Managing Static in A Public Safety
Emergency 911 Call Center
by David H. Long
How to Choose Anti-Static Carpet for 911 Call Centers and FAA Applications
We recommend watching this video, "How to Choose Anti-Static Carpet for 911 Call Centers and FAA Applications" before reading this archived article about static electricity discharge problems in emergency 911 dispatch call centers. You will learn why it is important to reference compliance with standards like Motorola R56 and ATIS 0600321 before ever installing any static control carpet in any type of call center or command room.
ENPM | April/May 2004
See note at bottom of page regarding edits
to bring this article current with telecommunication industry grounding standards.
Random static discharge will wreak havoc inside your call center--lost or corrupted data, dropped calls, PC lookup, and blown headsets.
|
|
ESD carpet attracts built up static charges and safely channels the charges away from an operational environment to an established ground point. |
Designers of mission critical spaces such as 911 call centers, mission control command centers and flight control towers routinely design their spaces to withstand external threats-weather, power outages, earthquakes and, in some cases, even biological threats. While clearly all of these external threats must be addressed, an invisible threat, inside the call center, is sometimes overlooked. Electrostatic discharge (ESD) can wreak havoc inside the mission-critical command center. Dropped calls, blown headsets, PC lockup and lost or corrupted data represent just a few of the problems caused by random static discharge.
Microcircuits inside electronic equipment perceive a static discharge as an overwhelming burst of energy. Older, more rugged components, though still prone to ESD failure, contained special microcircuit gate protectors, capable of diverting the random charge away from the heart of the device. These interior shields, while protecting the circuitry, slowed the performance of the devices. Today, many designers of the new breed of electronics have done away with these cumbersome internal protection devices. This progress in design translates into a world of faster, more capable computers and telephony equipment. Without the internal shields, however, devices are far more susceptible to the invisible threat of static electricity, a phenomenon even more ubiquitous than the common cold.
Most people, having experienced the nuisance of static cling or felt the zap of a shock, assume that static is something that can be seen and felt. Yet it takes 3500 Volts of static electricity for human beings to perceive the effects of a static discharge. To put that number in perspective, sensitive electronic components can be damaged or destroyed by a discharge of fewer than 25 Volts. Random static discharge and field effects caused by such common events as sliding a chair, rising from a seated position or walking across a floor can wreak havoc on computers and sophisticated telephone systems. Last year, Palm Source, Inc., the manufacturer of the Palm Pilot, was engaged in a class action suit after low levels of static inside its PDA caused lost and corrupted data during transmission to PCs.
Defining Antistatic
In almost all cases, the floor is the primary site of ESD generation. Fortunately, it is also the easiest place to mitigate the problem. At one time, conductive vinyl was the only choice for a static control flooring material. Today, almost every conceivable floor covering can be manufactured with some sort of static protective properties. Products ranging from ergonomically-friendly static dissipative carpets to super hard, carbon-filled epoxies are used everywhere, from networked office spaces to circuit manufacturing facilities that require maximum static protection along with a tough, durable surface. Resilient materials such as rubber and vinyl are also available in static-free versions.
Selecting the right static control floor can be confusing, particularly when people toss around terms such as static dissipative or static dissipative-words that are unfamiliar and often meaningless to architects and facilities managers. Most flooring materials currently on the market claim to have some antistatic properties. Almost every carpet product produced in the U.S. contains some form of antistatic ingredient, with companies often advertising their products as computer-grade or 3kV.
For the call center facilities manager, these terms may be misleading. As with any industry, the static control field has its own technical jargon. In fact, relative to the selection of flooring, the word antistatic is too broad to be useful. By antistatic, people usually mean that the floor will reduce the generation of static between footwear and the floor. But which footwear? What type of floor?
Some shoe soles produce low levels of static when they rub against certain flooring materials and high levels of static when they interact with others. When the resultant charge measures in the low range, we call the condition antistatic. When the charge is high, we call the condition static-generating. The important distinction is that antistatic is a snap shot condition that will easily change if any parameter-from humidity to surface hardness to footwear composition- is altered.
