Guidance Note
Area Contamination Monitoring
By Wipe Testing
CM2
1
General
Tritium contamination cannot be detected with any hand-held instrument- wipe tests must be used.
In laboratories which are not equipped with hand-held monitors, other isotopes may also be
monitored via this method (e.g. 14C). In each series of wipes an uncontaminated sample should
be counted as a control in order to obtain a "background" count.
In this Guidance Note, the term “active area” refers to an area or piece of equipment within which
either: unsealed sources of radioactivity are manipulated (e.g. workstation, designated sink); or
contamination is likely to occur due to the activities undertaken within it (e.g. centrifuges).
“Inactive area” refers to an area or piece of equipment which may become contaminated (e.g.:
floor & bench areas around workstations & designated sinks; fridges & freezers used for storing
radioactive materials). Some areas (e.g. hybridisation ovens) may be defined as either “active” or
“inactive”, depending on the level of isotope use and the liklihood of contamination within a
particular laboratory.
2
Active Area Monitoring
All active areas where tritium (3H) is used must be monitored both before and after each session.
The wipes taken prior to the session will indicate whether any contamination occurred during the
session or prior to it. If prior contamination is discovered the RPS must be informed and the
incident investigated. Minor spills or splashes, which occur during the course of an experiment,
should be cleaned up by the user in accordance with the local rules. Where it is impossible to
remove contamination to below the working limit for the radioisotope in question, the RPS should
be contacted for advice.
All measurements of contamination must be recorded in a Contamination Monitoring Record
(CMR) as Bq/cm2 after following the procedure given in section 4.
3
Laboratory Monitoring
Once per month, all active & inactive areas should be surveyed for contamination. A schematic
diagram of the lab should be used to demarcate all the areas to be surveyed and identify the
points at which wipe tests should be taken. All results should be recorded in the CMR. Any levels
of contamination above the working limit should be reported to the RPS.
4
Procedure for Monitoring
1.
Moisten a suitable wipe, such as a glass-fibre disc small enough to fit into a liquid scintillation vial, with
water or other solvent in which the contamination is soluble.
Wipe a known area of surface, normally 100 or 1000 cm2.
Place the wipe into a scintillation vial with 10 cm3 of liquid scintillant.
Count the activity in a liquid scintillation counter.
In the absence of any more accurate information assume that 10% of the activity on the wiped surface
has been transferred to the wipe.
2.
3.
4.
5.
6.
Calculate the contamination level using the formula: contamination level (Bq cm-2) 
where C
=
A
Eff
T
count-rate in cps, corrected for background
=
area wiped in cm2
=
percentage counting efficiency for isotope in question
=
percentage of contamination picked up (normally 10%)
Working Limits (Bq.cm-2)
Active Areas:
Inactive Areas:
July 2005
3H
300
30
14C
30
3
C 100 100


A Eff
T