Explosive environments require a thorough risk assessment to guarantee the safety of employees and prevent damage to installations. According to the ATEX Workplace Directive 1999/92, the employer is responsible for conducting an explosion risk assessment. This can be done with or without the help of experts, but must always be done systematically and completely, involving employees from all relevant disciplines and departments.

An important characteristic specific to risk assessments regarding explosion safety is that the chance of an explosion is extremely small, but the consequences are extremely large. This means that every potential risk, no matter how small, must be thoroughly analysed, because even the slightest deviation can lead to a catastrophic incident.

An effective ATEX risk assessment takes various important aspects into account, including:

• The likelihood and duration of explosive atmospheres occurring.
• The likelihood of ignition sources being present and becoming effective.
• The installations, substances used and processes, including their possible interactions.
• The extent of the expected explosion effects.
• The possible spread of explosive atmospheres via connected spaces.

Explosive Atmospheres: Probability and Duration

The probability and duration of the presence of an explosive atmosphere determine the zone classification of an area. This is the first step in a systematic explosion risk assessment.

Step 1: Inventory of flammable substances

All flammable substances used or produced at the location must be identified. Safety Data Sheets (SDS/MSDS) contain crucial information about the chemical properties of these substances, such as explosion limits and physical behavior under different conditions.

Step 2: Evaluation of evaporation and dispersion

The next step is to assess the evaporation and dispersion of flammable substances. This includes gases, vapors, mists and dust particles. The following must be taken into account:

• • Process conditions such as temperature, pressure and turbulence.
  • The explosion parameters of the substances (such as minimum ignition energy, explosion limits and ignition temperature).
  • Possible release points, such as leaks, vents and overflow zones.

Step 3: Zone classification

Based on the collected data, a decision is made as to whether an area should be classified as explosion hazardous. If only very small amounts of flammable substances are present and the spread is negligible, the atmosphere is considered non-hazardous and no additional measures are necessary.

If a hazardous atmosphere may be present, technical possibilities to prevent the development of an explosive atmosphere are considered.

When preventive measures are not sufficient, the area is classified based on the duration and extent of the explosive atmosphere:

• Zone 0 / Zone 20: Explosive atmosphere is present continuously or for long periods.
• Zone 1 / Zone 21: Explosive atmosphere occurs regularly during normal operation.
• Zone 2 / Zone 22: Explosive atmosphere is present occasionally and only briefly.

Sources of ignition: Presence and effectiveness

An explosive atmosphere does not in itself lead to an explosion; an ignition source is needed for this. The assessment of possible ignition sources focuses on the presence and effectiveness of these sources. Some common ignition sources are:

• Mechanical sparks – caused by grinding, drilling, wear of metal surfaces or impact between materials.
• Hot surfaces – Engines, bearings and other equipment can generate heat and thus exceed the ignition temperature of a substance.
• Electrical ignition source – Short circuits, faulty wiring and sparks from switches can ignite explosive atmospheres.
• Electrostatic discharges – Although electrostatic charges are often underestimated, they can ignite a flammable substance under certain circumstances. Good grounding and charge dissipation are therefore essential.

When assessing ignition sources, one should not only consider normal use, but also possible malfunctions, maintenance situations and deviations in operational processes.

Installations, Substances Used and Processes

In addition to the presence of explosive atmospheres and ignition sources, the substances used and installations play a major role in the risk analysis. There are three main factors that must be assessed here:

1. The chemical properties of flammable substances
   • Minimum ignition energy (MIE)
   • Explosive limits (LEL and UEL)
   • Flash point and ignition temperature
2. Process conditions that can influence the risk of explosion
   • High temperatures and pressure levels
   • Turbulent air currents that can stir up dust
   • Rapid movement of powders or liquids that can build up an electrostatic charge
3. Interaction between different substances and process steps
   • Combinations of chemicals that can generate reactive vapors or heat
   • Storage methods and the possible release of flammable substances
   • Effects of maintenance and cleaning activities on the spread of hazardous substances

By systematically mapping these aspects, it is possible to determine which risks arise and which control measures are necessary.

The Extent of Explosion Effects

If an explosion occurs, the consequences can be serious. The extent and impact of an explosion depend on:

• The quantity and concentration of flammable substances – The greater the quantity and the closer the concentration, the more violent the explosion.
• The physical environment – An explosion in a confined space leads to a higher build-up of pressure and destruction than in an open, well-ventilated space.
• Secondary explosions – Dust accumulations or vapor concentrations can be ignited by an initial explosion, leading to a chain reaction with even greater damage.
• Impact on employees and equipment – In addition to direct damage, explosions can also spread toxic gases or heat waves, which entails additional risks.

To minimize the severity of an explosion, preventive, technical and organizational measures must be taken, such as explosion relief, escape routes and protective barriers.

Spread through connected spaces

Explosive atmospheres can not only form in a specific space, but also spread to adjacent areas. This entails additional risks, especially if these spaces are not designed to withstand explosions. Factors that contribute to the spread are:

• Ventilation systems – Can transport flammable vapors and mists to other spaces.
• Open connections – Doors, hatches and open passageways can allow an explosive atmosphere to spread to other parts of a factory or workshop.
• Pipe penetrations and cracks – Small openings in walls, floors or pipes can facilitate the spread of flammable vapors and gases.

The risk assessment must determine which parts of a facility are connected and how the risk of propagation can be limited.

Conclusion

An ATEX risk analysis is essential for a safe working environment in potentially explosive atmospheres. By systematically looking at explosive atmospheres, ignition sources, installations, explosion consequences and possible spread, risks can be better managed.

Employers have a responsibility not only to identify these risks, but also to implement appropriate measures. This can vary from technical solutions such as explosion-proof equipment and ventilation systems to organizational measures such as training, clear work procedures and regular inspections.

A thorough and precise approach reduces the risk of explosions and ensures a safe working environment.