Risk Rating Matrix: How to Assess and Prioritise Workplace Risks
Risk Rating Matrix: How to Assess and Prioritise Workplace Risks
A risk rating matrix is a fundamental tool for assessing and prioritising workplace hazards. This guide shows you how to use one effectively.
What Is a Risk Rating Matrix?
A risk rating matrix is a grid that helps you calculate risk levels by combining:
- Likelihood - How probable is the harm?
- Severity - How bad would the harm be?
The result gives you a risk rating that helps prioritise which hazards to address first.
The 5x5 Risk Matrix
The most common format uses a 5-point scale for both likelihood and severity:
Likelihood Scale
| Score | Rating | Description | |-------|--------|-------------| | 1 | Rare | May occur only in exceptional circumstances | | 2 | Unlikely | Could occur at some time | | 3 | Possible | Might occur at some time | | 4 | Likely | Will probably occur in most circumstances | | 5 | Almost Certain | Expected to occur in most circumstances |
Severity Scale
| Score | Rating | Description | |-------|--------|-------------| | 1 | Negligible | No injury or illness | | 2 | Minor | Minor injury, first aid only | | 3 | Moderate | 7-day injury, medical treatment | | 4 | Major | Serious injury, permanent disability | | 5 | Catastrophic | Death or multiple serious injuries |
Risk Calculation
Risk = Likelihood × Severity
This gives a score from 1 to 25:
| Score | Risk Level | Action Required | |-------|------------|-----------------| | 1-4 | Low | Monitor, no immediate action | | 5-9 | Medium | Action within reasonable timeframe | | 10-15 | High | Priority action required | | 16-25 | Extreme | Immediate action, stop work if needed |
Visual Risk Matrix
SEVERITY
1 2 3 4 5
┌────┬────┬────┬────┬────┐
1 │ 1 │ 2 │ 3 │ 4 │ 5 │
├────┼────┼────┼────┼────┤
2 │ 2 │ 4 │ 6 │ 8 │ 10 │
L ├────┼────┼────┼────┼────┤
I 3 │ 3 │ 6 │ 9 │ 12 │ 15 │
K ├────┼────┼────┼────┼────┤
E 4 │ 4 │ 8 │ 12 │ 16 │ 20 │
L ├────┼────┼────┼────┼────┤
I 5 │ 5 │ 10 │ 15 │ 20 │ 25 │
H └────┴────┴────┴────┴────┘
O
O
D
Legend:
1-4 = Low (Green)
5-9 = Medium (Yellow)
10-15 = High (Orange)
16-25 = Extreme (Red)
How to Use the Matrix
Step 1: Identify the Hazard
Be specific. Instead of "machinery," identify "unguarded rotating shaft on lathe."
Step 2: Assess Likelihood
Consider:
- How often is the person exposed?
- What is the duration of exposure?
- What is the probability of the hazardous event?
- Are control measures already in place?
Step 3: Assess Severity
Consider:
- What type of harm could occur?
- How many people could be affected?
- Is the harm temporary or permanent?
- What is the worst realistic outcome?
Step 4: Calculate Risk Score
Multiply likelihood by severity to get the risk rating.
Step 5: Determine Action Priority
Use the score to decide:
- Is the risk acceptable?
- What controls are needed?
- How urgent is the action?
Practical Examples
Example 1: Trailing Cable in Office
- Hazard: Network cable across walkway
- Likelihood: 3 (Possible - people walk there regularly)
- Severity: 2 (Minor - trip could cause bruising)
- Risk Score: 3 × 2 = 6 (Medium)
- Action: Cable cover or reroute cable within 1 week
Example 2: Working at Height on Roof
- Hazard: Falls from unprotected roof edge
- Likelihood: 4 (Likely - workers near edge daily)
- Severity: 5 (Catastrophic - fall could be fatal)
- Risk Score: 4 × 5 = 20 (Extreme)
- Action: Immediate edge protection, stop work until installed
Example 3: Chemical Storage
- Hazard: Flammable liquid stored near heat source
- Likelihood: 3 (Possible - ignition could occur)
- Severity: 4 (Major - fire could cause serious burns)
- Risk Score: 3 × 4 = 12 (High)
- Action: Relocate storage within 24 hours, install proper cabinet
Example 4: DSE Workstation
- Hazard: Poor posture from non-adjustable chair
- Likelihood: 4 (Likely - daily exposure)
- Severity: 2 (Minor - discomfort, possible strain)
- Risk Score: 4 × 2 = 8 (Medium)
- Action: Provide adjustable chair within 2 weeks
Before and After Controls
The matrix helps show the impact of control measures:
| Scenario | Before Controls | After Controls | |----------|----------------|----------------| | Trailing cable | L:3 × S:2 = 6 (Medium) | L:1 × S:2 = 2 (Low) | | Roof edge | L:4 × S:5 = 20 (Extreme) | L:1 × S:5 = 5 (Medium) | | Chemical storage | L:3 × S:4 = 12 (High) | L:1 × S:4 = 4 (Low) |
Common Mistakes
1. Underestimating Severity
People often rate severity lower because "it's never happened." Consider worst realistic outcomes.
2. Overestimating Likelihood Without Evidence
Score based on actual exposure and conditions, not fear.
3. Ignoring Cumulative Risk
Low risks that occur frequently can have high cumulative impact.
4. Not Reassessing After Controls
Always recalculate risk after implementing controls.
5. Using the Matrix Alone
The matrix is a tool, not a complete risk assessment. You still need to identify hazards and controls.
Alternative Scoring Systems
3x3 Matrix (Simpler)
| | Minor | Moderate | Major | |---|-------|----------|-------| | Likely | Medium | High | High | | Possible | Low | Medium | High | | Unlikely | Low | Low | Medium |
Numerical Scales
Some organisations use:
- 1-3 scales (Low/Medium/High)
- 1-10 scales (more granular)
- Qualitative descriptors only
Choose the system that works for your organisation.
Recording Risk Ratings
Your risk assessment should show:
- Initial risk rating - Before controls
- Control measures - What you've implemented
- Residual risk rating - After controls
- Action needed - If residual risk is still high
Summary
The risk rating matrix is a practical tool for prioritising hazards. Use it consistently, involve your team, and always reassess after implementing controls.