What can be done to allow the safe dispersal of static charges (ESD)?

The two main types of danger from ESD are areas that contain (albeit only occasional or briefly) explosive vapours (eg. hospital operating areas or chemical laboratories) or areas containing electronic equipment (eg. computer rooms, control rooms etc.). Such rooms should have conductive floors installed so that the charges on people or trolleys can be dispersed.

Specific work areas on benches etc. should have conductive mats installed. These are directly connected to earth. If the floors are adequately conductive, then as we move around, the static charges are constantly dispersed and do not build up to dangerous levels. Most conductive floors are made with either copper sheet or strip under conductive PVC or other plastic sheeting, which allows for adequately fast, but not surging, dispersal.

The Standard: ANSI/ESD-S20.20-1999

In this Standard the ESD Association recommends (section 6.2.3) that in a Protected Area the floor should have a resistance of less than 10⁹ ohms. Our wheels measure 10⁶ and therefore are better than the minimum requirement of the Standard.

If suitably conductive floors are installed do they need special maintenance?

Modern conductive floors if properly installed have a working life in excess of 20 years. BUT – they depend on the ‘earthing’ being maintained. Any changes to the surrounds of the floor that might disrupt the earth path must be guarded against and the floor must not be ‘waxed’ or treated with ‘protective layers’ that will increase the resistance. Cleaning is best done with ammonianated water, as most commercial cleaners contain ‘polish’. NEVER wax the floor, or apply a ‘protective coating’.

What about the castors and wheels for use in ESD Protected Areas?

Once you have a conductive floor you need conductive wheels on the trolley. To ensure the wheels have a reasonable life the Standard recommends they have a resistance of less than 10⁹ Ohms. Until recently the only way to ensure sufficient conductivity was to use carbon powder (carbon black) in rubber tyres. Unfortunately this marked floors and lost its conductivity over (about) 3 years. Recently additives have been developed that retain their conductivity for longer, and hold it at the recommended standard. Our ESD wheels have been developed to provide the necessary conductivity and provide a non-marking tyre with enhanced durability.

Installation of ESD wheels:

ESD wheels must be properly installed to ensure a conductive path from the trolley leg, through the stem, and the castor and the axle and the bearing, and through the centre and tyre. Solid metal pintles will provide such a conductive path. If plastic expanding stems are selected, they will need to be installed with a copper wire attached to the stem and wrapped between the adaptor and tube inner to ensure a conductive path.

Which ESD wheels do Fallshaw offer?

We offer 75mm (3″), 100mm (4″) and 125mm (5″) wheels that can be assembled into our M series castors. Our ESD wheels are non-marking and have resistance of less than 10⁶ ohms – well under the maximum 10⁹ ohms recommended by the Standard and therefore Industry Best Practice.