ATEX: how to assess the risk of explosion of plants
The CAMLogic column dedicated to ATEX revamping continues. Since in the previous article we explained what it means, it’s time to expand on the topic, starting with the preliminary analysis of the explosion risk.
Assessing the risk of explosion in industrial plants is necessary and mandatory, especially in plants processing flammable gases, liquids and dusts such as in the oil&gas, chemical-pharmaceutical or food sectors. In these plants there is a risk of a chemical explosion, linked to a possible involuntary combustion reaction which can generate an explosion or detonation with potential damage to people, environment and production facilities.
The combustion reaction can take place only in the simultaneous presence of fuel and oxidant, in concentrations such as to fall within the explosive limits, and a source of ignition. These three factors (fuel, oxidizing agent and source of ignition) represent the linchpin of the risk of explosion assessment and of the pertinent regulatory plan that oversees it.
Types of fuel and oxidant
In industrial plants fuel consists of the substances processed and/or present on site, whether they are gases, liquids or powders.
- Combustible gases and liquids can be themselves the target of the process, with ensuing gaseous emissions into the environment through pipe junctions, valves or tanks. They can, however, also be found inside process equipment and other systems, such as those for lubrication or cleaning through solvents.
- Combustible dusts in the form of a layer or cloud are commonly the target of the process or storage. They are present within the process and most likely in the proximity of loading hoppers, hatches and valves of communication between inside and outside of pipes and containers.
As an oxidizing agent for gases and dusts there is always an abundance of oxygen outside or inside the process. Fuel and oxidant are typical of the environment and their relative concentration could pose a risk.
How to assess the risk of explosion?
Based on these premises, how to assess the risk of explosion? It is essential to look at frequency and duration within the explosive limits for fuel and oxidant.
Classification of hazardous places and level of risk
The application of ATEX Directive 1999/92/EC (Annex I), incorporated in Italy in 2003, requires the preparation of an “Explosion protection document” by the plant manager, which usually corresponds to the employer.
However, given the complexity of the classification of hazardous places and of the relative level of risk of explosion, it is advisable to rely on highly specialized personnel capable of evaluating additional factors such as:
- the characteristics of the potentially explosive substance;
- the degree of ventilation of the environment;
- the process parameters;
- any other relevant aspects.
Evaluation of ignition sources
Once the zones, frequency and duration of fuel and oxidant in the explosive limits have been identified, the probability of an effective ignition source must be evaluated. This process allows to keep the risk of explosion within acceptable levels. Common sources include hot surfaces, static electricity or mechanical sparks.
Evaluation of the equipment protection level
Every type of zone is then associated with a required level of protection from the risk of explosion for the equipment, precisely in consideration of the probability that an effective ignition source could be present. The protection level from the risk of explosion for equipment in conformity with Directive 2014/34/EU is defined by the category of its marking (respectively: 3 - 2 - 1) which therefore represents the main selection criterion, based on the installation zone.
How to assess the risk in pre-2003 contexts?
But how to behave for plants with equipment and machinery “before 2003”, year of the entry into force of the first Directive 94/9/EC (later replaced by 2014/34/EU)?
Obviously, the minimum level of security must be insured, therefore a constructive and formal adaptation is necessary.
In the next article we will specifically talk about ATEX revamping, meanwhile you can discover a project created by CAMLogic and focused precisely on the safety of plants in the presence of ceramic dusts.
Referenced directives and standards:
ATEX 1999/92/CE (Annex I)
Directive 2014/34/UE, which replaced Directive 94/9/CE
CEI EN 60079-10-1:2016
CEI EN 60079-10-2:2016
DL 81/2008 - Titolo XI
UNI EN 1127-1:2019
Article written in collaboration with Fabrizio Bellini, consultant for the design, the revamping and the certification of equipment and machinery intended for use in explosive atmospheres. For further information and clarifications, you can contact Engineer Bellini by sending an email to firstname.lastname@example.org.