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All ESD carpet tiles generated lower walking body voltages than dissipative PVC tile. Triboelectric generating properties of the 50cm PVC tiles were significantly impacted by the chair caster abuse test.

Damage from chair caster abuse raised the resistance to ground per ESD STM7.1 of the PVC backed carpet tile from acceptable (10⁶ to 10⁸) to unacceptable (over 10^10.) There were no measurable consequences from 100,000 cycles of chair caster rolling over the thermoplastic backed conductive carpet tiles.

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.

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

 

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"
 

*This article originally appeared in the May 2005 issue of Conformity Magazine.