Combustion and explosion are risks that must be prevented in any plant. In this guide, we will look at all the key aspects of the ATEX Directive, also known as "ATEX legislation", with a special focus on distilleries.
- How the combustion process works
- How explosions are triggered
- The Danger of an explosion in a distillery
- How we got to the ATEX Directive
- How to manage ATEX in a distillery
- The importance of ventilation in the ATEX directive
- Penalties for non-compliance
How the combustion process works
The combustion process is a chemical reaction of oxidation. It involves:
- fuel - e.g. ethyl alcohol derived from distillation
- oxidizer - oxygen in the air
- ignition source
Every combustion process needs a combustible substance in a specific environment triggered by an external energy source. Every substance has its own flashing point.
One of the parameters that are carefully looked at is the "Vapor Pressure" of a liquid: vapor pressure is the ease or speed with which the substance goes from the liquid to the gaseous state, producing vapor.
A liquid is defined as flammable when its evaporation allows the gas to be ignited by a trigger.
How an explosion is triggered
Let us consider the molecules of single particles suspended in the air. When triggered by an external energy source and then hit by heat starting them off in the oxidation process, these molecules head to combustion.
Combustion develops heat and energy, resulting in a chain reaction with exponential progression over time. An enormous amount of energy is released by this process, and the result is an explosion.
Now, the importance of the ethanol concentration is clear: if the alcohol particles in the air were scattered around, the effect of energy transmission would be lost, and there would be no chain reaction between the particles.
The concept of the flammable range
Two notions are needed to explain the flammable range or explosive range:
- Dilution: more details about it are provided in the ATEX directive. Dilution allows air to drive the ethyl alcohol particles away from each other; the lower limit of this concentration is called LFL (Low Flammable Limit);
- Excessive concentration: an excessive concentration may not allow the oxidation/combustion/explosion process. In fact, there would not be enough comburent (oxygen in the air). The upper limit of this concentration is called UFL (Upper Flammable Limit).
These two concentration limits, the minimum limit (LFL) and the maximum limit (UFL) constitute what is called the flammable range, or explosive range.
Outside this range, even in the presence of ignition, there is no combustion nor explosion.
The danger of an explosion in a distillery
The plant of a distillery is structured indifferent components: pipe bundles, mechanical control or shut-off devices, balanced ventilation systems, and cauldrons. Here, the distillation process takes place. So, the hydroalcoholic substance goes through temperature, pressure, and physical changes which stabilize in the final product: ethyl alcohol. The final alcoholic strength is about 85% vol. at 20°C temperature.
In such a picture, there may be a danger of two conditions, one possible (although remote), the second intentional:
- Ethyl alcohol can leak from overused mechanical components and spill onto the floor below, creating an amount of “free” flammable liquid;
- The vents, in the regular distillation process, produce continuous emissions, in order to balance tension and pressure. This may also favor the outflow of the distillate.
Both conditions emit ethyl alcohol vapors into the atmosphere, and this might constitute an explosion hazard.
The ATEX directive addresses these potential risks, with the intention of ensuring the safety of the workers involved.
Are distillation plants safe?
First things first: we would like to say again that distillation plants are absolutely safe. They are well-designed and well-built by specialized technical teams. Its materials are suitable for the purpose and the chemical and physical dynamics to which they are subjected.
ATEX norms are here to avoid the worst-case scenario.
How we got to the ATEX Directive
The European Community produced two directives in the 1990s, then translated by the member states.
Directive 94/9/EC and 2014/34/EU
Directive 94/9/EC dates back to 23 March 1994 and is about the approximation of the laws of the Member States relating to equipment and protective systems which should be used in potentially explosive atmospheres. It is called the "product directive" and establishes the type of materials to be used in the above-mentioned places, associating a specific marking for the category of use. It has since been replaced by 2014/34/EU.
The second important directive is dated 16 December 1999 and is about the minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres. It explains the concept of a hazardous zone and divides it into three degrees of severity. Each degree is matched with behavior by those involved in the activity, and with prescriptions for the adoption of materials for use within these zones (later established by 2014/34/EU).
In addition, the legislation establishes through specific calculation parameters the possible extent of the hazardous zones, in order to set the limit of the hazard with appropriate terms/tools.
Italian perspective: Testo Unico on worker safety
In April 2008, the well-known Legislative Decree No. 81/08 was issued. It’s called “Testo Unico” (Whole Text) because it contains a set of rules and regulations about workers’ safety and health. Title XI - "Protection from explosive atmospheres" - ensures the safety of workers in places where explosive atmospheres may occur.
