OC 130/11 - Enforcement management model (EMM): application to ionising radiations

Review Date:

27/07/2015

Open Government Status:

Fully Open

Version No & Date:

2: 06/06/2008

Author Unit/Section:

Corporate Specialist Division 4

Target Audience:

All HSE Inspectors

Introduction

1 Exposures to ionising radiation have two classes of health effect associated with them, Stochastic Effects and Deterministic Effects.   Version 2 contains some minor changes to update terminology and responsibilities.

2 Any whole body exposure to ionising radiations is assumed to result in an increase in the risk of an individual suffering from a radiation induced disease in direct proportion to the dose (these are referred to as Stochastic effects and the dose response relationship is known as the linear no threshold model). When considering stochastic effects the primary concern is the induction of fatal cancers which are considered to be a "serious health effect" and equivalent to serious personal injury under the terms of the EMM. Any whole body radiation dose therefore increases the chance that an individual might suffer from a radiation induced fatal cancer and the greater the dose the greater the risk of occurrence.

3 In addition to stochastic effects, exposures to individual organs may result in health effects which only occur after a threshold dose has been exceeded and are called deterministic effects. The threshold dose above which an effect will occur is thought to vary considerably between individuals but there are established levels for typical population members. Deterministic effects range from erythema (reversible skin reddening) to death from "radiation poisoning".

4 The Ionising Radiations Regulations 1999 (IRR99) require that stochastic effects of radiation doses are restricted so far as is reasonably practicable and deterministic effects prevented by compliance with dose limits. The IRR99 and associated Approved Code of Practice & Guidance (L121) form the defined minimum standard for health and safety risk for exposure to ionising radiations. Radiation dose limits in IRR99 take the form of whole body dose limits, single organ dose limits and a limit on the dose to the abdomen of any woman of reproductive capacity.

5 Compliance issues associated with control of ionising radiations which do not directly result in control of risk are dealt with in the usual way using table 5.2 of the EMM. The application of the EMM to Stochastic and Deterministic effects of radiation exposure is described in more detail below.

Stochastic Effects

6 The overarching requirement of IRR99 to restrict exposures so far as is reasonably practicable (SFARP) results in a level of exposure which is as low as reasonably practicable (ALARP) and is the benchmark in terms of the EMM. Any increased actual or potential dose above the ALARP level could actually or potentially increase the likelihood of a serious health effect (radiation induced disease such as fatal cancer).

7 The extent to which the ALARP level either has or could have been exceeded should form the basis of enforcement decisions.

8 Due to the difficulty in assessing the appropriate ALARP level for an incident across the range of situations and sectors likely to be encountered by HSE Inspectors a Radiation Specialist Inspector (HSE Radiation Specialist Team) or Health Physics Assessor (ND) should be consulted in all cases where there is potential for enforcement action to be considered.

Likelihood of harm for stochastic effects

9 The EMM uses categories of likelihood of harm to inform the decision making process which is relatively simple and straightforward to apply in cases of actual or potential physical injury. In the case of ionising radiation, the ALARP consideration requires a slightly different approach based upon the excessive exposure above the ALARP level. In addition the use of the descriptors "nil" and "probable" present great difficulties when used with the linear no threshold model of radiation dose and effect . The following descriptors are therefore used in respect of stochastic effects for "likelihood of harm" and are reflected in Table 1, below.

• Exposures or potential exposures at or below the determined ALARP Level the likelihood should be regarded as Negligible ,
• Exposures or potential exposures just greater than the determined ALARP level, the likelihood should be regarded as Remote
• Exposures or potential exposures much greater than the determined ALARP level the likelihood should be regarded as Possible.
• Exposures or potential exposures very much greater than the determined ALARP level the likelihood should be regarded as Significant.

Consequence when considering stochastic effects

10 For cases where stochastic effects are being considered then the consequence of exposure should be regarded as a potentially "Serious Health Effect"^[1] this being equivalent to "Serious Personal Injury" under the terms of the EMM. This relationship has been established inOC130/5. Although there are many stochastic effects the dominant consideration for adult workers is fatal cancer induction.

11 Please note that Operational Circular (OC130/5, Appendix 1) entitled "EMM General guidance on application to health risks" already defines the following as Serious Health Effects; Inflammation, ulceration or malignant disease of the skin due to ionising radiation, cataract due to electromagnetic radiation, malignant disease of the bones due to ionising radiation and blood dyscrasia due to ionising radiation. No radiation induced disease is included inOC130/5Appendix 2 Significant Health Effects.

