(Preventive) Explosion Protection Measures

How to ensure explosion protection in the event of an explosion?

In many cases, it is impossible to avoid explosive atmospheres and ignition sources due to technological or process limitations within the facility. Therefore, appropriate measures must be taken to limit the effects of an explosion to an acceptable level – ideally, to zero.

Secondary explosion protection includes

• explosion-resistant structures,
• explosion vents,
• explosion suppression systems,
• methods for preventing the spread of flames and secondary explosions.

These measures primarily address the limitation of the hazardous effects of explosions originating in installations. Protective equipment and systems that meet the requirements of Directive 94/9/EC are typically used as containment measures. Structural measures, such as protective pillars, partitions, embankments, etc., can also be used.

Explosion-resistant equipment

Plant components, such as containers, vessels, and pipes, are designed to withstand an internal explosion without rupturing. The initial pressure in a system component must be taken into account if it differs from normal atmospheric pressure.

Generally, a distinction is made between types of explosion-resistant designs. These include:

• designs resistant to the maximum explosion overpressure
  or
• designs resistant to reduced explosion overpressure associated with its release or suppression.

A system design can be resistant to explosion pressure or to explosion pressure surge.

Explosion Relief

In a broad sense, "explosion relief" encompasses all means of enabling, in the event of an explosion occurring or spreading to some extent, the brief or sustained opening, in a direction that does not pose a hazard, of a closed system in which an explosion has occurred, once the pressure that activates the release device is reached. The purpose of an explosion relief device is to ensure that the system is not exposed to the risk of an explosion exceeding its strength. The result of this action is a value known as reduced explosion overpressure.

Examples of explosion relief devices

Examples of devices that can be used as "explosion relief devices" include bursting discs and explosion relief valves. Safety-related mixture parameters must be determined to calculate the required relief area for the installation. Explosion relief is not permitted if it could result in the release of substances that pose a hazard to humans or the environment (e.g., the release of toxic substances).

Explosion Suppression

Explosion suppression systems prevent the maximum explosion pressure from reaching by rapidly introducing extinguishing agents into containers and systems in the event of an explosion. Components protected in this way must be designed to withstand only the reduced explosion pressure. Unlike an explosion escape, this ensures that the effects of an explosion are contained within the container. Depending on the design, the explosion overpressure can be reduced to 0.2 bar.

Preventing Explosion Propagation (Technical Isolation)

An explosion occurring in one part of the system can propagate to the upper or lower parts, where it can trigger further explosions. The acceleration effect caused by system components or propagation in pipework can intensify its effects. The resulting explosion pressure can be much higher than the maximum pressure under normal conditions and can destroy system components, even if their design is resistant to explosion pressure or pressure surge. Therefore, it is important to limit the probable explosion to individual system components. This can be achieved through technical isolation using:

• quick-acting mechanical isolation,
• extinguishing flames in narrow gaps or by introducing an extinguishing agent,
• stopping flames using a powerful countercurrent,
• water shutoff,
• rotary valves.

The explosion protection measures described above are maintained, monitored, and activated by safety, control, and regulatory devices. In general, fire protection devices can be used to prevent the occurrence of hazardous explosive atmospheres or ignition sources, or to limit the harmful effects of an explosion. Potential ignition sources, such as hot surfaces, can be monitored by fire protection devices and controlled to ensure that a safe value is not exceeded.

Potential ignition sources can also be shut down if a hazardous explosive atmosphere occurs. For example, a non-explosion-resistant device can be shut down if a gas detector is activated if this prevents potential ignition sources from occurring within the device. The occurrence of hazardous explosive atmospheres can be prevented, for example, by starting a fan before the maximum permissible gas concentration is reached. The use of fire alarm systems (SSP) can reduce the size of hazardous areas and prevent or reduce the likelihood of a hazardous explosive atmosphere occurring. Combined with solutions designed to limit the harmful effects of explosions, SSP devices constitute protective systems, such as explosion suppression systems. The design and range of these SSP devices, as well as the measures they trigger, depend on the likelihood of hazardous explosive atmospheres and effective ignition sources. The reliability of SSP devices, combined with the implemented technical and organizational measures, must ensure that the explosion hazard is limited to acceptable levels under all operating conditions. In some cases, it could be useful to combine SSP devices for preventing ignition sources with SSP devices for preventing the formation of hazardous explosive atmospheres.