Explosion Protection Services
BCE explosion protection is engineered to meet and exceed your requirements to provide the best protection for your staff.
Dust Explosion Requirements
For a dust explosion to occur, the following factors must be present:
- A concentration of dust in suspension above its flammable limit.
- A sufficient concentration of oxygen to ignite the fuel.
- A source of energy (e.g., a spark) to ignite the fuel.
- Confinement of the dust/oxygen mixture.
Particle size has a major influence on combustibility. Any oxygen concentration above 13% will support combustion. Additionally, the smaller the particle size, the greater the specific surface and the higher the likelihood of spontaneous combustion.
Ignition can be initiated from several possible sources. For example, there could be friction on collector surfaces from hard impurities in the coal, such as pyrites, metals, or rock, or sparks coming off of defective fan blades or dampers. Reaction rate increases with temperature; therefore, an explosion is more likely with a high operating temperature.
Standards for Explosion Protection
The National Fire Protection Association (NFPA) issues a wide variety of safety standards about securing buildings and equipment against damage from fire. The accepted standard in the United States for dust collector explosion venting is NFPA-68, called the "Standard on Explosion Protection by Deflagration Venting." A deflagration is defined as the propagation of combustion at less than the speed of sound in the unreacted medium, as opposed to a detonation, which exceeds the speed of sound. Dust collector explosions are deflagrations by nature.
NFPA-68 Evolution
This publication was first introduced as a guide in 1954, compiling the best available test data on the fundamentals of explosions. The earlier revisions incorporated the research of the German VDI and the Factory Mutual Research Corporation with the object of improving the accuracy of the vent ratio calculation. The latest edition (2007) is a "standard" rather than a "guide" for the first time. ATEX is the European equivalent with the additional requirement that its use in the EU is legally mandatory.
Key Explosion Vent Sizing Parameters
Kst
The deflagration index, maximum rate of pressure rise attained by combustion of a particular dust.
Pmax
Maximum pressure developed for an optimal mixture of a particular dust in a contained deflagration.
Pstat
Static activation pressure of the vent closure, pressure at which the closure opens.
Pred
"Reduced pressure" or maximum pressure developed in a vented enclosure after an explosion.
Types of Explosion Vents
Rupture Membranes
Composite diaphragm installed on a flanged duct that tears away at scoring lines when design burst pressure is reached.
Doors
Specialty hinged doors under 2.5 lb/ft² inertia designed to meet NFPA-68 requirements.
Flame-arresting Vents
Combines rupture membrane with flame-arresting element for indoor dust collectors.
BCE Expertise: We recommend vent closures under 2.5 lb/ft², which have been proven in thousands of installations and comply with current NFPA standards.