It represents an annoying source of painful electric shocks to both occupants and visitors and contributes to low morale amongst staff and workers. In department stores for example it often generates complaints from customers, sometimes resulting in litigation. In a recent incident a cup of hot coffee was spilt on a child after the parent received a shock from a hand rail in a department store café.
Uncontrolled static electricity can also cause chaos by interfering with computer systems and electronic point of sales (EPOS) equipment. In the most extreme cases it can even constitute a fire or explosion risk.
It is possible for a person to generate electrostatic charge by movement — particularly walking. The contact and separation of the sole of the shoe with the floor creates a small imbalance of charge with every step, and this slowly accumulates on the body. The person involved may be blissfully unaware of this condition until they reach for a grounded object such as a hand rail, radiator or lift button whereupon a spark jumps from their finger. In this spark the body releases all of its accumulated charge at once giving the resultant sensation of electric shock.
If electrical charge on the body reaches a voltage in excess of about 3000V (3 kilovolts) it is likely that the person will experience a shock when touching an earthed metal object such as a radiator. At 10,000V or greater most people would consider the shock to be painful and experience involuntary recoil.
As well as electric shocks, a significant problem is now also being encountered in offices, stores and other commercial premises in the form of electrical interference to computers, and accidents due to recoil. More often than not the fault lies with the materials used in construction — in particular flooring — and unfortunately some of the most attractive floors produce the most severe static problems.
Tackling the problem
In virtually every case that has been investigated the prime causes of repeated electrostatic problems in buildings are the material of construction of the floors and the floor coverings.
Traditional materials such as wood, natural-fibre carpets, concrete and antistatic-grade vinyl are electrically dissipative. Modern synthetic materials, although generally more hard wearing, are often highly electrically insulating. Quartz tiles, ceramics, epoxy resin, plain vinyl and synthetic carpets fall into this latter category.
In many buildings the incorporation of polished steel hand rails exacerbates the problem by providing a convenient grounded metal object for the person to discharge to.
The following steps are recommended prior to design and installation:
- Determine the electrostatic properties of the proposed materials well in advance. A specialist laboratory will be able to predict whether there will be a static problem once the building is completed.
- Do not rule out any generic flooring material (for example ceramic tiles) as there can be a great variation in the electrostatic performance of different varieties. Materials used for the base or underlay may also have a significant effect.
- Do not rely on claims that a particular product is 'antistatic'. Experience has shown that this term is often applied without foundation.
- Fixtures and fittings such as door handles, hand rails etc are less likely to cause shocks and accidents if made of a natural 'dissipative’ material like wood. Partially conductive composites are also available which have the advantage of removing the charge from the human body without producing a shock.
If static electricity only becomes an issue after the building is completed, the approach becomes one of 'damage limitation’ rather than a full solution. An electrostatic audit will determine the source of the problem, quantify the properties of the materials and levels of static and recommend the most practical and cost-effective solution.
View the full article 'Controlling Static Electricity in Modern Buildings'
