2.2 Hierarchy of Control Measures & Risk Matrices

Hierarchy of Control Measures & Risk Matrices

When a risk assessment identifies significant site hazards, site managers must determine how best to control them. UK health and safety law does not allow managers to select arbitrary controls or rely immediately on personal protective equipment (PPE). Instead, controls must be selected by strictly applying the General Principles of Prevention specified in Schedule 1 of the Management of Health and Safety at Work Regulations 1999 (MHSWR) and Regulations 9 and 11 of the Construction (Design and Management) Regulations 2015 (CDM 2015).

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The General Principles of Prevention

The statutory principles set out a logical hierarchy of thought when designing out or managing site risks:

1. Avoiding risks altogether (eliminating hazards).
2. Evaluating risks which cannot be avoided.
3. Combating risks at source.
4. Adapting work to the individual (ergonomics, workplace layout).
5. Adapting to technical progress (using safer machinery or materials).
6. Replacing the dangerous by the non-dangerous or less dangerous.
7. Developing a coherent overall prevention policy.
8. Giving collective protective measures priority over individual protective measures.
9. Giving appropriate instructions to workers.

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The 6-Stage Hierarchy of Control (ERIC PD)

In construction management, the General Principles of Prevention are operationalized through the Hierarchy of Control. A common industry mnemonic used in SMSTS training is ERIC PD (Elimination, Reduction, Engineering Controls, Administrative Controls, PPE, Discipline):

[1. ELIMINATION]        <-- Most Effective (Risk Removed)
  └── [2. REDUCTION / SUBSTITUTION]
        └── [3. ENGINEERING CONTROLS / ISOLATION]
              └── [4. ADMINISTRATIVE CONTROLS / PROCEDURES]
                    └── [5. PERSONAL PROTECTIVE EQUIPMENT (PPE)] <-- Least Effective (Last Resort)

1. Elimination (Most Effective)

Removing the hazard entirely from the construction process so exposure is impossible.

• Site Examples: Off-site prefabrication of timber roof trusses (eliminating roof carpentering at height); using trenchless (no-dig) technology for utility installations; eliminating overhead line contact by rerouting underground cabling.

2. Reduction / Substitution

Replacing a high-hazard material, item of plant, or process with a significantly lower-risk alternative.

• Site Examples: Substituting solvent-based paints with water-based coatings to reduce COSHH chemical risks; substituting 230V mains electric tools with 110V reduced low voltage (RLV) tools or cordless battery tools; using hydraulic block splitters instead of abrasive wheels to eliminate dust and noise.

3. Engineering Controls & Isolation

Using physical technical measures to isolate workers from the hazard or contain the energy source.

• Site Examples: Fixed perimeter guardrails and toe-boards; acoustic enclosures around diesel generators; local exhaust ventilation (LEV) on cut-off saws capturing silica dust; trench box shoring systems; safety nets and crash decks.

4. Administrative Controls

Establishing procedural safety rules, safe systems of work, and operational organization to reduce hazard exposure.

• Site Examples: Implementing Permit to Work (PTW) systems; establishing exclusion zones around slewing excavators; job rotation to limit Hand-Arm Vibration Syndrome (HAVS) exposure; delivery management timing; mandatory safety inductions.

5. Personal Protective Equipment (PPE)

Providing protective equipment worn by individual workers to shield them from residual hazards. PPE is strictly the last line of defense because it does not eliminate the hazard and relies entirely on user compliance.

• Site Examples: High-visibility vests, hard hats, steel toe-cap boots, respiratory protective equipment (RPE), hearing defenders, safety harnesses.

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Collective vs. Individual Protection

Under UK legislation—most notably Regulation 6 of the Work at Height Regulations 2005—site managers must legally prioritize collective protection over individual protection.

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Risk Rating Matrices (5x5 Quantitative Scoring)

To objectively evaluate residual risk and determine whether proposed controls are adequate, construction managers utilize a 5x5 Risk Matrix.

$\text{Risk Rating (RR)} = \text{Likelihood (L)} \times \text{Severity (S)}$

Scoring Definitions

• Likelihood Scale (1 to 5):

  1. Rare / Unlikely (Has never occurred on site; highly improbable).
  2. Unlikely (Possible under unusual site conditions).
  3. Possible (Might occur at some point during the project).
  4. Likely (Easily expected to occur regularly).
  5. Almost Certain (Continuous exposure; virtually inevitable without controls).

• Severity Scale (1 to 5):

  1. Minor (First-aid treatment only; minor scratch or bruise; no lost time).
  2. Moderate (Medical treatment required; minor cut/sprain; lost time < 7 days).
  3. Serious (RIDDOR-reportable injury; over-7-day incapacitation; bone fracture of digit).
  4. Severe (Major life-changing injury; amputation; complex fracture; single fatality).
  5. Catastrophic (Multiple fatalities; structural collapse; extensive off-site disaster).

Risk Action Thresholds

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Statutory Employer Duties Regarding PPE

Under the Personal Protective Equipment at Work Regulations 1992 (as amended in 2022):

• Free Provision: Employers cannot charge workers (including employees and limb (b) gig-economy/agency workers) for PPE required for work duties.
• Compatibility & Fitting: Where multiple PPE items are worn simultaneously (e.g., hard hat, safety eyewear, and ear defenders), they must be compatible. Tight-fitting Respiratory Protective Equipment (RPE) requires formal Face-Fit Testing.
• Maintenance & Storage: Employers must provide suitable clean storage facilities and ensure PPE is regularly inspected and replaced when defective.