🎓 Lesson 5 D3

HAZOP Study Facilitation: Guide Words & Deviation Mapping

HAZOP is a structured team method that asks 'What if?' questions using simple words like 'No', 'More', or 'Less' to find hidden hazards in mining or blasting systems.

🎯 Learning Objectives

✓ Explain how each HAZOP guide word (e.g., NO, MORE, LESS) generates meaningful deviations for blasting-related parameters
✓ Apply guide words to map deviations for at least three key parameters (e.g., delay time, stemming length, hole diameter) in a surface blast design
✓ Analyze a completed HAZOP worksheet to identify missing safeguards or inadequate risk controls for explosive initiation systems
✓ Design a simplified HAZOP worksheet for a detonator charging station, including causes, consequences, and recommended actions

📖 Why This Matters

In mining, a single undetected deviation—like 'NO delay between holes' or 'MORE charge than designed'—can trigger flyrock, misfires, or catastrophic ground vibration. HAZOP isn’t just paperwork: it’s the frontline defense against systemic oversights in blasting plans, explosives handling, and blast area clearance procedures. Over 62% of major blasting incidents investigated by ICMM (2022) traced back to unexamined operational deviations—precisely what HAZOP is engineered to catch.

📘 Core Principles

HAZOP relies on two foundational elements: (1) Guide words—standardized modifiers (e.g., NO, MORE, LESS, AS WELL AS, PART OF, REVERSE, OTHER THAN) that systematically challenge each parameter; and (2) Parameters—measurable system variables (e.g., charge weight, stemming height, air gap, delay interval). Each guide word–parameter pair creates a deviation (e.g., 'NO stemming' or 'LESS confinement'). For blasting engineering, parameters must be selected from the blast design specification (e.g., burden, spacing, subdrill), equipment operation (e.g., drill depth accuracy, emulsion pump pressure), and safety-critical controls (e.g., lockout/tagout status, radio silence verification). The team then brainstorms causes, consequences, existing safeguards, and actions—always anchored to real mining contexts, not hypotheticals.

📐 Deviation Generation Matrix

While HAZOP itself is qualitative, deviation coverage is quantified via the Deviation Coverage Ratio (DCR)—a metric used internally by HAZOP leaders to ensure comprehensiveness. DCR measures the proportion of parameter–guide word combinations formally evaluated versus the theoretical maximum.

Deviation Coverage Ratio (DCR)

DCR = (N_dev / (N_param × N_guide)) × 100

Quantifies completeness of HAZOP deviation generation across all relevant parameters and guide words.

Variables:

Symbol	Name	Unit	Description
DCR	Deviation Coverage Ratio	%	Percentage of theoretically possible deviations actually evaluated
N_dev	Number of documented deviations	unitless	Count of unique, substantiated deviations recorded in HAZOP worksheet
N_param	Number of selected parameters	unitless	Parameters chosen for HAZOP based on blast design or operational relevance
N_guide	Number of guide words applied	unitless	Typically 7 per IEC 61882 (NO, MORE, LESS, AS WELL AS, PART OF, REVERSE, OTHER THAN)

Typical Ranges:

Routine production blast: 75 – 85%

Blast near infrastructure or community: 90 – 100%

💡 Worked Example

Problem: A HAZOP team reviews a surface blast design with 5 critical parameters (burden, spacing, stemming length, delay time, charge concentration) and applies the standard 7 IEC 61882 guide words. They document 28 deviations. Calculate DCR and assess completeness.

1. Step 1: Compute theoretical maximum deviations = 5 parameters × 7 guide words = 35

2. Step 2: Apply formula: DCR = (documented deviations / theoretical maximum) × 100 = 28 / 35 × 100

3. Step 3: Interpret result: 80% coverage indicates acceptable rigor for routine blasts—but IEC 61882 recommends ≥90% for high-risk operations (e.g., near infrastructure or water bodies)

Answer: The DCR is 80%, which meets minimum requirements for standard production blasts but falls short of the 90% threshold required for high-consequence scenarios per IEC 61882 Annex C.

🏗️ Real-World Application

At the Telfer Mine (Western Australia), a HAZOP study on electronic detonator programming identified the deviation 'REVERSE delay sequence'—where initiation order was inverted due to software configuration error. Cause: technician loaded delay files in reverse chronological order. Consequence: premature breakage of toe zone, leading to excessive backbreak and unstable highwalls. Safeguard: Missing validation step in blast software UI. Action: Implemented mandatory pre-blast digital signature check and added auto-sorting logic in i-kon™ software—reducing sequencing errors by 100% over 18 months (Rio Tinto Safety Bulletin, 2021).