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RADIATION SAFETY UNIT
DEPARTMENT OF COMPLIANCE AND RISK
GENERIC PRIOR RISK ASSESSMENT FOR UNSEALED SOFT BETA EMITTERS, RIA
KITS AND CHROMIUM-51
Figure 1
Workstation set up for soft-beta work
THIS ‘PRIOR RISK ASSESSMENT’ COVERS
This prior risk assessment has been prepared to assess the hazards arising through the use of the
commonly used ‘life sciences / medical-related’ unsealed radioisotopes having beta particle
energies <0.3 MeV, for example 14C, 33P, 35S and also for low levels (<0.5 MBq) of 125I in radio
immune assay kits or 51Cr.
Author
Ian Haslam
Owner
Radiation Safety Unit
Version
1.0
This document is approved by the Head of Radiological Safety
Issue date
12/2014
Review date
11/2017
Generic risk assessment for practices utilising soft beta emitters, RIA and Cr-51
CAVEAT
This assessment will need a further statement appending should any of the radioisotopes or their
chemical forms be suspected as being volatile or thought to be likely to give rise to volatile states.
PERSONS AT RISK OF EXPOSURE
Laboratory workers
The persons most at risk of exposure are radiation workers and other laboratory occupants who
are at risk to exposure through:
the intake of radioactive contamination or uncontrolled releases (e.g. aerosols / vapours, dusts,
•
or spillages), and,
external exposure of the hands and / or body by unshielded radioactive materials.
•
Cleaners, service engineers, visitors
Cleaners, plumbers and other maintenance engineers are at risk because of the potential
contamination of laboratory fittings, furniture, equipment, light switches and door handles etc. Of
particular concern are waste liquids in sinks and the drainage system.
Radioisotope
energy; emission
physical half-life
biological half-life
critical organs
14
156 keV; β
5730 y
10 days
whole body & fat
C
Most 14C compounds are readily metabolised and excreted.
14
C in aqueous based solution is readily absorbed through the skin.
14
C labelled halogenated are readily absorbed through the skin and may give high radiation
doses.
There is the risk of volatility risk for 14CO2.
33
P
249 keV; β
25.3 days
257 days
whole body &
bone
Radio-phosphorous compounds are not readily excreted and substantially decay in the body.
35
S
167 keV; β
87 days
90-623 days
whole body &
testes
35
S is not readily metabolised and tends to decay in the body.
S-amino acids may be volatile and can be a particular contamination problem.
On account of the volatility and tendency to dissociate, it is recommended that 35S sources are
opened in fume cupboards.
35
45
Ca
45
Ca is not excreted and mostly decays internally.
257 keV; β
162.7 days
45 years
whole body &
bone
Generic risk assessment for practices utilising soft beta emitters, RIA and Cr-51
125
I
60 days
35.5 keV γ,
27 keV x-ray
120-138 days
thyroid gland
Low pH causes dissociation and volatilisation.
Iodine strongly targets the thyroid; volatile forms must be handled in a fume cupboard.
51
Cr
320 keV γ,
5 keV x-ray
27.7 days
616 days
whole body
Chromium is not strongly bound by biological tissue, although a substantial activity would decay
in the body, emitting a penetrating gamma component.
ESTIMATED DOSE RATES / EXPOSURES (WORSE CASE)
External irradiation: worse case dose rates from 1 mCi (37 MBq) soft beta’s
Soft-beta particles having energies <0.3 MeV have insufficient energy to penetrate the skin and
therefore do not present an external irradiation hazard. The low energy electrons are mitigated
by collision reactions in
•
the solution (self-absorption),
•
vessel / container walls,
•
air,
•
the stratum corneum (dead outer layer of skin).
External irradiation: typical dose rates from 1 mCi (37 MBq) 125I and 51Cr
Iodine-125
Whole body: 0.014 mSv h-1 (standing at bench)
Extremities: 0.13 mSv h-1 (holding Eppendorf)
Chromium-51
Whole body: 0.002 mSv h-1 (standing at bench)
Extremities: 0.003 mSv h-1 (holding Eppendorf)
Internal irradiation: the ingestion or inhalation of 1 mCi (37 MBq)
Radioisotope
Inhalation
Ingestion
Skin absorption
(mSv)
(mSv)
(mSv)
14
C
22
22
22
33
P
52
8.9
no sorption
35
S
48
28
no sorption
51
Cr
1.3
1.5
92
270
555
130
125
I
ESTIMATED ROUTINE EXPOSURES
External irradiation
Body exposure: nil.
