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Consultancy on ATEX standard for Explosive Atmosphere environments

SERVICE MERCATO CLIENT petrochemical industry YEAR 2006 - ad oggi

Client brief

Analyse risks linked to the presence of substances and mixtures, in liquid, gaseous or solid powder form, capable of generating potentially explosive atmospheres.

This analysis can be carried out both at the design stage, in order to identify the characteristics of the equipment and the prevention and/or protection systems necessary to minimise the risks of new installations, and during operations, in order to assess the risk in accordance with Italian Legislative Decree no.81/08 as amended and thus implement the organisational and management measures aimed at controlling and reducing the exposure and vulnerability of workers.

Project challenge

The risk analysis must take into account the complexity of the process and the control systems envisaged, as well as the environment in which the process is embedded and the various configurations and operational phases, including the need for personnel to be present in the vicinity.


Identification of the team of analysts and technical experts needed for the analysis. Meeting with the client, use of specific software and calculation systems to simulate releases and model the expected consequences.

The risk assessment originates from the classification of areas specified in the IEC 60079-10-1:2016 and EN 60079-10-2:2016 standards, which regulate the identification of areas in which potentially explosive atmospheres may occur.

In particular, the classification of explosion hazard zones is to be understood as the operation which, excluding catastrophic accident scenarios, under normal operating and maintenance conditions, assesses the probability of the presence of an explosive atmosphere both indoors and outdoors.

The goals of the analysis are, on the one hand, to guide the correct selection, installation and operation of equipment to be used safely in such environments, and on the other, to assess the risk of areas where the formation of a potentially explosive atmosphere can be considered credible.

In this context, the classification of the areas of the plant facility is performed according to the following phases:

Esecution phases


1) Identification of substances/mixtures capable of generating potentially explosive atmospheres;



2) identification of the emission sources;




3) determination of the degree of emission based on the probability and duration of the release;




4) evaluation of ventilation in terms of effectiveness and availability, according to the type of environment (closed/open);




5) quantification of the gas flow rate of the flammable substance dispersed in the atmosphere;




6) assessment of the degree of dilution of the substance, also as a function of its background concentration;




7) determination of the type of ensuing hazard zone;





8) determination of the extension of the area subject to explosion risk.


  • Subsequently, the risk assessment is conducted considering:
    • Presence of personnel in classified areas;
    • Characteristics of the environment: degree of confinement;
    • Activities undertaken: e.g. presence of any ignition sources;
    • Installed prevention and protection systems capable of reducing the probability of ignition and/or the extent of possible damage.


For classification purposes, liquid or gas escape simulation models are often used, through the use of TNO’s EFFECTS GIS software (validated and internationally recognised software based on TNO’s Yellow Book and Green Book methodologies). These advanced models are associated with the formulas suggested by the Guidelines referenced in the above-mentioned CEI standards (e.g. CEI 31-35 for gases and vapours).

Achieved results

Specific Risk Assessment Documents were drafted for explosion events and filed as part of the client’s generic risk assessment documentation (Italian acronym DVR).

Plans and sections representing the classified areas were drawn up.

Equipment suitability and job description checks were conducted.

Procedures, work permits and operating instructions were updated.

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