What is the largest size particle of coal dust that can initiate an explosion?

The largest size particle of coal dust that can initiate an explosion is any particle that will pass through a 20 mesh screen. This is significant because, in the context of coal dust explosions, the particle size is critical to the explosive potential of the dust cloud. Particles that fit through a 20 mesh screen are small enough to remain suspended in the air and become airborne, creating an atmosphere conducive to explosion when combined with an ignition source.

Particles larger than this size tend to settle quickly and do not contribute effectively to the dust cloud that is needed for an explosion to occur. The mesh size refers to the number of holes per square inch in a sieve screen; hence, a 20 mesh means that particles that are smaller than the openings in the screen will pass through, while larger particles will not. Understanding this threshold is essential for safety practices in environments where coal dust is present, as it informs the necessary measures to control dust and mitigate explosion risk.