atex.stat.glor static electricity iss

Systematic Assessment of Ignition Hazard Satic Electricity

Dr. Martin Glor

Swiss Institute for the Promotion of Safety and Security,

Switzerland

www.swissi.ch

Dr. Martin Glor Systematic Assessment of Ignition Hazard Static Electricity 2

Contents

� General Approach

� Zones and Ignition Sources (ATEX)

� Charge Build-up in Industrial Processes

� Basic Scheme of Static Electricity

� Handling and Processing of

� Flammable Liquids, Suspensions and Emulsions

� Flammable Gases and Vapours

� Hybrid Mixtures

� Flammable Powders and Wet Cakes

� Guidelines and Codes of Practice

� Summary and Conclusions


Contents








� Hybrid Mixtures





Zones and Ignition Sources (ATEX)

Assessment of the probability of explosions

� Coincidence in space and time of

� Explosive atmosphere

� Effective ignition source

Effectiveness

Fuel

Ignition Source

Oxy

gen

Coincidence


Zones and Ignition Sources (ATEX)

explosive atmosphere

ignition source

Zone 2,22

Zone 1,21

Zone 0,20

during normal operation

no no no

from time to time yes no no

seldom yes yes no


Contents








� Hybrid Mixtures





Charge Build-up in Industrial Processes

Most frequent charging mechanisms�Contact and frictional charging

� (tribo charging)

� solids, granules, powders

++++ +

++ +

_ ___

_

_ __

++ ++

+

- --- -



Most frequent charging mechanisms�Double layer charging

� liquids, suspensions, emulsions



Most frequent charging mechanisms� Induction charging

– conductive objects exposed to electrical fields


Contents








� Hybrid Mixtures





Basic Scheme of Static Electricity

charge separation

chargedissipation

chargedissipation

charge accumulation

on equipment etc.

charge accumulation

on product

discharge

ignition

explosive atmosphere

discharge

ignition


Contents








� Hybrid Mixtures





Flammable Liquids, Suspensions and Emulsions

• Is all conductive equipment properlyearthed?

• Are all conductive parts of equipment properly earthed?

• Are there insulating gaskets or fittings?

• Do such gaskets or fittings prevent earthing and bonding of conductive parts?

• Are there insulating coatings or paintings?

• Do such coatings or paintings preventearthing and bonding of conductive parts?

• Is the personnel properly earthed?

• Are all conductive mobile parts as well as all conductive packaging (containers, bags, etc.) and auxiliary devices properly earthed during transfer?


• Is any equipment or parts of it made from insulating material?

• Can this be tolerated with respect to the zoning and the explosion group as well as with respect to the size of the insulating areas?


• Can these be tolerated with respect to the zoning and the explosion group as well as with respect to their thickness and possible charging mechanisms?

• Are there used insulating packaging and auxiliary devices?

• Can these be tolerated with respect to the zoning and the explosion group as well as with respect to their size?



• What is the conductivity of the liquid?

• Are the limits for the filling velocitydepending on liquid conductivity, pipe diameter and tank size met in case of pure liquids?

• In case of suspensions or emulsions of low or medium conductivity: Is the tank inerted or has there been made a comprehensive assessment of electrostatic ignition hazards?

• Is the liquid of high viscosity? In this case the charge build-up may be very high and a special hazard assessment is required.

• Are there performed washing or cleaning operations with high pressure liquid jets? In this case special guidance is recommended.



Contents








� Hybrid Mixtures



� Conclusions


Gases and Vapours

• Pure gases and vapours do not become charged

• However, as soon as gases or vapours contain even

small amounts of droplets or particles these may become highly charged.

• This becomes obvious e.g. during the release of high

pressure oversaturated water vapour.

• Depending on the nature of the gas or the vapour the

recommendations for liquids and/or powders should be considered.


Contents








� Hybrid Mixtures





Hybrid Mixtures

• A hybrid mixture is commonly defined as a mixture of

flammable gases or vapours in combination with flammable powders.

• From the point of view of an ignition hazard due to static

electricity, hybrid mixtures require special precautions:

- Charge build-up may be as high as for pure

powders.

- Minimum ignition energy may be as low as for pure gases or vapours.

• Special guidance or expert advice is recommended.


Contents








� Hybrid Mixtures





Flammable Powders and Wet Cakes

• Is all conductive equipment properlyearthed?

• Are all conductive parts of equipment properly earthed?

