.
RADIATION SAFETY UNIT
DEPARTMENT OF COMPLIANCE AND RISK
GENERIC PRIOR RISK ASSESSMENT FOR UNSEALED P-32
Figure 1
RHS - workstation set up for P-32 work, LHS - all-round enclosure
recommended for procedures involving activities >250 µCi (9.25 MBq)
THIS ‘PRIOR RISK ASSESSMENT’ COVERS
The use of P-32 for applications including: in vitro labelling of nucleic acids and proteins, sub
cellular localization of biological molecules, receptor second messenger assays, radio-ligand
binding techniques, ion channel assays, enzyme assays, general labelling, metabolic or probe
studies.
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 phosphorous-32 (32P)
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.
THE SOURCE OF IONISNG RADIATION
Phosphorous-32 emits high energy beta particles (1.7 MeV) capable of penetrating the stratum
corneum (dead outer layer of skin) and irradiating the epidermis.
Ingested phosphorous is readily metabolised and used by the body in the synthesis of nucleic
acid and skeletal material (bone is a ‘critical / target organ’). This means that incorporated
phosphorous-32 may ionise molecules thereby impairing functionality, and / or cause deletions in
DNA / RNA through ionisation and in vivo decay (to sulphur).
Inhaled phosphorous will enter the bloodstream via the alveoli.
The retention time of phosphorous in the body (biological half-life) is 257 days. Given that the
physical half-life is 14 days, this means that risks are enhanced as ingested or inhaled P-32 will
decay almost completely inside the body.
The risk for expectant mothers is enhanced high because the foetus scavenges phosphorous
from the mother during gestation.
ESTIMATED DOSE RATES / EXPOSURES (WORSE CASE)
External irradiation: worse case dose rates from 1 mCi (37 MBq) 32P
In the absence of radiation shielding, dose exposure estimates for the body are 4 mSv h-1 and
900 mSv h-1 to the fingers whilst pipetting (Delacroix, 2002).
Blots (northern and Southern) and probe hybridisation, for example, usual require 1 mCi of
activity per assay.
External irradiation: typical dose rates from 10 µCi (0.37 MBq) 32P
Again in the absence of protective measures, dose rates to which the body will be exposed
whilst handling lower activities are in the order of 50 µSv h-1.
Generic risk assessment for practices utilising phosphorous-32 (32P)
Internal irradiation: the ingestion or inhalation of 10 µCi (0.37 MBq) 32P
The ingestion or inhalation of 10 µCi of activity will result in an internal effective dose of 1 mSv.
Notes:
(i)
Radiation dose in context
The average annual ‘background’ dose received by the people in the UK is 2 mSv y-1 (within an
approximate range of 1-10 mSv y-1), which means that 2 mSv spread out over one year is safe.
(ii)
Occupational dose constraint
It is reasonable to ensure that workers are not exposed to external (whole body) dose rates in
excess of 0.5 µSv h-1, which means that a worker will not receive an annual occupational dose
(due to external irradiation) greater than 50% of the annual background dose.
ESTIMATED ROUTINE EXPOSURES
External irradiation
1 cm Perspex® shielding in the form of body shields, pipette guards, storage boxes, Eppendorf
cells are used as standard routine equipment.
Body exposure: nil.
Hands / finger exposure: nil (although occasional one-off exposures above limits of detection are
expected in a small percentage of workers).
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.
Generic risk assessment for practices utilising phosphorous-32 (32P)
EVIDENCE OF EXPOSURES BASED ON PREVIOUS PERSONAL DOSIMETRY AND AREA
MONITORING
(i)
Dosimetry
The radiation dosimetry ‘historical record’ indicates that existing practices and control measures
are effective. With the exception of a small number of ‘near miss’ incidents, dosimetry returns
show exposures at or below the limit of detection
The greatest risk is to the fingers when manipulating activity, therefore all workers wear a finger
stall dosemeter (usually on the index finger) on the right or left hand (whichever hand is closest
to the manipulation), with the dosemeter ‘chip’ on the underside of the forefinger.
(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.
CONTROL MEASURES
External irradiation: control measures
Activity
Radiation work is only carried out at suitably equipped workstations such as shown in the image
at the top of this document.
Perspex body shields are erected at the front edge of workstations, ‘hot’ materials held in
Perspex boxes when not in use, waste pipette tips dropped into bench top Perspex bins (or
similar) and pipette shields used (where practicable).
Where higher levels of activity are dispensed it is strongly recommended that beta cabs (see
image), fume cupboards or similar shielded areas are used.
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.
Generic risk assessment for practices utilising phosphorous-32 (32P)
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).
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.
Generic risk assessment for practices utilising phosphorous-32 (32P)
DESIGNATED AREAS
General
Not following good practice or using appropriate shielding may result in significant radiation
exposures, i.e. whole-body access to dose rates in excess of 0.5 µSv h-1 and exposures in
excess of 1 mSv y-1.
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.
Controlled areas
Reg 16(1) states that controlled areas must be designated when ‘special procedures’ are
necessary because effective (whole body) doses are likely to exceed 6 mSv y-1 or where the
time averaged dose rate over 8 hours is >75 µSv h-1. Special procedures are not necessary for
work undertaken on University premises. Work in fume cupboards and shielded areas etc. are
only regarded as ‘general procedures’ (GN paragraph 258 & 259, GN reference below).
Supervise areas
The University has designated supervised areas in order to keep working conditions under
review, ensure workers follow procedures are followed (local rules) and prevent contamination
from being spread. This assessment notes that the whole of all designated supervised areas are
subject to legal requirements (GN paragraph 271).
All high level work involving activities of phosphorous-32 is carried out in Supervised Areas.
PLANNED SYSTEMS OF WORK
As designated areas have been created (Supervised Areas), local rules and contingency plans
have been prepared to direct the safe uses of P-32.
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
[email protected]:
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 phosphorous-32 (32P)
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.
Reference
Health and Safety Commission. Work with ionising radiation: Ionising Radiations Regulations 1999,
Approved Code of Practice and Guidance. L121. 2000. www.hse.gov.uk/pubns/books/l121.htm.
Generic risk assessment for practices utilising phosphorous-32 (32P)
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