skills/wsh-risk-assessment/references/risk-scoring.md

# Risk Evaluation

## Definition

Risk evaluation is the process of determining the significance of a risk by assessing the relationship between the potential consequences of a hazard and the likelihood that those consequences may occur.

Risk evaluation should:

* Consider existing control measures already in place.
* Be based on reasonably foreseeable scenarios rather than worst-case assumptions alone.
* Take into account the nature, duration, and frequency of exposure.
* Consider the number and vulnerability of persons who may be affected.
* Evaluate both immediate and long-term health effects where applicable.
* Consider potential secondary consequences such as fire, explosion, environmental contamination, or operational disruption.

The objective is to determine whether the risk is acceptable, requires additional controls, or should be prioritised for immediate risk reduction.

### Additional Considerations for Chemical Hazards

When evaluating chemical risks, consideration should be given to:

* Intrinsic toxicity and health hazards of the substance
* Quantity and volume handled
* Concentration and dilution
* Physical form (e.g., gas, vapour, liquid, powder, aerosol)
* Exposure routes (inhalation, skin contact, eye contact, ingestion, injection)
* Frequency and duration of use
* Potential for accidental release or loss of containment
* Existing engineering controls and containment measures
* Compatibility with other chemicals and potential reactions
* Flammability, explosivity, and reactivity characteristics
* Potential for escalation into fire, explosion, or environmental release
* Availability and effectiveness of emergency response measures

### Additional Considerations for Biological Hazards

When evaluating biological risks, consideration should be given to:

* Pathogenicity and disease-causing potential of the biological agent
* Route(s) of transmission (inhalation, ingestion, skin contact, mucous membrane exposure, sharps injury, vector-borne transmission)
* Infectious dose
* Environmental stability and survivability of the agent
* Potential for aerosol generation
* Availability of vaccines, prophylaxis, or effective treatment
* Susceptibility of exposed individuals
* Quantity and concentration of biological material handled
* Containment level and laboratory practices required
* Potential for environmental contamination or secondary transmission
* Waste handling and decontamination requirements
* Availability and effectiveness of emergency response measures

### Additional Considerations for Ionising Radiation Hazards

When evaluating ionising radiation risks, consideration should be given to:

* Type of radiation source (alpha, beta, gamma, X-ray, neutron)
* Activity or strength of the source
* Exposure dose and dose rate
* Duration and frequency of exposure
* Distance from the radiation source
* Shielding effectiveness
* Potential for internal exposure through inhalation, ingestion, absorption, or injection
* Potential contamination of personnel, equipment, or work areas
* Regulatory dose limits and monitoring requirements
* Access control and security of radioactive materials
* Emergency arrangements for spills, contamination, or overexposure incidents
* Availability and effectiveness of radiation protection measures

### Additional Considerations for Non-Ionising Radiation Hazards

When evaluating non-ionising radiation risks, consideration should be given to:

* Type of radiation source (laser, ultraviolet, visible light, infrared, radiofrequency, microwave, electromagnetic fields)
* Power output or intensity of the source
* Wavelength or frequency characteristics
* Exposure duration and frequency
* Potential for direct or reflected beam exposure
* Potential effects on eyes, skin, or other tissues
* Beam enclosure, shielding, and interlock systems
* Controlled access to hazardous areas
* Alignment, maintenance, and non-routine activities
* Compatibility with implanted medical devices where relevant
* Warning systems, signage, and administrative controls
* Availability and effectiveness of emergency response measures

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# Severity Assessment

Severity reflects the reasonably foreseeable consequence should the hazard result in an incident.

| Level | Severity     | Description                                                                          |
| ----- | ------------ | ------------------------------------------------------------------------------------ |
| 5     | Catastrophic | Fatality, multiple fatalities, permanent total disability                            |
| 4     | Major        | Amputation, major fracture, permanent injury, serious occupational disease           |
| 3     | Moderate     | Medical treatment injury, burns, sprains, minor fractures, musculoskeletal disorders |
| 2     | Minor        | First-aid injury, minor cuts, bruises, temporary discomfort                          |
| 1     | Negligible   | No injury or insignificant injury                                                    |

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## Severity Calibration Examples

### Severity 5 – Catastrophic

Examples:

* Laboratory explosion causing fatality
* Electrocution
* Fall from height resulting in death
* Acute high-dose ionising radiation exposure resulting in fatal radiation injury
* Uncontrolled high-power laser beam causing fire leading to fatal injuries
* Toxic gas release causing multiple fatalities
* Exposure to highly pathogenic biological agents resulting in fatal infection
* Major release of hazardous chemicals causing multiple fatalities

