Sources of Ignition Covered by the ATEX Directive

An effective ignition source is one of the three basic elements used to describe an explosion hazard. Without sufficient energy delivered to the system of flammable substances (in the form of gas, vapor, or dust) and air (or another oxidizer), there is no risk of an explosion. Therefore, one of the basic ways to manage the hazard is to eliminate or reduce the likelihood of their occurrence as much as possible.

Just as there are standards that describe most issues related to explosion protection, there is also a standard specifying which sources of ignition are covered by the ATEX directive.

According to PN-EN 1127-1:2019-10 “Explosive atmospheres and explosion protection – Part 1: Basic concepts and methodology,” 13 factors can initiate an explosion.

The standard distinguishes

Hot Surfaces

Explosive atmospheres can ignite upon contact with hot surfaces if their temperature reaches the atmosphere’s ignition temperature. Where hot surfaces may come into contact with explosive atmospheres, a safety margin must be ensured between the maximum surface temperature and the atmosphere’s ignition temperature. This margin depends on the zone classification and is determined in accordance with PN-EN 1127-1.

Flames and Hot Gases

Both flames and incandescent solid particles can ignite explosive atmospheres. Even very small flames are among the most effective ignition sources and must therefore be eliminated from hazardous areas in zones 0 and 20. Flames can only occur in zones 1, 2, 21, and 22 if they are securely enclosed, as described in PN-EN 1127-1. Unshielded flames from combustion or welding must be prevented by organizational measures. For example, for explosive gases, an open flame is almost always an effective ignition source.

Mechanical Sparks

Friction, impact, and abrasion, for example, during grinding, can cause sparks. Sparks can ignite flammable gases and vapors, as well as certain mist/air or dust/air mixtures (particularly metal dust/air mixtures). In dust deposits, smouldering can be caused by sparks, which can constitute a source of ignition for explosive atmospheres.

Electrical Devices

Even at low voltages, electrical sparks and hot surfaces can constitute ignition sources in electrical devices (e.g., when making and breaking electrical circuits and as a result of stray electrical currents). Therefore, it is generally assumed that electrically powered devices – regardless of their form – are potential sources of ignition.

Stray Currents

Electrostatic Discharges: corona, brush, gliding, cone, spark

The formation, accumulation, and decay of an unbalanced electric charge on the surfaces of various types of electrically non-conductive objects and isolated conductive objects (including the human body). The work put into separating opposite charges (e.g., by friction, separating different materials from each other, crushing, splashing, external electric field, etc.) is converted into the potential energy of the electric field surrounding the separated charges.

Lightning

This factor is rather random in nature, but significant due to the energy transferred. Hence, the need to use appropriate grounding for all conductive components.

• Radio frequency (RF) electromagnetic waves from 10⁴ to 3×10¹² Hz
• The use of portable, battery-powered devices is permitted in explosive atmospheres only if they are ATEX certified.
• Electromagnetic waves from 3×10¹¹ to 3×10¹⁵ Hz
• Ionizing Radiation
• Ultrasound
• Adiabatic Compression

Exothermic Reactions, Including Self-Ignition of Dust

• Substances can heat up as a result of chemical reactions that generate thermal energy (exothermic reactions), which therefore constitute a source of ignition. This self-heating is possible if the rate of thermal energy generation is higher than the heat dissipation rate. If heat dissipation is difficult or the ambient temperature is high (e.g., during storage), the reaction rate can increase to such an extent that ignition conditions are reached. The most important parameters are the volume/air ratio of the reacting systems, the ambient temperature, and the residence time.
• High temperatures can lead to smouldering and/or combustion, and the ignition of explosive atmospheres. Any flammable substances generated by the reaction (e.g., gases or vapors) can then form explosive atmospheres with the surrounding air, significantly increasing the hazard to such systems. Substances that are spontaneously ignited should be avoided in all zones wherever possible. If handling such substances is necessary, the necessary protective measures should be adapted to each individual case.

Other standards and regulations regarding explosion protection are also important and are briefly described here: EX zone regulations. It is worth familiarizing yourself with them.