SAFETY AND RISKS IN HAZARDOUS AREAS - EXPLOSION PROTECTION

Explosive atmosphere – a mixture with air under atmospheric conditions of flammable substances in the form of gases, vapors, mists or dusts, in which, after ignition, combustion spreads spontaneously to the entire mixture.

Explosion risk – a combination of the frequency or probability of an explosion of mixtures of flammable substances in the form of gases, vapors, mists or dust with air in atmospheric conditions, causing hazard and consequences related to this event.

Lower explosion limit (LEL) – the lower limit of the concentration range of a flammable substance in air in which an explosion may occur.

Upper explosion limit (ULG) – the upper limit of the concentration range of a flammable substance in air at which an explosion may occur.

Combustible materials – materials that may create an explosive atmosphere, unless testing of their properties shows that when mixed with air they cannot automatically contribute to the spread of an explosion.

Flash point – the minimum temperature at which, under specified test conditions, a liquid releases flammable gas or vapor in an amount sufficient to ignite immediately using an effective ignition source.

Minimum ignition energy (MIE) – the lowest energy that is sufficient to cause ignition of the most flammable mixture of a given dust under specified test conditions.

Minimum dust cloud ignition temperature TCL – corresponds to the lowest temperature of hot surfaces which, in contact with the dust cloud, cause it to ignite.

Minimum dust layer auto-ignition temperature – the lowest temperature of the hot surface at which the dust layer ignites under specified test conditions.

Minimum ignition temperature of the dust layer T5 mm – the lowest temperature of the hot surface at which the 5 mm thick dust layer located on this surface is ignited.

Working persons – this should be understood as: employees, natural persons performing work on a basis other than an employment relationship or running a business on their own account, students or apprentices taking part in practical classes, persons performing short-term work or inspection activities.

Non-hazardous spaces – these are spaces in which explosive atmospheres are not expected to occur in quantities requiring special precautions to ensure occupational health and safety of workers and third parties.

Inspection – an activity aimed at assessing the condition of devices and protective systems intended for use in potentially explosive atmospheres.

Explosion risk – a combination of the frequency or probability of an explosion of mixtures of flammable substances in the form of gases, vapors, mists or dust with air in atmospheric conditions, causing hazard and consequences related to this event.

Protective system – “protective systems” are considered to be all parts and components whose task is to immediately stop an emerging explosion and/or limit the effective flame range and explosion pressure. Protective systems can be integrated into the device or marketed separately for use as stand-alone systems.

Devices – means machines, equipment, fixed or movable devices, control components and instrumentation and their detection and prevention systems, which, separately or interconnected, are intended for the generation, transmission, storage, measurement, regulation and conversion of energy and for transforming materials which, due to their own potential ignition sources, are capable of causing an explosion.

Explosion – a violent oxidation or decomposition reaction causing an increase in temperature and/or pressure.

Emission source – a point or place from which flammable gas, flammable vapor or flammable liquid may be released into the atmosphere so that an explosive gas atmosphere may be created.

Emission levels – there are three emission levels, arranged in order of decreasing probability of the occurrence of an explosive gas atmosphere:

(a) continuous emission rate; that occurs continuously or is expected to occur over long periods.
(b) first stage emission; which may be expected to occur periodically or occasionally during normal operation.
(c) second stage emission; which cannot be expected to occur under normal operating conditions, and if it does occur, it may only occur rarely and only for short periods.
Sources causing a continuous level of emissions – e.g. the surface of a flammable liquid in a fixed roofed tank with continuous venting to the atmosphere, the surface of a flammable liquid that is open to the atmosphere

continuously or for a long period of time.

Primary emission sources – e.g., pump, compressor or valve seals, relief valves, air vents and other openings from which flammable materials are expected to be emitted to the atmosphere during normal operation.

Sources causing secondary emissions – e.g., pump, compressor and valve seals, orifices, joints and fittings, sampling points, relief valves, air vents and other openings from which flammable materials are not expected to be emitted to the atmosphere during normal operation.

Temperature class – a conventional division of mixtures of vapors and gases with air, at risk of explosion as a result of contact with the external surfaces of electrical or heating devices with a temperature in one of six ranges:

The division into temperature classes is the basis for the construction and selection of electrical devices depending on the temperature that their surface (housing) may reach during operation in potentially explosive areas.

