Distribution between the thoracic and inhalable particle fractions where sulphuric acid aerosols occur in working areas

Status:

completed 08/2011

Aims:

Sulphuric acid is the most important inorganic acid in industrial installations. It is used in numerous technical processes, for example as battery acid in lead-acid batteries, in the fertilizer industry, in the anodizing of aluminium, and in galvanic processes. At the end of 2009, the European Commission published a limit value for sulphuric acid of 0.05 mg/m³, measured as the thoracic particle fraction. Sulphuric acid was previously measured in the inhalable particle fraction. The Senate Commission of the German Research Foundation (MAK Commission) has published an atmospheric limit value of 0.1 mg/m³ (inhalable fraction). Before now, no suitable sampling system has been available for measurement of the thoracic sulphuric acid mist. Comparative parallel measurements were not therefore possible. Such measurements are desirable in order to support the formulation of limit values in the Committee for Hazardous Substances (AGS).

Activities/Methods:

For measurement of the thoracic fraction, six 10 l cyclones to the specification of the Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) were first fabricated from high-grade steel (V4A type 1.4404) resistant to sulphuric acid. This cyclone type has the required collection characteristics (PM10) at a volumetric flow of 5.34 l/minute. For comparison of the thoracic fraction with the inhalable fraction, the cyclone and the GSP 47 were used to perform measurements in various areas of application in 20 companies. Each of the parallel measurements was performed by means of a stationary and duplicated test arrangement and in the vicinity of the emission source.

Results:

Low quantities of sulphuric acid aerosol (c(inh) < 0.01 mg/m³) in working areas (e.g. battery charging, production of sulphuric acid) give rise to only small differences between the thoracic and inhalable particles. These are generally encapsulated systems from which droplets can be emitted only through a small ventilation aperture. Larger droplets are decisive for the measured values when for example they can be created through the formation of bubbles in open systems (such as tank formation of lead-acid batteries, copper electrolysis, anodizing of aluminium, production of titanium dioxide). At measured values of c(inh) > 0.01 mg/m³, larger droplets, which are also detected only in the inhalable fraction, accounted for more than half of the overall sulphuric acid exposure. A relationship of c(thor) =~ 0.35 * c(inh) was derived for concentrations in excess of 0.005 mg/m³ for the thoracic fraction. When compared, the limit values proposed by the EU and by the MAK Commission are found to represent absolutely comparable levels of protection.

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