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About Static:

What is Static Electricity? 
'Static electricity' arises when surfaces in contact are separated. If the charge that arises from differences between the surfaces cannot run away to earth quickly enough then it is trapped - it is 'static'. The 'quickly enough' relates to the time for the charge to leak away to earth (or to spread out over the surface of a material) compared to the time of separation of the contacting or rubbing surfaces.

Examples of 'static electricity' are the picking up of small pieces of paper by a rubbed comb or piece of plastic and the cling of thin light fabrics after they have been rubbed. Thunderstorms are another good example.

Static Electricity is important in industry as it can cause risks and problems that need to be avoided. It is also the basis for many useful applications.

How Can I Test for it? 
You can make measurements of the electrostatic conditions that are present in the practical situation and you can measure that characteristics of materials to assess whether they are likely to be suitable to avoid problems from static in particular applications or to be appropriate for particular applications.

Measurement of 'electrostatic conditions' involves the use of a fieldmeter to measure electric fields. These can be interpreted to give values for surface and space potentials, surface and volume charge densities and rate of charge dissipation. It may also involve the use of a Faraday Pail to measure the nett charge on items or on powder or on a volume of liquid.

Assessment of materials may involve measurement of how quickly surface charge can dissipate, the surface voltage created by deposition of a certain amount of charge and/or the ability of a material to provide shielding against transient electric fields.

The above matters are dealt with in a book by John Chubb published by Nova Publishers (ISBN: 978-1-61668-251-4) "AN INTRODUCTION TO ELECTROSTATIC MEASUREMENTS"

In What Industries is it Relevant and How? 
Paper, packaging, parmaceuticals, microelectronics, petrochemicals, retail garments, cleanroom and personal protective garments, meterology, electrostatic spraying and powder coating, electrostatoc clamping.

Why Bother About Static? 
Many materials, in particular plastics, easily become electrostatically charged when rubbed against other materials. Such 'triboelectric' charging can be used constructively - for example, in photocopying, electrostatic clamping and the retention of powder in electrostatic precipitation and paint spraying. Retained electrostatic charge also creates risks and causes problems in many areas of industry. It can cause ignition of flammable gases and give shocks to personnel. It can make thin films and light fabrics cling, attract airborne dust and debris, damage semiconductor devices and upset the operation of microelectronic equipment.

Most of the uses and problems of static electricity relate to the influence of charge retained on surfaces. The 'suitability' of materials thus needs to be judged in relation to charge retention. The way to assess the charge retention performance of materials is to measure the 'charge decay time' - how quickly any charge put on the material dissipates over and through the material and away to earth. (Note: we are talking about 'decay time' - not 'resistivity'!). To avoid risks and problems it is necessary to ensure that static charge can dissipate more quickly than charge is generated. For normal manual handling and body motion activities this means the charge decay time needs to be ¼ second or less. A new concept, relevant to risk control, is that if static charge experiences a high capacitance on a material then only low surface voltages will be observed - and many problems and risks will not arise (see JNC papers for the IEEE-IAS meeting Oct, 1999 and for the ESA meeting at Niagara Falls, June 2000). Another area of work has concerned the ability of materials to provide shielding against electrostatic discharges and transient electric fields.

Measurements enable you to find out if, where, when and how much static electricity is present . They tell you whether materials are suitable, or not. With reliable and appropriate measurements you can assess risks, can design and check the effectivenss of remedial measures and can be confident in the selection and performance of materials. Without reliable measurements it is all guesswork...!

Useful Links and Resources 
For more information about static electricity see 'An Introduction to Electrostatic Measurements' and the 'papers page' on this website.



John Chubb, email: jchubb@infostatic.co.uk