Prior Risk Assessment
‘Open / Unsealed Source’
Ionising Radiation Work Activity
A risk assessment must be prepared for all ionising radiation work activities. This assessment
form should be completed for the use of ‘open / unsealed’ radioactive sources and be agreed by
the Departmental Radiation Protection Supervisor and approved by the Radiation Protection
Officer before the work starts. Additional guidance and information at the end of this form is
provided to assist in the preparation of the assessment.
1. General Information
ACTIVITY TITLE:
ASSESSMENT CODE:
(e.g. Group Leaders initials + 1, 2, etc)
ASSESSMENT PREPARED BY:
NAME OF GROUP LEADER
RESPONSIBLE FOR THE
SAFETY OF THE WORK:
DEPARTMENT:
LOCATION(S) OF WORK:
(area / room)
2. Activity Details and Hazard Identification
Activity Details
Why are you proposing to use radioactive material? If there is a safer
alternative technique, why is it not being used?
Radioisotope and Molecule:
Radioisotope(s), principle emissions (i.e. ,β,) and energies (MeV) (see
tables):
Form of Material:
(e.g. liquid / powder/gas)
Page 1 of 8
Identify the hazards using information supplied by the supplier of the radioisotope
together with guidance information at the end of this form:
External radiation hazard (i.e. medium-high energy isotopes)
Internal radiation hazard (Ingestion) (all isotopes could potentially be ingested)
Internal radiation hazard (Inhalation) (i.e. is it volatile?)
Internal radiation hazard (Absorption) (i.e. is the material easily absorbed through the skin)
Yes/No
Yes/No
Yes/No
Yes/No
Maximum amount of radioactive
material (MBq) / Experiment:
Maximum Stock Activity to be
Stored (MBq):
Brief Description of Work Activity:
Hazardous Procedures:
Identify and describe those stages of the
work activity most likely to cause an
exposure
Estimated Handling Time / Expt:
Estimated Frequency of
Experiment (no. times per annum):
Persons at Risk
Identify all categories of people
who may be directly or indirectly
at risk:
Consider e.g. laboratory staff /
postgraduates, undergraduate students,
cleaners / contractors
Waste Disposal Requirements
Waste Disposal Routes
Solid
Aqueous
Liquid
(via designated
sinks)
Estimate % to each route
Estimate of Monthly Disposals
(MBq) and % of local sink
disposal limit (aqueous liquid only):
Page 2 of 8
Organic
Scintillant
Gas
Estimated External Radiation Exposures
1. Dose Rates:
Estimate the unshielded external radiation dose rate (mSv/min) to which anyone could be
exposed during the work for high energy beta (includes 32P & 36Cl) and gamma emitting
radioisotopes, using the formulae in the Guidance Notes at the back of this form. Calculations
need to consider dose rate to hands (extremities) from a distance of 1 cm, and dose rate to the
whole body from a distance of 30 cm. This should be supported by actual radiation dose rate
measurements where available.
Note: External Dose rate calculations are not required for 3H as the betas have insufficient energy to
penetrate the dead layer of skin and do not present an external dose hazard. Other low energy Beta
emitters (<0.3 MeV) (includes 14C, 45Ca, 33P, 35S) can penetrate the outer layer of skin and give a skin dose
(these are calculated later in the ‘accident considerations’).
a) ‘Extremity’ (hand accessible) dose rate (mSv/min) (D; calculated at 1cm):

Dose rate when dispensing radioactive material from stock
container (assume first use of stock material):
For example, dose rate from stock bottle containing 9.25 MBq P-32 when full

Dose rate from radioactive material used in a typical experiment:
For example, dose rate from experiment that uses1.8 MBq P-32
b) ‘Whole Body’ dose rate (mSv/min) (D; calculated at 30 cm) from radioactive
material used in a typical experiment:
2. External Exposures:
The dose rates (calculated above) can now be used to estimate the annual exposures you and
other laboratory workers would receive if work were carried out without local shielding. To
estimate annual external exposures to the hands or whole body requires you to consider
approximately how long you will be exposed to the radioactive material during the experiment,
and approximately how many times a year you will be performing the experiment.
Unshielded Annual External Exposure=
Dose rate (D) X duration of exposure at each distance (mins.) X annual frequency of exp’t
a) Annual ‘extremity’ dose (calculated at 1 cm) (mSv):

From dispensing radioactive material removed from stock bottle:

