WHAT IS STATIC ELECTRICITY?
...AND HOW CAN WE HELP?
WHAT IS STATIC?
When a material or object holds a net electrical charge, either positive or negative
it is said to have a static charge. The term static is a relative one as in many cases
static charges will slowly decrease over a period of time. The length of time that this
takes is dependent on the resistance of the material. For practical purposes the two
extremes can be taken as plastics and metal. Plastics generally have a very high
resistivity. This allows them to maintain static charges for long periods of time; on
the other hand metals have very low resistances and an earthed metal object will
hold its charge for an imperceptibly small period of time.
Static Electricity is sometimes referred to as:
An electrical effect as generated by:
a) the contact and separation of solids e.g. the movement of conveyor belts, plastics film, etc. over rollers,
b) the movement of a person;
c) the flow of liquids or powders, and the production of sprays;
d) induction phenomena, i.e. objects reach high potential or become charged due to being in an electric field.
The accumulation of electrostatic charge can give rise to hazards and problems in a wide range of industries and working environments, and to ignition and explosion hazards particularly in chemicals, pharmaceuticals, petroleum and food processing industries.
Hazards caused by electrostatic charge include:
a) ignition and / or explosion of flammable atmospheres, see IEC 60079-0 and EN 13463-1;
b) electrostatic shock in combination with another hazard (e.g. fall, trip) see ISO 12100-1;
c) electrostatic shock giving rise to injury or death, see ISO 12100-1;
d) damage to electronics
In addition, static electricity can introduce operational problems during manufacturing and handling processes, e.g. by causing articles to adhere to each other, or by attracting dust. Dust attraction during food grade operations is of major concern.
Static electricity is usually measured in kilo volts (KV). Levels of static electricity of 100 KV+ are common. Static electriciy however can be dangerous at levels as low as or below 1000V or 1KV. Specifically where static electricity is present in or around flammable or combustible material. In hazardous areas/zones, it is critical that the level of static electricity is reduced to or as close to 0KV as possible. Levels above 0KV increase the risk of fire or explosion.
Operators of equipment or general personnel can experience static discharge or static shocks at levels as low as 500V - 1000V or 1KV. Levels above 1000V or 1KV up to 5000V or 5KV can cause discomfort to personnel. Levels form 5Kv and above can cause injury to personnel. When static electricity reaches levels as high as 100+ Kv there is a real risk of injury to personnel in the form of serious burns. In 2010 the USA department of Occupational Safety and Health (OSHA) recorded a fatality at the 3M plant in Cynthiania where an operator came in contact with static electricity during an unwind process and was electrocuted. Understanding the risk that static poses to personnel, plant and equipment is critical in providing a safe work place environment.
Static Electricity can be measured by a device known as a static locator. Most static locators are only able to read measurements up to 20KV. These devices are not safe to use when measuring static electricity as they are unable to accurately measure above 20KV. The difference between a static discharge at 20KV and a static discharge at 117KV is significant. It can mean the difference between serious injury or in some extreme cases a fatality. Only use meters that have the capability to measure + or - 200KV
The voltage present on a material is dependent on two factors; the amount of charge on the material and the capacitance of the material. Plastics generally have very low capacitive values and hence a small charge can produce very high voltages. Conversely metals tend to have high capacitive values and therefore a relatively high charge will produce low voltages. This is why, in practice, problems with static electricity are most noticeable when working with plastic, as it is the voltage level which causes the attraction of dust, operator shock and misbehaviour of materials. There are two main types of static electricity, volumetric and surface. Volumetric static charges are charge imbalances within the body of a material whereas surface static electricity is only present on the very outer surface of a material. In practice most of the static electricity problems found in industry relate to surface charges. Whilst there is no way of neutralising volumetric static charges they rarely cause a problem and their effects are normally minimal when compared to surface static charges.
HOW CAN WE HELP?
At Static Electricity Control (SEC) and Meech Australia Static Control (MASC) we only use meters capable of reading between + or - 200KV. Meech 987V3 Static Locator.
As we are sometimes asked to attend post incident fires & explosions caused by lack of static control equipment or incorrectly specified equipment, malfunctioning equipment, non maintained equipment or general misundertanding and misdiagnosis, we take a different approach to Static Electricity.
Our approach is simple:
MEASURE> TEST> MEASURE.
We measure the level of static at your site, in location, with a view to understanding, diagnosing and setting a reference baseline. We have meters that can be used in hazardous and non hazardous environments. This enables us to specify the appropriate static control equipment and set a preventative maintenance program to suit. We will often set up test equipment to validate the results and ensure that the correct equipment has been specified.
If you have been sent static control equipment without testing and establishing a baseline then you may be operating with equipment that is not suitable for the application.