Benchmark

12 The benchmark reflects the minimum legal standard the duty holder should meet. To allow for sufficient flexibility over the wide range of practices involving the use of ionising radiation, the benchmark for stochastic effects should be assumed to be equivalent to the ALARP level.

13 In order to assess the degree to which a practice had exceeded the requirements of ALARP and apply the risk matrix (Table 1), the Inspector/Assessor should at least consider (not an exhaustive list);

• The expected ALARP dose for the practice,
• The degree to which the expected ALARP dose has or may have been exceeded,
• The degree of reasonable practicability expected,
• Adequacy & evidence of planning,
• The dose constraint used in planning (if relevant), and
• Any unforeseen factors.

NB Both actual and potential doses should be considered.

14 When assessing the extent to which the actual or potential dose exceeds ALARP, consideration should be given to the magnitude of the benchmark. Examples of doses greater than the ALARP level which might be considered to lead to negligible, remote, possible or significant likelihood's are given in Table 1, below.

15 Duty holder factors should be taken into account; In cases where there are multiple failings (such as described below in the Medical Sector example, paragraph 1.8.3 of Version 3.0 of the EMM) then enforcement action should be considered more likely (for the same degree of ALARP failure) than in a case of a single failure of an otherwise compliant employer.

16 Using the principle of ALARP in the benchmarking for each case will avoid the occurrence of edge effects ie no enforcement action at a fraction below a dose limit and full enforcement (Notices and Prosecution) at a dose fractionally greater than a dose limit.

Risk matrix for stochastic effects

Table 1, Risk Matrix for Stochastic Effects

Gap analysis for stochastic effects

17 The risk gap is determined by comparing the actual risk (assessed by inspection or investigation) "where the duty holder is" and the Benchmark "where the duty holder should be".

18 For stochastic effects we always use the serious health effect consequence in the EMM risk gap table. Then having decided the benchmark ALARP dose level with the help of radiation specialists, use table 1 to decide the appropriate EMM likelihood descriptor for doses in excess of ALARP and then use this descriptor in the EMM risk gap tables in the usual way. EMM Tables 2.1 and 2.2 have been amended to reflect this approach and are reproduced in appendix C.

Initial enforcement expectation

19 The initial enforcement expectation relates to enforcement after any immediate risks have been dealt with. Where immediate risks are identified at an inspection then they should be addressed in the normal way, for example by issuing a Prohibition Notice.

20 The Risk Gap which has been determined by reference to the amended EMM Table 2.1 or 2.2 may then be used with the appropriate standard in the EMM Initial Enforcement Expectation table 5.1 (reproduced in Appendix C).

Whole body dose limits

21 Whole body dose limits represent a "special" consideration of stochastic effects. Situations may occur in which a dose limit may be exceeded when the ALARP level is a substantial part of a dose limit. If the ALARP requirement only was to be considered in the EMM then this would not reflect the regulatory status and purpose of the Whole Body Dose Limits. An additional table has been included in Appendix C which relates to whole body dose limits and links them with the requirement to restrict doses SFAIRP.

Deterministic Effects

22 Since deterministic effects only occur above threshold values and the dose limits for single organs in IRR99 have been set at much lower doses than accepted threshold doses application of the EMM is similar to that for other health risks involving significant or serious personal injury.

Likelihood of harm for deterministic effects

23 The normal EMM descriptors for likelihood of harm may be used

• Exposures or potential exposures at or below the single organ dose limit the likelihood should be regarded as Negligible,
• Exposures or potential exposures just greater than the single organ dose limit, the likelihood should be regarded as Remote.
• Exposures or potential exposures greater than the accepted threshold the likelihood should be regarded as Possible .
• Exposures or potential exposures much greater than the accepted threshold the likelihood should be regarded as Probable .

Consequence when considering deterministic effects

26 It might be considered that ocular opacities which have little detrimental effect on vision, transient erythema or temporary depilation could be regarded as significant health effects.

Benchmark for deterministic effects

27 The benchmark reflects the minimum legal standard the duty holder should meet. The benchmark for deterministic effects is nil/negligible which is achieved by compliance with the dose limits in the defined standard IRR99.

