Ex systems: the operator bears the responsibility

In a good 25 per cent of all Ex-systems, inspectors find significant defects before initial commissioning. This could be avoided if all operators fulfilled their obligations: a thorough risk assessment and comprehensive protective measures based on this. This also applies to small and medium-sized companies such as bakeries or cosmetics manufacturers that manage powdery substances.

Written by Dr. Ulla Reutner

Various warning and prohibition signs hang on a green metal gate, including a yellow triangular Ex symbol and a no smoking sign, as well as a sign indicating a biogas plant. — There are Ex systems in numerous industries. The operator is always responsible for the protection concept.

A group of people in front of a glass front observes an industrial machine outside from which smoke and an orange flame are rising. The machine is equipped with several components. One of them is labelled Explosion Isolation EXXOP. — During POWTECH TECHNOPHARM, explosions at an industrial plant and the function of protective systems are regularly demonstrated in the outdoor area of NürnbergMesse.

The live explosions in the outdoor area at NürnbergMesse are a highlight for many visitors at every POWTECH TECHNOPHARM. However, nobody wants to experience this in their own company. Accordingly, there are numerous products on display that can be used to prevent explosions. They range from extraction and inertisation systems, pressure, and spark detectors to bursting discs, flame arresters and extinguishing systems. Explosion-proof measuring and analysing devices and systems that prevent static charges round off the safety technology range.

Preventing dust explosions in silos, mixers and conveyors

The European hexagonal Ex symbol (Epsilon-x in hexagon) for explosion-protected electrical equipment is just as relevant for anyone who manages flammable liquids and gases as it is for processors of powdery substances. Dust explosion protection is extremely important for silos and cyclones, mixers and mills, pneumatic conveying systems and dryers, bagging systems and warehouses.

However, it is not enough for operators to equip their systems with components and devices that bear the Ex-hexagon on their type plate in conjunction with information on the device and explosion group, type of protection, etc. Explosion protection starts much earlier: with the initial considerations when designing a system. Operator responsibility is paramount here. After all, no product or system provider can ultimately know what conditions will prevail during subsequent operation. According to the ATEX Product Directive 2014-34/EU, manufacturers and distributors of products intended for potentially explosive atmospheres must design their products accordingly to exclude ignition sources.

For the operator of the system, however, the ATEX Operating Directive 1999/92/EC applies. And this sets ambitious standards. This is usually not a problem in large corporations in the chemical industry or in mining, where there are entire departments that deal with all safety issues and ensure an elevated level of safety. However, small manufacturing companies that handle solvents, gases and/or bulk materials also have an obligation. This includes bakeries or small grain mills as well as many cosmetics, food and pharmaceutical companies that receive raw materials in the form of bulk goods or process and package them. Explosion risks can also arise in the production of wood pellets, for example, in recycling companies or when handling disinfectants and cleaning agents.

Significant deficiencies: petrol stations safer than storage facilities

The annual plant safety report from the German ZÜS, the ‘Authorised Inspection Bodies’, shows that ensuring explosion protection is anything but child's play. In 2023, significant defects were found in 5.4 per cent of storage systems and 25 per cent of storage systems during the inspection of Ex systems before commissioning. In the case of filling and emptying points, 2.7 per cent had dangerous defects and 18.9 per cent had significant defects. Filling stations performed significantly better (0.2 per cent and 6.7 per cent respectively). However, only 48.6 per cent of the 7,188 inspections of ‘other facilities’, which include facilities in the areas mentioned above, were free of defects. Significant defects were found in 24 per cent. Dangerous defects were found in 1.3 per cent.

Extensive obligations of the plant operator

So, are many operators not aware of their responsibilities? They are obliged to ensure the safety of their employees. It is also in the interests of the company to avoid damage to the system and thus production downtime. Or are they overwhelmed by the tasks arising from the ATEX Operating Directive 1999/92/EC? Plant operators have the following obligations:

Primarily is the risk assessment: are flammable substances present and can an explosive atmosphere arise in hazardous quantities? If this cannot be prevented (e.g. by ventilation, inertisation or gas warning systems), the operator must define zones for the areas in and around the system in accordance with the ATEX Regulation. (Zone 0, 1 or 2 or, for dust explosion protection, zones 20, 21, 22)
Appropriate protective measures must be defined on this basis. First and foremost, this means that effective ignition sources (sparks, hot surfaces, electrostatic charge) must be prevented as far as possible within the zones (primary explosion protection). Secondary explosion protection measures, which limit the effects of any explosions that occur to a harmless level, are secondary, but cannot usually be completely avoided. This constructive explosion protection includes, for example, bursting discs or pressure relief devices. These measures are supplemented by the explosion decoupling of plant components. This prevents the explosion from spreading or secondary explosions from occurring. The protective measures also include regular employee training.
All of this must be carefully recorded in an explosion protection document. It contains a general description of the operation, the assessment of the explosion hazards, the zone categorisation, potential ignition sources and the measures for explosion protection. It also sets out which monitoring and maintenance measures are relevant to safety in the future and which instructions and training are planned for employees.

The group of people who draw up such an explosion protection document must, of course, have the relevant knowledge. The responsible company manager can seek advice, for example from an occupational safety specialist or an external expert. The persons who manage hazardous explosive mixtures or who are responsible for the affected operating areas must be involved. In Germany, in addition to the above-mentioned EU Regulation, the Hazardous Substances Ordinance, the Technical Rules on Explosion Protection (TRGS and TRBS) and the relevant publications of the accident insurance institutions, in particular DGUV Rule 113-001 ‘Explosion Protection Rules’ and DGUV Information 213-106 ‘Explosion Protection Document’, also apply.

The upper body of a person wearing a white T-shirt, apron and protective gloves can be seen handling a white powder-like material in a production environment. This forms a dense dust. — An explosive atmosphere can also occur in larger food processing plants, for example due to finely dispersed flour.

The protection concept is the basis for the explosion protection equipment

A system can then be planned and designed based on the resulting protection concept. The products required for this must be suitable for the explosion protection zone for which they are intended. In Europe, if they fall under the ATEX directive, they must be labelled accordingly. Operators and manufacturers must therefore work well together in this phase. Before commissioning, but also after modifications that require testing and periodically during the operating phase (at least every six years), an authorised inspection body must check the explosion safety.
Similarly stringent requirements and regulations apply internationally. The applicable regional regulations must be observed: including the IECEx certification system (worldwide), NEC in the USA, CEC in Canada, EAC Ex in Russia and Kazakhstan.

Once safe, always safe? Importance of the state of the art

Unfortunately, a one-off risk assessment is not enough. During the life cycle of the system, the operator must repeatedly scrutinise whether his systems can be operated safely or whether improvements need to be made. Knowledge of the state of the art is important here. There is no grandfathering. The safety concept should be continually optimised to reflect the latest state of the art. Employers also contribute to a high level of safety by regularly training their employees and ensuring that the systems are regularly maintained. In this way, the residual risk can always be minimised.

Author

Dr. Ulla Reutner

Chemist and freelance specialised journalist