From radioactive material used in a typical experiment (consider
the main handling stages of the expt.):
Express total annual extremity dose (from dispensing & experimental
work) as a % of annual ‘extremity’ dose limit (500mSv):

b) Unshielded annual ‘whole body’ dose: (calculated at 30 cm)(mSv):
Express dose as a % of annual ‘whole body’ dose limit (20mSv):
Page 3 of 8
Internal Radiation Exposure Risk
Establish if there is a significant risk of radioactive materials being inhaled, ingested or
absorbed. Refer to the safety data provided by the supplier of the materials and the
information at the back of the document for guidance.
Ingestion:
Assume a worst case scenario (because of very poor working
practices) of 5% of the total experimental activity being ingested.
Dose (mSv) / experiment:
Annual Dose (mSv):
Inhalation:
Is the radioisotope volatile or could the work activity generate
gaseous emissions?
If yes, what is:
a) the dose (mSv) / experiment
b) annual dose (mSv)?
Yes/No
(Assume a worst case scenario of 5% of the total experimental activity
being inhaled).
Skin absorption / penetration:
Is the radioisotope easily absorbed through skin?
If yes, what is:
a) the dose (mSv) / experiment
b) annual dose (mSv)?
Yes/No
(Assume a worst case scenario that 5% of the total experimental activity is
absorbed through skin).
TOTAL ANNUAL INTERNAL WHOLE BODY DOSE (mSv):
(i.e. sum of ingested, inhaled and absorbed doses)
Express dose as a % of annual ‘whole body’ dose limit
(20mSv):
Total Annual Whole Body Dose Summary (without controls)
a) External ‘whole body’ dose estimate:
(see external ‘whole body’ dose (mSv / annum) calculation (2b) above)
b) Internal ‘whole body’ dose estimate:
(see calculation above) (mSv / annum)
TOTAL (UNCONTROLLED) ANNUAL WHOLE BODY
DOSE (a + b): (mSv / annum)
4
Identification of Control Measures
Potential doses must be reduced As Low As Reasonably Practicable
The hierarchy of control measures for restricting exposure:
1. Engineering controls, safety features and warning devices
2. Administrative controls
3. Finally, personal protective equipment.
Control Measure Considerations
Description of Control Measures
Assuming justification for the use of
radiation has been made earlier, confirm
that the amount of material has been
optimised for your work.
Is radiation shielding required?
e.g. 1 cm Perspex for 32P or
lead impregnated Perspex for 125I
If yes, describe what shielding will be
provided. The following should be available:
screens, shielded storage / transport / waste boxes /
microtube blocks.
What measures are being taken to
minimise exposure to hands from high
energy betas (>0.3 MeV)?
Consider minimising time exposed to radiation;
maximising distance (e.g. use of tongs etc), and
shielding (Perspex blocks for pipettes).
If volatile material has been identified, or
if the work activity generates gaseous
emissions, what measures will be taken
to prevent inhalation?
Containment: how will the spread of
contamination be controlled?
 Describe access restrictions to radiation work

area and storage arrangements for stocks and
waste material
Note: a basic workstation should be established
consisting of Benchkote (absorbent side up); drip
tray; warning tape, tissues, decontamination
liquid, appropriate contamination monitor
Type of contamination / dose monitor to
be used? e.g. Mini Instruments Type EP15
Note: since monitors are not sensitive to detect 3H,
5
‘wipe testing’ is used to detect 3H
Designation of radiation room / area:
Supervised or Controlled?
(most areas used for modest amounts of unsealed
sources are designated a ‘Supervised’ area unless
high risk activities are taking place- see Guidance
Notes for further details)
Approved ‘Local Rules’ in place?
Written protocol in place?
A protocol briefly describing how the procedure will
be performed safely (including key safety features to
be applied) MUST be prepared for workers &
attached to this report.
Is Personal Dosimetry required? (required for
high energy betas (32P, 36Cl), & gammas)
Will radioactive material be transported
outside the radiation room / area? If yes,
describe arrangements for the safe
transport of material.
Note: movement of radioactive materials in or
between labs. Must be minimised. Where it is taken
outside the lab. Work area, double containment must
be used to reduce the risk of spillage.
Training:
 Research Groups: confirm that all workers
will receive formal University training + ‘local
practical induction training’