Table 2, Risk matrix for deterministic effects and dose limits

Gap analysis for deterministic effects

28 The risk gap is determined in the usual way by comparing the actual risk (assessed by inspection or investigation) "where the duty holder is" and the Benchmark "where the duty holder should be" using the EMM risk gap table 2.1 table for deterministic effects provided in Appendix C.

29 The descriptors used in the EMM for the risk gap are Extreme, Substantial, Moderate & Nominal. ie If the assessed risk at inspection is a Significant risk of a Serious Health Effect and the Benchmark is negligible then the risk gap is Extreme (using the version of the EMM risk gap table 2.1 amended for deterministic effects provided in appendix C).

Initial enforcement expectation

30 The initial enforcement expectation relates to enforcement after any immediate risks have been dealt with. Where immediate risks are identified at an inspection then they should be addressed in the normal way, for example by issuing a Prohibition Notice.

31 The Risk Gap which has been determined by reference to the amended EMM Table 2.1 may then be used in the amended EMM Initial Enforcement Expectation table 5.1 (Appendix C).

Relevant standards

32 For ionising radiation, standards occur in legislation, national standards, research reports and guidance.

Date Issued: 27/07/2005

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Appendix A

Serious Health Effects

Stochastic effects

• Malignant Disease
• Hereditary Effects
• Childhood cancer resulting from Foetal exposure

Deterministic effects

• Radiation Sickness
• Cataract formation
• Ulceration
• Necrosis
• Sterility
• Foetal damage
• Malformation of organ(s)
  IQ reduction
  Retardation
• Radiation erythema/dermatitis

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Appendix B

Significant Health Effect

Deterministic effects

• Ocular Opacity
• Depilation
• Transient Erythema

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Appendix C

EMM Tables

EMM table 2.1 amended for stochastic effects

EMM table 2.2 amended for stochastic effects

EMM Table 2.1/2.2 amended for whole body dose limits

EMM Table 2.1/2.2 amended for deterministic effects and dose limits

EMM Table 5.1 Revised

EMM Table 5.2

View Appendix C Printable Version

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Appendix D

Example 1 - Stochastic Effects, Nuclear Sector (Hypothetical case)

The Actual Risk: Whilst monitoring during defueling, an operator opens a cover at an unplanned point in the procedure resulting in a small but measurable dose (approximately 10μSv) from a release of reactor gas.

Where the Duty Holder was: The likelihood of an exposure was probable , the low actual dose only occurred due to an error in procedure.

Consequence: Actual dose of 10μSv and a potential dose in the region of 10mSv (resulting in the risk of stochastic effects of ionising radiation which are defined as Serious Health Effects for the purpose of the EMM).

Benchmark: The ALARP level of this particular procedure was assessed by the Health Physics Assessor to be a nil release of reactor gas resulting in a dose of 1-2μSv for the procedure. This would result in a Negligible likelihood of serious health effect. This is where the duty holder should have been.

Risk Gap: The potential dose to a member of staff was very much greater than the ALARP level , on the basis described above for the purposes of the EMM this would result in the likelihood of a serious health effect being considered significant for a procedure with a Negligible benchmark had reasonably practicable precautions been taken. Using EMM Table 2.1 amended for stochastic effects (Appendix C, above) results in an " Extreme " risk gap for this incident.

Initial Enforcement Expectation: The initial enforcement expectation for an extreme risk gap derived from EMM table 5.1(Appendix C, above) is an improvement notice followed by consideration of prosecution .

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Example 2 - Stochastic Effects, Industrial Sector (Historical case)

The Actual Risk: A transport company involved in the movement of radioactive materials by air was inspected and found to have general non compliance with IRR99 in that doses to employees were not ALARP due to the company's failure to take RPA advice, provide sufficient shielding or remote handling of material in temporary storage or transit. Employees subject to a dose limit of 20mSv per annum received doses of approximately 15mSv per annum.

Where the duty holder was: The likelihood of persons being exposed was probable due to the lack of engineering and administrative controls on exposure to the radiation dose rates from packages.

Consequence: Whole body exposure to gamma rays generated at a range of energies with a dose of 15mSv per year (resulting in the risk of stochastic effects of ionising radiation which are defined as Serious Health Effects for the purpose of the EMM).

Benchmark: The Radiation Specialist Inspector determined that the doses to the employees as a result of working at the company with sufficient shielding, remote handling and suitable procedures (Local Rules) would be between zero and 1mSv per year. Regulation 8 requires the dose to employees or other persons to be restricted as far as is reasonably practicable which in this case would result in a zero or negligible dose and therefore a Negligible likelihood of Serious Health Effect.

