tatic-control flooring provides protection against electrostatic discharge (ESD) in multiple industries servicing disparate applications that range from eliminating annoying shocks to protecting aircraft flight-tower operations from equipment malfunctions. Often referred to by the term ESD flooring, this category of flooring can protect static-sensitive electronic devices and equipment from harmful (but, due to its invisibility, seemingly inconsequential) levels of static discharge, far below the threshold of human sensitivity. In other instances, ESD flooring is installed to prevent static sparks from causing ignition of flammable chemicals, munitions, explosives, and energetic materials.
In their article “Are Data Centers Drying Up,”1 authors Beaty and Quirk discuss alternatives to humidification, like ESD flooring, for preventing real-life ESD problems in data centers, such as:
- Self-correcting errors (such as a lost package in LAN traffic);
- An upset that may need user intervention; or
- Actual physical damage to IT equipment
Specified and used properly, ESD flooring prevents the generation of static electricity and provides a path to ground for charged objects, including people, materials, machines, and transport equipment. ESD flooring also grounds any object with intrinsic conductivity that makes contact with the floor. For data centers, multiple ASHRAE-funded studies strongly suggest the use of at least moderately conductive flooring systems in controlled areas to reduce the overall level of electrostatic charge accumulation, regardless of environmental moisture or the type of footwear used in the space.
It’s critical to match the right standard and static mitigation strategy to your specific application. When comparing the value, jurisdiction, and viability of any organization and standards, it’s worth noting the possibility of legal complications should the wrong floor be installed. In a January 2012 article published by In Compliance Magazine, nationally recognized liability attorney Kenneth Ross says that in a lawsuit:
Given that standards vary, how do you determine which standards and test methods should be referenced for which environment? To understand why this is important, consider the different requirements for resistance testing between UL 779, DoE/DoD, and the ANSI/ESD test requirements. DoE and DoD resistance testing of conductive flooring is usually performed with an ohm meter set at 500 volts. The ANSI/ESD and ASTM requirement for the same resistance test specifies applying either 10 volts or 100 volts, depending on the resistive properties of the material under test.
Flooring manufacturers do not typically provide product specifications based on 500-volt resistance testing, and most flooring specifiers don’t ask for results obtained at different voltages. Why would using different voltages in a resistance test present a problem? In the case of the DoD, the government set a minimum flooring resistance of 40,000 ohms tested at 500 volts to assess “safety” from electrocution. According to Ohm’s Law, increasing applied voltage lowers resistance. A floor that measures 40,000 ohms using test method ANSI/ESD STM 7.1 at 10 volts will measure well below the 40,000-ohm requirement when subject to 500 V applied voltage.
What happens if resistance testing isn’t performed until after the floor has been installed? This occurred at a U.S. Air Force base earlier this year. The facility handles explosives, and the floor, tested post-installation, was not in compliance with government requirements. The supplier has spent over $100,000 in labor and materials to remove their ESD floor and install a new floor that complies with the government standard. Either floor would have eliminated static satisfactorily, but the Department of Defense doesn’t provide waivers for non-compliant materials used in explosives applications.
The bond between the old floor tiles and the concrete (see Figure 1) had deteriorated due to age and adhesive breakdown. Flooring directly under racks could not be removed because the facility operates 24/7. Removing the floor surrounding the racks was risky due to potential problems with dust containment. These obstacles and preexisting conditions steered the cable company towards solutions that could be installed directly over the existing floor.
Several different ESD flooring materials were evaluated. The primary objective was to find a material that could be installed without adhesives. This limited the options to interlocking tiles or a floating solution such as rubber, vinyl, or ESD carpet tile. The carpet option was dismissed due to the need to move heavy equipment without adding rolling resistance. This led directly to the decision to install a hard-surface interlocking floor.
The next question: did they want dissipative or conductive flooring? To ESD program managers in electronics manufacturing facilities, this may seem like a simple choice, but this application required grounding people who were handling and changing circuit boards in an operational environment. The client wanted to know how high the resistance could be before it was too high to effectively decay charges and what resistance might be considered too low or unnecessarily conductive, thus posing a potential safety risk. The floor also needed to inhibit charge generation on a person wearing regular footwear in an environment with varying humidity.
Per ANSI/ESD STM 7.1, conductive flooring is defined as any flooring with a resistance to a groundable point of less than one million (< 1.0 x 106) ohms. A dissipative floor measures from one million ohms to less than one billion ohms (< 1.0 x 109). This test’s ANSI/ESD S20.20 qualification phase is typically performed in a lab at low relative humidity (RH). An ohm meter is used to measure the aggregate resistance of all the components required to install the floor. With glue-down floor tiles, this entails installing tiles to a test substrate with the proper adhesive and then measuring the resistance from the tile’s surface to a ground connection buried into or under the adhesive. The measurements obtained from this simple lab test determine whether a floor is categorized as conductive or dissipative.
