Contamination levels are usually expressed in terms of Contamination Control
Limits, or CCL's .
1 CCL = 
, which corresponds to about 
A level of fixed contamination below 1 CCL is not considered to be much of a
problem, but above 1 CCL some controls may have to be introduced. 1 CCL of
contamination gives about 
to the underlying skin.
Activity at the CCL level is low enough to present a minimal health hazard, yet is still detectable with portable contamination meters .
Table 9.1 
shows a list of the permissible limits for both fixed
and removable contamination .
Table 9.1: Limits on
fixed and removable radioactivity
Notes:
.
I
and
H. To measure
I in swipe use the Beckman 8000
gamma counter do 
-spectrometry using a HPGe
detector.
To measure H,
moisten swipe with glycerine and then wipe
a 100 cm
surface. Place swipe in a 20 ml vial and add
20 ml of scintillation fluid. Count vial in a liquid
scintillation counter.
I.
Under certain circumstances, such as in an area of high residual ambient radiation fields, a higher level of fixed contamination may be tolerated. This is because the decontamination of such an area could result in much larger doses to the clean up crew from the ambient field than would be delivered by the contamination.
Loose contamination must be cleaned up immediately to prevent it being spread all over the place, or else it must be contained by setting up a boot box area , described later.
Hand-and-foot monitors or portable contamination meters (friskers ) are located at the exits from areas that have a potential for loose contamination. Tools and equipment must also be checked for contamination before removing them from these areas.