Undergraduate Teaching Practicals:
describe the training to be provided
Lone Working: does lone working (e.g. out
of normal working hours) need to be
avoided for this activity? Lone working
restrictions should be applied to all activities
involving stocks of 32P and 125I.
Identify any other measures that will be
used to control exposure?
‘Personal Protective Equipment’ (PPE)
What PPE will be used?
Note: all workers must wear a lab. coat, disposable
gloves as a matter of course. Safety glasses must
also be used for splash protection when manipulating
all liquid isotopes and for shielding eyes against high
energy isotopes such as 32P and 125I
Are further measures still required to
reduce a potential dose ‘as low as
reasonably practicable’?
6
Estimate Effectiveness of Local Shielding
(if applicable) at reducing annual exposures:
Shielded annual ‘whole body’ dose:
(assume appropriate local shielding (e.g. from shields, Perspex blocks etc)
reduces dose from >0.3 MeV beta emitters by a factor of 1x106). Shielding should
be used for all >0.3 MeV beta emitters, and gamma emitters if, a) accessible
‘whole body’ dose rate is > 2.5 µSv/h, and b) accessible extremity dose rate is >75
µSv/h
Express dose as a % of annual ‘whole body’ dose limit (20mSv):
Possible Accident situations
Skin contamination dose: assume 5% of total
stock material (not experimental activity) is spilt
uniformly on hand and left on skin for 1 hour (refer
to Table 2, ‘External Exposures’ in Guidance Notes
for dose from uniform deposit of 1kBq/cm2 on the
skin)
Loss / theft of material: describe measures to
prevent loss / theft of material e.g. storage facilities
and any other security measures
Failure of fume cupboard: describe steps to
be taken in the event of fume cupboard failure
during use
Note: All ionising radiation workers should be familiar with the procedure for dealing with
spillages of radioactive material. This procedure is documented in the ‘local rules’ of all
radiation rooms / areas, and should be included as part of the ‘local practical induction
training’ provided to all radiation workers.
Contamination Considerations
Estimate the surface contamination
(Bq/cm2) that would occur if the whole
aliquot of stock material (not experimental
activity) was spilled over an area of 300 cm2
Estimate the airborne contamination that
could occur if the whole aliquot of a volatile
stock material was spilled
What (if any) equipment is expected to
become contaminated during the course of
the work activity? Describe the extent of
any contamination and how this will be
decontaminated.
7
Group Leader’s Declaration:
1. I confirm that all the information contained in this assessment is correct.
2. I will ensure that no work associated with this activity will be carried out until
this assessment is approved and all necessary control measures are in
place.
3. I have considered ways of conducting this work using non-radioactive
methods and I cannot find a suitable non-radioactive alternative. The amount
of radioactive material will be kept to a minimum.
4. I agree to provide or organise full and proper training for all persons involved
in this specific activity to ensure they use radioactivity safely.
5. I will monitor the work of all persons involved in this activity and ensure that
both Local Rules and University of York rules / codes of practice are followed.
Name:
Date:
Signature:
SEND THE COMPLETED FORM TO YOUR RADIATION PROTECTION SUPERVISOR
FOR APPROVAL BEFORE WORK STARTS
Assessment Review:
REVIEW AND UPDATE YOUR ASSESSMENT WHEN SIGNIFICANT CHANGE(S) IN
PRACTICE HAS OCCURRED (E.G. ACTIVITY LIMITS, PROCEDURE, RADIOLABELLED
COMPOUND) OR AN INSPECTION SHOWS THAT A REVIEW IS NECESSARY.
REVISED ASSESSMENTS TO BE SENT TO BIOLOGY RPS FOR APPROVAL.
RPO approval
Name:
Date:
Signature:
8
Guidance Notes
1. ESTIMATION OF RADIATION EXPOSURES
Simplified formulae for estimation of external and internal radiation exposures are
provided below and should be suitable for most scenarios.
a) Estimation of External Dose Rates
(i) High Energy Beta-emitting Radioisotopes
Refer to Table 1, ‘Properties of Radioisotopes’, to determine the energy of the beta
emitter(s) being used.