To attain a compliant resistance, floors with conductive surfaces are sometimes installed with dissipative adhesive. As long as the adhesive assures a path to ground above 1.0 x 106 and less than 1.0 x 109, this type of flooring system would be characterized as a static-dissipative flooring system. Lab testing cannot predict whether or not this may be problematic in the field because labs don’t present variables found in the intended installation environment. For example, a dissipative flooring system that relies on dissipative adhesive to control its resistance to ground could be rendered conductive if installation conditions introduce concrete moisture vapor transmission or if grounded equipment placed on the flooring surface creates an unintended ground path.
Depending on the construction of the flooring system, certain types of floors could also measure differently in the field than in the qualification test. A composite floor such as carpet tile or a floating vinyl floor, for example, might be manufactured with a more conductive surface layer than the layers below the surface. Performing tests on a mock-up installation can catch such possible pitfalls ahead of time, preventing surprises after the floor has been installed.
Given that S20.20, IEC 61340-5-1 (the international equivalent of S20.20), and FAA standards all set an upper limit of < 1.0 x 109, the point at which the performance of static-control flooring is significantly diminished, it’s logical that this would be a universally accepted upper threshold.
This leaves us with requisite policies such as following national and local electrical codes, limiting electrical work to only qualified personnel and organizations along with developing, implementing, and enforcing an electrical safety program. This isn’t to say that we shouldn’t consider a minimum resistance. It just means that we shouldn’t rely on electrical resistance as a safety measure. But whether resistance is a reliable predictor of leakage current or not, flooring manufacturers should take Ken Ross’s advice into consideration, i.e., a standard (UL, NFPA, DOD, FAA) establishes a reasonable alternative design, and in the case of an accident, the “manufacturer would have to justify why it didn’t comply.”
According to a major ASHRAE-funded study:
ASHRAE research project RP-1499 shows that the installation of static control flooring in data centers and server rooms can control, reduce and prevent problematic levels of static generation and, as a result, enable a significant reduction of long-standing humidification and energy requirements in these spaces.
Combatting these problems with a one-and-done infrastructure solution like ESD flooring makes sense, particularly compared with wasting energy to cool a highly humidified space. In “The Effect of Humidity on Static Electricity Induced Reliability Issues of ICT Equipment in Data Centers” (Endnote #5), authors Wan, Swenson, Hillstrom, Pomerenke, and Stayer strongly suggest the use of:
Combined with static-control chairs and grounding straps, static-control flooring can provide a highly effective, single-expense solution for all types of ICT spaces.
- ANSI/ESD S20.20-2021, Standard for the Development of an Electrostatic Discharge Control Program
- ATIS 0600321.2020, Electrical Protection For Network Operator-Type Equipment Positions, September 9, 2020
- FAA 019F, Lightning and Surge Protection, Grounding, Bonding, and Shielding Requirements For Facilities and Electronic Equipment
- ANSI/UL 779, Electrically Conductive Floorings, December 15, 2020
- “Are ESD Chairs Good Enough to Be Used as Primary Means of Personnel Grounding?” 2019, 41st Annual EOS/ESD Symposium (EOS/ESD)
- “Dependence of ESD Charge Voltage on Humidity in Data Centers (Part 1 – Test Methods),” ASHRAE Journal 2016
- “Determination of The Effect of Humidity on the Probability of Failure or Upset in Data Centers,” 2014, ASHRAE
- “Footwear and flooring: charge generation in combination with a person as influenced by environmental moisture,” Journal of Physics: Conference Series 646 (2016) 012061
- DOD Contractor’s Safety Manual 4145.26 For Ammunition and Explosives, 2018
- DOE-STD-1212-2019, Explosives Safety, November 27, 2019
- “Static Control Flooring – Conductive or Dissipative?” In Compliance Magazine, April 2020
- “Are Data Centers Drying Up?” Beaty and Quirk, ASHRAE Journal (Vol. 57, Issue 3)
- “Compliance with Product Safety Standards as a Defense to Product Liability Litigation,” Kenneth Ross, In Compliance Magazine, October 2010
- “Static electricity and floor resistance,” documentation for the IBM Cloud Pak System W4600/2.3.3, May 6, 2022, https://www.ibm.com/docs/en/cloud-pak-system-w4600/2.3.3?topic=planning-static-electricity-floor-resistance
- Actual AC and DC electrical currents measured on conductive and dissipative flooring, conducted July 19, 2012
- “The Effect of Humidity on Static Electricity Induced Reliability Issues of ICT Equipment in Data Centers,” Wan, Hillstrom, Stayer, Swenson, and Pommerenke, ASHRAE Transactions (Vol. 119, Issue 2), July 2013