What is Explosion Protection?
Explosions are suddenly, with enormous speed, occurring oxide reactions that generate a temperature and pressure increasement. Most well-known are reactions of flammable gases, vapors, or dust together with oxygen out of the air.
The Basis for an Explosion
As a rule, three factors must be present simultaneously for explosions to happen in atmospheric air.
- Flammable material (in ignitable quantities)
- Oxygen (in the air)
- Ignition Source
Hazardous areas can develop in production and workplaces wherever the first two preconditions for an explosion are fulfilled. Typical hazardous areas form in chemical factories, refineries, enameling plants, paint workshops, cleaning equipment, mills and stores for milled products and other combustible dust, in-tank facilities, and loading areas for flammable gases, liquids, and solids.
The first two preconditions – the flammable material and air – must be present in justified quantities between LFL and UFL (Lower Flammable Limit and Upper Flammable Limit) to form an explosive atmosphere. The statutory definitions of explosion protection – derived from the health and safety at work regulations – are about workplaces. For this reason, explosion protection is generally limited to describing reactions with oxygen in the air.
Oxidation reactions commonly involve increases in heat and pressure and therefore fulfill the criteria of an explosion.
1). Flammable Material
Flammable Materials can be either gaseous, a vapor from liquid, or solid. Their reactivity with atmospheric oxygen is considered for a general discussion relevant to workplaces.
1.1 Flammable Gases
A Flammable Gas may be an element such as hydrogen, which can react with oxygen with little additional energy. Flammable gases are often compounds of carbon and hydrogen.
These flammable gases and vapors require only small amounts of energy to react with atmospheric oxygen. A vapor is the proportion of a liquid – if talking about the explosion protection of flammable liquids which has evaporated into the surrounding air as the result of the vapor pressure above the surface of the liquid, around a jet of that liquid, or droplets of the liquid. Because of its explosion behavior, the mist is a particular type that can be included with the vapors to fulfill safety considerations.
1.2 Flammable liquids (Actually the Vapor Only)
Flammable Liquids are often hydrocarbon compounds such as ether, acetone, or petroleum spirit. Even at room temperature, sufficient quantities of these can change into the vapor phase so that an explosive atmosphere forms near their surface. Other liquids form such an atmosphere near their surface only at increased temperatures. Under atmospheric conditions, this process is strongly influenced by the temperature of the liquid.
For this reason, the flashpoint, or the flash point temperature, is essential when dealing with flammable liquids. The flashpoint relates to the lowest temperature at which a flammable liquid will, under certain test conditions, form a sufficient quantity of vapor on its surface to enable an effective ignition source to ignite the vapor air mixture.
The flashpoint is essential for the classification of potentially explosive atmospheres. Flammable liquids with a high flash point are less dangerous than those with a flash point at room temperature or below.
When spraying a flammable liquid, a mist consists of very small droplets with a large overall surface area, well-known from spray cans or car paint spraying stations. Such a mist can explode. In this case, the flashpoint is of lesser importance. For a fine mist made from a flammable liquid – the behavior relevant to safety can be roughly derived from the known behavior of the vapor.
1.3 Flammable Solids (Actually Dust Only)
Flammable Solids in the form of dust or flying can react with atmospheric oxygen and produce disastrous explosions. Typically, more energy is required for activating the explosion in the air than with gases and vapors. However, once combustion starts, the energy released by the reaction produces high temperatures and pressures. In addition to the solid’s chemical properties, the particles’ fineness and the overall surface area, which increases with increasing fineness, play an important role.
The properties are determined by processes that occur immediately at the surface of the solid particles. For example, igniting and extinguishing a paraffin wax candle demonstrates a series of processes undergone by a solid material within a short period which cannot easily be presented in a simplified form.
An experiment shows that when the wick of a candle is lit, the paraffin wax melts and then vaporizes, which feeds the flame. After extinguishing the candle, the paraffin vapor can still be smelled, the melted paraffin wax solidifies, and the paraffin vapors disperse. Now the paraffin wax candle is once again a harmless object.
