ATEX Zone Classification: Dust Explosion Risks & Zoning Guide

Section summary
1. Introduction : what is ATEX zoning
2. Zones definition criteria and classification chart
3. Examples of ATEX zoning for dust explosion risks
4. Common mistakes and Best Practices when defining ATEX zoning

1. Introduction : What is ATEX zoning ?

The european ATEX directives 94/9/CE and 1999/92/CE, revised in 2014, have introduced the notion of zoning in order to identify and classify areas within a factory that present a risk of presence of a powder cloud in explosive conditions. It is a notion related to the european regulation but in general, for every Dust Hazard Analysis - DHA - the areas where an explosion can occur should be determined.

The factory operator must carry out a dust explosion risk analysis, often called ATEX study, in order to classify the areas according to the probability of presence of a dust cloud (zoning).

On the other side, the equipment supplier must supply an equipment that is compliant for the zone defined by the process operator.

2. Zoning definition and classification chart

How to define the ATEX zoning for dust ?

The following ATEX zone classification chart for dust explosion hazard helps you to determine if an area in your factory / working area is to be classified ATEX. The presence of a classified ATEX area, and its rating, is depending on the probability of presence of a dust cloud.

Probability of presence of dust cloud -> ATEX classification

ATEX zone	Definition
Zone 20	What is ATEX zone 20 ? An ATEX zone 20 is a Location where an explosive atmosphere is permanently present or during long periods or frequently Order of magnitude : Dust in explosive concentration is present 1000 h or more / y (= normal process conditions)

Zone 21	What is ATEX zone 21 ? An ATEX zone 21 is a Location where an explosive atmosphere is likely to be present occasionally in normal working conditions Order of magnitude : Dust in explosive concentration is present 10 h 1000 h / y (= in certain process conditions)

Zone 22	What is ATEX zone 22 ? An ATEX zone 22 is a Location where an explosive atmosphere is not likely to be present in normal working conditions or, if it is present, it is only for short duration Order of magnitude : Dust in explosive concentration is present from 1h to 10h / y (= very rare process conditions or abnormal conditions - leaks)

Table 1 : ATEX dust zone classification chart

The zoning is fundamental to help the process operator to put in place the measures necessary to reduce the risks of inflammation of a dust cloud, or to put in place protections in case of explosions.

Note that layers and deposits of powder must be considered as well as it could start burning in case of high temperature or be put in suspension and form an explosive dust cloud.

3. Examples of ATEX zoning for dust explosion risks

[Laurent] is giving some common examples of equipment often falling in one category or another.

WARNING : this is only a general indication, only the specific risk assessment of a process will be able to confirm if one equipment belongs to one zone or another depending on a particular context.

ATEX zone	Example
Zone 20	Inside silos, hoppers, mixers, dryers, cyclones, filters Inside transport systems of bulk solids...etc...

Zone 21	Immediate surrounding of silos, hoppers, mixers, dryers, cyclones, filters and system of transport...etc... Found also around tipping station, when powder is poured into a container or vessel

Zone 22	Occasional leaks at manholes, filters, in case of failure of flexible...etc..

The process is strongly influencing the ATEX zoning. For example if a process is designed to have powder tipped to a hopper without dust aspiration, the area around the tipping is likely to be classified zone 21, while if a dust aspiration system is present, dust around the tipping will be much more rare, only present when the dust aspiration system is defective or if the operator drops a bag, the area around the tipping can then be defined as zone 22.

Example of ATEX zoning classification for a bulk powder sack tipping station

Figure 1 : Example of ATEX zoning classification for a bulk powder sack tipping station

The zoning definition and the reasons justifying a particular zoning, or the absence of zoning, must be described in the ATEX risk analysis and the measures to put in place explained. Conclusions of the risks analysis must be implemented by the factory.

4. Common mistakes and Best Practices when defining ATEX zoning

4.1 Common Mistakes in ATEX Zoning

While understanding the principles of ATEX zoning is crucial for workplace safety, there are common mistakes that businesses should avoid. Recognizing and rectifying these errors can make a significant difference in minimizing the risks associated with dust explosion hazards. Here are some of the common mistakes in ATEX zoning:

Neglecting Regular Updates: A frequent mistake is failing to keep ATEX zoning documents and assessments up to date. As your facility evolves, zoning requirements may change. Regularly review and update your ATEX zones to ensure they accurately reflect the current state of your operations.
Incomplete Risk Analysis: Inadequate risk assessments can lead to incorrect ATEX zone classifications. Some businesses may overlook specific areas or underestimate the potential for dust clouds. A comprehensive risk analysis is essential for proper zoning.
Overlooking Maintenance: Equipment breakdowns, improper maintenance, or the absence of safety mechanisms can result in unexpected dust releases. Ignoring maintenance needs can lead to changes in ATEX zones. Regular equipment checks and maintenance are vital.
Inadequate Training: If your employees are not adequately trained in recognizing and responding to ATEX zone risks, safety measures may be compromised. Ensure that your staff understands the significance of ATEX zoning and the procedures to follow.
Ignoring Hybrid Zones: Some areas may exhibit characteristics of multiple ATEX zones. Ignoring these hybrid zones can be a mistake. It's essential to assess and classify areas accurately, considering all potential risks.
Failing to Document Zoning Changes: Whenever there are adjustments to ATEX zones due to process modifications or safety improvements, it's crucial to document these changes. Failure to do so can result in confusion and non-compliance.

4.2 Best Practices for ATEX Zoning

To ensure that your facility complies with ATEX zoning requirements and maintains a high level of safety, follow these best practices:

Comprehensive Dust Hazard Analysis: Begin with a thorough Dust Hazard Analysis (DHA) to assess the risk of dust explosions accurately. A well-conducted DHA is the foundation of proper ATEX zoning.
Regular Reviews and Updates: Periodically review and update your ATEX zones to account for changes in equipment, processes, or safety measures. This practice helps you stay in compliance and maintain a safe working environment.
Employee Training: Train your employees to recognize ATEX zones and understand the safety measures associated with each zone. Well-informed staff members are essential for accident prevention.
Clear Signage: Use clear and standardized signage to indicate ATEX zones within your facility. Proper labeling ensures that employees and visitors are aware of the potential hazards.
Equipment Compliance: Choose and maintain equipment that complies with the specific ATEX zones in your facility. Verify that suppliers provide ATEX-certified equipment designed for the intended zone.
Documentation: Maintain detailed records of your ATEX zone classifications, risk assessments, and any changes made over time. Documentation is essential for regulatory compliance and safety audits.
Emergency Response Plans: Develop and implement clear emergency response plans for each ATEX zone. These plans should include procedures for evacuation, shutdowns, and firefighting

ATEX zone classifications 20,21,22 : An overview