Choosing the Right ESD Flooring

(continued from prior page)

Conclusions

1.) The data suggest that a dissipative PVC floor without conductive footwear offers marginal static control advantages and in fact could represent an unnecessary liability.

2.) Based on the cross section of shoe soles and conditions, it is unlikely that moving people will generate over 400 volts as a result of interactions with a conductive rubber floor or over 600 volts on a conductive carpet tile with conductive thermo-plastic backing. It is more likely that the walking body voltages will be around the respective mean values of 250 volts and 450 volts.

3.) The normal distribution of both rubber (RUB_KV) and carpet (CAR_KV) flooring graphs suggests that triboelectric performance may be more predictable for certain flooring materials than other materials. In the case of rubber this may be the result of triboelectric tendencies influenced by material work function (see ESD Association ADV11.2-1995 for further explanation.) Conductive carpet’s antistatic tendency may be explained by the principle of “charge backflow.” (Also see ADV11.2)

4.) The bi-modal nature of graphs of the PVC (PVC_KV) testing illustrates tremendous voltage variation depending on shoe soles.

5.) Any performance evaluation of ESD flooring materials should consider the amount of procedural control and the level of compliance an organization can reasonably expect in their environment. Unless access to and procedures within technical spaces are carefully controlled, conductive rubber flooring or conductive carpet may offer a significantly lower threshold of risk from static charge generation than dissipative PVC. In uncontrolled environments the data suggest viewing flooring materials as preventive/environmental controls that should attenuate static on moving bodies independent of heel strap compliance.

6.) A fault tolerant floor grounding system can be achieved by installing ESD flooring materials with a combination of antistatic and conductive properties.

These findings present significant implications on the selection criteria of flooring for uncontrolled environments where sophisticated electronics are used for health, safety, security and other mission critical activities.

All tests were performed between 62 and 68 degrees F at RH between 19 and 24% Please note: Testing was based on an evaluation of materials for specific client applications at the time the testing was performed. The selection of materials should in no way be considered exhaustive. Further testing is underway using a larger sample of shoes and additional flooring materials. More clothing variable will be introduced.

Excessive tribocharging induced by a particular flooring material should not be interpreted as reason to dismiss all materials in that material composition category. When new, all materials measured less than 35 megohms in combination with a person wearing conductive heel straps per ESD-STM-97.1 Carpet products were exposed to accelerated life tests (100,000 caster cycles) because most carpet warranties exclude chair caster damage from warranty claim coverage. Presently there are no manufacturers promoting performance after chair cast exposure. Failure Total electrical failures of two out of three carpet designs reinforces the need for this testing.

A. New ESD carpet tile with PVC backing 50cm X 50cm
B. ESD carpet tile (A) after 100,000 cycle chair caster durability test
C. New ESD carpet tile with conductive thermoplastic backing 24” x 24”
D. ESD carpet tile (B) after 100,000 cycles chair caster test
E. ESD vinyl laminated to access floor panel with conductive adhesive
F. Conductive two layer rubber with black reverse side 24” X 24”

Shoes used for tests:

Dress leather loafers with synthetic soles
Dress laced shoes with thick rubber soles
Hiking boots with rubber soles
Dress shoes with leather soles
Running shoes with plastic soles

About the Author:
David H. Long is the principle of Staticworx® , based in Newton, MA. He can be reached by phone at (617) 923-2000 or by e-mail at .

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