Dust reacts very differently, depending on whether in a deposited layer or a swirled dust cloud. Dust layers are liable to begin smoldering on hot surfaces, while a dust cloud that has been ignited locally or through contact with a hot surface can explode immediately. Dust explosions often result from smoldering dust layers, which become swirled up and already carry the ignition initiation. When such a layer is stirred up, for example, by mechanical cleaning methods during transportation or inappropriate extinguishing attempts, this can lead to a dust explosion.
A gas or vapor/air explosion can also swirl up the dust, which often turns from the first gas explosion into the second, the dust explosion. For example, methane/firedamp explosions in deep coal mines often have triggered off coal dust explosions whose consequences were more severe than those of the original firedamp explosion.
The Oxygen available in the air can only oxidize/burn a certain amount of the flammable material. The ratio can be determined. Theoretically, it is called the stoichiometric mixture. When the quantity of the flammable material and the available atmospheric oxygen are near the optimum (most ideal) ratio, the effect of the explosion temperature and pressure increase is most violent.
If the quantity of flammable material is too small, combustion will only spread with difficulty or cease altogether. The situation is similar when the quantity of explosive material is too great for the amount of oxygen available in the air.
All flammable materials have their explosive range depending on the available activation energy. This is usually determined by igniting
the mixture with an electric spark. The explosive range is bounded by the lower flammable (previously referred to as explosive) limit and the upper flammable (previously referred to as explosive) limit. This means that below and above these limits, explosions will not happen. This fact can be utilized by sufficiently diluting the flammable substances with air or preventing the ingress of air/oxygen into parts of the equipment. However, the latter option is not or only with restrictions possible in environments where people regularly work (inerting means danger for suffocation) and must therefore be reserved for technological equipment only.
3). Avoidance of Ignition Sources
Various sources can cause ignition:
- Hot surfaces.
- Electrical arcs and sparks.
- Electrostatic discharge.
- Atmospheric discharge (lightning).
- Mechanical friction or impact sparks.
- Electromagnetic radiation.
- Adiabatic compression (shock waves).
- Ionizing radiation.
- Optical radiation.
- Chemical reactions.
- Open flames.
Measures of Explosion Protection
1). Primary Explosion Protection
Primary Explosion Protection aims at either sub-situating or reducing the quantity of the flammable substances or the atmospheric oxygen to a level where there is no danger of an explosive mixture forming.
Increased air supply air flushing through ventilation can be achieved by structural measures; for example, the open layout of filling stations where the potentially explosive atmosphere is minimal. Replacing atmospheric oxygen is not an option for areas where people work. For this reason, the measures available for such locations are limited to:
- Avoidance or restriction of flammable substances which are capable of forming an explosive atmosphere.
- Avoidance or restriction of the release of the flammable substances and, therefore, formation of explosive mixtures inside and around fittings/valves.
For Example, by:
- Limiting their concentration.
- Using enclosures filled with an inert substance.
- Natural or artificial ventilation.
- Concentration monitoring using a gas detection system will give an alarm and switch off the system.
2). Secondary Explosion Protection
Suppose, despite primary Explosion Protection measures, a hazardous, potentially explosive atmosphere can form (to the degree that requires measures to protect employees against explosion hazards). In that case, the ignition of this hazardous, potentially explosive atmosphere must be effectively prevented. Therefore, all possible ignition sources are evaluated, and the appropriate protective measures are applied.
Effective ignition sources on equipment and installations can, for example, be prevented using types of protection corresponding to the necessary level of protection. The classification of potentially explosive areas into zones (The frequency and duration of a hazardous explosive atmosphere and the local environmental conditions) forms the basis for defining the level of protection for equipment. Furthermore, it is necessary to know the critical explosion-related figures for the flammable materials (grouping, temperature classes, dust ignition, and smoldering temperatures) and the local ambient conditions.
The explosion characteristics help the owner/ managing operator specify the risk in the area precisely and allow the operating equipment manufacture to select a suitable solution for the operational equipment. Finally, they help the installation engineer select and assign suitable Ex Equipment. Ultimately, this data is found in the Ex Equipment labeling.
3). Tertiary Explosion Protection
If the primary and secondary explosion protection measures are insufficient, additional protective measures shall be taken. The purpose of these is to limit the impact of an explosion and reduce it to occupational health and environmental safety level.