As for computer-grade, the term means only that the floor will suppress static charges to a level of 3.5 kilovolts-so you won't feel a discharge. As we know, call centers and other mission-critical command centers house some of the most sophisticated electronics and telephony equipment available today. What good is a computer grade flooring product that will reduce static charges to fewer than 3.5 kV when sensitive equipment can be destroyed by a static charge of less than 1/100 of that? And how will an antistatic or computer grade floor tested in the summer at 50 percent humidity fare in dry winter conditions when the RH drops to 10 percent? The keys are finding a product that requires no special sprays or coatings, provides a low static rating at all humidity levels and one that also provides a verifiable path to ground.
Two objectives - One solution
To ensure electrical performance, the static control floor must meet two basic objectives:
1) The floor must not contribute to static generation;
2) It must be groundable after it is installed.
Many static control floors are capable of meeting one of these objectives, but not the other. A computer-grade carpet, for example, might marginally address the first objective, but it cannot be grounded. An ungrounded floor can allow a person to remain charged just as electrical capacitors store energy. And because electricity is always looking for the path of least resistance, as soon as the charged person makes contact with equipment or some other item in the room - unwanted rapid discharge will take place.
What is to be gained from a floor that prevents shocks if it cannot be grounded so will not reduce charges below the threshold of damage to the mission critical equipment it was intended to protect? That type of floor could provide false security and contribute to the very problem it is supposed to eliminate.
Similarly, certain excellent conductors- conductive vinyl, for instance-are comprised primarily of ordinary static generating materials (standard VCT) with a small distribution of carbon or graphite chips or veins to provide conductivity. Although the embedded conductors do make the floor groundable, the regular VCT in the floor is highly static generating. When shoe soles contact and separate from the VCT, static builds. To prevent static buildup, everyone who walks on the floor must wear special conductive shoes or conductive heel straps, a requirement that would be difficult if not impossible to enforce in a call center: Can you imagine the local sheriff putting on heel grounders every time she touches her computer?
Static Control Carpet
Intuitively, it makes sense that static dissipative carpet would be less effective than conductive vinyl in preventing static buildup, but in fact the opposite is usually true. Static dissipative carpet tiles contain thousands of grounded conductive fibers that sweep off static from shoes, safely discharging the static to ground, similar to the way small brushes eliminate static on high speed copiers as the paper is fed into the collator. This does not mean that conductive vinyl is an inferior product. It simply means that conductive vinyl works best in applications-such as electronic manufacturing and assembly- where footwear and traffic are monitored and controlled.
Static dissipative carpet resembles standard carpet except for the addition of special carbon fibers that are woven throughout the surface and backing. (See figure 1, below). When a person walks on the carpet, the dissipative fibers extract excess static build-up from the shoe sole-before it damages components- and safely discharge the static through the dissipative backing. The charge is then routed through a conductive release adhesive that secures all of the tiles in place. The release adhesive-also known as pressure-sensitive adhesive- contains millions of conductive fibers. These fibers create a conductive network below all of the tiles in the installation. The adhesive is connected to ground along the edges of the room through eighteen-inch copper strips (one ground strip per one thousand square feet) that bridge the gap between the perimeter floor tiles and electrical conduit. When properly installed, every single floor tile is at the exact same electrical potential as all of the others. This condition is called electrical continuity. This procedure may sound technically challenging but in actuality requires no more skill than a standard carpet tile installation. The key to success is doing the homework up front and specifying carpet tile products manufactured with dissipative fibers in conjunction with conductive adhesive and grounding strips.
