What is the principle of an explosion?

Principles of Explosion-Detonation and Blast Waves-Explosion Parameters-Explosion Venting-Inert Gases -Plant for Generation of Inert Gas-Rupture Disc in Process Vessels & Lines Explosion, Suppression System based on Carbon Dioxide (CO2) & Halons-Hazards in LPG, Ammonia(NH3),Sulphur Dioxide( SO-3),Chlorine(CL2) etc.Indian Explosive Act and Rules -Static and Mobile Pressure Vessel (SMPV) rules

EXPLOSION

An explosion is defined as a sudden reaction involving a rapid physical or chemical oxidation reaction or decay generating an increase in temperature or pressure or both simultaneously. The most familiar reactions are those of flammable gases, vapors or dusts with the oxygen contained in the air.

Basis for an explosion

For explosions to happen in atmospheric air, three factors have to be present at the same time:

■ flammable substance

■ oxygen (air)

■ source of ignition

PREVENTION OF EXPLOSIONS
  • Explosion proof equipment is able to exclude one of the preconditions for an explosion – the ignition source
  • The conscious restriction of these measures, e. g. the intended, unimpeded flow of flammable gases or a reduction in ventilation can lead to explosions if an ignition source is also present.
  • The easiest and simplest way to understand small and safe explosions is by looking at a gas lighter.
  • When the nozzle of the lighter is opened, it releases a small amount of flammable gas. This gas mixes with the surrounding air, the spark from the flint ignites the mixture, and a weak sound is heard – the burning.
  • Some distance away from the nozzle the proportion of the flammable gas is already so low that the explosion and the flame are restricted to the immediate vicinity of the nozzle.
PROTECTION PRINCIPLES
  • Protection principles are defined to exclude equipment and components as ignition sources.
  • Ignition sources which are caused by sparks from friction or impact or from electro-static charging have to be prevented in explosion protected equipment by selecting appropriate materials and by constructive measures, and this must be verified and confirmed by the appropriate tests.
  • Four protection principles can prevent equipment from becoming an ignition source.

I.Explosive mixtures can penetrate the item of equipment and be ignited. Measures are taken to ensure that the explosion cannot spread to the surrounding atmosphere.

Types of Protection : Flameproof enclosures, powder filling and Enclosed-break device.

II. The item of equipment is provided with an enclosure that prevents the ingress of   an explosive mixture and/or contact with sources of ignition arising from the normal.

Types Of Protection:Pressurized enclosures, Restricted breathing, oil immersion, liquid    immersion and encapsulation.

III. Explosive mixtures can penetrate the enclosure but can not be ignited. Sparks and temperatures capable of causing ignition must be prevented.

Types of Protection:Increased Safety, Non-Sparking Device and Protection by construction safety.

IV. Explosive mixtures can penetrate the enclosure but can not be ignited. Sparks

and temperatures able to cause ignition may only occur within certain limits.

Types of Protection: Intrinsically safe, Energy limitation and Protection by control of ignition sources

