Note: This information pertains to flooring concerns associated with ESD protected areas (EPAs) in electronics manufacturing and handling. This information is not pertinent to static-control concerns in end-user environments. If your interest focus is on ESD flooring for data centers, server rooms, 911 call centers, school labs, networked offices, FAA flight towers, communication rooms or telecommunication areas – go to this page for technical articles
ANSI/ESD S20.20 provides specific test methods to qualify and evaluate ESD flooring materials. Other methods – such as European test methods or NFPA methods – yield results that differ from and are incompatible with ANSI/ESD test results. While a material may pass European or NFPA tests, the floor may still fail to comply with S20.20. The only way to ensure that your ESD floor complies with relevant standards is to test according to test methods in S20.20. For best results, require tests performed by an independent lab.
Case Study: ESD Flooring Failure, Incorrect Testing
A military defense contractor (electronics application), trying to meet static-control requirements in ANSI/ESD S20.20-2014, contacted us about a problem they were having with their new ESD floor. They had purchased the new floor under the assumption that it would meet all the requirements of Table 2 in the S20.20 document.
The caller explained that the floor wasn’t meeting any of the requirements – even though the manufacturer had assured them nothing was wrong with the flooring. The client described the floor as a static conductive linoleum sheet floor. Made in Europe, the floor was new to the US market. After reviewing the client’s test data, we agreed to meet with and help them find out why the floor wasn’t doing what it was supposed to do.
Immediately after arrival, we were asked to measure the floor with our Prostat megohm meter.
After several tests, we quickly concluded that our meter and theirs were arriving at consistent results. The floor was incapable of meeting any of the S20.20 requirements: it was far too resistive.
The resistance to ground exceeded 1 billion ohms (1.0 x 10E9) – the upper limit in the S20.20 resistance standard.
The building representative was extremely agitated. He knew it would be difficult to shut down the facility and replace the floor. The client admitted that the floor had been a value-engineered substitution, selected late in their project. The manufacturer had guaranteed them that the floor would do everything the originally specified floor was supposed to do.
Under the guidelines in ANSI/ESD S20.20, we use Standard Test Method 7.1 to test for electrical resistance.
Upon review of the floor manufacturer’s documents, we discovered the real problem with the floor: the manufacturer’s specifications referenced a resistive properties test method used in Europe. Unlike North American standard test method ANSI/ESD S7.1, the European method tests for electrical resistance using a much higher applied voltage of 500 volts.
According to Ohms Law, higher applied voltages result in lower electrical resistance measurements. In other words, the more voltage you apply, the lower ohms resistance you will see.
Following the European test method, the resistance reading appeared much lower than, in fact, it actually was. At an applied voltage between 10 and 100 volts, required by ANSI/ESD S20.20, the resistance measurement was extremely high. Unfortunately for this end user – because no one in their organization had picked up on the test methods referenced by the European manufacturer – they were probably stuck with the floor. The test method was clearly printed on their spec sheet.
There was one other forewarning this client had missed. Despite the reference to a static dissipative value < 1.0 x 10E8 ohms, the manufacturer’s brochure recommended the floor for “areas with sensitive equipment.” Their generic recommendation made no reference – on any of their promotional materials – to electronics manufacturing, EPAs or ANSI/ESD S20.20. There was also no mention of a lifetime static-control warranty.
Conclusions
- Only accept materials that have been specified using ANSI/ESD Standard Test Methods: www.esda.org
- Test for electrical resistance, according to test method STM 7.1
- Test for walking body voltage (charge generation) according to STM 97.1
- Always ask for test data from independent labs when qualifying any kind of static-control flooring.
- Labs like Fowler Labs can perform the full battery of tests needed for qualifying floors to the requirements in ANSI/ESD S20.20.
- Insist on a lifetime static-control warranty.
- Always include in your contract a requirement for post installation tests – demonstrating that the flooring meets Method One in ANSI/ESD S20.20 for Personnel grounding.
- Method One requires ANSI/ESD S97.1 System resistance testing. ANSI/ESD S20.20 confuses many engineers; without reading closely, it’s easy to conclude that the floor merely needs to measure below 1.0 x 10E9 using test method s7.1-2005. This is a fallacy.
- The floor must also meet charge generation requirements. For electronics facilities, the floor may not generate more than 100 volts of static electricity; for Class-0 electronics the upper limit is 10 volts.
You might also take a look at this video for further understanding. Static dissipative versus conductive:
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