a significant challenge for high-speed lines such as Japan's Shinkansen and the French TGV. Tunnel boom has become a principal limitation to increased train speeds in Japan where the mountainous terrain requires frequent tunnels. Japan has created a law limiting noise to 70 dB in residential areas, which applies to many tunnel exit zones.
   Seals in high-pressure vessels are also susceptible to explosive decompression; the O-rings or rubber gaskets used to seal pressurised pipelines tend to become saturated with high-pressure gases. If the pressure inside the vessel is suddenly released, then the gases within the rubber gasket may expand violently, causing blistering or explosion of the material. For this reason, it is common for military and industrial equipment to be subjected to an explosive decompression test before it is certified as safe for use.
  
  Section::::Myths.
  
  Section::::Myths.:Exposure to a vacuum causes the body to explode.
   The escape testing proceeds as in the pressure test, except that this time, a hatch in the floor of the pressure chamber is opened. The chamber immediately adjoins a cylindrical tower full of water, tall enough to simulate the depth of a stranded submarine. Because the air pressure inside the chamber is equal to the pressure of the water in the tower, the water does not enter the chamber.
   Section::::Known or suspected rogue wave incidents.
  
  Section::::Known or suspected rogue wave incidents.:Before 1950.
  
  BULLET::::- On 11 March 1861 at midday the lighthouse on Eagle Island, off the west coast of Ireland was struck by a large wave that smashed 23 panes, washing some of the lamps down the stairs and damaging beyond repair the reflectors with broken glass. In order to damage the uppermost portion of the lighthouse, water would have had to surmount a seaside cliff measuring 40 m (133 ft) and a further 26 m (87 ft) of lighthouse structure.
   In 1992, a cable television employee in the tunnel underneath the Chicago River videotaped mud and water oozing in where the bottom of the wooden pilings had cracked the tunnel wall. The pilings making up the dolphin had been driven only a few feet from the side of the tunnel, and the wooden pilings were visible through the collapsed tunnel wall where wet clay had slumped away from the wood into the tunnel.
   Section::::Effects.
  
  Effects of an underwater explosion depend on several things, including distance from the explosion, the energy of the explosion, the depth of the explosion, and the depth of the water.
  
  Underwater explosions are categorized by the depth of the explosion. Shallow underwater explosions are those where a crater formed at the water's surface is large in comparison with the depth of the explosion. Deep underwater explosions are those where the crater is small in comparison with the depth of the explosion, or nonexistent.
   Blowhole (geology)
  
  In geology, a blowhole or marine geyser is formed as sea caves grow landwards and upwards into vertical shafts and expose themselves towards the surface, which can result in hydraulic compression of sea water that is released through a port from the top of the blowhole. The geometry of the cave and blowhole along with tide levels and swell conditions determine the height of the spray.
  
  Section::::Mechanics.
   The story tells of a visit to a tunnel on the surface of the Moon which goes awry when a pressure seal fails, trapping three men (a supervisor, a reporter, and a tunnel worker). The title of the story derives from the way they plug an air leak while awaiting rescue: by sitting on it.
   The pressure difference between both sides of the leak can affect the movement of material through the leak. Fluids will commonly move from the higher pressure side to the lower pressure side. The larger the pressure difference, the more leakage there will typically be. The fluid pressures on both sides include the hydrostatic pressure, which is pressure due to the weight from the height of fluid level above the leak. When the pressures are about equal, there can be an exchange of fluids between both sides, or little to no net movement of fluid across the leak.
  
  Section::::Testing.
   In an oil or gas field, hydrocarbons migrate into rocks and can be trapped if there is a permeability barrier to prevent upward escape. Gas and oil are lighter than water, so they will form a bubble at the high end of the "trap" formed by the impermeable barriers. A simple physical model of this would be a coffee cup held upside down underwater with an air bubble occupying the highest portion of the cup's interior. The base of the bubble is the water contact.
   BULLET::::- Depth and the time taken to find and navigate the tunnel inevitably makes this dive a decompression dive requiring possibly lengthy decompression stops on ascent in order to avoid decompression sickness (DCS). Also, the rate of diving gas consumption increases with depth resulting in divers either becoming out of gas or beginning the ascent with insufficient gas to make the decompression stops required.
  
  BULLET::::- Likelihood of nitrogen narcosis is significant at this depth, causing confusion leading to poor judgement in an already demanding situation.
  
presuppositions: Cracks in the ceiling of an underwater tunnel will cause a vacuum effect. A crack in the ceiling of an underwater tunnel causes a powerful vacuum effect.
corrections: Cracks in the ceiling of an underwater tunnel may only cause water to squirt in. A crack in the ceiling of an underwater tunnel does not create a vacuum.
raw_presuppositions: Cracks in the ceiling of an underwater tunnel will cause a vacuum effect. A crack in the ceiling of an underwater tunnel causes a powerful vacuum effect.
raw_corrections: Cracks in the ceiling of an underwater tunnel may only cause water to squirt in. A crack in the ceiling of an underwater tunnel does not create a vacuum.