Prostat Corporation | ESD Blog

Note: This is an article that appeared in the FAcilities Engineering Journal in the July/August 2014 Edition. You can visit the journal’s website at http://www.afe.org

A person walking across an insulative tile floor can build-up static electricity resulting in electrostatic discharges (ESD). When a hand touches a doorknob, it can take 3000 to 3500 volts to feel a sudden shock. In 1971, Intel’s 4004 microprocessor equaled about 2300 transistors. At the end of 2008, Intel’s Dual Core Itanium 2 smashed the 2 billion transistor equivalency barrier.

 

In 2011, Astronaut Buzz Aldrin commented that today’s hand held smart phone has more processing speed than NASA’s Apollo 11 guidance system computer[1]. Hand held touch screen phones are much faster with colossal memory in comparison to the Lunar bound Apollo 11 computer. Traditional electrostatic discharge (ESD) flooring is found in aerospace & defense, data centers, ammunition storage, semiconductor, medical device and data centers. Today, static control resilient flooring is installed in FAA towers, Navy ship control centers, operating rooms, call centers, aircraft, pharmaceutical delivery and labs. Static control flooring consists of the follow:

Raised Data Center Flooring	Polymer Cushion Floor Mats
Tile	Laminated Steel Framed Flooring
Concrete	Coated Floor Tile
Modular interlocking or Snap In Polymer Lay Down Floor Sections	Special ESD Composite Flooring Special Antistatic Coatings
Epoxy
Carpet

Both non-compliant and suspect counterfeit static control flooring have infiltrated the  supply chain. Today, a very common practice by federal agencies is to require 3^rd party certification of a static control floor installation before payment is issued. In order to  prevent the potential bias of supplier self-certified testing, a 3^rd party insures independent verification.

 

 

 

 

 

 

 

 

 

To insure proper selection and installation of static control flooring, there are several ESD flooring standards in place. U.S. Government agencies call out a 096XX designation for static resilient flooring. For instance, the DOT & FAA utilize 096536. The federal sector references ASTM F150 and ANSI/ESD LBS7.1[2] resistance testing for static control flooring protocols. So that everyone is on the same page, ASTM F150 defines:

Conductive flooring – a floor material that has a resistance between 2.5 x 10⁴ ohms and 1.0 x 10⁶ ohms. Dissipative floor material – floor material that has a resistance between 1.0 x 10⁶ ohms to 1.0 x 10⁹ ohms.

A new installation shall have no individual reading greater than the stated limits defined in ESD DSTM7.1 or ASTM F150. In addition, the plant or facilities engineer should consider the following four testing methods.

 

 

 

 

 

 

 

 

 

1. Resistance:

The Resistance to a Groundable Point (RTG) and Point to Point (R_PP) or Surface to Surface Test or Top to Top (R_TT) resistance shall be between 2.5 x 10⁴ ohms to <1.0 x 10⁶ ohms for conductive flooring with a constant voltage (CV) of 10 volts and a RTG (Figure 3-Left) and R_TT(Figure 3-Right) between 1.0 x 10⁶ ohms to < 1.0 x 10⁹  ohms for static dissipative flooring CV=100 volts).

 

 

 

 

 

 

 

 

 

2. Static Generation or Voltage in Combination with a Person (Figure 4) testing requires a result <300 volts for static control carpet when tested per AATCC-134-2011 (Electrostatic Propensity of Carpets) wearing conductive footwear. The ANSI/ESD STM97.2-2006 sets a requirement of <+/-100 volts. However, ANSI/ESD STM97.2 applies for all types of flooring and is not limited to carpets.

 

 

 

 

 

 

 

3. Resistance in combination with a person. ESD DSTM97.1-2013[3] measures the electrical system resistance of floor materials in combination with person wearing static control footwear which sets a limit of <3.5 x 10⁷ ohms or <1.0 x 10⁹ ohms depending on the method utilized. This test has not been listed on the federal list as a requirement. However, it is useful in determining resistance of a floor and a person wearing static control footwear such as shoes, heel grounders, ground strip booties (Figure 5, left) and temporary adhesive removal strips. This test method is often utilized for initial static control flooring qualification.

 

 

 

 

 

 

 

 

 

 

4. Electrostatic Decay (Static Decay): Current federal 096XX requirements incorrectly call out Fed-STD-101C/4046.1. This test method has been revised to Mil-STD-3010B, Method 4046 and should be conducted in a lab and not in the field where relative humidity cannot be controlled. This test is conducted using precut floor samples measuring 3-1/2” x 5-1/2” and clamped into the fixturing of an electrostatic decay testing system. The specimens are charged to +/-5000 volts and grounded to facilitate static decay to 0 volts for a limit of <0.25 seconds.

 

 

 

 

 

 

 

 

 

Before the measurement process takes place, grounding validation should be facilitated per ANSI/ESD S6.1-2009 (grounding). Connection to the electrical system insures that the floor is at the same potential as the facility.

 

 

 

 

 

 

 

 

It is critical to validate the ESD floor material before installation. For initial qualification, both ASTM F150 and ANSI/ESD S7.1 call out the use of scaled down prototype samples.  In ASTM F150, a 48” x 48” sample (Figure 8) is used for conducting both RTG and R_TT measurements. Securing a pre-made sample for initial testing from the static control floor manufacturing company can ultimately prevent a poor installation.

In past couple of years, the author received two (2) flooring company prototype specimens, both companies had failed ESD compliance testing. Consequently, these testing results led to reformulation of the product.

Non-compliant flooring can be attributed to the following:

 

1. ESD flooring system had not system grounding
2. Flooring adhesive was not conductive
3. Static Control flooring was unnecessarily coated leading to insulative readings
4. Formulation issues for tiles and epoxies flooring not in compliance with

 

ANSI/ESD S7.1 or ASTM F150

 

1. Improper selection of copper ground stripping
2. Improper test instrumentation used by Contractor or End-User
3. Knock off product

 
In an on-site experiment, a static dissipative floor produced a RTG and R_TT reading below 1.0 x 10⁹ ohms; the floor did not prevent ESD discharges from taking place. Thus, a special ESD event antenna peaked out at 2.7kV (see Figure 9) for several operators wearing insulative tennis shoes and walking over a static dissipative tile floor. Later, the test was repeated wearing ESD footwear and no ESD events were recorded.

 

 

Conductive flooring that exhibits readings of <1.0 x 10⁶ ohms demonstrated better ESD performance wearing both ESD and insulative tennis shoes in comparison to a static dissipative floor measuring 1.0 x 10⁶ ohms to <1.0 x 10⁹ ohms. It is clear from Table 1 that both conductive and static dissipative flooring provide better performance wearing ESD shoes.  Walking over a conductive floor wearing tennis shoes produces better results in the prevention of charge build-up than wearing the same footwear on static dissipative flooring.

 

 

 

 

 

 

 

 

In short, due to the significant investment required for static control flooring, dependence upon a supplier’s technical data sheet alone can prove costly! There is no substitute in not subjecting the floor to the following tests methods:

 

1. Grounding Validation
2. Resistance to a Groundable Point & Point to Point Resistance
3. Voltage in Combination with a Person wearing ESD Footwear
4. Resistance in Combination with a Static Control Floor and ESD Footwear