Risk Gap: The potential dose to a member of staff was very much greater than the ALARP level , on the basis described above for the purposes of the EMM this would result in the likelihood of a serious health effect being considered probable for a procedure with a Negligible benchmark. Then using EMM Table 2.1 (reproduced in Appendix C, above) gives an " Extreme " risk gap for this incident.

Initial Enforcement Expectation: The initial enforcement expectation for an extreme risk gap derived from EMM table 5.1(Appendix C, above) is an improvement notice followed by consideration of prosecution . In this case an improvement notice was issued.

Further Action: The firm was prosecuted by HSE for failing to restrict doses to ALARP which resulted in a guilty verdict, fine and costs awarded to HSE.

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Example 3 - Stochastic Effects, Health Sector (Hypothetical case)

The Actual Risk: A private professional radiological practice radiographing patients for Medico-Legal purposes was inspected following a complaint. The inspection found that there was no awareness of IRR99 and what little compliance existed was accidental. No assessment of radiation shielding or doses around the X-ray room had been carried out and no shielding was provided in the entrance door. No room warning lights were provided to indicate that an exposure was taking place and there were no signs restricting access to the room during exposures. The potential dose to a person standing by the unshielded door could range from 1-10mSv per year.

Likelihood: The likelihood of a person being exposed at the entrance of the room was probable since it provided the only access to the room, was in the main corridor of the practice and it was impossible to detect whether an exposure was in progress without entering the room.

Consequence: Potential whole body exposure to X-rays generated at 50-150 kVp with a dose of up to 5mSv per exposure (resulting in the risk of stochastic effects of ionising radiation which are defined as Serious Health Effects for the purpose of the EMM).

Benchmark: The Radiation Specialist Inspector considered that the dose to a person in an undesignated area outside the X-ray room should be designed to be less than 0.3 mSv per year (planning dose constraint in established standard). In addition, Regulation 8 requires the dose to employees or other persons to be restricted as far as is reasonably practicable which in this case would result in a negligible dose and therefore a negligible likelihood of Serious Health Effect.

Risk Gap: The potential dose to a member of staff was very much greater than the ALARP level , on the basis described above for the purposes of the EMM this would result in the likelihood of a serious health effect being considered significant for a procedure with a negligible benchmark. Then using EMM Table 2.1 amended for stochastic effects (Appendix C, above) gives an " Extreme " risk gap for this incident.

Initial Enforcement Expectation: The initial enforcement expectation for an extreme risk gap derived from EMM table 5.1(reproduced in Appendix C, above) is an improvement notice followed by consideration of prosecution . In this case an improvement notice was issued and prosecution considered.

Further Action: A prosecution file was compiled.

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Example 4 - Deterministic Effects, Industrial Sector (Hypothetical case)

The Actual Risk: An industrial radiographer repeatedly held in place a collimator on pipework he was radiographing and received an estimated equivalent dose to one hand in excess of 600mSv. The radiographer stated that he only carried out the testing in this fashion due to pressure from the client company to complete the job ahead of schedule.

Where the duty holder was: The duty holder failed to restrict the dose of an employee who exceeded the relevant dose limit.

Consequence: Actual equivalent dose to one of the employees hands was estimated to be in excess of 600mSv which is below the threshold for deterministic effects but greater than the annual dose limit for exposure of the hand in IRR99 resulting a Remote risk of deterministic effects of ionising radiation which are defined as Serious Health Effects for the purpose of the EMM).

Benchmark: The Radiation Specialist Inspector considered that the dose to the hands of an industrial radiographer carrying out the type of work in which this employee was involved should have been considerably less than the relevant dose limit. This would result in a nil/negligible likelihood of Serious Health Effect .

Risk Gap: The actual dose to an employee was in excess of the relevant dose limit , on the basis described above for the purposes of the EMM this would result in the likelihood of a serious health effect being considered remote for a procedure with a nil/negligible benchmark. Then using EMM Table 2.1 amended for deterministic effects (Appendix C, above) gives an " Substantial " risk gap for this incident.

Initial Enforcement Expectation: The initial enforcement expectation for a substantial risk gap for a defined standard derived from EMM table 5.1(Appendix C, above) is an improvement notice .

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Notes

1.OC130/5 Para 5. Back