 DETONATION
  • Detonation involves a supersonic exothermic front accelerating through a medium that eventually drives a shock front propagating directly in front of it.
  • Detonations occur in both conventional solid and liquid explosives,as well as in reactive gases.
  • The velocity of detonations in solid and liquid explosives is much higher than that in gaseous ones.
  • An extraordinary variety of fuels may occur as gases, droplet fogs, or dust suspensions. Oxidants include halogens, ozone, hydrogen peroxide and oxides of nitrogen.
  • Gaseous detonations are often associated with a mixture of fuel and oxidant in a composition somewhat below conventional flammability ratios.
  • They happen most often in confined systems, but they sometimes occur in large vapor clouds.
APPLICATION OF DETONATION
  • When used in explosive devices, the main cause of damage from a detonation is the supersonic blast front (a powerful shock wave) in the surrounding area.
  • This is a significant distinction from deflagrations where the exothermic wave is subsonic and maximum pressures are at most one quarteras great.
  • Therefore, detonation is most often used for explosives and the acceleration of projectiles.
  • However, detonation waves may also be used for less destructive purposes, including deposition of coatings to a surfaceand cleaning of equipment (e.g. slag removal). 
  • Pulse detonation engines use the detonation wave for aerospace propulsion.
BLAST WAVES
  • blast wave in fluid dynamics is the pressure and flow resulting from the deposition of a large amount of energy in a small very localized volume.
  • The flow field can be approximated as a lead shock wave, followed by a ‘self-similar’ subsonic flow field.
  • In simpler terms, a blast wave is an area of pressure expanding supersonically outward from an explosive core. It has a leading shock front of compressed gases.
  • The blast wave is followed by a blast wind of negative pressure, which sucks items back in towards the center.
  • The blast wave is harmful especially when one is very close to the center or at a location of constructive interference. High explosives, which detonate, generate blast waves.
SOURCE OF BLAST WAVES
  • High-order explosives (HE) are more powerful than low-order explosives (LE).
  • HE detonate to produce a defining supersonic over-pressurization shock wave.
  • Several sources of HE include Trinitrotoluene, C-4, Semtex, nitroglycerin, and ammonium nitrate fuel oil (ANFO).
  • LE deflagrate to create a subsonic explosion and lack HE’s over-pressurization wave.
  • Sources of LE include pipe bombs, gunpowder, and most pure petroleum-based incendiary bombs such as Molotov cocktails or aircraft improvised as guided missiles.
  • HE and LE induce different injury patterns. Only HE produce true blast waves.
DAMAGE CAUSED BY BLAST WAVES
  • Blast waves cause damage by a combination of the significant compression of the air in front of the wave (forming a shock front) and the subsequent wind that follows.
  • A blast wave travels faster than the speed of sound and the passage of the shock wave usually only lasts a few milliseconds.
  • Like other types of explosions, a blast wave can also cause damage to things and people by the blast wind, debris, and fires.
  • The original explosion will send out fragments that travel very fast. Debris and sometimes even people can get swept up into a blast wave, causing more injuries such as penetrating wounds, impalement, broken bones, or even death.
  • The blast wind is the area of low pressure that causes debris and fragments to actually rush back towards the original explosions.
  • The blast wave can also cause fires or even secondary explosions by a combination of the high temperatures that result from detonation and the physical destruction of fuel-containing objects.
EXPLOSION VENTING
  • An explosion vent or rupture panel is a safety device to protect equipment or buildings against excessive internal, explosion-incurred pressures, by means of pressure relief.
  •  An explosion vent will relieve pressure from the instant its opening (or activation) pressure has been exceeded.
  • Explosion vents are available in the versions self-destructive, non-self-re-closing and re-usable, self-re-closing.
  • Explosion vent construction must balance the contradictory requirements “low inertia” and “high strength”. Inertia negatively affects an explosion vent’s efficiency.
  • High strength is required to endure the considerable forces that move the vent’s venting element in order to open the venting orifice.
  • During normal venting, the explosion is freely discharged, allowing flames to exit the process being protected.
  • When the protected vessel or pipe is located indoors, ducts are generally used to safely convey the explosion outside the building.
  • However, ductwork has disadvantages and may result in decreased venting efficiency.
  • Flameless venting, in combination with explosion vents, can extinguish the flame from the vented explosion without the use of expensive ducting, limitations to equipment location, or more costly explosion protection.
  • During normal venting, the explosion is freely discharged, allowing flames to exit the process being protected.
  • When the protected vessel or pipe is located indoors, ducts are generally used to safely convey the explosion outside the building.
  • However, ductwork has disadvantages and may result in decreased venting efficiency.
  • Flameless venting, in combination with explosion vents, can extinguish the flame from the vented explosion without the use of expensive ducting, limitations to equipment location, or more costly explosion protection.
INERT GASES
  • During normal venting, the explosion is freely discharged, allowing flames to exit the process being protected.
  • When the protected vessel or pipe is located indoors, ducts are generally used to safely convey the explosion outside the building.
  • However, ductwork has disadvantages and may result in decreased venting efficiency.
  • Flameless venting, in combination with explosion vents, can extinguish the flame from the vented explosion without the use of expensive ducting, limitations to equipment location, or more costly explosion protection.
  • The inert gases are obtained by fractional distillation of air.
  • For specialized applications, purified inert gas may be produced by specialized generators on-site.
  • They are often used aboard chemical tankers and product carriers (smaller vessels). 
  • Because of the non-reactive properties of inert gases they are often useful to prevent undesirable chemical reactions from taking place.
  • Food is packed in inert gas to remove oxygen gas. This prevents bacteria from growing. Chemical oxidation by oxygen in air is avoided.
  •  An example is the rancidification of oil. In food packaging, inert gases are used as a passive preservative, in contrast to active preservatives like sodium benzoate (an antimicrobial) or BHT (an antioxidant)
