GB/T 25285.1-2021Explosive atmospheres—Explosion prevention and protection—Part 1: Basic concepts and methodology (English PDF)

3.1 Flammable substance

A substance in gas, vapor, liquid, solid form, or a mixture of these forms, that reacts exothermically with air when ignited.

3.2 Component

Devices, that are essential to the safety functions of equipment and protective systems but have no independent function.

3.3 Deflagration

An explosion, that travels at subsonic speeds.

3.4 Detonation

An explosion, that travels at supersonic speeds and has the characteristics of a shock wave.

3.5 Equipment

Machinery, equipment, fixed or mobile devices, control units, instruments, detection or prevention systems, which are used alone or in combination, for the generation, transmission, storage, measurement, control, conversion and/or material processing of energy, AND which can cause explosions due to their own potential ignition sources.

4.1 General

For non-electrical equipment, components, protective systems, devices and their combinations, if they themselves have potential ignition sources and are expected to be used in explosive atmospheres, a risk assessment shall be carried out in accordance with GB/T 3836.28.

4.2 Identification of explosion hazard

4.2.1 General

Explosion hazards are often associated with materials and substances that are handled, used or released by equipment, protective systems, components, as well as with the materials from which equipment, protective systems, components are made. Some of these released substances undergo a combustion process in the air.

4.2.2 Combustion characteristics

Since the material itself is not used here, but the contact or mixing of dust and air is used to illustrate potential hazards; therefore, it shall determine the characteristics of the mixture of flammable substances and air.

4.2.3 Explosion characteristics

The characteristics of explosive atmospheres after ignition shall be described using the following data.

4.2.4 Possibility of hazardous explosive atmospheres

The possibility of a hazardous explosive atmosphere occurring depends on the following.

4.3 Identification of ignition hazard

4.3.1 General

First, it shall be determined which types of ignition sources are possible and which are associated with the equipment (or components, protective systems).

4.3.2 Ignition characteristics

The ignition characteristics of hazardous explosive atmospheres shall be determined. Relevant data such as.

4.3.3 Possibility of effective ignition source

Potential ignition sources shall be classified, according to their likelihood of becoming an effective source of ignition, as follows.

4.4 Estimating the possible effects of an explosion

In order to estimate the possible effects of an explosion, the following factors need to be considered, such as.

5.1 Hot surfaces

If an explosive atmosphere comes into contact with a heated surface, ignition may occur.

Not only the hot surface itself can become an ignition source, but also the dust layer and combustible solids that are in contact with or ignited by the hot surface can become an ignition source in explosive atmospheres (see 5.2).

5.2 Flames and hot gases (including hot particles)

Combustion reactions at temperatures above 1000 °C are usually accompanied by flames. Hot gases are the products of the reaction; in dusty and/or soot-laden flames,

5.3 Impact, friction, grinding caused by machinery

As a result of friction, impact or abrasive processes such as grinding, particles can be produced that are separated from the solid material and heated by the application of energy during the separation process. If these particles contain oxidizable substances, such as iron or steel, they can undergo oxidation processes, that reach higher temperatures.

5.4 Electrical equipment and components

Sparks and hot surfaces (see 5.1) of electrical equipment and components can become sources of ignition. Sparks and hot surfaces can be generated under the following conditions.

5.5 Stray current and cathode anti-corrosion measures

Stray currents may occur in conductive systems or conductive parts of systems for the following reasons. currents and cathodic corrosion.

6.1 Basic principles

Based on the necessity of the simultaneous existence of a dangerous explosive atmosphere and an effective ignition source, as well as the expected effects of explosions described in Chapter 4, the basic principles of explosion prevention and explosion protection are derived directly in the following order.

6.2 Avoid explosive

atmospheres or reduce the amount of hazardous explosive atmospheres

6.2.1 Process parameters

6.2.1.1 Replace or reduce the amount of substances capable of creating an explosive atmosphere

6.2.1.2 Limit concentration

If it is unavoidable to handle substances that can form an explosive atmosphere, measures can be taken to control the amount and/or concentration of flammable substances, to prevent or limit the amount of hazardous explosive atmospheres within equipment, protective systems, components.

6.2.2.3 Ventilation and dilution

Ventilation is important to control the effects of releases of flammable gases and vapors.

It can be used inside and outside equipment, protective systems, components.

Note: GB 3836.14 provides relevant content on the use of ventilation, to control and classify gas and vapor hazardous locations.

6.3 Hazardous locations

6.3.1 General

Hazardous locations may depend on the design and use of certain equipment, protective systems, components. They shall be taken into account, when planning the design and specified uses (see GB 3836.14 and GB/T 12476.3).

GB/T 16855.1 covers general principles in this field.

7.1 General

This Chapter specifies information on use and maintenance, which shall be provided with the equipment, protective systems, components, OR as part of the instructions for use (e.g., user manual).