• Are there insulating gaskets or fittings?

• Do such gaskets or fittings prevent earthing and bonding of conductive parts?


• Do such coatings or paintings preventearthing and bonding of conductive parts?

• Is the personnel properly earthed?

• Are all conductive mobile parts as well as all conductive packaging (containers, bags, etc.) and auxiliary devices properly earthed during transfer?


• Is any equipment or parts of it made from insulating material?

• Can this be tolerated with respect to the zoning?


• Can these be tolerated with respect to the zoning as well as with respect to their thickness and possible charging mechanisms?

• Are there used insulating packaging and auxiliary devices?

• Can these be tolerated with respect to the zoning, the minimum ignition energy and the particle size distribution of the powder as well as with respect to their size?



• What is the resistivity of the bulked powder?

• In case of high resistivity powder: Do incendive cone discharges have to be expected? This depends on the resistivity, the particle size distribution and the minimum ignition energy of the powder as well as on the silo diameter and the way and rate of filling (see guidelines or ask experts for advice).

• Are silos with a diameter larger than 3 m filled?

• Does the powder contain more than 0.5%w/w of a flammable solvent?

• Are there performed any further diminution processes?




• In case of handling low minimum ignition energypowders in large amounts in plants of high complexity:

• Are you sure that you can reliably ensure earthing and bonding of all your equipment and personnel?

• The only application of the safety measure

“Avoidance of Effective Ignition Sources”may be very difficult.

• Consider additional measures of explosion prevention

or protection


Contents








� Hybrid Mixtures





Guidelines and Codes of Practice

� CENELEC Technical Report CLC/TR 50404 „Electrostatics - Code of practice for the avoidance of hazards due to static electricity”, June 2003.

� BGR 132 „Vermeiden von Zündgefahren infolge

elektrostatischer Aufladungen”, Hauptverband der gewerblichen Berufsgenossenschaften, Fachausschuss „Chemie“ der BGZ, 2004.

� Expertenkommission für Sicherheit in der

Chemischen Industrie der Schweiz (ESCIS) Heft Nr.2 „Static Electricity – Rules for Plant Safety“ , revised2nd Edition, January 2005.


Contents






� Liquids, Suspensions and Emulsions

� Gases and Vapours

� Hybrid Mixtures

� Powders and Wet Cakes




Summary and Conclusions

Is there a classified area?

Is the personnel earthed RE < 100 MOhm?

Are all conductive parts earthed RE < 1 MOhm?

Is all equipment including auxiliary devices and packaging, etc. made from conductive material?

Can equipment, etc. made from insulating material be tolerated with respect to the substances handled and processed as well as with respected to the zoning?

yes

Exchange equipment

Earth all conductive parts of equipment

no

Earth personnelno

yes

yes

no no

no No explosion hazard exists

yesyes

Short decision tree – details have to be taken from guidelines


Are there insulating coatings or paintings?

no

Can these insulating coatings or paintings be tolerated with respect to the substances handled and processed as well as with respected to the zoning?

Remove or modify coatings or paintings

yes

no

Ensure earthing and bonding of all conductive parts

yes

Are there insulating gaskets, fittings, etc.?

no

Ensure earthing and bonding of all conductive parts

yes

No electrostatic ignition hazards associated with incendive discharges from equipment, packaging and personnel have to be expected.




Take additional measures of explosion prevention and/or protection.

Are there handled flammable liquids, suspensions or emulsions?

no

Assess occurrence and incendivity of discharges associated with liquids, suspensions, emulsions, mists, droplets, etc.

yes

no

Can the occurrence and incendivity of discharges be tolerated with respect to the substances handled and processed as well as with respect to the zoning?

yes




Are there handled granules, powders, dusts or hybrid mixtures?

No electrostatic ignition hazards associated with incendive discharges from the substances handled and processed have to be expected.

yesAssess occurrence and incendivity of discharges associated with granules, powders, dusts, hybrid mixtures, etc.

Take additional measures of explosion prevention and/or protection.

no

Can the occurrence and incendivity of discharges be tolerated with respect to the substances handled and processed as well as with respect to the zoning?

yes

no




� This Presentation gives guidance to identify the most frequently encountered electrostatic ignition hazards in the process industry

� It is far from being comprehensive

� Details should be taken from existing guidelines and codes of practice

� In case of further questions expert advice is strongly recommended


atex.stat.glor static electricity iss

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