The ATEX Directive in the European Union
How do we comply with those provisions?
What criteria make it possible to control and avoid an explosive event?
To answer this question, we have to introduce the "ATEX" (acronym for ATmosphères EXplosives) standard, i.e. CEI EN 60079-10-1, which is legally valid in Europe. In part "10-1" we learn that this is a standard concerning explosive atmospheres caused by emissions of flammable GASES or VAPORS.
For the sake of completeness: part "10-2" deals with explosive atmospheres caused by combustible dust.
The ATEX Directive describes the criteria needed:
- To determine, through appropriate calculation parameters, the extent, and type of hazardous areas;
- To define how to limit and extinguish ATEX zones.
The ATEX legislation also provides for the figure of the "classifier", the specialist in assessing ATEX zones.
How to manage ATEX in a distillery
In the case of an existing distillery, it is advisable to hire a specialized firm to check that the production premises comply with the ATEX directive.
If, on the other hand, a new distillery is to be opened, our advice is to carry out an integrated plan that matches building strategy, implants position, and the ATEX assessment altogether.
This provides the company a foresight of construction, electricity, and distillation installations.
ATEX check will be just included, and no unexpected problems will occur.
Spaces will be safely designed right from the start.
The importance of ventilation in the ATEX directive
Going back to the ATEX legislation, it is worth mentioning the importance of good ventilation.
Ventilation allows the dilution of the concentration of flammable gas or vapor within the distillery plant, as we mentioned a few paragraphs above.
What does "ventilation" mean?
From IEC 60079-10-1; in art.3.5.1 we find the following definition of "ventilation": "Movement and exchange of air with new air, caused by the effect of wind, temperature gradients, or artificial means (e.g. fans or extractors)".
In an enclosed space, the volume we consider may be the whole room or a larger space, in which adequate ventilation can dilute the gas/vapor from a given Emission Source.
Such ventilation controls the dispersion and persistence of the explosive atmosphere. The "degree of dilution" together with the "availability of ventilation" will contribute to the best result possible, when analyzing the extent of ATEX zones.
Please note that ventilation alone may not be sufficient to prevent the formation of an explosive atmosphere.
However, it may be sufficient to prevent its persistence and limit its extent.
To achieve this goal, mechanical engineering offers us two ways:
- Forced/mechanical/artificial ventilation
- Natural ventilation
Both are suitable, but each is subject to its own limitations and benefits, which must be taken into account in the design and analysis according to the ATEX directive.
Artificial mechanical ventilation systems have a high degree of reliability: the airflow rate is constant and the exchange of air is maintained over time.
However, mechanical ventilation systems can be subject to failure. Emergency criteria are needed to keep the general safety level always high.
Natural ventilation systems
Natural ventilation systems require knowledge of specific concepts. In the case of naturally ventilated enclosed spaces, it is necessary to consider unfavorable conditions, such as atmospheric conditions.
Normally, upwind openings will perform as entry openings. Downwind and roof openings will perform as exit openings.
Penalties for non-compliance
The legislator (in Italy) can sentence an employer to prison if he fails to assess certain specific risks (as provided by the Italian Law, Article 290, Legislative Decree 80/01).
The risks are:
- the probability and duration of the presence of explosive atmospheres
- the probability of ignition sources becoming effective
- the risks coming from the plant itself
- Risks arising from the substances used and their possible interactions
- Other foreseeable effects and their extent
The employer must be able to assess all these elements together to get a full picture of the explosion risks (first paragraph of Article 297).
The second paragraph of Art. 297 extends criminal liability also to managerial staff.
At least, the managerial staff has some obligations (Title XI) which can’t be neglected, such as:
- preventing explosive atmospheres
- setting up structures according to the type of hazard
- compiling the explosion protection sheet
- training and informing workers on how to behave
- complying with Annexes XLIX and L.
This description is a summary of what the intention of the sanctions is in Italy.
A final clarification on the ATEX directive: Article 293 of Legislative Decree 81/08 refers compliance with the law to Annex XLIX, where explicit reference is made to standard EN 60079-10 (GAS - 2003) and standard EN 61241-10 (DUST - 2003).
The quotation of the above standards is correct but misplaced: they have now been replaced with two other versions over time.
But that is another story.
This article has been written by the Italian industrial expert Giuliano Porta, from StProgel technical office.