Beta particles having energies <0.3 MeV do not penetrate the skin, and are
considered to present a negligible external dose risk. As such, there is no need to
estimate external doses for low energy beta-emitting radioisotopes.
For beta-emitting radioisotopes with energies >0.3 MeV (e.g. 32P and 36Cl) calculate
external dose rates using the following formulae
Extremity dose rates (@ 1 cm):
D = 1.3 x A
For whole body dose rates (@ 30 cm):
D = 1.5 10-3 x A
where:
D = dose rate in mSv/min
A = the experimental activity in MBq (1 mCi = 37 MBq, 1 MBq = 27 µCi)

32P
and 36Cl are both high energy beta-emitting radioisotopes that are capable of
giving significant extremity (i.e. hand) doses.
Experimental Activity
32

P
37 MBq (1 mCi)
3.7 MBq (0.1 mCi)
1 MBq (27 µCi)
Extremity Dose Rate
2886 mSv/h (3Sv/h)
289 mSv/h
78 mSv/h
If you are handling high activities of 32P and 36Cl your risk assessment must carefully
consider and identify how exposure will be minimised. You will need to consider:
o dispensing material, especially stock material- a Perspex ‘pipette guard’
should be used
o how you will manipulate radio-labelled materials in centrifuge tubes,
eppendorf tubes etc

o how you will transfer radioactive material onto chromatographic plates, gels
etc, and how you will handle the plates and gels
A safety protocol should be written describing how you will handle radioactive
materials so as to reduce exposure to a level that is as low as reasonably practicable.
(ii) Gamma-emitting radioisotopes
For gamma-emitting radioisotopes:
D= CA
where
D = dose rate in mSv/min
A = the experimental activity in MBq (1 mCi = 37 MBq, 1 MBq = 27 µCi)
C = gamma factor at either 1 or 30 cm
Radioisotope
Cr-51
1-125
Na-22
Gamma Factor (C) for
‘Extremity’ Dose Rates (1 cm)
8 10-4
5.9 10-3
7 10-2
Gamma Factor (C) for ‘Whole
Body’ Dose Rates (30 cm)
8 10-7
6.5 10-6
7 10-5
b) Estimation of Internal Doses
Internal doses (also known as the ‘Committed Effective Doses’) can be estimated using
‘dose coefficients’ which give the dose per unit intake (Sv/Bq) for different radioisotopes
and give a useful indication of the radiotoxicity of a radioisotope Dose coefficients vary
depending on a number of factors including the radioisotope, the labelled substance and
route of entry into the body. For the purpose of this assessment the most restrictive
effective dose coefficients for the common isotopes are given in the table below.
Internal Doses Per Unit Uptake
 Radioisotope
H-3 Water
H-3 Organically
Ingestion
Dose
Intake for 1
coefficient
mSv dose
Ingestion
(MBq)
Sv/Bq*
1.8 x 10-11
55.6
4.2 x 10-11
23.8
Inhalation
Dose
Intake for
coefficient
1 mSv
Inhalation
dose
Sv/Bq*
(MBq)
1.8 x 10-11
55.6
4.1 x 10-11
24.4
5.8 x 10-10
2.4 x 10-9
2.4 x 10-10
1.9 x 10-10
7.6 x 10-10
1.5 x 10-8
5.8 x 10-10
2.9 x 10-9
1.3 x 10-9
1.1 x 10-9
2.7 x 10-9
7.3 x 10-9
bound tritium
C-14
P-32
P-33
S-35
Ca-45
I-125
1.7
0.42
4.2
5.2
1.3
0.067
1.7
0.34
0.77
0.91
0.37
0.14
*Council Directive 92/29/Euratom, Tables C.1 and C.2
Example of Internal Dose Calculation
Consider internal dose from work activity involving P-32:
 Assume 5% of total activity 10 MBq (i.e. 0.5 MBq) is ingested because of poor
handling practices
 Since P-32 gives an ingestion dose of 2.4 mSv / MBq, 0.5 MBq would give a dose of
1.2 mSv
Absorption
 Some organic compounds may be absorbed through surgical gloves
 Some tritium compounds and C-14 labelled halogenated acids can be easily
absorbed through skin
Inhalation
 Consider the possibility of your work activity generating radioactive carbon dioxide;
this must be contained to avoid inhalation.
 Radiolysis of sulphur-35 labelled amino acids may lead to the production of labelled
volatiles such as sulphur dioxide, hydrogen sulphide and acidic gases. Open
sulphur-35 vials in a fume cupboard to avoid inhalation of radioactive volatiles.


