FAQ: Proper floor grounding: under the surface
As the local EMS provider, we employ automated external defibrillator (AED). If the patient is on the floor and the defibrillator discharges a shock, will the shock be transmitted over the entire floor, possibly shocking other individuals in the area?
You have asked a perennial question that has been an ongoing concern since the first conductive floors were installed in hospital ORs back in the late 1940s.
If you have regular flooring with no conductivity, you should not have any concerns.
We are operating on the assumption that your question was prompted by the fact that your space has a grounded floor (a floor with conductivity). We call grounded floors either conductive or static dissipative floors, based on their electrical resistance.* Some people call them ESD floors because they prevent electrostatic discharge.
If you are working on a grounded floor, there are some simple best practices that you should follow:
- It is best to choose a floor that does not have too much conductivity. The absolute minimum resistance for a floor per NFPA and ASTM standards is a floor that has an electrical resistance of no less than 25,000 ohms (2.5 x 10E4 ohms). However, you don’t want to start out selecting flooring materials that approach the bare safety minimum. For this reason, for most environments, we always recommend the use of what are called static-dissipative (SD) floors and carpet. These floors get rid of static but they are not so conductive that they support high electrical currents.
- The second thing to consider is how the floor is grounded. Best practice is to place grounding strips underneath the floor. In order to ground under the floor most effectively, the floor should be more conductive on the underside than it is on the surface. That’s an easily achieved outcome as long as the floor is installed with either conductive adhesive or an underlayment that is more conductive than the surface.
- Be sure the floor is grounded to either electrical ground or to building steel. That is where charges will flow.
- The resistance of a conductive floor measures < 1.0 x 10E6 ohms
- A static-dissipative floor measures from ≥ 1.0 x 10E6 ohms to < 1.0 x 10E9 ohms.
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- ESD Footwear for Electronics Manufacturing and Handling Applications
- Facility Managers' Guide to Selecting ESD Flooring
- The Need for Due Diligence in Specifying Static-Free Flooring
- Standard of Care for Specifying Floors in Mission-Critical Spaces
- Understanding the Hidden Costs of ESD Flooring