Dust Explosion - Mallika Gharpure Ravikumar gogar Trupti Gawai Gokul Gopal Samyak Gayakwad
Introduction What it is? • Dispersion of powders in air • Form of cloud • Suitable concentration • Presence of effective ignition source
Where it can occur? • Combustible powders • Fine materials • Foods, pharmaceuticals • wood, plastics • Metals, rubber
How it can occur? • Explosible Dust • Particle size distribution for propagation of flame • Presence of oxidant in atmosphere • Dust cloud concentration within explosion range • Ignition source
What are the associated factors? • Dust and explosion violence : pressure, speed • Composition of Dust • Particle Size • Concentration of dispersed dust : LEL,UEL • T, P, moisture content, scale of vessel
Case Study Process : • equipment used to pulverize aluminum-alloy • air recycled through a grinder, cyclone product separator, blower • a side stream to extract undesired dust to a dust collector
Batch To Continuous • a much higher rate of dust generation • high concentrations of very fine dust in the recycle stream • accumulation of heat in the recycle stream. • installer of the recycle system with no experience with combustible powders • no explosion prevention or protection devices or systems provided.
The Accident • concentration of dust in the circulating air stream above LEL in most of the recycle system • relatively high temperature of the circulating air • exothermic oxidation of accumulated combustible dust in the return-air ductwork • an access door on the grinder forcibly ejected, the door struck the LPG cylinder on a nearby forklift truck. Escaping LPG vapors – ignited by the dust fireball from the open grinder door – resulted in a flash fire • fatal burn injuries to the forklift driver
lessons learned from this incident • Every significant change in a process should be subjected to a Management of Change analysis • Producers of hazardous materials (and particularly small-company producers) need to follow Codes and Standards that apply to their processes • Code-enforcing authorities should become more familiar with Codes and Standards that apply to dust-explosion hazards • Dust-explosion characteristics need to be included in Material Safety Data Sheets.
Dust Control • Use dust collection systems and filters • Utilize surfaces that minimize dust accumulation and facilitate cleaning • Provide access to all hidden areas to permit inspection • Inspect for dust residues in open and hidden areas, at regular intervals • Use cleaning methods that do not generate dust clouds, if ignition sources are present • Locate relief valves away from dust hazard areas • Develop and implement a hazardous dust inspection, testing, housekeeping, and control program (preferably in writing with established frequency and methods).
Ignition Control • Use appropriate electrical equipment and wiring methods • Control smoking, open flames, and sparks • Control mechanical sparks and friction • Use separator devices to remove foreign materials capable of igniting combustibles from process materials • Separate heated surfaces from dusts • Separate heating systems from dusts • Proper use and type of industrial trucks • Adequately maintain all the above equipment.
Damage Control • Separation of the hazard (isolate with distance) • Segregation of the hazard (isolate with a barrier) • Deflagration venting of a building, room, or area • Pressure relief venting for equipment • Provision of spark/ember detection and extinguishing systems • Explosion protection systems • Sprinkler systems
References • ‘Dust Explosion Prevention and Protection’ By John Barton • Process safety progress2007, vol. 26, no4, pp. 324-329 • NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids • Occupational Safety and Health Administration (OSHA), the Massachusetts Office of the State FireMarshall, and the Springfield Arson and Bomb Squad. "Joint Foundry Explosion Investigation Team Report." OSHA, Springfield