Previously, we talked in greater detail about how ESD flooring works. But when it comes to choosing what type of static control flooring to use, the biggest question you need to answer is this:
Should I use static dissipative flooring or static conductive flooring?
Perhaps the most important factor you’ll need to consider in making this decision is safety.
Shouldn’t I Always Choose the Fastest Pathway to Ground?
At first glance, it might seem like a no-brainer: just put in the flooring that has the lowest resistance so that electrostatic discharge is carried most quickly and efficiency to ground. If that’s true, then static conductive flooring is an obvious choice.
But if the floor is too conductive, then we introduce another set of risks to personal safety.
This is where we start to get into safety standards developed by OSHA and the National Fire Protection Association (NFPA), among others.
Put simply, “static dissipative” flooring and “static conductive” flooring are two very specific classifications based upon levels of conductivity which is measured in terms of the materials’ resistance to electricity.
Resistance of ESD Flooring Options
Resistance, or impedance, is measurable, and is expressed in ohms. The ohm is a unit of measurement named after Georg Ohm, the German physicist who discovered Ohm’s law. In specifications documents, schematics, and other materials, the ohm is represented by the symbol Ω (the Greek letter omega).
Put simply, higher resistance = lower conductivity.
A substance with resistance measured at zero ohms (0 Ω) would highly conductive conductive (carbon, silver, and copper all have resistance measured in a fraction of an ohm). On the opposite end of the spectrum, a substance with 1 billion ohms (1 × 109 Ω) would have very low conductivity (rubber, which is so resistive that it’s used as an insulator, has a resistance in the 1.00×1013 Ω range, or 10,000,000,000,000 Ω, AKA ten trillion ohms).
In general terms defined by the ESD Association, “conductive” is describes any flooring with a resistance of up to 1 million ohms. “Dissipative” is used for anything greater than 1 million ohms and up to 1 billion ohms.
|ESD Flooring Type||Resistance (Ω) Range (Low End)||Resistance (Ω) Range (High End)|
|Static Conductive||–||1 × 106|
|Static Dissipative||1 × 106||1 × 109|
Unfortunately, these categories are so broad that they aren’t entirely useful.
Thankfully, the ANSI 20.20 specification helps clarify things for us. It indicates that the maximum resistance of the flooring and the person (measured together) should be less than 3.5 × 109 ohms.
The NPFA has also specified that flooring should have no less than 25,000 ohms resistance. Below this number, the conductivity of the floor is considered to be too high and therefore unsafe due to risk of electric shock and other hazards.
As you can see, neither the minimum resistance specified by the NFPA nor the maximum specified by ANSI 20.20 lines up perfectly with our terms for “static conductive” or “static dissipative” flooring.
So… we’re left with making a selection based upon the specific needs of your industry. What is the application of the flooring? Will it be used in a clean room? Will it be used in electronics manufacturing? What are the considerations around flammable materials?
Other factors will affect the decision as well. Will the humidity and temperature of the environment be maintained within specific parameters? Both will affect conductivity, not just in the floor, but in the environment as a whole. What other building materials will be used?
Additionally, when specifying the levels of conductivity in flooring, there is a diversity in testing and measurement that exists which will cause test results to vary widely depending upon the methodologies used. It’s important to understand how these measurements will affect the final outcome where conductivity is concerned.
The Bottom Line?
There are a number of factors involved in the decision when you’re selecting between static conductive or static dissipative flooring. Our ESD control experts will be more than happy to help walk you through the decision-making process and the range of options available to you — both from a performance standpoint and from an aesthetic one. Contact us today!