🎓 Lesson 7 D4

Building Your First SMV Using Observed Time & Rating

Standard Minute Value (SMV) is the time it takes a trained worker to complete a task at a normal pace, measured in minutes.

🎯 Learning Objectives

✓ Calculate SMV from observed cycle time and performance rating
✓ Apply allowance factors (e.g., fatigue, personal, delay) to derive standard time
✓ Explain how rating bias affects SMV accuracy and propose mitigation strategies
✓ Analyze discrepancies between observed time and SMV to identify process inefficiencies

📖 Why This Matters

In mining support operations—like drill rig servicing, blast hole inspection, or explosive loading—labor efficiency directly impacts blasting schedule adherence, cost per ton, and safety compliance. An inaccurate SMV leads to understaffing (causing fatigue and near-misses) or overstaffing (wasting capex). Building your first SMV isn’t just arithmetic—it’s engineering judgment that bridges field observation and operational planning.

📘 Core Principles

SMV rests on three pillars: (1) Observed Time (OT): raw stopwatch-measured duration of a task, repeated across multiple cycles to eliminate anomalies; (2) Performance Rating: a trained analyst’s assessment of worker pace relative to ‘normal’ (100% = average skilled worker under standard conditions); (3) Allowances: time added for physiological (fatigue, rest), personal (hydration, restroom), and unavoidable delays (e.g., waiting for blast clearance). Critically, rating is *not* subjective opinion—it’s calibrated against predetermined motion-time systems (e.g., MTM-2) or video-based benchmark libraries. In mining contexts, environmental factors (heat, dust, slope access) must be explicitly factored into rating and allowances.

📐 SMV Calculation Workflow

SMV is computed in three sequential steps: Normal Time (NT) = Observed Time × Rating Factor; then Standard Time (ST) = NT × (1 + Allowance Factor); finally, SMV = ST (expressed in minutes). The allowance factor is expressed as a decimal (e.g., 15% → 0.15). This workflow ensures consistency across tasks—from checking detonator continuity to assembling down-the-hole tools.

SMV Derivation Formula

SMV = OT × (R/100) × (1 + A)

Calculates Standard Minute Value from observed time, performance rating, and total allowance factor.

Variables:

Symbol	Name	Unit	Description
OT	Observed Time	min	Average measured time per cycle, after outlier removal
R	Performance Rating	%	Analyst-assigned pace rating relative to defined normal (100% = standard pace)
A	Total Allowance Factor	decimal	Sum of fatigue, personal, and delay allowances expressed as fraction (e.g., 15% = 0.15)

Typical Ranges:

Underground drilling support: 2.1 – 3.8 min

Surface blast hole inspection: 1.4 – 2.6 min

💡 Worked Example

Problem: A blaster performs 10 cycles of 'detonator continuity check & logging' on a mobile blast console. Average observed time = 2.4 min/cycle. Analyst rates performance at 95% (i.e., worker is slightly slower than normal pace due to PPE bulk and site noise). Allowances: 12% (8% fatigue, 2% personal, 2% unavoidable delay). Calculate SMV.

1. Step 1: Compute Normal Time = OT × Rating Factor = 2.4 min × (95/100) = 2.28 min

2. Step 2: Apply allowance: ST = NT × (1 + Allowance) = 2.28 × (1 + 0.12) = 2.28 × 1.12 = 2.5536 min

3. Step 3: Round to nearest 0.01 min (industry convention): SMV = 2.55 min

Answer: The SMV is 2.55 minutes, which falls within the typical range of 2.4–2.7 min for this task in underground hard-rock mines per ILO Mining Safety Guidelines.

🏗️ Real-World Application

At Rio Tinto’s Koodaideri Iron Ore Operation (Pilbara, WA), engineers recalibrated SMVs for ‘pre-blast perimeter sweep’ after introducing new thermal imaging drones. Observed time dropped from 4.8 min to 3.1 min per 200-m sweep segment. Initial rating was 110% (workers accelerated due to reduced walking distance), but analysts down-rated to 102% after cross-verifying with MTM-2 elemental data—revealing that drone setup added unseen micro-motions. Final SMV settled at 3.26 min (3.1 × 1.02 × 1.15), enabling accurate staffing for simultaneous blast zones without compromising safety audit frequency.