Explosive Atmospheres

An explosive atmosphere (ATEX) occurs when air mixes with flammable substances, creating dangerous conditions in industrial environments such as chemical plants, refineries, and grain silos

An explosive atmosphere (ATEX, from the French "ATmosphères EXplosibles") is a mixture of air with flammable substances in the form of gas, vapor, dust, or fibers. In these atmospheres, after an explosion, combustion spreads throughout the unburned mixture. Explosive atmospheres are common in industrial environments where hazardous materials are handled, such as chemical plants, refineries, grain silos, and wastewater treatment plants.

Components of Explosive Atmospheres

The main components of an explosive atmosphere include:

Fuel: This can be combustible gas, vapor, dust, or fibers.
Oxygen: Present in the air in sufficient quantities to sustain combustion, also known as an oxidizer.
Ignition Source: This can be a spark, a flame, a hot surface, or an electrical discharge.

The combination of these elements in the correct proportions, along with an ignition source, can lead to an explosion. This combination is known as the "fire triangle." For an explosion to occur, the amounts of fuel and oxidizer must be correct; otherwise, the reaction will not take place.

Prevention and Protection in Explosive Atmosphere

To mitigate the risks associated with explosive atmospheres, it is essential to implement prevention and protection measures, such as:

Avoiding the formation of explosive atmospheres: Using appropriate equipment and facilities to prevent the presence of ignition sources.
Risk assessment through energy audits: Analysing the likelihood of forming an explosive atmosphere, its extent, duration, and the possibility of contact with an ignition source (according to Royal Decree 681/2003).
Protection measures: Mitigating the effects of the explosion by controlling its direction to minimize personal and material damage.

Normativa ATEX y clasificación de emplazamientos

The ATEX regulations govern working conditions in environments with explosion risks in Europe. They define guidelines for the classification of areas and the selection of appropriate equipment and protection systems for explosive atmospheres.

ATEX sites are areas where an explosive atmosphere exists or may exist, requiring specific prevention and protection measures to ensure safety. There are two types of sites for these atmospheres:

Class I Sites: Areas affected by gases, vapors, or mists, such as digesters, gas stations, or paint shops. Key factors: physical state of the substance, containment system, flash point, ignition temperature, among others.
Class II Sites: Areas affected by flammable dust, such as grain silos or pharmaceutical facilities. Key factors: particle size, moisture, ignition temperature, among others.

ATEX Zone Classification in Explosive Atmospheres

Once the site is selected, it is classified according to ATEX zones, which are risk areas where explosive atmospheres can form and require special precautions:

Zone 0 (Class I) and Zone 20 (Class II) : Areas where the explosive atmosphere is continuously present or for long periods.
Zone 1 (Class I) and Zone 21 (Class II) : Areas where the formation of an explosive atmosphere is likely under normal operating conditions.
Zone 2 (Class I) and Zone 22 (Class II) : Areas where the formation of an explosive atmosphere is unlikely and of short duration.

Equipment and Protection Systems for Explosive Atmospheres

Equipment and protection systems are classified according to their ability to prevent ignition of explosive atmospheres:

Category 1: Maximum level of protection, to be used in areas where explosive atmospheres are continuously present (Zones 0 and 20).
Category 2: High level of protection, for areas where explosive atmospheres are likely under normal operating conditions (Zones 1 and 21).
Categoría 3: Protección básica, para áreas donde la atmósfera explosiva es improbable y de corta duración (Zonas 2 y 22).