Hands / finger exposure: nil.
Generic risk assessment for practices utilising soft beta emitters, RIA and Cr-51
Internal irradiation
No volatile forms, no dusts or aerosols, contamination control measures in place.
Effective dose: nil.
LIKELIHOOD OF CONTAMINATION ARISING AND BEING SPREAD
(i)
Airborne contamination
(ii)
Surface contamination arising
Nil.
Minor contamination events are likely during pipetting.
Near misses such as dropped source pots or tubes are possible, but rare.
Transfer of activity from gels to cling film or paper ‘supports’ during incubation or gel analysis is
possible.
(iii)
Surface contamination being spread
Very low. Drips trays and disposable covers and / or absorbent papers including Benchkote® are
used to contain spillages. Monitoring regimes are followed to monitor workstations before, during
and after use, and also to check fittings, furniture and other equipment.
EVIDENCE OF EXPOSURES BASED ON PREVIOUS PERSONAL DOSIMETRY AND AREA
MONITORING
(i)
Dosimetry
Radiation dosimetry is unnecessary on account of the fact that the particles will not penetrate the
skin (or in the case of radio iodine and 51Cr not deliver measurable doses).
(ii)
Area monitoring
The absence of persistent contamination or repeat contaminating events in annual radiation
monitoring surveys and local checks show that existing working practices are acceptable.
SUPPLIERS INFORMATION AND ADVICE
Radioactive sources
Information leaflets relating to safe use and storage are supplied with each isotope. The
information also includes practical notes on chemical and physical stability (including volatility),
and the recommended ‘use by’ date of the product.
Associated equipment
Supplier’s information and local training on the safe use of laboratory equipment such as
centrifuges, gel dryers and incubators is available, and mandatory regarding certain items of
equipment.
Generic risk assessment for practices utilising soft beta emitters, RIA and Cr-51
CONTROL MEASURES
External irradiation: control measures
Radiation work is only carried out at suitably equipped workstations such as shown in the image
at the top of this document.
Although the radioisotopes and activities covered by this assessment do not give rise to
measureable external irradiation doses it is good practice, and in any case a University
requirement, to use shielded containers wherever appropriate:
materials held in Perspex boxes when not in use, waste pipette tips dropped into bench top
Perspex bins (or similar).
Radioactive sources are at all times be held / stored in their proprietary source pots and never
removed for dispensing.
Long handled tongs and tweezers are available for use when required.
Techniques are be rehearsed until users are both confident and able to minimise handling times.
Internal irradiation: control measures
(i)
Personal behaviours
Personal behaviour is a root cause of many (inadvertent) contamination events.
Workers are aware that work should be planned and carried out methodically, and not when
feeling rushed, under pressure or unwell. In addition, as mentioned above, the rehearsal of
techniques helps familiarise the worker and can bring to light any limitations and handling
difficulties.
(ii)
Dispensing
Dispensing is carried out in a fume cupboards / beta-cab or similar or behind beta shields.
Workers are aware that aerosols can be generated when syringing activity out of septum-sealed
source pots.
(iii)
Contamination control
Work is carried out in drip trays that are fitted with suitable liners, and the drip trays must be
underlain with Benchkote® or a similar absorbent layer. The image at the top of this document
shows a well laid out workstation designed to control any potential contamination events.
(iv)
Storage in use and short term storage in fridges / freezers
Sources and materials are held in shielded Perspex boxes which are themselves held in
sealable plastic containers.
If radioactive materials are stored in fridges or freezers they are in leak-proof containers and not
crammed in.
Aerosols are rarely generated when opening source pots (septum type pots), however these do
not travel any distance, mostly being intercepted on the ‘hot’ side of body screens and on the
drip trays.
(v)
Personal protective equipment (PPE)
Laboratory coats, lab specs and gloves are always be worn when working in radiation facilities
(unsealed source areas). Such PPE is found to be suitable and sufficient.
(vi)
Monitoring
Work surfaces, clothing, equipment, pipettes, benches, sinks, taps, the floor, fridges, etc. are
monitored frequently (before, during and after work).