  • The noble gases have weak interatomic force, and consequently have very low melting and boiling points.
  • They are all monatomic gases under standard conditions, including the elements with larger atomic masses than many normally solid elements.
  • The noble gases are colorless, odorless, tasteless, and nonflammable under standard conditions.
  • These gases are used for Microlithography, Micro fabrication and  Laser Surgery.
 RUPTURE DISCS IN PRESSURE VESSELS
  • rupture disc, also known as a burst discbursting disc, or burst diaphragm, is a non-reclosing pressure relief device that, in most uses, protects a pressure vessel, equipment or system from over pressurization or potentially damaging vacuum conditions.
  • A rupture disc is a type of sacrificial part because it has a one-time-use membrane that fails at a predetermined differential pressure, either positive or vacuum.
  • The membrane is usually made out of metal,but nearly any material (or different materials in layers) can be used to suit a particular application.
  • Rupture discs provide instant response (within milliseconds) to an increase or decrease in system pressure, but once the disc has ruptured it will not reseal.
  • Major advantages of the application of rupture discs compared to using pressure relief valves include leak-tightness and cost.
  • Rupture Discs are Commonly used in Petrochemical, Aerospace, Aviation, Defense, Medical, Railroad, Nuclear, Chemical Pharmaceutical, Food Processing and oil field Applications.
  • They can be used as single protection devices or as a backup device for a conventional safety valve, if the pressure increases and the safety valve fails to operate, the rupture disc will burst.
  • Rupture discs are very often used in combination with safety relief valves, isolating the valves from the process, thereby saving on valve maintenance and creating a leak-tight pressure relief solution.
  • Although commonly manufactured in disc form, the devices also are manufactured as rectangular panels.
  • Device sizes range from under 0.25 in (6 mm) to at least 3 ft (0.9 m), depending upon the industry application.
  • Rupture discs and vent panels are constructed from carbon steel, stainless steel, hastelloy, graphite, and other materials, as required by the Specific use environment.
  • Rupture discs are widely accepted throughout industry and specified in most global pressure equipment design codes (ASME, PED, etc.).
  • Rupture discs can be used to specifically protect installations against unacceptably high pressures or can be designed to act as one-time valves or triggering devices to initiate with high reliability and speed a sequence of actions required.
GAS LINE EXPLOSIONS
  • The leading cause of accidents in both transmission and distribution systems is damage by digging near existing pipeline.
  • Frequently, this damage results from someone excavating without asking or without waiting the standard 48-hours for the gas company to mark the location of its lines. 
  • Excavation damage accounted for almost 60 percent of all reported distribution pipeline incidents between 1995 and 2004, according to statistics kept by the U.S. Department of Transportation’s Office of Pipeline Safety. 
  • Other causes include corrosion, a fire or explosion causing a pipeline incident, or even a vehicle striking an aboveground meter or regulator. 
  • Corrosion sometimes results from excavation damage, which, while not severe enough to trigger a puncture or failure of the pipeline, could create weaknesses in the pipeline that later render it more susceptible to corrosion.
  • According to DOT statistics, the other leading causes of natural gas distribution pipeline incidents in 2004 included a fire or explosion that caused a natural gas incident (26 incidents) and a vehicle striking above-ground facilities (12 incidents). There were 3 incidents related to corrosion on distribution lines.
SUPPRESSION SYSTEM CO2
  • Carbon-di-oxide has a high ratio of expansion , which facilitates rapid discharge and allows for three-dimensional penetration of the entire hazard area quickly.
  • It extinguishes a fire by reducing the oxygen content of the protected area below the point where it can support combustion. However the environment created is not safe for the employees.
  • When designed, engineered and installed properly, carbon dioxide systems will not damage sensitive electronic equipment.
  • Carbon dioxide has no residual clean-up associated with its use. when properly ventilated, the gas escapes to the atmosphere after the fire has been extinguished.
  • Carbon dioxide is most often used for localized applications such as printing presses and engine turbines.
HALON SYSTEMS
  • Halon is a Clean Agent with a chemical formula CBrF3. The National Fire Protection Association defines, a Halon as “an electrically non-conducting, volatile, or gaseous fire extinguishant that does not leave a residue upon evaporation.“
  • Halon is a liquefied, compressed gas that stops the spread of fire by chemically disrupting combustion.
  • Halon 1211 (a liquid streaming agent) and Halon 1301 (a gaseous flooding agent) leave no residue and are remarkably safe for human exposure.
  • Halon is rated for class “B” (flammable liquids) and “C” (electrical fires), but it is also effective on class “A” (common combustibles) fires.
  • Halon 1211 and Halon 1301 are low-toxicity, chemically stable compounds that, as long as they remain contained in cylinders, are easily recyclable.
  • Halon is an extraordinarily effective fire extinguishing agent, even at low concentrations.
  • According to the Halon Alternative Research Corporation: “Three things must come together at the same time to start a fire. The first ingredient is fuel (anything that can burn), the second is oxygen (normal breathing air is ample) and the last is an ignition source (high heat can cause a fire even without a spark or open flame).
  • Traditionally, to stop a fire you need to remove one side of the triangle – the ignition, the fuel or the oxygen.
  • Halon adds a fourth dimension to fire fighting – breaking the chain reaction. It stops the fuel, the ignition and the oxygen from dancing together by chemically reacting with them.”
  • A key benefit of Halon, as a clean agent, is its ability to extinguish fire without the production of residues that could damage the assets being protected.
  • Halon has been used for fire and explosion protection throughout the 20th century, and remains an integral part of the safety plans in many of today’s manufacturing, electronic and aviation companies.
  • Halon protects computer and communication rooms throughout the electronics industry.
  • It has numerous military applications on ships, aircraft and tanks and helps ensure safety on all commercial aircraft.
INDIAN EXPLOSIVE ACTS AND RULES
  • The compressed or liquefied gas filled in containers under pressure are notified by the Government of India as explosives and brought under the purview of Explosive Act,1884 in 1938. The Chief Controller of Explosives administers the statutory provisions of this Act.

