🎓 Lesson 14
D5
Mapping Idle Time with Spaghetti Diagrams & 5-Why
A spaghetti diagram is a simple hand-drawn map that shows the actual path workers or materials take during a task—like tracing spaghetti noodles on a floor plan—to spot wasted movement and idle time.
🎯 Learning Objectives
- ✓ Analyze a recorded shop-floor activity sequence to identify and quantify idle time segments using timestamped spaghetti mapping
- ✓ Apply the 5-Why technique to trace idle time in blasting support operations from symptom to systemic root cause
- ✓ Design an improved workflow layout by calculating and comparing total travel distance before/after intervention using spaghetti diagram metrics
- ✓ Explain how idle time correlates with blast schedule adherence, safety incident likelihood, and powder factor variability
📖 Why This Matters
In mining and blasting operations, up to 30% of labor time can be lost to unobserved idle time—waiting for drill rigs, moving between blast holes, or repositioning explosives carts. Unlike machine downtime, human idle time rarely triggers alarms—but it directly erodes fragmentation consistency, increases misfire risk, and inflates cost per ton. Spaghetti diagrams make this invisible waste visible in minutes; pairing them with 5-Why turns observation into actionable engineering insight.
📘 Core Principles
Spaghetti diagrams originate from lean manufacturing but are uniquely powerful in blasting support workflows where spatial constraints, hazardous zones, and sequential dependencies dominate. The method requires direct observation (not interviews or reports), real-time timestamping (±2 sec accuracy), and a scaled facility map (1:50 or 1:100). Idle time is defined as ≥15 seconds of no value-adding action—e.g., standing while waiting for surveyor clearance, holding detonator cord while others align stemming tools. The 5-Why technique then interrogates each idle segment through five successive 'why' questions—not to assign blame, but to expose latent system flaws: inadequate pre-blast staging, unclear role handoffs, or missing PPE staging points. Both tools converge on systemic causes—not individual behavior.
📐 Idle Time Ratio & Travel Efficiency Index
Two complementary metrics quantify waste from spaghetti diagrams: Idle Time Ratio (ITR) measures labor utilization loss; Travel Efficiency Index (TEI) evaluates spatial rationality. ITR uses observed timestamps; TEI compares actual path length to theoretical minimum (straight-line distance between first and last value-adding points). Both feed directly into RCA prioritization.
Idle Time Ratio (ITR)
ITR = Σ t_idle / t_totalQuantifies proportion of observed time spent in non-value-adding idleness.
Variables:
| Symbol | Name | Unit | Description |
|---|---|---|---|
| ITR | Idle Time Ratio | dimensionless | Fraction of total observed time classified as idle |
| t_idle | Cumulative idle time | seconds | Sum of all pauses ≥15 s with no value-adding action |
| t_total | Total observed time | seconds | Duration of complete activity observation period |
Typical Ranges:
High-efficiency certified blasting crew: 0.03 – 0.07
New pattern rollout (first 3 shifts): 0.12 – 0.25
💡 Worked Example
Problem: During observation of a 45-minute stemming crew shift, timestamps show 6 idle segments: 2×45s (waiting for drill rig vacate), 1×120s (retrieving mislaid primer box), 3×30s (adjusting harness near exclusion zone). Total observed time = 2700 s.
1.
Step 1: Sum all idle durations: (2 × 45) + 120 + (3 × 30) = 90 + 120 + 90 = 300 s
2.
Step 2: Calculate ITR = Total idle time / Total observed time = 300 / 2700 = 0.111
3.
Step 3: Convert to % and compare: 11.1% idle time — exceeds industry benchmark of ≤7% for certified blasting crews (IMM 2022)
Answer:
The result is 11.1%, which falls above the acceptable threshold of ≤7% and signals need for root cause investigation.
🏗️ Real-World Application
At Newmont’s Boddington Mine (Western Australia), a spaghetti diagram of explosive loading crews revealed 18.3% average idle time across 12 shifts—primarily at Hole #7–#12 due to single access lane congestion. 5-Why analysis traced the root cause not to crew training, but to blast design software outputting hole patterns incompatible with existing vehicle turning radius (minimum 12.5 m vs. required 14.2 m). Redesigning pattern spacing reduced idle time to 4.1% and cut misfire rate by 62% within one quarter.