STATIC CONTROL FLOORING CHECKLIST |
|
1. Only static dissipative and conductive floors can be grounded. Standard flooring installed with ground strips or conductive adhesive will not offer any static protection. 2. Any effective static dissipative floor can be verified with an ohmmeter to determine the electrical resistance of the material. If the material does not pass the ohmmeter test than it cannot be grounded. 3. Static dissipative floors should never require any antistatic sprays or waxes to enhance or maintain performance. The conductivity should be achieved by the actual permanent physical composition of the material. 4. The floor should reduce static electricity regardless of relative humidity. Ask the supplier specifically about performance in very dry conditions. |
5. The floor must prevent static buildup in real world conditions without special dissipative shoes or shoe straps. When in doubt, ask for independent test data verifying this property. It should be available. 6. Never assume that a shock-free environment means a static-free environment. A shock-free environment only means that static charges are below 3500 Volts. 7.Do the homework up front. Obtain and follow the grounding guidelines of Motorola R56 and ATIS 0600321-2001. Both standards recommend static dissipative flooring for emergency dispatcher areas. 8. Even if your present electronics are immune to static, if at some point in the future they will be upgraded or replaced with state-of- the-art equipment, then static will be a problem. As with any potential security breach, it is always best to plan ahead. |
Rubber Flooring
Carpet may be the wrong choice for certain applications. Entry areas can become a maintenance nightmare during inclement weather. Carpet could become unsightly or stained if continuously exposed to salt and chemicals used to control ice and snow buildup. Sometimes carpet is seen as a collector of dust and dirt. Although closed loop carpet tiles are easily vacuumed and steam cleaned, some facilities managers prefer floors that can be broom cleaned or damp mopped. Other people choose resilient flooring simply because a resilient floor was installed when their facility was built and no other flooring material has ever been tested or used. Some people see carpet as inferior to vinyl or other hard surfaces and there is no way to alter their thinking.
Fortunately, it is possible to meet the same static protection level of static dissipative carpet using certain rubber flooring alternatives. Eclipse rubber flooring, in particular, provides static inhibiting properties similar to dissipative carpet tiles, but for very different reasons. From high school physics, we know that whenever two dissimilar surfaces are rubbed together, they generate static. The corollary is also true: Similar materials generate less static when they interact. The base compound used in Eclipse rubber flooring sufficiently resembles most shoe soles to the degree that it inhibits the buildup of static by preventing static generation in the first place. Unlike conductive vinyl, Eclipse rubber is a homogenous dissipative material with dissipative properties distributed across one hundred percent of the surface and throughout the thickness of the tile. The full distribution of dissipative properties means that shoe soles will never contact anything on the surface of the floor that can generate static. And, like all effective dissipative flooring options, rubber meets the second critical criterion for a 911 call center: it can be grounded.
A typical rubber installation relies on the same conductive adhesive as carpet tiles. Without conductive adhesive, rubber tiles cannot attain electrical continuity or be grounded and an ungrounded installation offers no means of dissipating static away from the floor.
Summary
To protect their sensitive electronic equipment, call rooms and other mission-critical command centers need static protection on which they can rely. With so many options, choosing the right static control floor can be a challenge for architects, designers and facilities managers. The most important criteria to remember are these:
- The floor must be compatible with the environment.
- The material should require a minimal amount of maintenance.
- The floor must meet the electrostatic requirements of the facility. The reference documents for making this determination in a public safety 911 communication application are called Motorola R56 and ATIS-0600321-2010.
By following these few simple guidelines, choosing the right floor can be relatively painless and easy. And static, the invisible threat inside the call center, will no longer compromise job performance or threaten to damage or destroy sensitive electronic or telephony equipment.
Note: This article was originally published prior to the 2005 revisions to Motorola R56 and the 2010 revision to ATIS-0600321. The article has been modified to reflect important changes in the resistive properties of flooring used in networked operator equipment positions. Te current recommend ohms range is as follows:
Motorola R56
- The Motorola guidelines have become the recognized standard in the 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
- Link to Motorola R56 See pages 468-470
- Excerpt from Appendix C 3.3 - 68P81089E50-B
9/1/05 — UP Version:
"Carpeting or floor tiles within an equipment room or dispatch center, including raised flooring, should have a resistance to ground measurement of between 106 and 109 ohms when measured using the test method of ANSI/ESD STM7.1-2001 or later"
ATIS 0600321-2010
- Alliance for Telecommunications Industry Solutions
Electrical Protection for Network Operator-Type Equipment Positions - Link to ATIS-0600321-2010 Protection for Network Operator-Type Equipment Positions
- Available for purchase: Digital Edition available from www.engineers.ihs.com
- Excerpt from Page, Section 4.2 Flooring
"Any carpeting or floor tiles should have a resistance to ground between 10 E6 and 10 E10 ohms when measured using the method of ESD-S7.1." - ATIS publishes standards for the information, entertainment and communications industries
© 2004 ENMP
Products mentioned in this article
EC rubber
ShadowFX Carpet tile
Dave Long is the President of Staticworx®, based in Newton, MA. He can be reached by phone at (617) 923-2000.