 Various rules framed under the Act are contained in:

  • Indian Explosives Rules, 1981

These Rules regulate the manufacture, possession, use,

sale, transport and export/import of all types of

explosives used for various purposes like mines/rock

blasting, crackers, etc.

STATIC AND MOBILE PRESSURE VESSEL(SMPV) RULES
  • This Rules stipulate various safety guidelines for the storage and transport of compressed and liquefied gases filled in pressure vessels (exceeding 1000 litres capacity) at a pressure exceeding 1.5 kg/cm2 at 15 degrees Celsius or 2.0 kg/cm2 at 55 degrees Celsius.
  • Under these rules the storage and transport vessel should be designed for the specific gas, maximum operating temperature and working pressure, proper material of construction, capacity, shape, size etc., according to IS 2825 or any other approved code.
  • The Chief Controller of Explosives should approve its design/drawings. The vessel should be fabricated by an approved fabricator and installed as per the safety distances stipulated in the rules.
  • The rules call for periodic re-examination/testing of the pressure vessel and its fittings.
LPG
  • Liquefied petroleum gas (LPG) is a colourless, odourless liquid which readily evaporates into a gas. Normally an odourant has been added to it to help detect leaks.
  • LPG (either Butane or Propane), is generally stored and distributed as a liquid and it is widely used for process and space heating, cooking and automotive propulsion. 
  • It is classified as highly flammable and if it contains more than 0.1%Butadiene, it is also classified as  a carcinogen and mutagen.
  • LPG is non-corrosive but can dissolve lubricants, certain plastics or synthetic rubbers.
HAZARD OF LPG
  • LPG may leak as a gas or a liquid. 
  • Gas leaks can occur from defective rubber tube, faulty regulator fitting and poor handling of gas appliances. Leaving the cooking unattended can cause the vessel to overflow, which in turn douses the burner and causes gas leak.
  • If the liquid leaks it will quickly evaporate and form a relatively large cloud of gas which will drop to the ground, as it is heavier than air.  
  • LPG vapors can run for long distances along the ground and  can collect in drains or basements.  When the gas meets a source of ignition it can burn or explode.
  • Cylinders can explode if involved in a fire.
  • LPG can cause cold burns to the skin and it can act as an asphyxiant at high concentrations.
  • There are two main kinds of health hazards associated with the leak – a. those occurring due to inhalation of the gas and b. those occurring due to explosion of the gas if there is a source of ignition.
  • If inhaled, it can displace air, deprive the lungs of oxygen and cause hypoxia leading to suffocation.
  • The gas can affect the brain and nervous system and cause euphoria, difficulty walking or speaking, dizziness, hallucinations, lack of coordination, nausea and loss of consciousness.
  • Repeated exposure may cause mood swings, depression, seizures, brain hemorrhage and impaired memory.
  • It may damage the heart by causing irregular heart beat and high blood pressure. It may also reduce blood cells, damage lungs and cause liver and kidney inflammation.
  • Explosion from LPG can result in serious burns and can cause multiple injuries and even, death.
  • Blast shock waves can affect the ears, lungs and hollow organs of the gastrointestinal tract of a person is close proximity to the blast site.
  •  Lungs may be damaged with bleeding or swelling.
  • The explosion may also cause injury from fragments and other objects propelled in air.
  • It also causes displacement of air that can throw victims, especially young children, against solid objects and cause injury like bone fractures.
  • There may also be hidden brain injury and potential neurological consequences. Even if not injured, some people may experience post-traumatic stress disorder due to psychological trauma.
  • It is easy to recognize a gas leak due to its powerful, pungent odor.
HAZARDS  IN AMMONIA
  • Ammonia is a colorless gas with a strong, sharp and irritating odour.it is often used in water solution. It is used in fertilizers as a refrigerant, dyes, textiles , detergents and pesticides.
  • Main Routes of Exposure: Inhalation. Skin contact. Eye contact.
  • Inhalation: 
  1. VERY TOXIC, can cause death. Can cause severe irritation of the nose and throat. Can cause life-threatening accumulation of fluid in the lungs (pulmonary edema).
  2.  Symptoms may include coughing, shortness of breath, difficult breathing and tightness in the chest.
  3. Symptoms may develop hours after exposure and are made worse by physical effort. Long-term damage may result from a severe short-term exposure.
  4. Skin Contact: 
  1. The gas irritates or burns the skin. Permanent scarring can result. Direct contact with the liquefied gas can chill or freeze the skin (frostbite).
  2. Symptoms of more severe frostbite include a burning sensation and stiffness.
  3. The skin may become waxy white or yellow. Blistering, tissue death and infection may develop in severe cases.
  4. Eye Contact: 
  1. The gas irritates or burns the eyes. Permanent damage including blindness can result.
  2. Direct contact with the liquefied gas can freeze the eye. Permanent eye damage or blindness can result.
  3. Ingestion: Not a relevant route of exposure (gas).
  4. Effects of Long-Term (Chronic) Exposure: May harm the respiratory system. Can irritate and inflame the airways.
HAZARDS IN SO2
  • SO2 is a Colourless gas, Suffocating odour.
  • It May explode if heated.
  • It Will not burn and is VERY TOXIC i.e Fatal if inhaled.
  • Corrosive to the respiratory tract.
  • A severe, short-term exposure may cause long-term respiratory effects (e.g., Reactive Airways Dysfunction (RADS)).
  • CORROSIVE and Causes severe skin burns and eye damage. May cause frostbite.
  • SUSPECT MUTAGEN: Suspected of causing genetic defects.
  • Main Routes of Exposure: Inhalation.
  • Inhalation: 
  • VERY TOXIC, can cause death.
  • Can cause severe irritation of the nose and throat.
  •  At high concentrations: can cause life-threatening accumulation of fluid in the lungs (pulmonary edema).
  • Symptoms may include coughing, shortness of breath, difficult breathing and tightness in the chest.
  •  A single exposure to a high concentration can cause a long-lasting condition like asthma.
  • Symptoms may include shortness of breath, tightness in the chest and wheezing. {Reactive Airways Dysfunction Syndrome (RADS)}.