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### Severity 4 – Major

Examples:

* Permanent eye injury from laser exposure
* Amputation from machinery
* Major chemical burns
* Serious occupational illness
* Significant ionising radiation exposure resulting in long-term health effects
* Exposure to carcinogenic chemicals resulting in serious occupational disease
* Laboratory-acquired infection resulting in severe illness or permanent impairment
* Irreversible tissue damage from corrosive chemical exposure

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### Severity 3 – Moderate

Examples:

* Chemical splash requiring medical treatment
* Heat exhaustion
* Laceration requiring stitches
* Musculoskeletal injury requiring medical attention
* Localised radiation burn requiring medical treatment
* Laser-induced skin burn requiring medical treatment
* Exposure to infectious biological materials resulting in illness requiring medical treatment
* Acute chemical exposure causing respiratory irritation requiring medical evaluation

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### Severity 2 – Minor

Examples:

* Minor cut
* Bruise
* Mild skin irritation
* Temporary discomfort
* Mild allergic reaction from biological materials
* Minor skin irritation from chemical contact
* Temporary eye irritation from non-ionising radiation exposure within recoverable limits

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### Severity 1 – Negligible

Examples:

* No injury
* Minimal discomfort
* Transient exposure with no adverse health effects
* Minor reversible discomfort not requiring treatment

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# Likelihood Assessment

Likelihood reflects the probability that the hazard may result in injury or ill-health.

| Level | Likelihood     | Description                      |
| ----- | -------------- | -------------------------------- |
| 5     | Almost Certain | Continual or repeated occurrence |
| 4     | Frequent       | Common occurrence                |
| 3     | Occasional     | Possible or known to occur       |
| 2     | Remote         | Unlikely under normal conditions |
| 1     | Rare           | Not expected but still possible  |

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# Likelihood Calibration Examples

Likelihood ratings should be assigned based on a combination of factors, including frequency of exposure, duration of exposure, number of persons exposed, effectiveness of existing controls, historical incident data, industry experience, and the potential for human error. The examples below provide guidance for consistent application of likelihood ratings.

### Rare (1)

* The incident is not expected to occur under normal operating conditions.
* Exposure to the hazard is infrequent or highly controlled.
* No known incidents have occurred within the organisation, and industry occurrences are extremely uncommon.
* Multiple effective control measures are in place and routinely verified.

### Remote (2)

* The incident is unlikely to occur under normal conditions but remains possible.
* Exposure to the hazard occurs occasionally, with effective controls generally preventing incidents.
* Similar incidents have occurred infrequently within the industry or under abnormal circumstances.
* Existing controls are reliable and well maintained.

### Occasional (3)

* The incident could reasonably occur during the course of the activity.
* Exposure to the hazard occurs periodically or routinely.
* Similar incidents have occurred within the organisation, industry, or comparable activities.
* Existing controls reduce risk but may be dependent on human behaviour or procedural compliance.

### Frequent (4)

* The incident is likely to occur if current conditions persist.
* Exposure to the hazard is regular or prolonged.
* Similar incidents occur repeatedly within the activity, organisation, or industry.
* Existing controls may be insufficient, inconsistently applied, or vulnerable to failure.

### Almost Certain (5)

* The incident is expected to occur repeatedly or imminently without additional controls.
* Exposure to the hazard is continuous, widespread, or unavoidable.
* Historical evidence indicates repeated occurrences or a very high probability of occurrence.
* Existing controls are absent, ineffective, or unable to adequately manage the hazard.

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# Risk Prioritisation Number (RPN)

Risk Prioritisation Number is calculated using:

RPN = Severity × Likelihood

Example:

Severity = 4

Likelihood = 3

RPN = 12

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# Recommended 5 × 5 Risk Matrix

| Severity / Likelihood | 1 | 2  | 3  | 4  | 5  |
| --------------------- | - | -- | -- | -- | -- |
| 5 Catastrophic        | 5 | 10 | 15 | 20 | 25 |
| 4 Major               | 4 | 8  | 12 | 16 | 20 |
| 3 Moderate            | 3 | 6  | 9  | 12 | 15 |
| 2 Minor               | 2 | 4  | 6  | 8  | 10 |
| 1 Negligible          | 1 | 2  | 3  | 4  | 5  |

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