The most common measures to limit the hazardous effects of the explosion are as follows:
- Explosion-resistant design: containers, apparatus, and pipelines are built to be pressure shock resistant to withstand an explosion inside.
- Explosion relief: bursting discs or explosion flaps are deployed, which open in a safe direction if an explosion occurs and ensure that the plant is not subjected to strain over and above its explosion resistance.
- Explosion suppression and preventing propagation of the explosion: Explosion suppression systems prevent the attainment of the maximum explosion pressure by rapidly injecting extinguishing agents into containers and plants. Explosion decoupling restricts possible explosions to individual parts of the plant.
Prevention of Explosions
Explosion-proof equipment can exclude one of the preconditions for an explosion – the ignition source- essential to explosion protection. Architectural measures ensure that an explosive atmosphere cannot be formed in domestic areas. However, the conscious restriction of these measures, for example, the intended, unimpeded flow of flammable gases or a reduction in ventilation, can lead to explosions if an ignition source is also present.
The most straightforward way to understand small and safe explosions is by looking at a gaslighter. 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 has 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. In other words, the design of the gaslighter has ensured that it is safe to use.
The effect of an explosion in enclosed spaces and under non-atmospheric conditions – for example, under increased pressure is often more powerful. Just think of the practical application of explosions in vehicle engines.
To attain effective explosion protection against non-controlled, unintended explosions linked to disastrous consequences, it is necessary to remove one of the three factors.
In industries where Gases, Fuels, and Vapors are emitted during manufacturing, processing, transporting, and storage. These inflammable fluids include alcohol, acetylene, propane, hydrogen, and gasoline. In addition, dust, such as wood, sugar, and aluminum, are also potentially combustible substances.
When mixed with oxygen in the atmosphere, these combustibles can form an explosive mixture. Likewise, an explosion may occur if an electric spark externally ignites it.
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Our global network of specialist environment, health, and safety (EHS) operatives provides extensive, impartial detection services covering all potentially hazardous situations, promoting discussion, and proposing practical and implementable solutions. In addition, our multidisciplinary technical safety and risk management team provides fully integrated support, assistance, and solutions that enable you to manage the risk associated with major accidental events appropriately and systematically.
Working with the TUV Austria Bureau of Inspection & Certification will help you comply with your obligations to protect your stakeholders, the environment, and your business reputation.
In addition, to Explosion Protection Services, we also offer a range of complimentary services:
- Third-Party Inspection
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- QA/QC Services
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- Non-Destructive Testing Services
- Mechanical Testing Services
- Risk-Based Inspection
- Pressure Equipment Directive Certification
- Pressure Vessel Inspection
- Storage Tank Inspection
- Steam Boiler Inspection
- Supplier Expediting Services
- Emission Testing Services
- Plant Safety Services
- Equipment Safety Services
- Vendor Audit Services
- Fire Protection Services
- Communication Tower Inspections
- Asset Integrity Services
What is Hazardous Area?
A place in which an explosive atmosphere may occur in such quantities as requiring special precautions to protect the health and safety of the workers concerned is considered hazardous.
What is an Explosive Atmosphere?
An explosive atmosphere is a mixture of flammable substances in gases, vapors, mists, or Dust with air under atmospheric conditions.
What is the classification of a Hazardous Area?
Hazardous Areas are classified in terms of zones based on the frequency and duration of the colorants of an explosive atmosphere. Hazardous areas are classified into two major categories
Under gases or vapors, Hazardous Areas are classified into three different zones.
- ZONE 0
- ZONE 1
- ZONE 2
In ZONE 0, an Explosive Atmosphere is present continuously for long periods or frequently.
In ZONE 1, an Explosive Atmosphere is likely to occur in regular operation occasionally.
In ZONE 2, an Explosive Atmosphere is unlikely to occur. If they occur, they are likely to do so far in a short period.
Similarly, Dust classified into three different Zones
- ZONE 20
- ZONE 21
- ZONE 22
In ZONE 20, an Explosive Atmosphere is present continuously for long periods or frequently.
In ZONE 21, an Explosive Atmosphere is likely to occur in regular operation occasionally.
In ZONE 22, an Explosive Atmosphere is unlikely to occur.
If they do occur, they are likely to do so for a short period only.
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