Skin Contact:

  1. The gas irritates or burns the skin.
  2. Permanent scarring can result.
  3. Direct contact with the liquefied gas can chill or freeze the skin (frostbite).
  4. Symptoms of mild frostbite include numbness, prickling and itching.
  5. Symptoms of more severe frostbite include a burning sensation and stiffness.
  6. The skin may become waxy white or yellow. Blistering, tissue death and infection may develop in severe cases.

Eye Contact:

  1. The gas irritates or burns the eyes.
  2. Permanent damage including blindness can result. Direct contact with the liquefied gas can freeze the eye.
  3. Ingestion: Not a relevant route of exposure (gas).
  4. Effects of Long-Term (Chronic) Exposure: May harm the respiratory system. Can irritate and inflame the airways
CHLORINE AND ITS HAZARD
  • Chlorine is a Green – yellow gas with Pungent odour and will not burn.
  • It is a COMPRESSED GAS and Contains gas under pressure.
  • May explode if heated.
  • It is an OXIDIZER and may cause or intensify fire.
  • Highly Reactive and Incompatible with many common chemicals.
  • Main causes:
  1. Inhalation
  2. Skin Contact
  3. Eye contact

Inhalation: 

  1. VERY TOXIC, can cause death.
  2. Can cause severe irritation of the nose and throat.
  3.  Can cause severe lung injury. Can cause pulmonary oedema.
  4. Symptoms may include coughing, shortness of breath, difficult breathing and tightness in the chest.
  5. Symptoms may develop hours after exposure and are made worse by physical effort.

A single exposure to a high concentration can cause a long-lasting condition like asthma thus irritates the airways. Symptoms may include shortness of breath, tightness in the chest and wheezing.

Skin Contact:

  1. The gas irritates or burns the skin.
  2. Frostbite Occurs. Symptoms of mild frostbite include numbness, prickling and itching. Symptoms of more severe frostbite include a burning sensation and stiffness. The skin may become waxy white or yellow.
  3. Blistering, tissue death and infection may develop in severe cases.

Eye Contact:

The gas irritates or burns the eyes Causing blindness.

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