Brush discharge

From ArticleWorld

Brush discharge is a type of electrostatic discharge that occurs from charged non-conductive surfaces like plastics or highly charged non-conductive liquids like hydrocarbon-based fuels and solvents . The discharges are sent in the direction of a conducting surface. It is characterized by light emissions composed of ionized particles. These emissions are considered intermediary in between sparks, which are the most hazardous and corona discharges, which are the least dangerous.

Brush discharges and the ignition hazard

There are four common types of electrostatic discharge (ESD) that are put under scrutiny taking into consideration the dangers of fire or explosion due to them. These are sparks, brush discharge, propagating brush discharge and cone discharge. Corona discharges are usually not considered to be hazardous.

Among the different ESD, sparks are considered to be the most common cause responsible for fires and explosions in industrial environments. Discharges of sparks occur from conductive objects and personnel that are ungrounded and achieve an electrostatic potential enough to ignite a fire.

Electrostatic brush discharges that occur from charged insulating surfaces like plastics and highly charged non-conducting liquids like organic solvents and fuels can cause ignition, subject to a number of factors. The energy from the discharge cannot cross 4 millijoules.

Factors governing igniting power of brush discharge

The factors that govern the incendivity (ignition power) of brush discharge can be listed as below:

  1. The surface that is charged should have a potential of 20kV or even greater.
  2. The polarity of the charge on the surface from where discharges happen should be negative.
  3. An atmosphere consisting of a flammable mixture of an organic liquid and ignition supporting air should exist when the brush discharge happens. In particular, oxygen-rich environments containing hydrocarbon gases and regions with high concentration of hydrogen gas or carbon disulphide are examples of highly vulnerable atmospheres.
  4. The energy content of the brush should be greater than the threshold ignition energy of the surrounding inflammable atmosphere.