Let’s start with introduction
This presentation Electrostatic ignition hazards in the Process industry is the substance in Chapter 6. Fires and Explosions and this chapter talks about cause of occurring of Fires and Explosions in the Process industry
And the first important thing that we have to know is FIRE TRIANGLE which contains by
1. FUEL - Liquid (vapor or mist), gas, or solid capable of being oxidized. Combustion always occurs in the vapor phase; liquids are volatized and solids are decomposed into vapor prior to combustion
2. OXIDANT - A substance which supports combustion – Usually oxygen in air
3. IGNITION SOURCE - An energy source capable of initiating a combustion reaction Ignition
Such as Sparks, flames, static electricity, heat.
And in this presentation we focus on Electrostatic ignition which is one of the important causes of EXPLOSIONS and FIRES in industry
Actually, Electrostatic charges are usually generated when any two materials make and then break contact, with one becoming negative and the other positive
Magnitude and polarity of the charge depends on many factors, including:
» Nature of the contacting surfaces
» Actual contact area
» Speed and type of contact and separation
Electrostatic charge generation will only result in a discharge if charge is allowed to build up on surfaces/materials
Build up of charge on the following types of surfaces/materials can give rise to electrostatic discharges:
» Electrostatically Isolated Conductors
» Electrostatically Insulating Objects
» Non-Conductive Liquids
» Insulating Powders
Ignition occurs if discharge energy is greater than the Minimum Ignition Energy of the flammable atmosphere
The next is Electrostatic DISCHARGES
Incendivity (igniting power) of electrostatic discharges depend on resistivity and the geometric arrangement of the charged object and the geometry of the discharge initiating electrode.
Type of Electrostatic DISCHARGES
Several disparate categories of static discharge can be identified for the purposes of describing ignition and shock hazards. The most familiar (spark discharge) has an almost unlimited effective energy range. In roughly ascending order the maximum effective energies of the others are
1. Corona (positive) ≈ 0.1 mJ
2. Brush (negative) ≈ 1.0 mJ
3. Brush (positive) ≈ 10 mJ
4. Transitional Brush ≈ 10–100 mJ
5. Bulking Brush (also known as “cone discharge”) ≈ 20 mJ
6. Propagating Brush Discharge (PBD) ≈ 100–1000 mJ
As you see these are the Type of Electrostatic DISCHARGES
In the first picture is Corona discharge in point–sphere gap, next one is Positive brush discharge from negatively charged plastic to grounded sphere, next is Multiple bulking brush discharges on
powder bed (time exposure), next is Spark discharge between spherical electrodes.
And this is Propagating brush discharge (PBD) on charged layer initiated by grounded electrode and this is Approximately 1-m-long spontaneous PBD on plastic pipe and the last one is Surface Streamer Discharge in Stirred Reactor.
In this slide I’m gonna talk about Electrostatic CHARACTERISTICS OF MATERIALS AND PLANT ///// The first step in assessing electrostatic problems and hazards is to establish the electrostatic properties of the materials processed, handled, and/or used in the plant.
» Minimum Ignition Energy of flammable atmospheres
» Resistance-to-Ground of conductive (metal) objects and items of plant
» Electrical Resistance of operators’ footwear and floors
» Electrostatic Chargeability of powders and liquids (alternatively, measure surface voltage or electric field during processing)
» Volume Resistivity of powders
» Conductivity of liquids
» Surface Resistivity of solid objects such as plastic containers and liners
MINIMUM IGNITION ENERGY or MIE of a flammable material is the smallest electrostatic spark energy needed to ignite an optimum concentration of the material using a capacitive spark
And this picture is MINIMUM IGNITION ENERGY CIRCUIT
This table shows Typical Minimum Ignition Energy Values of substances both Vapor or gas and Dust cloud in mJ units
And the last part of presentation is CONTROL OF ELECTROSTATIC HAZARDS
First of all, Control of Electrostatic Hazards of CONDUCTIVE OBJECTS
• Electrostatic charge can accumulate on electrically isolated conductive (metal) plant and give rise to spark discharges
• Charge accumulation occurs if resistance-to-ground is greater than 1MΩ
• Spark energy depends on metal object’s capacitance and magnitude of static charge that accumulates on it
• Resistance to ground should be checked.
• If R>10 ohm, direct ground connection is required
» Grounding connections should be routed to protect them from accidental damage
» Their purpose should be known to operators
» Fixings for ground connections should be clearly visible
Second, Control of Electrostatic Hazards of LIQUIDS
Static electricity hazards can arise in various liquid handling operations including filling, sampling, filtrati