BLAST DESIGN RULES OF THUMB – Coal (Given: Hole depth, Rock type, and Distance to structure)

Effective blast design rules of thumb involve key principles such as safe distance to structures, optimal powder factor, accurate hole depth calculations, and adherence to established rules to ensure controlled and efficient blasting operations.

HOLE DIAMETER (d) = hole depth (H) divided by 5 to 10.

d(in)  =  H(ft) / 5  to  H(ft) / 10                           (Typically H/7)

BURDEN (B) = 2 to 3 times the diameter.

B(ft) =  2 × d(in)  to 3 ×  d(in)                            (Typically 2.5 × d)

SPACING (S) = 1 to 2 times the burden.

S(ft) = 1 ×  B(ft) to 2 ×  B(ft)                             (Typically 1.5 × B)

STEMMING (T) = 0.5 to 1.0 times the burden.

T(ft)  = 0.5  × B(ft)  to 1.0 × B(ft)                                  (Typically 0.7 × B)

POWDER COLUMN (PC) = hole depth minus stemming (T), backfill (F) and decking (T_d)

PC(ft) = H(ft) – T(ft) – F(ft) – T_d(ft)

LOADING DENSITY (LD) = 0.3405 times the explosive density times the hole diameter squared.

LD(lb/ft) = 0.3405 × density(gm/cc) × d²(in)       (or Mfg design guide)

CHARGE WEIGHT (CW) = powder column times the loading density.

CW(lb) = PC(ft) × LD(lb/ft)

POWDER FACTOR (PF) = powder per hole divided by rock volume per hole.

PF(lb/yd³) = CW(lb) / (B(ft) × S(ft) × H(ft) / 27)

SCALED DISTANCE (SD₂) = Distance to structure divided by square root of the                                                                       charge weight.

SD₂(ft/lb^1/2) = distance(ft) / CW^1/2(lb^1/2)              (Greater than 55)

PEAK PARTICLE VELOCITY (PPV) = 119 or 438 times scaled distance to the -1.52 power.

PPV(in/s) = 438 × (SD₂)^-1.52                                           (Compliance)

PPV(in/s) = 119 × (SD₂)^-1.52                                           (Expected)

Source: Office of Surface Mining Reclamation and Enforcement