A Simple Methodology Based on the Pittsburgh Coal Method for Assessing Specific Explosion Risks in Dust-Generated Explosive Atmospheres: A Case Study from Galicia (NW Spain)

Hazardous explosive atmospheres caused by dust may occur when powdered combustible material is present in an enclosed area. In general, dust explosions take place when high enough concentrations of combustible powdered dust particles are present in the atmosphere with another suitable gaseous medium such as oxygen. Because the manipulation of these substances in industrial activities entails a risk that could have devastating consequences (including serious injuries or loss of life, as well as significant damage in installations), the risk assessment to eliminate or control the risk of explosive atmospheres in the workplace is a challenging task. In European countries the assessment of these risks is evaluated using the ATEX Directives as per European legislation. However, using this legislation to assess the risk of explosion in powder atmospheres presents difficulties due to the variety and complexity of possible explosive atmospheres and the extremely high variety of ignition sources involved. Therefore, risk evaluation becomes a difficult and time-consuming task. In the present article, a simple empirical method for detecting and making an initial assessment of dust-generated ATEX atmospheres is presented. The force of possible explosions was estimated using the explosion index, which was obtained from other indices: explosion severity and ignition sensitivity. For a specific dust, both of these factorial indices were calculated on the basis of their explosive characteristics in relation to those of Pittsburgh coal (employed as a standard). The proposed methodology was applied to a real case study of an explosion in a milk spray dryer in Lugo (northwestern Spain). Taking into consideration the explosive characteristics of the products treated in this type of installation, the ATEX zones, the probability of the explosion, and the severity of the consequences (determined in accordance with the proposed Pittsburgh coal method), the risk assessment performed according to the methodology developed here provided results that agreed with the real accident in terms of probability and severity of the explosion as well as damages incurred.