Explosion protection programs involve demanding requirements of the regulatory authorities

Operators and planners of process systems and plants in a wide range of industries including chemicals, pharmaceuticals and biotechnology are frequently confronted with the question of what criteria their plants and systems must meet to fulfill explosion protection requirements (ATEX).
What and who are to be protected?
The explosion protection guidelines specify measures to prevent explosions and to protect employees from explosions in dangerous, potentially explosive atmospheres and the corresponding uncontrollable effects of fire and pressure as well as harmful products of the reaction.
A potentially explosive atmosphere is defined as a potentially explosive mixture of combustible gases, fumes, mists or dusts and air or oxygen. It becomes dangerous when it occurs in a hazardous quantity of more than 10 liters.
Explosion hazards originating from explosive substances and unstable substances and from physical processes are not included in the framework of explosion protection. These include hazards posed by explosives, compressed gas cylinders and steam boiler systems, for example.
Statutory requirements
The main directives in the area of explosion protection in the European Union are the ATEX directives 94/9/EC (Equipment Directive)1) and 1999/92/EC (Workplace Directive). The country-specific laws and regulations via which the ATEX directives are implemented at the national level are binding.  These include, for example, the German Explosion Protection Ordinance (Explosionsschutzverordnung) and the German Ordinance on Health and Safety) in the Workplace (Betriebssicherheitsverordnung) as well as the Austrian Ordinance on Potentially Explosive Atmospheres (Verordnung explosionsfähige Atmosphäre [VEXAT]). For Switzerland, the ATEX directives were specified in detail by the Swiss National Accident Insurance Institution (SUVA) in Memorandum 2153.
An extensive collection of the applicable rules in Germany related to this subject can be found in the Explosion Protection Rules (Explosionsschutz-Regeln [BGR 104]) of the German Social Accident Insurance (Deutsche Gesetzliche Unfallversicherung [DGUV]). Here you’ll also find a collection of relevant technical rules for health and safety in the workplace (Technische Regeln für Betriebssicherheit [TRBS]).
The primary issue in explosion protection
The main question is whether the formation of a dangerous, potentially explosive atmosphere is possible. If this question can be answered with “No”, explosion protection is not relevant for the area in question. This is the case if combustible substances are present only in minimal quantities or not at all. However, if a potentially explosive atmosphere can occur when there are hazardous quantities present, the implementation of and compliance with explosion protection rules are mandatory.
What must be done?
Primary explosion protection measures
The goal of these measures is to prevent the formation of a dangerous, potentially explosive atmosphere. These include:
• the replacement of critical components with incombustible or less volatile substances
• inertization of systems or system parts with inert gases such as nitrogen
• dilution of combustible liquids with inert components such as water
• reduction of the quantity of combustible components so that the dangerous quantity required to create a potentially explosive atmosphere is not reached
• moistening of dusts and regular cleaning measures to reduce the amounts of dusts
These measures usually succeed only in reducing the probability of the occurrence of the potentially explosive atmosphere and its spread. However, simpler and usually more cost-effective versions of other required protective measures can also be used.
Secondary and tertiary protective measures
If the occurrence of a dangerous, potentially explosive atmosphere cannot be reliably prevented, further explosion protection measures are required. These include the classification of the potentially explosive atmosphere into explosion protection zones in accordance with the criteria of probability and possible duration of the occurrence of a potentially explosive atmosphere. Based on the zone classification, only approved components may be used in these areas in order to eliminate sources of ignition. This leads to the prevention of ignition of an existing, potentially explosive atmosphere, which is designated as secondary explosion protection.
Structural explosion protection, which reduces the effects of a potential explosion to an acceptable level, is designated as tertiary explosion protection. This includes, for example, pressure-resistant construction or the securing of the plant against explosive pressure with safety features such as explosion vent panels and valves.
Explosion protection must be documented
Employers are responsible for preparing explosion protection documentation in which the explosion risks for the plant in question are determined and assessed. The zone classification and all necessary explosion protection measures must also be listed in this documentation. The documentation must be kept up-to-date and must therefore be revised after any remodeling and expansion of the plants.
Conclusion
If combustible materials are used in plants, the explosion protection requirements must be implemented by the plant operator as the employer in most cases. In these cases, the plant operator must prepare explosion protection documentation in which the fulfillment of these requirements, such as the classification of EX zones and the assessment and implementation of suitable explosion protection measures are documented.
1) As of May 2016, this has been superseded by Product Directive 2014/34/EU.
Many good sources of informations in Germany.
Keep up good work!
Source: http://www.chemgineering.com/en/Scientific%20Articles/$/Explosion-protection-%E2%80%93-ATEX-EX-zones-et-al./53