The transitional period for the new general dust limit value (ASGW) for granular biopersistent dusts in the A fraction ended at the end of 2018. This was already set at 1.25 mg/m³ in April 2014 and is based on an average density of 2.5 g/cm³. The limit value for inhalable particles is 10 mg/m³.

When applying the ASGW, the German Social Accident Insurance refers to the fact that it was defined as a shift average value and is to be used for poorly soluble and insoluble dusts that are not otherwise regulated or for mixed dusts. The determination and assessment of health risks from dusts in the workplace is quite complex, as the proportion of dust in the air is never constant. The composition of the dust fraction, the dust particle density and the possible solubility of the substances also play a role. In any case, it is not sufficient to provide respiratory protection measures.

Recording of air pollutants

The removal of airborne pollutants such as dusts, fumes, gases or vapors begins with their collection. In many companies, a hall extraction system is used for this purpose. However, hall extraction is far less effective than point extraction. Point extraction means that the particles are removed at the point of origin by a capture element or extraction arm so that they cannot enter the ambient air. The closer the extraction is to the source of the pollutant, the higher the degree of capture. The further away the capture is from the source of the emission, the higher the amount of energy required. In addition, the noise level increases with higher performance.

The selection of a suitable capture element is also important, as the majority of the resulting air pollutants should find their way into the filter system and not be distributed uncontrollably in the work area. Capture elements are available in a wide range of variants and shapes. Depending on the type of pollutant and its physical and chemical properties, thermal and air flow aspects, the appropriate capture element must be used. Ideally, specialists should select the appropriate solution, as the degree of capture forms the basis for the highest possible degree of filtration that subsequently takes place.

Requirements for filter technology

The requirements for the necessary filter technology are increasing, as the separation efficiency and therefore the filtration quality of the extraction systems must be guaranteed accordingly. Where previously common solutions such as H13 filter media (HEPA = High Efficiency Particulate Airfilter) were used, the new regulation requires the increased use of H14 filters, which in the past were only used for special applications.

Coarse dust filters are often used as pre-filters. This primarily separates coarse particles >10 µm. In industrial applications, filter mats, filter cassettes, pocket filters, knitted metal or wire frame filters have proven particularly effective. As coarse dusts are mostly dry particles, this filter technology is used as standard in industrial and trade applications.

Fine dust filters are primarily used to separate airborne pollutants >1 µm. Even if they are available as pocket filters or compact cassettes, their use in the form of cleanable or regenerative filters, for example in the form of cartridges, has proven successful. The advantage of cartridge filters lies in their relatively long service life; the separation efficiency is always high (up to 98 percent) even with fluctuating air flow.

Processes that apparently produce few pollutants are particularly critical, because with pollutant particles in the nanometer range, agglomeration often no longer takes place and the nanoparticles retain their size (<1 µm). These then enter the lungs and blood and, in the worst case, can shorten life expectancy. The use of HEPA filters (H13/H14) is crucial for the safe filtration of these nanoparticles. They are mainly used as storage filters in the form of cassettes. In accordance with the requirements of EN 1822-1:2009, the filtration efficiency of H14 filters is 99.995 percent.

As airborne pollutants are neither only coarse nor only fine in practice, but often result in particle sizes between >1 µm and <10 µm, extraction and filter systems that combine the advantages of the respective filter principles have proven their worth. These are special device and filter properties that can be designed depending on the application. In the case of particularly sticky dusts, there is a risk of irreversible clogging of the filter modules. This can be remedied by adding a filter aid in powder form. It binds the sticky particles and settles with them on the filter elements as an easily cleanable filter cake.

Gaseous or vaporous substances as well as odors can be stored in activated carbon or other sorbents. Activated carbon offers an adsorption surface of up to 1,700 m²/g. This results in a very high degree of separation and an enormous storage capacity, resulting in very long filter service lives.

At higher concentrations, combustion processes would also make sense, but are only worthwhile in terms of energy if the combustion process is stable and can run without its own energy supply. Catalytic processes are an intermediate stage, but these always require a constant pollutant mix. The bottom line is that sorbents can be used more flexibly, but require precise adherence to organizational measures and replacement intervals.

Stefan Meißner, Corporate Communications ULT