Freezing or acidification of solutions containing iodide ions can lead to the formation
of volatile iodine.
Active aerosols can be produced by opening a vial of high activity radioactive iodineopen vials of iodine-125 in a fume cupboard to avoid inhalation of volatile material
and exposure to aerosols.
2. DESIGNATION OF LABORATORY FACILITIES
Laboratories used for open source radiation activities are typically designated either a
‘Supervised’ or ‘Controlled’ area. Designation of the laboratory shall be determined
after consultation with the departmental Radiation Protection Supervisor with assistance
from the University's Radiation Protection Advisor where necessary.
Designation of areas is helpful to define areas where radiation work with unsealed
sources is being used, even if the conditions are insufficient to consider a supervised or
controlled area.
Supervised Areas
An area is designated a ‘Supervised’ area where:


annual dose to persons is likely to exceed 1 mSv (whole body) or 50 mSv (skin and
extremities)
where conditions need to be kept under review to determine whether it should be
designated as a controlled area
In practice, ‘Supervised’ areas are normally appropriate, and designated for laboratories
handling modest amounts of unsealed / open radioactive materials. Working procedures
for these radiation activities are likely to be similar to those required for good laboratory
practice; these are not regarded as a specified system of work and the designation of a
controlled area should not be necessary.
Areas are often designated as Supervised areas on the basis of surface contamination
reflecting the need for periodic contamination monitoring. Access restrictions might be
applied even though the area is not designated a controlled area.
Controlled Areas
An area is typically designated a ‘Controlled’ area where:



annual dose to persons is likely to exceed 6 mSv (whole body) or 150 mSv (skin and
extremities) (persons working in such an area would have to be designated as
‘Classified persons or work under a written system of work’)
the dose rate averaged over a working day exceeds 7.5 µSv h -1
if only the hands are exposed, the dose rate averaged over a working day exceeds
75 µSv h-1


there is a significant risk of spreading contamination outside the area
persons entering the area are required to follow ‘special procedures’ which are
designed to restrict exposure or limit the probability and magnitude of a radiation
accident.
Part Controlled
Part of a laboratory such as the interior of a fume cupboard may be designated a
controlled area, because of dose rates, or the potential for contamination, or both. A
controlled area would be designated where measures are needed to control exposure to
airborne contamination. For example, a fume cupboard could be designated as a
‘Controlled’ area within a ‘Supervised’ room if this was required to control exposure to
airborne 125Iodine.
Table 1: Properties of Radioisotopes
Radioisotope
& Risk Category
High
Medium
Low
Type of Radiation &
principle emission(s)
(MeV)
Travel Distance in
Air (cm)
Half Life
Suitable Contamination
Monitor
Mini Monitor E, EL,
EP15
Mini Monitor EL, EP15
Calcium-45
Beta (0.26)
52
165 days
Carbon-14
Beta (0.16)
24
5730 years
Chlorine-36
Beta (0.71)
200
3.0 105 years
Iodine-125
Gamma (0.04)
Electron Capture
(X-rays)
Several metres
60 days
Mini Monitor E, EL,
EP15
Mini Monitor 44A
Manganese-54
Gamma (0.83)
Several metres
303 days
Mini Monitor 44A
Phosphorus-32
Beta (1.71)
720
14.3 days
Phosphorus-33
Beta (0.25)
46
25 days
Sodium-22
Beta (0.54)
Gamma (1.28)
140
2.6 years
Mini Monitor E, EL,
EP15
Mini Monitor E, EL,
EP15
Mini Monitor EL, EP15,
44A
HVL Pb 0.02mm
HVL Pb 10mm
Sulphur-35
Beta (0.17)
30
87.4 days
Mini Monitor EL, EP15
Tritium (H-3)
Beta (0.02)
0.6
12.3 years
Swabs with
scintillation counting
HVL – Half Value Layer – the thickness of shielding material required to reduce the original intensity by one -half.
Table 2: External Exposures – Contamination Skin dose
mSv h-1 for 1 kBq
Radioisotope
& Risk Category
High
Medium
Low
uniform deposit of
1 kBq /cm2 on the skin
Carbon 14
0.32
Calcium 45
0.84
Iodine 125
2.1 10-2
Sodium 22
1.7
Sulphur 35
0.35
Phosphorus 32
1.9
Phosphorus 33
0.86
Tritium (H-3)
None
Reference: Delacroix, Leblanc, Hickman- ‘Radiation Protection Dosimetry’, Volume 76 Nos. 1-2, 1998