Measures against Dust Explosions in Dust Collection Equipment

Abstract

Background: If powders handled in industrial processes are flammable, there exists a risk of dust explosions and fires. Dust explosions cause severe damage through chain reactions, as explosion shock waves disperse accumulated dust to form additional dust clouds, leading to secondary explosions. The occurrence rate of dust explosions in crushing and dust collection processes is approximately 20% each, with particularly high probability in dust collection operations. Due to multiple interrelated factors—including not only the physical properties of the powders being handled, but also their particle size distribution, dispersion concentration in air, and humidity—it is difficult to regulate them uniformly through laws and regulations. Currently, there are no detailed regulations in Japan comparable to those in Europe and the United States. However, if a dust explosion occurs, penalties may be imposed for violations of the Industrial Safety and Health Act.

Filter-type Dust Collectors and Explosion Risks: Over 90% of dust collection equipment currently handled utilizes filter-type dust collectors. These devices employ felt fabric filters to capture particles larger than approximately 0.05 μm, with collected powder removed through pulse jet cleaning mechanisms. The cleaning process creates dust clouds that may reach concentrations above the lower explosion limit, posing explosion risks when ignition sources are present. Common ignition sources include static electricity, self-ignition, and external factors such as impact sparks from high-speed rotating components, friction heat from adhered powder growth, and hot particles from upstream processes.

Preventive Measures: Dust explosion countermeasures are categorized into ignition source prevention and damage mitigation strategies. Ignition source prevention includes spark removal/fire suppression, static electricity prevention, spark generation prevention, thorough maintenance management, and oxygen concentration control using inert gases. Damage mitigation measures include explosion venting (rupture discs, hinged panels), flame arresters, isolation valves, explosion-resistant design, explosion suppression systems, and facility cleaning protocols.

Case Studies and Implementation: Domestic implementation typically follows cost-effectiveness priorities, starting with anti-static measures, explosion-proof electrical equipment, and explosion venting. European installations demonstrate comprehensive approaches with explosion-resistant equipment rated for 1 MPa, complete with isolation valves and fire suppression systems for systematic dust explosion protection.

Conclusions: Despite the high explosion probability in dust collection processes, Japan requires enhanced safety measures considering material characteristics and installation environments to minimize accident risks and reduce post-explosion damage. This paper introduces the risks of dust explosions and countermeasures based on the principles and processes of filter-type dust collectors used in dust collection operations.