a. Method
The method is described and illustrated in ESD from A to Z by J. M. Kolyer
and D. E. Watson, Van Nostrand Reinhold, 1990, pages 26 and 27.
Twelve randomly selected test subjects walked in a normal manner on twelve
1.5 x 1.5 ft. ESD Carpet Tiles covering a 3 x 9 ft. area. The ESD carpet tiles
were grounded. For comparison, the same subjects walked on a vinyl-tile floor
finished with a conventional acrylic coating ("wax"0. The temperature
was 73° F, and the relative humidity was 42% by psychrometry.
Voltages were read with a grounded Trek Model 512 static meter.
b. Data
Data are given in Table 1.
c. Discussion
A proposed standard test for voltages generated by people on walking surfaces
(EOS/ESD Technology, August/September 1991, page 86) uses one type of "shoes
with insulative soles." This is a naïve approach because in real
life the results vary greatly from shoe to shoe, as seen in Table 1, and must
be averaged. Even if everyone wore identical shoes, the results still would
vary because triboelectric charging is controlled by the outermost surface,
which may be a microscopically thin film of grease or other contamination.
Therefore, our test uses twelve people with whatever shoes they happen to
be wearing to get a rough idea of the practical effectiveness of a walking
surface in controlling personnel voltage in a particular environment.
Table 1 shoes that the ESD Carpet Tile reduced voltage on personnel by 60%
vs. a "waxed" tile floor. For 9 of the 12 subjects, the ESD Carpet
Tile was superior to the tile floor, but for two subjects (Nos. 3 and 6),
the floor was better, and in one case (No. 7) the floor and tile were equal.
Obviously, a test with only one person could have been quite misleading.
Shoe sold materials are hard to identify; vinyl compositions, for example,
can masquerade as rubber. In three cases (Nos. 1, 3, and 7) the sole was embossed
with the trade name "Vibram," but a phone call to the Vibram manufacturer,
Quabaug Corp. (508-867-7731) revealed that Vibram compositions vary with the
type of shoe. All that can be said is that solid Vibram soles, as opposed
to sponge, are based on SBR or nitrile rubber.
Leather shoe soles tend to give low charges, as was true for one person,
No. 12.
In conclusion, Table 1 shoes the average superiority of ESD Carpet Tile vs.
a particular conventional (not antistatic) acrylic floor finish with a random
sample of 12 people. This is a promising indication, but every potential user
of ESD Carpet Tile should run h is own test with existing floor material as
a control.
a. Method
The method of the Statement of Work was used.
b. Data
Data are given in Table 2.
c. Discussion
The carpet fibers are nylon, which is resistant to the solvents tested. As
expected, the solvents had no effect on the Compu-Tile; they merely wetted
the fibers and then evaporated without leaving a trace.
a. In a walking test with 12 randomly selected people wearing their usual
shoes, grounded ESD Carpet Tile gave 60% less skin voltage than did a conventional
(not antistatic) floor finish on vinyl tiles.
b. Three solvents commonly used in the electronics industry (1, 1, 1—trichloroethane,
Freon TMS, and isopropyl alcohol) caused no dulling, bleaching, staining or
other visible permanent damage when poured onto the ESD Carpet Tile and covered
with watch-glasses to retard evaporation.
