Static Dissipative ESD Carpet
for 911 Emergency Call Centers
by Dave Long
Originally published in 9-1-1 Magazine.com
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Does the flooring in your 9-1-1
center comply with grounding
The expected standard of care in
specifying static-control flooring
The job of 9-1-1 dispatchers is to respond to calls from people who may be in danger. But what happens when electrostatic discharges (ESD) interfere with communications equipment and the call is lost?
Static-control flooring, particularly carpet tile, helps prevent ESD events from harming equipment in 9-1-1 dispatch centers and equipment rooms. Simply put, if this flooring doesn’t meet international industry standards—as well as the standard of care established by the American Institute of Architects (AIA)—callers and dispatchers could be at risk.
Recent research reveals a rather shocking finding: Approximately 70% of anti-static floors installed in end-user environments such as emergency dispatch centers are improperly specified.
What accounts for such a high level of faulty installation?
- The main culprit is a general lack of awareness regarding communication industry standards. This unfamiliarity is commonplace among not only facility managers but also professionals such as architects, engineers, other specifiers, and the contractors who install flooring. In fact, even most flooring manufacturers often don’t have the right technical information.
- Lack of information often leads to misinformation. Unfortunately, manufacturers and distributors sometimes confuse and mislead buyers by incorrectly recommending products that don’t meet the latest standards. Unsuspecting specifiers read their marketing claims and assume the information is technically valid, even if that’s not the case.
- Compounding the problem is the fact that industry standards are subject to change. However, electrical engineers are usually the only people who are up to speed regarding important revisions that impact the selection of grounded flooring. So, if you don’t conduct due diligence, you may be asking for trouble, especially if your carpet flooring is excessively conductive.
The upshot? Specialized flooring of this kind requires specialized skills that facility managers and design professionals don’t have.
Care, Caution, and Correct Conductivity
Facility managers and architects who write specifications for emergency call centers, radio dispatch sites, and PSAPs should exercise care and caution when specifying grounded flooring. Why? Because of the many implications related to performance, electrical safety, compliance, and liability.
- Performance: The floor needs to meet the needs of the application and prevent or ground static. In a call center, this requires choosing a floor that will prevent static on people wearing any kind of footwear. The challenge: many static-control floors like vinyl, epoxy, and interlocking plastic tiles are intended to be used with special static-control footwear. Independent studies have shown that static-dissipative carpet and rubber floors inhibit static regardless of footwear.
- Safety: A static-control floor isn’t just a walking surface; it is a connection to ground, and it must not create a safety hazard while it eliminates ESD. If the grounded floor will be used around operational computer equipment, it can’t be so conductive that it will act as a dangerous ground in the event of stray voltage or other electrical problems. An incorrectly specified static-control floor—particularly “low-resistance,” conductive carpet—might eliminate static discharges, but it may also put workers at risk because it is too conductive to be installed around electrical equipment.
The correct electrical resistance should be specified and verified after the floor is installed. Note that 1 million ohms (1.0 X 106) is the standard minimum resistance value for equipment rooms and call centers.
Compliance and Standard of Care: Any static-control floor is also a grounded pathway for electricity. Based on a specifier’s or architect’s standard of care, it should meet or exceed industry grounding standards, comply with state and local codes, and meet the needs of the client. Motorola R56 and ATIS O600321.2010 are considered the definitive guides to site grounding and electrical protection for communication sites like 9-1-1 dispatcher operations (see below). These standards clearly define the best practice ohms resistance rating range for call centers, and both documents recommend at least 1 million ohms.
Liability: At home, safeguards like ground fault interrupters and building code inspections protect against electrical shock and potentially harmful results. But what about safeguards in the workplace? The fact is that manufacturers, installers, and specifiers can be held liable for any damage or harm their products might cause.
In an article published by IN Compliance Magazine in January 2012, nationally known liability attorney Kenneth Ross states, “Industry standards and even certifications like UL are considered minimum. As a result, compliance with standards and certifications is not an absolute defense, although it is pretty good evidence that the product was reasonably safe. Therefore, as with laws and regulations, the plaintiff can argue that you should have exceeded the standards. However, noncompliance is a problem if it caused or contributed to the injury. The reason is that the standard establishes a reasonable alternative design and the manufacturer has to justify why it didn’t comply.”
In the case of static-control flooring, reasonable alternatives certainly exist. And in looking for the best solution, as noted above, it is prudent to exceed safety and electrical thresholds and never specify less electrical resistance than standards and compliance documents recommend. This means the floor should measure in the static dissipative range: over 1,000,000 ohms and less than 1,000,000,000.
While most people ascribe to the adage, “You can’t be too safe,” some buyers or sellers prefer to downplay the risks that come with disregarding industry standards, asserting that electrical accidents from a highly conductive floor would be highly unlikely. Yet it is hard to ignore the documented cases of people receiving shocks while walking over steel manhole covers that become electrified due to stray voltage, corroded wire insulation, or inadequate grounding. Other cases involve persons standing on a wet and conductive surface while in the presence of an electrical short circuit.
All about Ohms
Rather than relying on anecdotal evidence, let’s look at the scientific reasons electrical engineers don’t recommend conductive floors in operational equipment environments:
Suppose a room is outfitted with a server or telecom switch operating at 220 volts. This voltage could cause a dangerous and even lethal shock if a person touches the electrical source while grounded to the conductive floor. Ohm's Law tells us that electrical current (I) can be calculated by dividing voltage (V) by resistance (R) (I = V/R). For example, the calculated current between a 220-volt source and a floor measuring 25,000 ohms would be 220 volts divided by 25000 ohms or 8.8 milliamps. According to OSHA, 8.8 milliamps will inflict a painful shock and cause a person to begin to lose muscular control. Electrical current between 6 and 16 milliamps is commonly referred to as the freezing current or "let-go" range.
After installation, factors like wet shoe soles and high moisture can cause a drop in resistance, which creates a lesser resistance path to ground than lab testing would have predicted. Conductive carpet tiles, for example, can measure 10,000 ohms or less even though they are typically specified as having an average resistance of no less than 25,000 ohms and no more than 1,000,000 ohms. At 10,000 ohms, the same 220-volt appliance could expose a person to an electrical current of 22 milliamps. According to OSHA (see chart below), extreme pain, respiratory arrest, or severe muscular contractions could occur from exposure to this amount of current. At this level, the individual may not be able to let go, and death may result.
To put these calculations into perspective, on a “static-dissipative” floor that meets Motorola R56, the same 220-volt appliance would only generate .22 milliamps of current – 1/100th of the current allowed by the conductive floor. This explains why standards organizations recommend a 1 million ohm minimum resistance for static-control carpet installed in dispatcher areas.
This link to an Ohm's Law calculator allows you to mathematically determine electrical current based on the resistance of floors that might be used around energized equipment and appliances. Note:. Keep in mind that Ohm’s law likely presents a best-case scenario. In actual installations, environmental factors like moisture and wet shoes can and will reduce the resistance of any static control-floor. When resistance is reduced, electrical current will increase.
Continue reading this article:
Part 1: Static Dissipative ESD Carpet
Part 2: The Facts Speak for Themselves