ESD Floors & Seating for Data Centers, Server Rooms and Mission-Critical Flooring Applications
Selecting an antistatic floor for a data center, server room or other mission-critical space involves a number of considerations. The most important is the type of footwear people wear. The soles of some shoes – e.g., athletic shoes with polyurethane or PVC soles – generate static.
The conductive elements in ESD -protective footwear, such as heel straps, form an electrical bond between shoe soles and the conductive particles inherent in high-quality ESD flooring.
Typically, footwear is not controlled in data centers, server rooms and other end-user spaces. In other words, people are not required to wear special ESD-protective footwear. For this reason, the ESD floor must inhibit static regardless of the type of shoes people wear in the workplace.
Approaching the selection process from this perspective enables you to inhibit static generation on anyone, anytime, regardless of humidity, the sensitivity of your servers or the application and critical nature the servers represent to your mission or operation.
The effectiveness of static-control flooring is based on:
- The floor’s ability to prevent static regardless of traffic, humidity or the type of footwear worn by people occupying the space. This property, called preventing body voltage generation or BVG, is measured using test method ANSI/ESD S97.2. Tests should include measurements with and without static control footwear.
- The intrinsic ability of the floor to be grounded or produce a traceable ground path. Electrical conductivity is measured using test method ANSI/ESD S7.1. Test samples should be preconditioned at humidity levels below 20%. In the case of ESD carpet, the test should be performed on new and used carpet to determine if traffic and abuse will degrade the Groundable path.
Applicable ESD Standards
ESD standards are not universal. Standards vary, determined by industry and application. Applicable standards for data centers, server rooms, and mission-critical spaces include:
The Motorola guidelines have become the recognized standard in the telecom industry and serve as the most complete and rigorous specification for the protection of communication system equipment installed at public safety and commercial wireless communication sites.
Excerpt from Appendix C 3.3 – 68P81089E50-B: “Carpeting or floor tiles within an equipment room or dispatch center, including raised flooring, should have a resistance to ground measurement of between 1,000,000 and 1,000,000,000 ohms.”
ATIS 0600321 (Alliance for Telecommunications Industry Solutions)
ATIS publishes standards for the information, entertainment, and communications industries.
Excerpt from Section 4.2 Flooring: “Any carpeting or floor tiles should have a resistance to ground between 10E6 and 10E10 ohms when measured using the method of ESD-S7.1.”
Ensuring the maximum resistance for the flooring system is 2 x 10E10 ohms*, measured between the floor surface and the building (or an applicable ground reference). Flooring material with a lower resistance will further decrease static buildup and discharge.
For safety, the floor covering and flooring system should provide a resistance of no less than 150 kilohms** when measured between any two points on the floor space 1 m (3 ft.) apart.
Please note: Resistance and Body Voltage/Charge Generation tests are done following test methods STM 97.1 (resistance) and STM 97.2 (body voltage), outlined in ANSI/ESD S20.20.
Best-rated Floors for Data Centers, Server Rooms, and End-user Spaces
Not Recommended: High Pressure Laminate
HPL is comprised of six to eight layers of resin-impregnated kraft paper, decorative paper (with a pattern, color or woodgrain) and a decorative overlay. These layers are manufactured under 1000kg per-square-meter of pressure at temperatures of 140°C+ (284°F).
With HPL, the decorative layer does not inhibit body voltage generation. And HPL does a poor job of grounding the ESD casters on static-control seating.
Chart 1. Comparison of three (3) types of footwear on three (3) types of floor at three (3) environmental moisture levels – Peak walking voltage.
- Moisture levels, shown in grains of water per pound of dry air, are equivalent to 15%, 35% and 60% Rh at 23°C
- The ASHRAE group established 500 volts as the maximum on personnel for service operations.
Used by permission: David E. Swenson
ESD floors dissipate (and inhibit) static charges as we walk. When we sit in a regular (non-ESD) chair, we are no longer grounded – even if the chair itself is sitting on an ESD floor.
The friction we generate by moving – when we shuffle our feet, take off a sweater, set a disposable cup on our desk – creates static electricity. Static on our body stays in place and jumps to whatever we touch. If we’re sitting in a regular (non-ESD) chair and touch electronic equipment, the jolt of electricity can damage or destroy the component’s internal circuitry.
That’s why it’s crucial to complete the static-protective chain.
StaticWorx ESD Bolt™ chairs, made with static-dissipative materials, ground people while they sit – preventing static charges from building on their body – and discharge static to ground.
When standing up from a non-ESD chair, voltage rises. After standing up, voltage may drop slowly (figure above) or rapidly (Figure 2) depending on the shoe/floor resistance.
Used by permission: David E. Swenson
Figure 2 Definition of the chair event voltage for cases in which the shoe/floor system discharges rapidly from the person (shown here: Rubber ESD floor, mid-range dissipative shoes at 38C and 8% RH).
By permission: David E. Swenson
ESD Seating Features
(adapted directly from IBM Data Center Recommendations)
Use the guidelines below to minimize static electricity buildup in your data center.
Floor covering material can contribute to buildup of high static electrical charges resulting from the motion of people, carts, and furniture in contact with the floor material. Abrupt discharge of static charges causes discomfort to personnel and can cause malfunction of electronic equipment.
- Maintaining the relative humidity of the room within the server operating limits. Choose a control point that normally keeps the humidity between 35 percent and 60 percent. See the Air conditioning determination for further guidance.
- Providing a conductive path to ground from a metallic raised floor structure including the metal panels.
- Grounding the raised floor metallic support structure (stringer, pedestals) to building steel at several places within the room. The number of ground points is based on the size of the room. The larger the room, the more ground points required.
- Ensuring the maximum resistance for the flooring system is 2 x 10E10 ohms*, measured between the floor surface and the building (or an applicable ground reference). Flooring material with a lower resistance will further decrease static buildup and discharge.
- For safety, the floor covering and flooring system should provide a resistance of no less than 150 kilohms** when measured between any two points on the floor space 1 m (3 ft.) apart.
- Maintenance of ESD floor coverings (carpet and tile) should be in agreement with the supplier’s recommendations. Carpeted floor coverings must meet conductivity requirements. Use only antistatic materials with low-propensity ratings.
- Using ESD-resistant furniture with conductive casters to prevent static buildup.
* StaticWorx recommends a resistance ceiling of 1.0 x 10E9 ohms, per ANSI/ESD S20.20 (with an optimal ceiling of 1.0 x 10E8). With electrical resistance above 10E9 if the floor lost conductivity–due to its chemical makeup or environmental factors such as dry air, dirt and debris–it could become too resistant to properly discharge static to ground.
** 150 kilohms is the same as 150,000 ohms (1.5 x 10E5)
CHECKLIST: CHOOSING THE RIGHT STATIC-CONTROL FLOORING
In this episode, Dave discusses ESD floors and electrical safety. At some point when discussing grounded conductive floors, the question of safety always arises, along with whether or not grounding a conductive floor puts people in harm’s way. Referring to an actual case study, Dave talks about a situation in which a floor installed for the FAA was too conductive to meet the FAA safety standards. The client had been told that drying the pressure-sensitive adhesive would solve the problem, making the entire floor less conductive. Dave talks about why this is not true, and why it’s extremely important to adhere to electrical standards as they are written.
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