Generic risk assessment for practices utilising soft beta emitters, RIA and Cr-51
Workstations and clothing are monitored before the commencement of work, frequently during
work, and after work has been cleared away.
(vii)
Training
Prospective users are given a laboratory induction that includes local training on techniques and
radiation safety measures.
In addition to the ‘on the job’ training, users attend such courses and refresher instructions as
are required by the University. Typically, refresher training is provided every three years.
DESIGNATED SUPERVISED AREAS
Not following good practice or using appropriate shielding may result in internal radiation
exposures.
It is also imperative that work is carried out in a controlled manner and employing contamination
control measures to ensure that any contamination is contained.
Consequently, all work activities are carried out in Supervised Areas unless other arrangements
have been agreed with the Radiation Safety Unit.
PLANNED SYSTEMS OF WORK
As designated areas have been created (Supervised Areas), local rules and contingency plans
have been prepared.
Deviations from local rules and risk assessments are prepared as supplementary protocols.
Radioactive sources are supplied with safety instructions that identify all general and specific
hazards associated with a particular isotope and compound.
The following are essential reading, and copies can be obtained from
ian.haslam@manchester.ac.uk:
•
Amersham Biosciences. Safe and secure - a guide to working safely with radiolabelled
compounds. Publication 18-1137-88-AC.
•
Delacroix, D. et al. Radionuclide and radiation data protection handbook. Rad. Prot. Dos.
98 (1) 2002.
THE EXTENT OF UNRESTRICTED ACCESS TO SUPERVISED AREAS
Access to science research areas is controlled by building / area electronic identity pass cards.
Thereafter, access to Supervised Areas is managed by delineation, signs and rigorously
enforced administrative controls.
Radioactive sources, labelled materials and areas where there are instantaneous dose rates are
secured by lockable storage facilities (fridges, freezers, cabinets).
Benches are cleaned after use in order to prevent ‘removable’ contamination.
Generic risk assessment for practices utilising soft beta emitters, RIA and Cr-51
POSSIBLE ACCIDENT SCENARIOS, LIKELIHOOD AND SEVERITY
(i)
Spillages, near miss events, dropped sources
These have been covered throughout this assessment.
(ii)
Contained laboratory fire
A fire localised to and contained in the laboratory is and which would affect radiation work is
unlikely, and given the on-bench activities would be low.
A fire involving a storage fridge / freezer is unlikely, but the consequences regarding the spread
of contamination could be widespread (albeit locally contained) and the severity significant in
terms of collateral damage and the need for proper recovery.
THE CONSEQUENCES OF FAILURES OF CONTROL MEASURES (INCLUDING
MECHANICAL AND EQUIPMENT FAILURE)
(i)
(Human) failure to use safety equipment, shielding and follow local rules
All Supervised Areas are provided with safety equipment, shielding and contamination control
equipment appropriate to the nature of the work. Failure to use this would be a deliberate act of
deliberate personal negligence.
Accessible dose rates would be as described for worse case scenarios.
The likelihood of acts or failures being repeated would be low given the level of supervision and
mentoring by Radiation Protection Supervisors and co-workers.
Received doses would be of concern, but not harmful. Doses to pregnant workers would be of
serious concern.
(ii)
Failure of laboratory equipment (centrifuges etc.)
Unbalanced centrifuges can fail catastrophically and would release contamination. Not setting up
equipment properly or by unauthorised persons would be a deliberate act. Local systems for
training, authorisation, mentoring and supervision are in place.
(iii)
Failure of fume cupboards
Fume cupboards are inspected annually by insurance bodies as part of a planned process.
Failure and improper use would cause an alarm to sound. Workers receive local instruction and
proper use and actions to take in the event of failures.
Generic risk assessment for practices utilising soft beta emitters, RIA and Cr-51
GENERIC RISK ASSESSMENT: LOCAL DETAILS
This assessment is applicable to the following projects and locations(s)
Faculty
School / institute
Building
Research group and project
type
Location / room number(s)
Responsible person /
manager
Local approval
This assessment is approved for local adoption (usually by the lead PI and RPS, local conditions
may apply).
Approver
Role / position
Central approver
This assessment has been prepared by the Radiation Safety Unit and is approved for general use
by the Head of Radiological Safety.
Radiation Safety Unit
The University of Manchester
7th Floor, Williamson Building
Oxford Road
Manchester M13 9PL