Physical explosion
Physical explosions are explosions that are based neither on chemical nor on nuclear physical processes, but instead occur due to physical processes. Very often water vapor explosions are involved .
Physical explosions occur when a hot liquid meets a colder one and the temperature of the hot liquid is higher than the boiling point of the colder one. The explosion then follows from the fact that the hot liquid heats the cold one so much that the latter evaporates suddenly , the vapor has a much larger volume than the same substance in liquid state, but it cannot spread in space to the same extent.
The hot liquid can be liquid rock in nature , e.g. B. lava , or in the technical field in metal extraction or metal processing liquid metal ( melt ). The cold liquid is usually water , but other liquids such as silicone oils can also be used.
procedure
If z. B. a molten iron on water, then immediately from the liquid water, which touches the iron , steam, which forms a layer of steam around the iron. This does not come off evenly when it expands. The incoming water triggers a trigger pulse that tears the melt apart into small pieces. These are now suddenly all surrounded by water and heat it up, causing it to suddenly evaporate. The steam expands so quickly that the molten iron explodes with the pressure wave of the water vapor and is thrown around.
magma
Numerous physical explosions have already been triggered by liquid rock from the earth's interior , the magma .
Magma and water
So found z. For example, on May 17, 1724, a violent explosion took place in Iceland west of the ancient Krafla volcano . Ashes and slag were scattered within 10 km. Magma had come into contact with the groundwater . The eruption probably lasted only a day and left a stinking, steaming, boiling mud-filled crater 320 meters in diameter. Around 1840, the water in the Vitikrater slowly cleared . It remained a clear crater lake .
Such volcanic explosions with the participation of water vapor are referred to as phreatic eruptions , with simultaneous ejection of glowing liquid material as phreatomagmatic eruptions ; the resulting volcanic shape is often the maar .
Magma, volcanic gas and solid rock
Depending on local conditions, the pressure of magma pushing up to the surface of the earth and / or the gas it contains, which is held up by rock layers, can increase to such an extent that it forcibly blasts the obstacle away. Such an explosion creates a particularly explosive type of volcanic eruption , the Plinian eruption .
Famous Plinian explosions were that of Santorini around 1627 BC. BC, Vesuvius AD 79, Tambora 1815, Krakatau 1883, Mount St. Helens 1980 or Pinatubo 1991.
Meteorites
Meteors heated by the frictional heat of the air can also trigger a steam explosion when they hit water. The strong deceleration on impact itself releases further thermal energy.
In the case of very large meteorites , the energy can be sufficient to evaporate not just liquid, but solid matter. The effect of this explosion occurs in addition to the direct effect of the movement impulse caused by the impacting mass. An example of such an impact crater is Barringer Crater in Arizona .
pressure vessel
May rupture and pressure vessels if they technically no longer the intended internal pressure withstand or this is increased inadmissible or by accidents, such as the boiler explosion of steam boilers .
For example, the acetylene in an acetylene cylinder fills the entire volume of the pressure vessel at an internal cylinder temperature of 60 ° C. With further warming - z. For example, by a fire - increasing the pressure of the bottle at 7-8 bar per 1 K . When the bursting pressure of the bottle (230 bar) is reached, the bottle explodes (pops) due to excess pressure (physical explosion). The debris can be thrown up to 300 m. When the acetylene ignites, a chemical explosion immediately follows the physical explosion .
Oils and fats
A physical explosion - sometimes combined with a subsequent chemical explosion - can also occur if certain burning liquids are incorrectly extinguished . An attempt to extinguish burning oils or fats with water leads to a fat explosion with potentially devastating consequences for the person who extinguishes.
Although the consequences are comparable, the explosion occurs when a metal fire is extinguished with water as a result of a chemical reaction of the evaporating water (see section 'Overlay with chemical explosion').
Overlay with chemical explosion
If molten aluminum meets water, the physical explosion is intensified by a strongly exothermic chemical reaction:
The release of energy during this reaction is over 5 MJ / kg, it is visible through a flash of light.
As a result of a meltdown
A core meltdown , which can be the result of an accident in nuclear reactors , creates a situation that can lead to an explosion when the hot mass of the reactor core meets the coolant . The heat development is based on nuclear processes, but the actual explosion is of a non-nuclear nature (the same effect would also result in non-radioactive metal melts). For this reason, this is also a physical explosion. The greatest risk arises from a so-called melt jet jet, which can form when the liquid core mass passes either through the lower core plate of the reactor vessel or through individual ducts out of the reactor vessel. The coolant heats up very quickly and explosively evaporates.
Occupational safety
The physical explosions in smelting works and in the metal industry repeatedly lead to serious accidents , often with fatal results. The prevention of physical explosions is therefore an important part of occupational safety in such companies .
In the case of physical explosions - depending on the type and mass - pressures of several hundred megapascals (MPa), i.e. H. of several thousand cash arise.
Examples: Quotes from official accident reports
- Pure nickel should be placed in the furnace and dry rammed earth sintered at the same time. The furnace should be started up to the brim at approx. 1630 ° C. The nickel pellets were delivered in used barrels (previous use for transport not known). Before the time of the accident, half of the nickel was consumed. When the 14th barrel was filled with a forklift, there was a physical explosion and molten metal was thrown out of the furnace. It is believed that there was invisible liquid in the barrel.
- Fatal burns to the forklift driver due to ejected hot melt, minor injuries to another employee.
- In the casting hall of a non-ferrous foundry there was a gas boiling filtration box (GBF box) from which aluminum melt was drained into a residual melt bucket 1 m below it via a bunghole in the box. The bucket was covered with a grating, which made it possible to look into the bucket to check whether there was any water in the bucket. The grating also served as a standing area for the workers during the filling process. When the residual melt bucket was filled with liquid aluminum melt from the GBF box, the fatally injured person stood on the grating above the bucket, so that remnants of snow from the sole profile of his footwear probably got into the bucket over the grate. The water introduced led to a physical explosion, so that the molten aluminum was thrown out of the bucket and hit the fatally injured person and another worker.
See also
- Physical state
- Reversal process: steam hammer
Individual evidence
- ↑ Á ferð um Ísland - The Kraflaggebiet.
- ↑ Explosion. Fire Department Halle (Saale)
- ↑ B. Lafrenz: Physical explosions: explosions due to rapid thermal interactions. ( Page no longer available , search in web archives: Federal Institute for Occupational Safety and Health: Research: Project F 2097 )
- ^ Melt-Structure-Water-Interactions during postulated Severe Accidents in LWRs ; in ENSI : Experience and Research Report 2011
- ↑ Events for evaluation in the UA Event evaluation of the SFK. ( Memento of February 4, 2014 in the Internet Archive ) (PDF; 12 kB) Commission for Plant Safety (KAS)
- ↑ Events for evaluation in the UA Event evaluation of the SFK. ( Memento from January 11, 2005 in the Internet Archive ) (PDF; 4 kB) Commission for Plant Safety (KAS)