Explosion group – additional marking of devices intended for operation in explosion hazard zones, taking into account the type of explosive gas atmosphere present

Explosive spaces are spaces where there is a possibility of an explosive atmosphere requiring special precautions to ensure the occupational health and safety of workers and third parties. Explosive atmospheres are divided into zones, classifying them based on the probability and duration of occurrence of explosive atmospheres as:

zone 0 – a space in which an explosive atmosphere containing a mixture of flammable substances in the form of gas, vapor or mist with air occurs constantly, frequently or for long periods;

zone 1 – a space in which an explosive atmosphere containing a mixture of flammable substances in the form of gas, vapor or mist with air may occasionally occur during normal operation;

zone 2 – a space in which an explosive atmosphere containing a mixture of flammable substances in the form of gas, vapor or mist with air does not occur during normal operation, and if it does occur, it persists for a short period;

zone 20 – a space in which an explosive atmosphere in the form of a cloud of flammable dust in the air occurs constantly, frequently or for long periods;

zone 21 – a space in which an explosive atmosphere in the form of a cloud of flammable dust in air may occasionally occur during normal operation;

zone 22 – a space in which an explosive atmosphere in the form of a cloud of flammable dust in the air does not occur during normal operation, and if it does occur, it persists for a short period.

1. Hot surfaces A dangerous source of explosion initiation originating from hot surfaces is considered to be one whose temperature may exceed 2/3 of the minimum auto-ignition temperature of the substance (expressed in °C) that may occur in its presence.
2. Open flame, hot gases, fire-hazardous work is a special situation when this type of ignition source occurs. When performing fire-hazardous work, safety rules should be followed to minimize the likelihood of an explosion.
3. Electrical equipment and equipment may be ignited by electric sparks created when electrical circuits are turned on and off, by damaged connections in the installation and by stray currents, as well as in the form of hot surfaces
   Static electricity – short current pulses appearing in the space between objects with a sufficiently large electrostatic potential difference, leading to the complete or partial disappearance of the ES charge on these objects.

There are five basic types of electrostatic discharge:

• Capacitive spark discharges – ignite all explosive atmospheres
• Spreading sheaf discharges – ignite all explosive atmospheres
• Cone discharges – ignite some dust and all gas atmospheres
• Sheaf discharges – ignite all gas atmospheres, do not ignite dust atmospheres, except dust of initiating materials
• Corona discharges – discharges with very low energy, less than 0.1 mJ, it is believed that they can ignite the most sensitive gas atmospheres with an ignition energy below 0.1 mJ or atmospheres with increased oxygen concentration. The debate over the veracity of these claims is not yet resolved.

Mechanical sparks may come from any renovation and repair work as well as during grinding and grinding processes. In such situations, high temperature particles may be separated from the elements.
Lightning
Exothermic chemical reactions – a chemical reaction that has a positive heat exchange balance with the surroundings and can ignite
Adiabatic compression, shock wave, flowing
Optical radiation is electromagnetic radiation with wavelengths ranging from 100 nm to 1 mm. Optical radiation is divided into:
ultraviolet radiation;
visible radiation (light)
infrared radiation.

Radio frequency electromagnetic radiation RF from 104 to 3*1011 Hz is emitted by systems that generate and use electrical energy at a frequency characteristic of radio systems.

Ionizing radiation of radiation that causes the ionization of a material medium, i.e. the removal of at least one electron from an atom or molecule or its removal from a crystal structure.

Ultrasound – sound waves whose frequency is too high for humans to hear. The frequency of 20 kH is considered to be the upper limit of audible frequencies and, at the same time, the lower limit of ultrasound, and the frequency of 1 GHz is considered to be the upper limit of ultrasound.
Stray currents are a phenomenon of mostly uncontrolled flow of electric current between two or more points of current-conducting substances (metals, non-metals, electrolytes). This current is most often an undesirable phenomenon accompanying the transmission of electrical energy

Group I: devices intended for installation in underground workings of mines at risk of explosion of mixtures of methane with air and coal dust

Group II: devices intended for installation in areas at risk of gas explosion (outside mining)

Devices intended for use in places where an explosive gas or dust atmosphere may occur, other than in mines:

Group II, category 1 devices

Group II devices, category 2

Group II, category 3 devices

Category 1 devices (very high level of protection)

Products in this category should be characterized by integrated safety measures such that in the event of failure of one of the safety measures, at least a second independent measure ensures the required level of protection.

