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Many industrial sectors have to deal with the risk of explosion in their operations. This includes the chemical and petrochemical industries, but also mines, pharmaceuticals, food production, and waste management. There are binding standards and regulations for such environments, and the legislation varies by region. What obligations do operators of spaces with explosion hazards have in the Czech Republic?
To properly secure a space against explosion, you must first know the degree of danger and type of explosive environment. Based on this information, you can then implement various methods of explosion protection.
These are spaces where an explosive mixture of gas with air can form or is constantly present. This mainly concerns the chemical and petrochemical industries, petrol stations, or deep mines. Depending on the degree of danger, zones 0 (highest to permanent risk), 1 (explosion risk occurs under certain conditions), and 2 (low risk, for example, in the event of an unexpected leak of a flammable substance) are distinguished.
These are spaces where a cloud of stirred flammable dust can form or is permanently present. These include mills and sawmills, but also various other areas of the food industry (processing cocoa, flour, starch, etc.), the chemical industry, or pharmaceuticals. The degree of risk is indicated similarly to spaces with gas and vapour explosion hazards – 20 (highest or permanent risk), 21 and 22 (low risk).
An explosion can occur due to a spark or contact of a volatile substance with a hot surface. Different substances have different properties, and thus different levels of danger. They are divided into groups I, II, and III and further marked with letters A, B, and C.
Group I consists of mine gases, group II of other gases and vapours, and group III of dusts. The letter C indicates the most volatile substances, while the letter A indicates the least volatile.
In the USA and Canada, both mine and other gases and vapours are marked with the number I, and dusts with the number II. The degree of explosion hazard is indicated by letters, but in reverse order: A (highest risk) – G (lowest risk).
It is essential to prevent explosions by all available means, which means minimizing the concentration of volatile substances and preventing their contact with an explosion source (spark or hot surface, but also flame, sunlight, friction, etc.). The basic methods of explosion protection include:
From the above information, it follows that it is necessary to use only such electrical equipment in explosive environments that is certified for this specific environment. In ordinary electrical equipment, a number of tiny sparks are generated, which you do not usually perceive, but their effect can cause an explosion. The temperature of the equipment is also dangerous.
Labeling of equipment for explosive environments. Source: Wikimedia.org
The construction of electrical equipment for explosive environments must prevent access of flammable substances to a spark or hot surface. Electrical equipment for explosive environments must therefore have so-called intrinsically safe circuits or special enclosures for electrical circuits – for example, oil, sand, pressure, or the device can be encapsulated in a special material. The danger of explosion propagation is addressed by a so-called flameproof enclosure.
At the same time, each device has a certain surface temperature. In spaces with explosion hazards, the maximum surface temperature must not exceed 2/3 of the ignition temperature of the given explosive substance. If there is a substance in the environment that poses an ignition risk at 60°C, only devices with a maximum surface temperature of 40°C can be used. The surface temperature of the equipment is indicated by the so-called temperature class (T1 – T6).
NOTE: The ignition temperature of a substance is the temperature at which the substance undergoes spontaneous ignition without an external ignition source – preventing contact with fire or a spark is therefore not sufficient.
In explosive environments, only those electrical devices can be used that, in terms of security, correspond to the given or higher risk. This means that if a device is suitable for an environment with the presence of substances from group IIB, it can also be used in an environment with gas from group IIA, but not IIC. If a device is marked only with a number (I, II, III), it can be used for all hazard categories – A, B, and C. Numerical designations I, II, III cannot be interchanged, so a device for substances of category IIC is not suitable for environments with risk IA or IIIB.
Devices are divided into categories:
For mining environments:
For surface environments:
The EU directive on the sale of equipment and protective systems intended for use in explosive environments is called ATEX. It was incorporated into Czech legislation as Government Regulation No. 406/2004 Coll. Devices that meet this directive are marked with the Ex mark in a hexagon.
The label on the device further includes:
For exporting devices outside the EU, you must comply with the legislation applicable to the given country. In the territory of the Russian Federation and other post-Soviet countries, certification TR TS 012/2011 - On the safety of equipment for work in explosive environments and EAC certification applies. In the USA and Canada, the most commonly used certification is NEC 500.
To prevent explosions, it is also important to maintain the lowest possible concentration of explosive gases and dusts. Dust must be regularly cleaned and vacuumed, including from crevices, but especially from hot surfaces. Dangerous gases and vapours must be ventilated using extractors and fans.
For extracting dangerous gases, fans for explosive environments with the appropriate certification are used, including fire dampers that prevent the spread of a potential fire. Fans can be built into the wall or air duct.
An important part of fans and air duct dampers for explosive environments is, of course, the motor, which must have security according to the type of environment and a robust metal casing. Only electric motors with emergency function can be used in explosive environments, so that in the event of an explosion and power failure, the fans do not stop.
Fan for explosive environments. Source: Ventilatory.cz
The issue of explosion protection is, of course, much more complex and individual. Every employer operating spaces with explosion hazards is therefore obliged to have Explosion Protection Documentation (EPD), in which they identify the hazards and propose a solution plan. This documentation is prepared by an expert – however, ensure that the documentation does not only contain a summary of applicable legislation and general recommendations. Each EPD must be tailor-made – only then can you be sure that the risk of explosion will be truly minimal.
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