Explosive atmospheres

What are explosive atmospheres and where do they occur?

Workplace explosions occur when a flammable substance dispersed in air at a concentration within its explosive limits, oxygen, and a sufficiently energetic ignition source come into contact. They occur in a wide variety of industries: refineries and chemical plants, fuel storage and transfer, paint booths, gas plants, water treatment plants, silos and the handling of grains, flour, sugar, wood, plastics, or powdered metals, the pharmaceutical industry, and workshops using solvents. Combustible dust is a frequent and often underestimated cause of serious explosions.

The European Union regulates this matter with two complementary directives: Directive 2014/34/EU, addressed to manufacturers, which establishes the essential requirements for equipment and protective systems intended for potentially explosive atmospheres and their marking (categories M1 and M2 for Group I and 1, 2, and 3 for Group II), and Directive 1999/92/EC, addressed to employers, which establishes the minimum provisions for protecting workers. In Spain, these are transposed by Royal Decree 144/2016 and Royal Decree 681/2003, respectively, and the National Institute for Safety and Health at Work (INSST) publishes the Technical Guide for the Assessment and Prevention of Risks Arising from Explosive Atmospheres in the Workplace.

The preventive approach follows a clear hierarchy: first, prevent the formation of an explosive atmosphere (substitution of substances, inerting, ventilation, leak and dust accumulation control); if this is not possible, prevent ignition (equipment and clothing appropriate for the area, static electricity control, hot work with permits, grounding); and finally, mitigate the effects (venting, suppression, decoupling, building resistance). These measures are documented in the explosion protection document.

Obligations of Royal Decree 681/2003

• Specific assessment. Evaluate explosion risks considering the probability of formation and duration of explosive atmospheres, the probability of presence and activation of ignition sources, the facilities, substances, processes and their interactions, and the proportions of foreseeable effects.
• Zone classification. Classify into zones the areas where explosive atmospheres may form: zone 0 (permanent or frequent presence of gas, vapor or mist), zone 1 (probable in normal operation), zone 2 (unlikely and of short duration); and zones 20, 21 and 22 for combustible dust.
• Equipment by zone. Use in each zone protective equipment and systems of the corresponding category: category 1 in zones 0 and 20, category 1 or 2 in zones 1 and 21, categories 1, 2 or 3 in zones 2 and 22, unless the explosion protection document justifies otherwise.
• Explosion protection document. Prepare and keep up-to-date the document that reflects the assessment, the measures adopted, the classification of zones, the places where the minimum provisions apply and the safe design, use and maintenance of places and equipment.
• Coordination. When several companies are involved, the business owner of the center coordinates the measures and specifies their objective and application in the protection document.
• Signage and access. Mark the access points to the areas with the triangular pictogram EX and control the entry of people and equipment.
• Organizational measures. Specific training, written instructions and work permit system for hazardous activities, verification of facilities before commissioning by competent persons, and maintenance of safety in the event of power outages.

Standard technical measures

• Control of the substance. Substitution with less flammable substances, reduction of quantities, inerting with nitrogen, natural or forced ventilation with gas detection, and systematic cleaning of dust deposits.
• Ignition control. Electrical and non-electrical equipment with ATEX marking of the appropriate category, grounding and equipotential bonding, static electricity control (clothing, footwear, materials), lightning protection, controlled surface temperatures and non-sparking tools.
• Mitigation of effects. Venting panels, explosion suppression systems, decoupling between equipment, pressure-resistant design, and safety distances.
• Detection and response. Gas detectors with alarms and interlocks, emergency stops and evacuation procedures.
• Maintenance and inspection. Programs in accordance with UNE-EN 60079 standards for electrical installations in explosive atmospheres, with records of inspections and repairs by competent personnel.

Organizational application: how to manage ATEX risk

1. Inventory the flammable substances and combustible dusts present, with their properties (explosive limits, ignition temperature, minimum ignition energy) and the processes in which they are handled.
2. Perform the specific explosion risk assessment and classify the areas using documented criteria, based on UNE-EN 60079-10-1 and 60079-10-2 standards.
3. Prepare the explosion protection document with the assessment, classification, technical and organizational measures, equipment by zone and responsibilities, and review it in case of changes.
4. Verify that the equipment installed in each area has the appropriate marking and category, and establish the inspection and maintenance program by competent personnel.
5. Implement the work permit system for hot work and other hazardous activities in classified areas, with access control and signage.
6. Train exposed workers and contractors, and coordinate business activities in classified areas.
7. Integrate the risk of explosion into the emergency plan and change management, and record incidents (leaks, detector activations) as indicators.

Preventive management software allows you to maintain the explosion protection document, the inventory of ATEX equipment with its inspections, work permits in classified areas and staff training, with traceability for inspections and audits.

Limits and common mistakes

1. Ignoring the risk of combustible dust in food, timber or plastics industries.
2. Failure to prepare or update the explosion protection document after changes in processes or facilities.
3. Installing equipment without ATEX marking or of an inappropriate category in classified areas, or carrying out repairs that cancel the protection mode.
4. Performing hot work in classified areas without a work permit or prior measurement.
5. Neglecting static electricity, grounding, and cleaning dust deposits.
6. Omit coordination with contractors who bring in equipment or perform work in the areas.

The evaluation and classification of zones require specialized technical expertise; this sheet is for informational purposes only.

Regulatory and reference framework

• Royal Decree 681/2003, of June 12. Protection of the health and safety of workers exposed to the risks arising from explosive atmospheres in the workplace.
• Royal Decree 144/2016, of April 8. Essential health and safety requirements for equipment and protective systems for use in potentially explosive atmospheres.
• Directive 1999/92/EC . Minimum provisions for the protection of workers exposed to explosive atmospheres.
• Technical guide for the assessment and prevention of risks arising from explosive atmospheres in the workplace (INSST) . Guide for the application of Royal Decree 681/2003.
• NTP 876: Evaluation of specific risks arising from explosive atmospheres (ATEX) . INSST Technical Note.

The standards of the UNE-EN 60079 series (classification of sites, selection, installation, inspection and maintenance of electrical installations in explosive atmospheres) and UNE-EN 1127-1 (prevention and protection against explosions) are acquired through the Spanish Association for Standardization.