Wipe Material

DOE-HDBK-1129-99

The measurement of removable surface contamination has not been standardized by the technical

disciplines, and, as a result, it is difficult to compare readings between facilities. Reasons for

variations between facilities may be due to the following:

Instrumentation: The instruments used for counting wipes are of different manufacturers and

models providing varying accuracy and precision. The methodologies used are not

standardized or cross-checked against each other to determine if results are similar.

Units: The measurement units used at the different sites are either dpm/100 cm2 or dpm/cm2

with the former being the more common. Comparing results from one facility to another

requires careful checking to make sure that the dpm values discussed are for the same area of

surface.

Wipe Material: The wipe materials most commonly used are dry filter paper, Styrofoam, and Q-

Tips. There is no standardization of materials across facilities.

Wipe Preparation: Dry wipes and wet wipes are used at the facilities. The wet wipes are

prepared by soaking the Q-Tip or the filter paper in water, counting solution, or other liquids.

Wipe Technique: The technique used to determine the area wiped and pressure applied when

using the different materials varies from site to site.

Dry versus wet wipes: Recent comparative tests performed at the LLNL Tritium Facility show

that there are differences in the results obtained between a dry and a wet wipe of the same

surface. In some cases, the dry wipe resulted in measured values higher than those measured

by a wet wipe, while in other cases the wet wipe was higher. These tests, using de-ionized

water as the wetting agent, indicate that the difference between a dry or wet wipe is a function

of the type of surface and the level of contamination. Generally, the levels measured by wet

and dry wipes of the same surface are within a factor of 3.

Good practices in this area for consideration include:

When the surface of the object is less than 100 cm2, the activity per 100 cm2 should be

calculated based on the area wiped, and the entire object should be wiped.

Records should be kept in units of dpm/100cm2.

Either dry or wet wipes can be used to satisfy regulatory requirements. The requirements do

not identify a wetting agent, nor do they specifically require a wet wipe. Some facilities use wet

wipes in the belief that this is a more conservative approach. In fact, depending on the specific

surface conditions, either method may produce somewhat higher measured values. Given the

high intrinsic variability of the wet swipe process and the fact that the dry method is less

complex and can be standardized and performed more consistently, the dry process is the

preferred method of this Handbook.

The methods used to measure removable surface contamination are not presently

standardized and are not the same at all facilities. The following discussion describes a

Generic Wipe Survey Technique that could be used at any DOE facility.