Method of Test for Conductive Flooring

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Technical Note (National Research Council of Canada. Division of Building Research), 1953-11-13

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Method of Test for Conductive Flooring

Sereda, P. J.

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t·

DIVISION OF BUILDING RESEARCH

NATIONAL RESEARCH COUNCIL OF CANADA ｾＮ

TECHNIICAlL

NOTlE

No.

165

NOT FOR PUBLICATION

PREPARED BY P.J. Sereda CHECKED BY E.V. Gibbons

FOR INTERNAL USE

APPROVED BY ｒＮｆＮｾＮ

PREPARED FOR National Fire Protection Association Hospital Operating Room Committee

DATE Nov.

13, 1953

SUBJECT

Method of Test for Conductive Flooring

The Committee on Hospital Operating Rooms of the National Fire Protection Association has for years done

out-standing work in formulating standards for safe practice in hospital operating rooms. The National Fire Protection

Association Standard No.

56

contains recommendations pertaining to conductive flooring and outlines a test method which serves as a practical guide to those directly responsible for the construction and use of the operating rooms in hospitals. In this capacity this document has served well.

In the development of materials suitable for conductive floors and in the evaluation of their performance characteristics, a laboratory method for testing surface con-ductivity was found lacking and therefore, an attempt was made to develop such a test. In the course of the development of a laboratory test method, data were obtained which might serve to define limits of the field test given in the standard, and might further suggest some modifications in the test method. It is for this reason and to solicit comments from those expert in the field that this resume of the results was prepared.

Electrode System

It has been found that aluminum foil reacted electro-chemically when in contact with moist surfaces of materials such as concrete terrazzo. Electrodes made from platinum or gold foil .001 inches thick were found to give results a grea·t deal more reproducible. It has been found that the volume resistance of materials used in conductive floors was usually much ｬｯｾ･ｲ than the resistance between

electrode and the surface. Thus, measurement of the resistance of the floor by means of two electrodes placed on the surface represented predominantly the contact resistance. Because of this fact, the spacing and the geometry of the electrodes was not a critical factor. Two rectangUlar electrodes,

tit

x 21t

, spaced

t"

apart and backed by

t"

rubber sheet rubber (as de-signated in Bulletin

56)

were found to serve the purpose quite adequately.

• f' .: , b

.-e

r

e 2 e

-Pressure on Electrodes

The unit pressure on electrodes as specified in Bulletin

56,

is about one pound per square inch. Experiments using the above electrodes has showed that in the case of some materials, the resistance may vary a gl'eat deal with changes

in this pressure. In addition, it was found that reproducibility of measurements was improved as the unit pressure was increased.

Potential Source

The National Fire Protection Association standard specifies the use of a calibrated ohmmeter with a nominal open-circuit output voltage of 500 volts D.C. Generally, such an instrument produces a voltage which varies with the resistance being measured. Results of tests have indicated that resistance of some materials ｶ｡ｲｩｾｳ inversely with the applied voltsge. This variation of resistance was found to be very high in ｴｨｾ

case of some relatively dry materials (low R.H.). For this reason, it wes thought advisable to use a variable D.C. source which could be controlled to produce any desirable voltage.

The resistance was computed from the measured voltage and current.

Conditions of Test

It has been found that surface conductivity is a function of the moisture content of the material and indirectly a function of the R.R. The R.R. deterl1Jines the equilibrium moisture content of the material or more specifically, it

de-termines the amount of adsorbed water on the surfaces. If the material contributes soluble salts or general impurities, the

extent of the moisture film would have a profound effect upon thG surface conductivity. To account for this factor, it was found essential to condition the sample to an equilibrium

moisture content with a controlled R.H. To enhance this equi-librium, the sample was placed in vacuum over a sulphuric acid bath of certein concentration to give the desired R.H. In va-cuum, the sample usually attained moisture equilibrium in about

24

hours. In this manner it was possible to determine the cha-racteristic curve of the resistance versus R.H. for different flooring materials. It was found that 8 carbon terrazzo

ex-hibited a large variation of resistance with R.H. In fact, the results indicated that this flooring would not meet the specified upper limit at conditions of R.H. below

35%.

Some materials, such as conductive linoleum and conductive rubber, showed very little change in resistance over the range of 10 to

85%

R.H.

.e

3

-It is hoped that this summary of somewhat limited investigations will assist in general understanding of the pro-blem and, more specifi08lly, that it will stimulate an interest in the development of a suitable laboratory test. It is felt that e reliable laboratory test is absolutely essential for the development of satisfactory flooring materials to meet the safety standards required in modern hospital operating rooms •