Part 1. Flyrock Control: Main Rules, Energy Management, and Surface Protection in Blasting Operations

Part 1. Flyrock Control: Main Rules, Energy Management, and Surface Protection in Blasting Operations

Petr Explosives Group (PEG)

“Blasting mats are NOT protection — good blast design is.”

In a recent Practical Explosives Training School (PETS)  class discussion on flyrock control, the rapid growth of new construction and residential blasting sparked very interesting questions from students. Blasters working next to homes, schools, roads, pipelines, or any sensitive infrastructure wanted a simple, step-by-step checklist they could follow on site to ensure they could blast safely while justifying every decision in their blast design.

After talking with several industry experts and friends, we came up with these recommendations. Below is the practical PEG approach — built directly from the core rules, the risk equation, the three control levers, and the field-tested tools we have covered. It turns complex theory into an easy-to-use field checklist that every blaster can apply before every shot in high-risk areas.

The Key Principle Most Students Miss: “If one lever is weak, you must strengthen the others.” Real-life examples:  If you are using high-energy emulsion (Lever 1 is strong/high), you must use longer stemming or add sand + mats.  If the collar is soft or fractured (Lever 2 is weak), you cannot rely on stemming alone — you must add sand or mats (Lever 3). If you are blasting next to houses and cannot use very long stemming, you compensate with thicker sand and mats.

“The Most Powerful Field Question: Before you load any hole, ask yourself this one simple question: Can this collar hold this energy?”

• If YES → You can proceed with normal stemming and minimal surface protection.
• If NO → You must compensate before loading by doing one or more of the following:
  • Increase stemming length or improve stemming material
  • Reduce the explosive charge near the collar (decking)
  • Add sand cover
  • Install blasting mats
  • Use the full Sand + Mats system

Never load the hole until you have answered this question and taken the necessary actions.

Simple Step-by-Step Checklist for Blasting Near Residential Areas or Sensitive Zones

Use this checklist on every pattern. It takes less than 5 minutes once you are familiar with it and gives you clear documentation to justify your design to regulators, clients, or safety officers.

Step 1: Assess Site Sensitivity & Geology (Pre-Blast Site Walk)

• Confirm proximity to homes, roads, utilities, or other sensitive structures.
• Review driller logs for shallow burden, soft/weathered collars, fractured rock, or irregular geology. (We will publish a special blog for drilling and a driller checklist) 
• Note any urban or infrastructure constraints. Decision: If any “mandatory surface protection” condition exists (shallow burden, soft collar, fractured surface rock, high loading density, or urban proximity), mark HIGH RISK and proceed to full protection measures.

Step 2: Calculate or Confirm Loading Density (How well you seal the top of the hole) Use PETS, calculator.  This lever controls how well the energy is trapped inside the hole so it cannot escape upward.

• Stemming length – How deep you fill the top of the hole with inert material (usually 20–30 times the hole diameter).
• Stemming material – What you use (angular crushed rock is best because it locks together; sand or drill cuttings are weaker).
• Collar condition – How strong the rock is around the mouth of the hole (hard, competent rock = good; soft, weathered, or fractured collar = very weak).

Simple Rule: Good collar confinement keeps the high-pressure gases from blowing out the top of the hole. If the collar is weak or stemming is too short, gases shoot upward like a rocket and throw rocks into the air.

• Record hole diameter, explosive type, loading density, and loaded length.
• Example (common residential-scale hole): 3.5-inch hole, emulsion at 5 lb/ft, 22 ft loaded length = 110 lb per hole.
• Compare to standard ANFO. If using emulsion or heavy ANFO (>1.1 g/cm³), flag as high-energy and plan extra confinement or surface protection—consider dacking if possible.

Step 3: Evaluate Collar Confinement (“Can this collar hold this energy?”)

• Measure and record stemming length (minimum 20–30 × hole diameter).
• Check stemming material (angular crushed rock preferred) and collar condition.
• If the collar is weak, fractured, or stemming is inadequate → increase stemming or move to Step 4 immediately.

Step 4: Select & Apply Surface Protection System Use the PEG Energy Control Matrix:

Sand Thickness Guide:

• Normal blasting: 12–18 inches
• Soft/fractured collar: 18–24 inches
• High energy / urban sites: 24–36 inches (use this near homes or roads)

Place sand first (slightly moist, well-graded), then overlap blasting mats securely (no gaps).

Step 5: Check for Critical Failure Modes

• Under-stemming + no mats → immediate flyrock risk
• Mats with gaps → directional flyrock
• Dry sand → blown away
• Wet slurry sand → no resistance

Fix any issues before proceeding.

Step 6: Final Justification & Documentation

• Answer the PEG teaching point: “Stemming controls pressure. Sand absorbs energy. Mats stop velocity.”
• Record all decisions (loading density, stemming, protection system) on the blast report.
• If you cannot control the energy in the hole, you must control it on the surface.

Step 7: Go/No-Go Decision. Only initiate the blast when all steps are complete, and the collar can hold the energy (or surface protection fully compensates).

Quick Summary for Blasters (Easy to Remember)

• Lever 1 – Energy: Controls how much power you release.
• Lever 2 – Collar Confinement: Keeps the power inside the hole.
• Level 3 – Surface Containment: Catches anything that still escapes.

Golden Rule: Weak lever? Strengthen the other two. Unsure about the collar? Add surface protection.

Why This Checklist Works in Sensitive Areas

This checklist directly addresses the students’ questions: it is simple enough for daily field use yet rigorous enough to justify your design to anyone reviewing it. It forces you to balance the three levers, apply the risk equation, and use surface protection (especially the powerful Sand + Mats combination) whenever residential or road proximity raises the stakes.

Final PEG Rule: “If you cannot control the energy in the hole, you must control it on the surface.”

By following this 7-step checklist every time, blasters can confidently operate next to homes, roads, and sensitive infrastructure while maintaining an impeccable safety record and defensible blast designs. Proper planning, real-time adjustments, and thorough documentation protect people, property, and the environment — exactly what professional explosives engineering demands in today’s growing residential and construction environment.

Use this checklist. Teach it to your crews. It turns complex flyrock science into safe, repeatable field practice.