Category 2 devices (high security)

Products in this category can function and provide a high level of protection in spaces where explosive atmospheres are likely to occur

Category 3 devices (normal protection level)

Products in this category can function and provide a normal level of protection in spaces where an explosive atmosphere is unlikely to occur.

Products intended for use in atmospheres containing a mixture of gases and vapors of flammable liquids with air should have the G marking.

Division into subgroups:

Propane
Ethylene
Hydrogen
Products intended for use in atmospheres containing a mixture of flammable dust and air should be marked D.

Division into subgroups:

Explosive volatile particles “floc”
Non-conductive dust
Conductive dust

Unless the explosion protection document provides otherwise, protective devices and systems for all spaces where an explosive atmosphere may occur should be selected by the employer from one of three categories.

Depending on the types of flammable gases, mists or dusts present in the zones, the following categories of devices are used:

In zone 0 or 20 – category 1 devices
In zone 1 or 21 – category 1 or 2 devices
In zone 2 or 22, category 1, 2 or 3 devices
In places where the explosion risk assessment shows it is necessary, the following conditions should be met:

Devices and protective systems whose power supply failure may result in additional threats should be able to operate safely independently of other elements of the installation.
Devices and protective systems included in automatic processes that show deviations from normal operating conditions should be able to be disconnected manually by authorized persons, provided that this does not adversely affect safety conditions,
If the emergency shutdown system is activated, the accumulated energy should be dissipated or isolated in such a way that it no longer constitutes a source of hazard.
Installations, devices, protective systems and connecting elements, in particular cables, wires and pipes, are used only if it is specified in the pre-explosion document that they can be safely used in an explosive atmosphere.
In accordance with the regulatory requirements, the employer should take all necessary measures to ensure that the workplace, equipment and connecting elements accessible to working people have been designed, constructed, connected and installed, and are maintained and operated in a way that minimizes the risk of explosion.

If necessary, the employer should ensure that people are provided with optical or audible alarm signals so that they can leave the hazardous space before the conditions causing an explosion occur.

The table below allows you to select the devices for designated explosion hazard zones in the simplest way (table no. 1

According to the EN 1127-2007 standard, from the point of view of the manufacturer of protective system devices, parts and components, the division into categories can be illustrated in the table below.

Table nr 1

Marking of devices used in explosion hazard zones in accordance with the Regulation of the Minister of Development of June 6, 2016 on requirements for devices and protective systems intended for use in potentially explosive atmospheres:

Each device and each protective system must be marked legibly and permanently, including at least:

1) surname or name, registered trade name or registered trademark and address of the manufacturer;

2) CE marking;

3) series or type designation;

4) batch or series number, if any;

5) year of production;

6) special marking for explosion protection EX, followed by the symbol of the device group and category;

7) in the case of group II devices, the letter “G” (regarding explosive atmosphere caused by gases, vapors or mists)

8) the letter “D” (concerning explosive atmosphere caused by dust).

The types of explosion-proof structure are as follows:

d – flameproof cover

e – reinforced structure

ia – intrinsic safety, security level “ia”

ib – intrinsic safety, security level “ib”,

ic – intrinsic safety, security level “ic”,

ma –  encapsulation, security level “mb”,

mb  – encapsulation, security level “mb”,

nA – type n, protection method “nA”

nC – type n, protection method “nC”,

nL – type n, protection method “nL”

nR – type n, “nR” protection method,

o  – oil cover [N-10 PN-EN 60079- 6:2007],

px – gas cover with positive pressure, protection level “px”

py  – gas shield with positive pressure, “py” protection level,

pz  – gas shield with positive pressure, security level “pz”,

q – sand cover

s – electrical devices that do not meet the requirements of the PN-EN 60079 series standards