A great blast starts long before the first hole is drilled. Proper blast design ensures efficient rock breakage, cost control, and—most importantly—safety. Let’s break down the core elements every engineer should master. ⸻ 🔹 Key Elements of Blast Design (with Formulas) 1️⃣ Burden & Spacing • Burden (B): Distance from blast hole to free face. • Spacing (S): Distance between adjacent holes. Formulas: • B = K × D • S = (1.2 to 1.5) × B Where: • K is a rock constant (typically 25–35) • D is hole diameter (in mm) ✅ Example: For a 100 mm hole and medium hardness rock → B = 3 m, S ≈ 3.6 to 4.5 m 2️⃣ Hole Diameter & Depth • Depth = Bench Height + Subdrilling More depth = better floor control and fragmentation. 3️⃣ Stemming Length • Inert material (like crushed stone) used to confine explosive energy. Formula: • Stemming = (20 to 30) × D ✅ For 100 mm holes, stemming length = 2 to 3 m 4️⃣ Subdrilling • Additional drilling below bench floor to avoid toe problems. Formula: • Subdrilling = (0.2 to 0.3) × Bench Height 5️⃣ Initiation Timing • Delays between holes and rows improve fragmentation and reduce vibration. ✅ Typical values: • 25–50 ms between holes • 50–100 ms between rows ⸻ 📌 Why It Matters ✔ Prevents overbreak and flyrock ✔ Increases safety and control ✔ Optimizes loading and hauling ✔ Reduces total blasting cost per ton ⸻ Pro Tip from the Field: Always adjust your design based on geological structure, rock hardness, moisture, and proximity to structures. ⸻ Coming Up Next: ✅ Lesson 6: Environmental & Safety Considerations ✅ Lesson 7: Common Issues & Solutions ✅ Lesson 8: Case Study – Real blast pattern breakdown